Sage Journals: Discover world-class research

Abstract

We investigated the effects of donitriptan, which possesses a uniquely high affinity and efficacy at 5-HT_1B/1D receptors, on carotid and systemic haemodynamics in anaesthetized pigs. Donitriptan (0.16-100 μg kg^-1, i.v.) dose-dependently decreased total carotid blood flow and vascular conductance (maximum response: -25 ± 3%). This effect was entirely due to a selective reduction in the cephalic arteriovenous anastomotic fraction (maximum response: -63 ± 3%; ED_50%: 92 ± 31 nmol/kg); the nutrient vascular conductance increased. Donitriptan did not decrease vascular conductances in or blood flow to a number of organs, including the heart and kidneys; in fact, vascular conductances in the skin, brain and skeletal muscles increased. Cardiac output was slightly decreased by donitriptan, but this effect was confined to peripheral arteriovenous anastomoses. The haemodynamic effects of donitriptan were substantially reduced by the 5-HT_1B/1D receptor antagonist GR127935. These results show that donitriptan selectively constricts arteriovenous anastomoses via 5-HT_1B receptor activation. The drug should be able to abort migraine headaches and it is unlikely to compromize blood flow to vital organs.

Keywords

arteriovenous anastomoses cardiac output donitriptan migraine

Introduction

The last decade has seen tremendous progress in migraine therapy, with sumatriptan, belonging to a new class of drugs designated as 5-HT_1B/1D/1F receptor agonists, providing the lead (1–3). Several studies have clearly established the therapeutic value of sumatriptan as well as of other triptans (4–7). Pharmacologically, triptans inhibit dural plasma protein extravasation, suppress action potentials in trigeminal nucleus caudalis, constrict isolated cranial blood vessels and decrease carotid arteriovenous anastomotic blood flow in anaesthetized animals (6, 8, 9). Although the trigeminal neural effects of triptans may be involved to some extent in their anti-migraine action (7, 10, 11), the efficacy of triptans is primarily attributed to cranial vasoconstriction (6, 10). Using compounds selective at 5-HT_1B, 5-HT_1D or 5-HT_1F receptors, it is now well established that the vasoconstrictor effect of triptans is mediated via 5-HT_1B receptors (12–18).

Despite its success in the treatment of migraine headaches, sumatriptan has several shortcomings, such as low bioavailability, headache recurrence and propensity to elicit chest symptoms (6). Several newer triptans display a better pharmacokinetic profile, but this has not been translated into any substantial improvement in either the efficacy or side-effect potential compared with sumatriptan (for reviews, see 6, 7). Recently, another triptan, donitriptan (F11356 or F12640), has been synthesized by the Centre de Recherche, Pierre Fabre, Castres, France (Fig. 1). Donitriptan displays a very high affinity at recombinant human as well as porcine 5-HT_1B/1D receptors with little affinity for the 5-HT_1F receptor and, more importantly, it has uniquely high intrinsic efficacy (inhibition of cAMP accumulation and enhancement of [³⁵S]GTPγS binding) at human 5-HT_1B/1D receptors (Tables 1, 19–23). John et al. (19, 24) have hypothesized that the relatively low intrinsic activity of the currently available triptans at 5-HT_1B/1D receptors may explain this ceiling effect in therapeutic response and therefore donitriptan may show a high therapeutic efficacy.

Table 1

Affinity and efficacy of donitriptan, sumatriptan and 5-HT at human (h) and porcine (p) 5-HT receptors

Receptors	Donitriptan∗	Sumatriptan†	5-HT†
Ligand binding affinity (pK _i )
h5-HT_1A	7.6	6.0	7.9
h5-HT_1B	9.4–10.1	7.4	8.0
p5-HT_1B	9.0‡	7.3§	7.8¶
h5-HT_1D	9.3–10.2	8.3	8.4
p5-HT_1D	9.7‡	8.1§	8.4¶
h5-ht_1E	5.9	5.7	8.2
h5-ht_1F	5.5	7.6	8.0
p5-ht_1F	5.5††	5.4††	7.8††
h5-HT_2A	6.7	< 5.0	6.5
h5-ht₆	5.6	< 5.5	7.2
h5-HT₇	6.4	6.0	8.1
Inhibition of forskolin-evoked cAMP accumulation (pEC ₅₀ )
h5-HT_1B	8.91	7.16∗∗	7.81∗
h5-HT_1D	9.57	8.79∗∗	8.62∗
Enhancement of [ ³⁵ S]GTPγS binding (pEC ₅₀ )
h5-HT_1B	8.74	6.63∗∗	7.04∗
h5-HT_1D	9.08	7.75∗∗	7.84∗

pK_i, Negative logarithm of the dissociation equilibrium constant; pEC₅₀, negative logarithm of the molar concentration that elicits 50% of its maximum effect.

^∗John et al. (19);

^†IUPHAR Compendium (20);

^‡Pauwels et al. Unpublished;

^§Bhalla et al. (21);

^¶Bhalla et al. (22);

^∗∗Pauwels et al. (23);

^††Bhalla et al. unpublished.

Figure 1

Chemical structures of donitriptan and sumatriptan.

In the present study, we report on the effects of donitriptan on the distribution of carotid blood flow into nutrient (capillary) and non-nutrient (arteriovenous anastomotic) fractions in the anaesthetized pig. Previous investigations from our laboratory have established that constriction of carotid arteriovenous anastomoses in the anaesthetized pig serves as a predictive model for the anti-migraine efficacy of 5-HT-based drugs (10, 25). Moreover, to establish the cardiovascular safety, we studied the effects of donitriptan on cardiac output and its regional distribution to vital organs.

Materials and methods

General

After an overnight fast, 36 pigs (Yorkshire × landrace; 10–15 kg) were anaesthetized with azaperone (140 mg, i.m.), midazolam hydrochloride (7.5 mg, i.m.) and pentobarbitone sodium (600 mg, i.v.). The animals were intubated and connected to a respirator (BEAR 2E, BeMeds AG, Baar, Switzerland) for intermittent positive pressure ventilation with a mixture of room air and oxygen. Respiratory rate, tidal volume and oxygen supply were adjusted to keep arterial blood gas values within physiological limits (pH: 7.35–7.48; pCO₂: 35–48 mmHg; pO₂: 100–120 mmHg). Anaesthesia was maintained with a continuous i.v. infusion of pentobarbitone sodium at 12–20 mg kg⁻¹ h⁻¹. It may be noted that with this anaesthetic regimen, arteriovenous anastomotic blood flow is considerably higher than that in pigs in a conscious state or under thiopentone anaesthesia (26), thereby producing one of the putative features of migraine, i.e. dilatation of carotid arteriovenous anastomoses (25, 27).

Heart rate was measured with a tachograph (CRW, Erasmus University, Rotterdam, The Netherlands) triggered by electrocardiographic signals. Catheters were placed in the inferior vena cava via the left femoral vein for the administration of drugs and fluids, and in the aortic arch via the left femoral artery for the measurement of arterial blood pressure (Combitrans disposable pressure transducer; Braun, Melsungen, Germany) and the withdrawal of arterial blood for determining blood gases (ABL-510, Radiometer, Copenhagen, Denmark). Body temperature was kept at about 37°C and the animals were continuously infused with saline to compensate for fluid losses during the experiment.

In the case of the carotid artery experiments, both common carotid arteries, external jugular veins and vagosympathetic trunks were identified. The vagosympathetic trunks were cut between two ligatures in order to avoid reflex-mediated cardiovascular changes. Subsequently, the right common carotid artery was dissected free and a needle was inserted against the direction of blood flow for the administration and uniform mixing of radioactive microspheres. Another catheter was placed in the right external jugular vein for the withdrawal of venous blood samples. Blood flow was measured in the right common carotid artery with a flow probe (internal diameter: 2.5 mm) connected to a sine-wave electromagnetic flow meter (Transflow 601-system, Skalar, Delft, The Netherlands).

In the case of the cardiac output experiments, a 6F Swan-Ganz thermodilution catheter (Braun Melsungen AG, Melsungen, Germany) was introduced into the pulmonary artery via the right femoral vein to measure cardiac output. Another catheter, connected to a pressure transducer (Combitrans disposable pressure transducer; Braun, Melsungen, Germany), was guided through the left carotid artery into the left ventricle for the injection of radioactive microspheres. The presence of the tip of the catheter in the left ventricle was confirmed by the observation of the sudden switch from an arterial to a ventricular pressure profile. Lastly, a catheter was placed into the right femoral artery and connected to a Harvard pump for the withdrawal of reference blood samples during the injection of radioactive microspheres.

Heart rate, systolic, diastolic and mean arterial blood pressure as well as carotid blood flow were continuously monitored on a polygraph (CRW, Erasmus University, Rotterdam, The Netherlands). Vascular conductance was calculated by dividing blood flow or cardiac output (ml/min) by mean arterial blood pressure (mmHg), multiplied by hundred and expressed as 10⁻² ml/min mmHg⁻¹. Stroke volume (cardiac output dividing by heart rate) and nutrient cardiac output (cardiac output minus lung blood flow, i.e. mainly total arteriovenous shunting) were calculated.

Distribution of carotid blood flow

The distribution of common carotid blood flow was determined with 15.5 ± 0.1 (SD) µm diameter microspheres labelled with either ¹⁴¹Ce, ¹¹³Sn, ¹⁰³Ru, ⁹⁵Nb or ⁴⁶Sc (NEN Dupont, Boston, USA). For each measurement, a suspension of about 200 000 microspheres, labelled with one of the isotopes, was mixed and injected into the carotid artery. At the end of the experiment, the animal was killed, using an overdose of pentobarbital, and the heart, kidneys, lungs and the different cranial tissues were dissected out, weighed and put in vials. The radioactivity in these vials was counted for 5 min in a γ-scintillation counter (Minaxi autogamma 5000, Packard Instruments, Downers Grove, IL, USA), using suitable windows for discriminating the different isotopes (¹⁴¹Ce: 120–167, KeV, ¹¹³Sn: 355–435 KeV, ¹⁰³Ru: 450–548 KeV, ⁹⁵Nb: 706–829 KeV and ⁴⁶Sc: 830–965 KeV). All data were processed by a set of specially designed programs (28), using a personal computer.

The fraction of carotid blood flow distributed to different tissues was calculated by multiplying the ratio of tissue and total radioactivities by the total common carotid blood flow at the time of the injection of microspheres. As little or no radioactivity is detected in the heart or kidneys, all microspheres trapped in lungs reach lungs from the venous side after escaping via carotid arteriovenous anastomoses. Therefore, the amount of radioactivity in the lungs can be used as an index of the arteriovenous anastomotic fraction of carotid blood flow (28, 29).

Distribution of cardiac output

The distribution of cardiac output was also determined with radioactive microspheres (see above). For each measurement, about 1000 000 microspheres, labelled with one of the isotopes, were injected into the left ventricle. Starting 15 s before microsphere injection and lasting 70 s, a reference arterial blood sample was drawn at the rate of 6 ml/min. Blood loss during this procedure was compensated for by infusing the corresponding volume of Haemaccel. At the end of the experiments, the animals were killed as described above and a number of tissues (lungs, kidneys, heart, stomach, small intestine, spleen, liver, adrenals, brain, skin and skeletal muscles) were dissected out, weighed, put into vials for counting radioactivity (see above). As described by Saxena et al. (28), tissue blood flow was calculated by multiplying the ratio of tissue and reference blood sample radioactivity by the blood withdrawal rate (6 ml/min). Radioactivity in the lungs mainly represents peripheral arteriovenous anastomotic blood flow (non-nutrient part of the cardiac output), although a small part (1–1.5% of cardiac output) is derived from the bronchial arteries (30).

Experimental protocol

After a stabilization period of about 1 h, the animals were divided into two groups (n = 18 each) used for either carotid blood flow or cardiac output experiments. The two experimental groups, where an identical experimental protocol was followed, were subdivided into three subgroups (n = 6 each). The first and second subgroups received physiological saline, whereas the third subgroup was pre-treated with 0.5 mg kg⁻¹ of the 5-HT_1B/1D receptor antagonist GR127935 (31–33); both were given intravenously over a period of 10 min at a rate of 0.5 ml/min. Ten minutes after the end of these infusions, baseline values of heart rate, mean arterial blood pressure, carotid blood flow or cardiac output and their distributions, as well as arterial and jugular venous blood gases were measured. Then, the first group received four consecutive infusions of vehicle (5 ml of distilled water, containing 40% polyethylene glycol, v/v), whereas the second and third groups received consecutive doses of donitriptan (0.16, 2.5, 40 and 100 µg kg⁻¹). Both vehicle and donitriptan were administered intravenously over a period of 10 min at a rate of 0.5 ml/min, given every 20 min. Ten minutes after the end of each infused dose of vehicle or donitriptan, all haemodynamic variables were again collected.

The Ethics Committee of the Erasmus University Rotterdam dealing with the use of animals in scientific experiments approved the protocol for this investigation.

Data presentation and statistical analysis

All data have been expressed as the mean± SE mean. The significance of changes within one group was evaluated with Duncan's new multiple range test, once an analysis of variance (randomized block design) had revealed that the samples represented different populations (34). The percentage changes from baseline values caused by donitriptan in the GR127935 pre-treated group were compared with those with the corresponding doses of donitriptan in the saline-pre-treated group by using Student's unpaired t-test. Statistical significance was accepted at P < 0.05 (two-tailed).

In the saline pre-treated group, the dose of donitriptan needed to decrease baseline values of carotid arteriovenous anastomotic blood flow or vascular conductance by 50% (ED_50%) was calculated using linear regression analysis.

Drugs

Apart from the anaesthetics, azaperone (Janssen Pharmaceutica, Beerse, Belgium), midazolam hydrochloride (Hoffmann La Roche b.v., Mijdrecht, The Netherlands) and pentobarbitone sodium (Apharma, Arnhem, The Netherlands), the compounds used in this study were: donitriptan (4-[4-[2-[3-(2-aminoethyl)-1H-indol-5-yloxy]-acetyl]-piperazin-1-yl] benzonitrile mesylate; F12640 and GR127935 (N-[methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl) [1,1-biphenyl]-4-carboxamide hydrochloride (both from Centre de Recherche Pierre Fabre, Castres, France), haemaccel® (Hoechst Marion Roussel b.v., Hoevelaken, The Netherlands) and heparin sodium (Leo Pharmaceutical Products, Weesp, The Netherlands) for preventing clotting of the catheters. Donitriptan was dissolved in distilled water, containing 40% polyethylene glycol (v/v).

Results

Carotid blood flow experiments

Systemic haemodynamics and arterio-jugular venous oxygen saturation difference

As shown in Table 2, donitriptan as well as its vehicle did not change heart rate. There was a slight decrease in mean arterial blood pressure after the second and third infusions of vehicle. In the saline pre-treated group donitriptan did not change mean arterial blood pressure, but there was a moderate hypotensive response (− 7.4 ± 1.9%) following the highest dose of the drug in the GR127935 pre-treated animals. Donitriptan produced a dose-dependent increase in arterio-jugular venous oxygen saturation difference in both saline and GR127935 pre-treated animals; vehicle was devoid of this effect.

Table 2

Values of heart rate (HR), mean arterial blood pressure (MAP) and arterio-jugular venous oxygen saturation difference (A−V SO₂) at baseline and after 10 min intravenous infusions (0.5 ml/min) of either donitriptan or the corresponding volumes of vehicle (n = 6). The effects of donitriptan were analysed in animals pre-treated with saline (n = 6) or the 5-HT_1B/1D receptor antagonist GR127935 (0.5 mg kg⁻¹; n = 6)

Pre-treatment		HR (beats/min)	MAP (mmHg)	A−V SO₂ (%)
Saline	Vehicle (ml)
	Baseline	92 ± 5	93 ± 4	8 ± 4
	5	91 ± 6	87 ± 4	9 ± 3
	5	90 ± 6	84 ± 5∗	10 ± 4
	5	89 ± 5	84 ± 6∗	10 ± 4
	5	89 ± 5	89 ± 6	10 ± 5
Saline	Donitriptan (µg/kg)
	Baseline	100 ± 3	98 ± 3	6 ± 2
	0.16	99 ± 3	98 ± 3	6 ± 1
	2.5	99 ± 3	98 ± 5	8 ± 2
	40	99 ± 3	93 ± 6	17 ± 4∗
	100	99 ± 4	88 ± 7	18 ± 3∗
GR127935	Donitriptan (µg/kg)
	Baseline	103 ± 1	96 ± 3	6 ± 3
	0.16	103 ± 2	97 ± 5	6 ± 3
	2.5	103 ± 2	97 ± 4	7 ± 3
	40	103 ± 2	92 ± 4	10 ± 3∗
	100	104 ± 1	88 ± 3∗	13 ± 4∗

All values have been presented as the mean±SE mean.

Carotid haemodynamics

As shown in Figure 2 (absolute values) and Figure 3 (percentage changes from baseline), except for an increase in total carotid vascular conductance after the third infusion and a decrease in arteriovenous anastomotic conductance after the last infusion, vehicle did not produce any changes in carotid haemodynamics. On the other hand, donitriptan dose-dependently decreased total carotid and arteriovenous anastomotic blood flow and concomitant conductances; nutrient blood flow and conductance increased. The dose of donitriptan that was needed to decrease baseline values of arteriovenous anastomotic blood flow and conductance by 50% (ED_50%) was found to be 58 ± 27 µg kg⁻¹ (113 ± 52 nmol/kg) and 47 ± 16 µg kg⁻¹ (92 ± 31 nmol/kg), respectively. The maximum changes observed in total carotid, arteriovenous anastomotic and nutrient vascular conductances with the highest dose of donitriptan were −25 ± 3%, −63 ± 3% and + 87 ± 21%, respectively. After treatment with GR127935, donitriptan-induced decreases in the total carotid and arteriovenous anastomotic blood flows and vascular conductances were significantly less; the maximum decreases in total carotid and arteriovenous anastomotic vascular conductances were −12 ± 2% and −35 ± 5%, respectively, (see Figs 2 and 3). Compared with saline-treated animals, GR127935 appeared to reduce donitriptan-induced increases in nutrient blood flow and vascular conductance, but statistical significance (based on percentage changes from the baseline in the two groups) was achieved only in the case of blood flow increase observed with 40 µg kg⁻¹ of donitriptan.

Figure 2

Values of total carotid, arteriovenous anastomotic (AVA) and nutrient (a) blood flow (ml.min⁻¹) and (b) conductance (10⁻² ml.min⁻¹.mmHg) at baseline (□) and after 10 min intravenous infusions (0.5 ml/min) of either donitriptan (0.16, 2.5, 40 and 100 ▪ µg kg⁻¹) or the corresponding volumes of vehicle (5 ml; n = 6). The effects of donitriptan were analysed in animals pre-treated with either saline (n = 6) or GR127935 (0.5 mg kg⁻¹; n = 6). All values are presented as the mean ± SE mean. ∗P < 0.05 vs. baseline. ⁺ P < 0.05 vs. response (% change from baseline) by corresponding dose of donitriptan in animals pre-treated with saline.

Figure 3

Percentage changes from baseline values in total carotid, arteriovenous anastomotic (AVA) and nutrient blood flow (upper panels) and conductance (lower panels) after 10 min intravenous infusions (0.5 ml/min) of either donitriptan (0.16, 2.5, 40 and 100 µg kg⁻¹) or the corresponding volumes of vehicle (5 ml; n = 6). The effects of donitriptan were analysed in animals pre-treated with either saline (•n = 6) or GR127935 (□ 0.5 mg kg⁻¹; n = 6). ○ Vehicle. ▪ All values are presented as the mean±SE mean. ∗P < 0.05 vs. baseline. ⁺ P < 0.05 vs. response (% change from baseline) by corresponding dose of donitriptan in animals pre-treated with saline.

The distribution of carotid blood flow to the head tissues in the three groups of animals is shown in Fig. 4. Donitriptan produced significant increases in vascular conductance to the skin, ear, skeletal muscle, tongue, bone, fat, salivary gland, dura mater and brain; no change was observed in the eyes. In animals treated with GR127935, these increases were attenuated, but statistical significance (based on percentage changes from the baseline in the two groups) was reached only in skeletal muscle and fat. The corresponding volumes of vehicle did not produce changes in vascular conductance values.

Figure 4

Values of carotid vascular conductance in different cranial tissues at baseline (□) and after 10 min intravenous infusions (0.5 ml/min) of either donitriptan (0.16, 2.5, 40 and ▪ 100 µg kg⁻¹) or the corresponding volumes of vehicle (5 ml; n = 6). The effects of donitriptan were analysed in animals pre-treated with either saline (n = 6) or GR127935 (0.5 mg kg⁻¹; n = 6). All values are presented as the mean± SE mean. ∗P < 0.05 vs. baseline. ⁺ P < 0.05 vs. response (% change from baseline) by corresponding dose of donitriptan in animals pre-treated with saline.

Cardiac output experiments

Systemic haemodynamics

The effects of vehicle and donitriptan on systemic haemodynamic variables are presented in Fig. 5. No changes were observed with vehicle. In animals pre-treated with saline, donitriptan did not change heart rate, mean arterial blood pressure, nutrient cardiac output or systemic vascular conductance, but it moderately decreased cardiac output (maximum change: −10 ± 6%) and stroke volume (maximum change: −12 ± 6%). These changes in cardiac output and stroke volume were absent in animals pre-treated with GR127935, where donitriptan did decrease blood pressure by up to 18 ± 3%.

Figure 5

Systemic haemodynamic values of heart rate (HR), mean arterial blood pressure (MAP), cardiac output (CO), nutrient cardiac output (NCO), stroke volume (SV) and systemic vascular conductance (SVC) at baseline □ and after 10 min intravenous infusions (0.5 ml/min) of either donitriptan (0.16, 2.5, 40 and ▪ 100 µg kg⁻¹) or the corresponding volumes of vehicle (5 ml; n = 6). The effects of donitriptan were analysed in animals pre-treated with either saline (n = 6) or GR127935 (0.5 mg kg⁻¹; n = 6). All values are presented as the mean±SE mean. ∗P < 0.05 vs. baseline; ⁺ P < 0.05 vs. response (% change from baseline) by corresponding dose of donitriptan in animals pre-treated with saline.

Regional haemodynamics

Apart from a slight decrease in skeletal muscle vascular conductance, vehicle did not change tissue vascular conductances (Table 3). Donitriptan decreased vascular conductance in lungs (maximum change: −75 ± 6%), which was significantly less in GR127935 pre-treated animals (maximum change: −32 ± 13%). Whereas no changes were observed in vascular conductances in the kidneys, heart and portal tissues (liver, spleen, stomach, adrenals and small intestines), donitriptan slightly increased brain, skin and skeletal muscle vascular conductances.

Table 3

Effects of 10 min intravenous infusions (0.5 ml/min) of either donitriptan or the corresponding volumes of vehicle (n = 6) on regional vascular conductance in anaesthetized pigs. The effects of donitriptan were analysed in animals pre-treated with either saline (n = 6) or the 5-HT_1B/1D receptor antagonist GR127935 (0.5 mg kg⁻¹; n = 6)

Pre-treatment		Vascular conductance(10⁻² ml/min. mmHg⁻¹.100 g⁻¹)
Pre-treatment		Lungs	Kidneys	Heart	Portal	Brain	Skin	Muscle
Saline	Vehicle (ml)
	Baseline	236 ± 72	234 ± 18	98 ± 12	44 ± 3	34 ± 4	15 ± 4	4 ± 1
	5	202 ± 50	223 ± 20	94 ± 15	41 ± 3	31 ± 6	12 ± 4	3 ± 1
	5	201 ± 45	248 ± 17	98 ± 18	45 ± 3	35 ± 6	15 ± 5	4 ± 1
	5	218 ± 61	254 ± 15	107 ± 18	47 ± 4	38 ± 5	16 ± 4	4 ± 1
	5	173 ± 39	215 ± 21	93 ± 13	43 ± 4	33 ± 4	12 ± 3	3 ± 0∗
Saline	Donitriptan (µg/kg)
	Baseline	175 ± 31	231 ± 13	100 ± 8	52 ± 4	31 ± 3	12 ± 3	3 ± 0
	0.16	176 ± 28	247 ± 4.2	111 ± 8	56 ± 5	35 ± 2	11 ± 3	4 ± 0∗
	2.5	108 ± 18∗	225 ± 12	111 ± 10	49 ± 5	36 ± 1∗	12 ± 3	3 ± 0
	40	46 ± 7∗	241 ± 11	112 ± 9	57 ± 5	41 ± 2∗	17 ± 3∗	4 ± 0∗
	100	39 ± 5∗	223 ± 5	112 ± 12	57 ± 4	40 ± 2∗	18 ± 4∗	3 ± 0
GR127935	Donitriptan (µg/kg)
	Baseline	161 ± 29	266 ± 30	117 ± 17	40 ± 4	30 ± 2	25 ± 5	3 ± 0
	0.16	149 ± 34	278 ± 29	115 ± 8	44 ± 5	35 ± 2∗	26 ± 7	4 ± 0
	2.5	137 ± 38	268 ± 21	106 ± 6	46 ± 5∗	38 ± 2∗	25 ± 6	4 ± 0∗
	40	31 ± 34 +	265 ± 23	105 ± 7	48 ± 5∗	42 ± 3∗	27 ± 6	4 ± 0∗
	100	101 ± 22∗ +	233 ± 23∗	106 ± 5	46 ± 5∗	39 ± 2∗	27 ± 5	4 ± 0∗

All values have been presented as the mean±SE mean.

^∗ P < 0.05 vs. baseline.

⁺ P < 0.05 vs. response by corresponding dose of donitriptan in animals pre-treated with saline.

Discussion

John et al. (19, 24) have reported that donitriptan equals 5-HT in potency and efficacy in contracting rabbit isolated saphenous vein and in increasing outward K⁺-current in guinea-pig trigeminal ganglion cells. Donitriptan also decreases carotid blood flow in anaesthetized pigs and conscious dogs. In both in vitro and in vivo experiments, the responses to donitriptan can be antagonized by GR127935 and, thus, donitriptan shows a high affinity as well as efficacy at 5-HT_1B/1D receptors (Table 1).

Heart rate and blood pressure

In contrast to the clinical experience (for references, see 6), sumatriptan as well as other triptans exert small bradycardic and hypotensive responses in anaesthetized pigs (17, 35). Donitriptan was devoid of these systemic effects in saline-treated animals. The exact reason for the difference between donitriptan and other triptans is not clear. However, this difference may be partly related to the slightly higher affinity of donitriptan at the 5-HT_2A receptor (Table 1), which, by virtue of its capacity to mediate hypertension, could annul a potential hypotensive effect of donitriptan. This view seems to be supported by the appearance of hypotension with donitriptan in animals treated with GR127935 (see Table 2; Fig. 5), which can moderately attenuate 5-HT_2A receptor-mediated hypertension in rats (33).

Carotid haemodynamics

In agreement with earlier findings (19, 24), donitriptan dose-dependently decreased total porcine carotid blood flow and conductance in the present experiments. In addition, we observed that this vasoconstrictor effect of donitriptan, as is the case with other triptans, including sumatriptan, avitriptan and eletriptan (see 36), was exclusively confined to cephalic arteriovenous anastomoses; the total nutrient fraction distributed to the head tissues increased. In this respect donitriptan exhibited the highest potency amongst several triptans that we have examined in this porcine model; the mean±SE mean ED_50% (nmol/kg) of donitriptan in decreasing arteriovenous anastomotic vascular conductance (92 ± 31) was lower than that of avitriptan (150 ± 37), sumatriptan (156 ± 54), eletriptan (400 ± 91) or GMC2021 (2317 ± 734) (36). The increase in the arterio-jugular venous oxygen saturation difference with donitriptan confirmed its constriction action on arteriovenous anastomoses.

It is now well recognized that the vasoconstrictor effect of triptans is mediated via 5-HT_1B receptors (12, 13, 15–18). Accordingly, in the present experiments, GR127935 (0.5 mg kg⁻¹) antagonized the constriction of cephalic arteriovenous anastomoses elicited by donitriptan. However, unlike sumatriptan, but as observed with some other triptans, for example eletriptan and GMC2021 (36), this dose of GR127935 did not completely abolish the donitriptan-induced arteriovenous constriction, suggesting the involvement of another, yet uncharacterized, receptor to some extent. Indeed, this is also the case for the arteriovenous anastomotic constriction elicited by ergotamine, dihydroergotamine and 5-HT (36, 37). On the other hand, it is possible that higher doses of GR127935 may be needed for a complete blockade of the effects of donitriptan. Unfortunately, the partial agonist property of GR127935 precludes the use of much higher doses of this antagonist in our experiments (33).

Similar to other 5-HT_1B/1D agonists, donitriptan produced a dilatation of carotid arterioles (nutrient vascular bed) and, as a result, blood flow and vascular conductance in many cranial tissues increased (see Fig. 4). In view of the partial antagonism by GR127935, this dilatation seems to be at least partly due to the activation of the 5-HT_1B receptor, probably mediating endothelium-dependent relaxation in different vascular preparations. Indeed, the 5-HT_1B receptor has been located on vascular endothelium (12) and there is some evidence that 5-HT_1B/D receptors may mediate endothelium-dependent vasodilatation (38–40). Alternatively or in addition, it may be due to an indirect consequence of the closure of arteriovenous anastomoses.

Cardiac output and regional haemodynamics

In previous studies in anaesthetized pigs, it has been shown that sumatriptan reduces total cardiac output and systemic vascular conductance, including decreases in vascular conductances in the kidneys and spleen (41). A decrease in renal vascular conductance by sumatriptan has also been reported in anaesthetized dogs (42). In our study, no decrease in blood flows to or vascular conductances in vital organs (brain, heart, kidneys and portal tissues) were observed with donitriptan; in fact there was a small increase in vascular conductance in the skin, skeletal muscle and brain. Donitriptan was also devoid of any effect on the total systemic vascular conductance, but cardiac output decreased. However, as was the case with carotid blood flow, the decrease in cardiac output was also entirely in the non-nutrient part, i.e. lung blood flow, which mainly reflects peripheral arteriovenous shunting (29). Indeed, the nutrient fraction of cardiac output (blood distributed to peripheral tissues) remained unchanged (Fig. 5).

Therapeutic implications

Our study shows that donitriptan selectively constricts porcine carotid arteriovenous anastomoses, with a higher potency compared with several other triptans. As constriction of cephalic arteriovenous anastomoses is of high predictive value for anti-migraine activity (6), donitriptan should be effective in the treatment of migraine. The drug does not decrease blood flows to vital organs, including the heart, brain and kidneys; sumatriptan can decrease renal blood flow in dogs (42). Lastly, it may be mentioned here that donitriptan has little affinity at the 5-HT_1F receptor, which, in view of the effects of the 5-HT_1F receptor agonist LY334370 (43, 44), may be responsible for side-effects, such as somnolence, asthenia, numbness and paresthesia.

Footnotes

Acknowledgements

This study was supported by Erasmus Pharma B.V., Rotterdam, The Netherlands, on the basis of an agreement with Centre de Recherche, Pierre Fabre S.A., 17 Avenue Jean Moulin, F 81106 Castres Cédex, France.

References

Humphrey

PPA

Feniuk

Perren

Connor

Oxford

Coates

Butina

. GR43175, a selective agonist for the 5-HT₁-like receptor in dog isolated saphenous vein. Br J Pharmacol 1988; 22:1123–32.

Humphrey

PPA

Apperley

Feniuk

Perren

. A rational approach to identifying a fundamentally new drug for the treatment of migraine. In: Saxena

Wallis

Wouters

Bevan

Cardiovascular Pharmacology of 5-Hydroxytryptamine: Prospective Therapeutic Applications. Dordrecht: Kluwer Academic, 1990:416–31.

Saxena

Ferrari

. From serotonin receptor classification to the antimigraine drug sumatriptan. Cephalalgia 1992; 22:187–96.

The Subcutaneous Sumatriptan International Study Group. Treatment of migraine attacks with sumatriptan. New Engl J Med 1991; 22:316–21.

Visser

De Vriend

Jaspers

Ferrari

. Sumatriptan in clinical practice: a 2-year review of 453 migraine patients. Neurology 1996; 22:46–51.

Tfelt-Hansen

De Vries

Saxena

. Triptans in migraine: a comparative review of pharmacology, pharmacokinetics and efficacy. Drugs 2000; 22:1259–87.

Goadsby

. Serotonin 5-HT_1B/1D receptor agonists in migraine. Comparative pharmacology and its therapeuthic implications. CNS Drugs 1998; 22:271–86.

Moskowitz

. Neurogenic versus vascular mechanisms of action of sumatriptan and ergot alkaloids in migraine. Trends Pharmacol Sci 1992; 22:307–11.

Goadsby

Knight

. Inhibition of trigeminal neurones after intravenous administration of naratriptan through an action at 5-hydroxytryptamine (5-HT_1B/1D) receptors. Br J Pharmacol 1997; 22:918–22.

10.

De Vries

Villalón

Saxena

. Pharmacological aspects of experimental headache models in relation to acute antimigraine therapy. Eur J Pharmacol 1999; 22:61–74.

11.

Hargreaves

Shepheard

. Pathophysiology of migraine— new insights. Can J Neurol Sci 1999; 22:S12–9.

12.

Nilsson

Longmore

Shaw

Olesen

Edvinsson

. Ontractile 5-HT_1B receptors in human cerebral arteries: pharmacological characterization and localization with immunocytochemistry. Br J Pharmacol 1999; 22:1133–40.

13.

Razzaque

Heald

Pickard

Maskell

Beer

Hill

Longmore

. Vasoconstriction in human isolated middle meningeal arteries: determining the contribution of 5-HT_1B- and 5-HT_1F-receptor activation. Br J Clin Pharmacol 1999; 22:75–82.

14.

Shepheard

Edvinsson

Cumberbatch

Williamson

Mason

Webb

Possible antimigraine mechanisms of action of the 5HT_1F receptor agonist LY334370. Cephalalgia 1999; 22:851–8.

15.

Bouchelet

Case

Olivier

Hamel

. No contractile effect for 5-HT_1D and 5-HT_1F receptor agonists in human and bovine cerebral arteries: similarity with human coronary artery. Br J Pharmacol 2000; 22:501–8.

16.

Verheggen

Hundeshagen

Brown

Schindler

Kaumann

. 5-HT_1B receptor-mediated contractions in human temporal artery: evidence from selective antagonists and 5-HT receptor mRNA expression. Br J Pharmacol 1998; 22:1345–54.

17.

De Vries

Willems

Heiligers

JPC

Villalón

Saxena

. Investigation of the role of 5-HT_1B and 5-HT_1D receptors in the sumatriptan-induced constriction of porcine carotid arteriovenous anastomoses. Br J Pharmacol 1999; 22:405–12.

18.

Van den Broek

MaassenVanDenBrink

de Vries

Bogers

Stegmann

Avezaat

Saxena

. Pharmacological analysis of contractile effects of eletriptan and sumatriptan on human isolated blood vessels. Eur J Pharmacol 2000; 22:165–73.

19.

John

Pauwels

Perez

Halazy

Le Grand

Verscheure

F 11356, a novel 5-hydroxytryptamine (5-HT) derivative with potent, selective, and unique high intrinsic activity at 5-HT_1B/1D receptors in models relevant to migraine. J Pharmacol Exp Ther 1999; 22:83–95.

20.

Martin

. 5-Hydroxytryptamine receptors. In: IUPHAR The IUPHAR Compendium of Receptor Characterization and Classification. London: IUPHAR Media, 1998:169–85.

21.

Bhalla

Sharma

Wurch

Pauwels

Saxena

. Molecular cloning, sequence analysis and pharmacological properties of the porcine 5-HT_1D receptor. Br J Pharmacol 2000; 22:949–57.

22.

Bhalla

Sharma

Wurch

Pauwels

Saxena

. Molecular cloning, pharmacological properties and tissue distribution of the porcine 5-HT1B receptor. Br J Pharmacol 2001; 22:891–901.

23.

Pauwels

Tardif

Palmier

Wurch

Colpaert

. How efficacious are 5-HT_1B/D receptor ligands: an answer from GTP gamma S binding studies with stably transfected C6-glial cell lines. Neuropharmacology 1997; 22:499–512.

24.

John

Perez

Pauwels

Le Grand

Verscheure

Colpaert

. Donitriptan, a unique high efficacy 5-HT_1B/1D agonist. Key features and acute antimigraine potential. CNS Drug Reviews 2000; 22:278–89.

25.

Saxena

. Cranial arteriovenous shunting, an in vivo animal model for migraine. In: Olesen

Moskowitz

Experimental Headache Models, Volume 27. Philadelphia: Lippincott-Raven, 1995:189–98.

26.

Den Boer

Van Woerkens

Somers

Duncker

Lachmann

Saxena

Verdouw

. On the preservation and regulation of vascular tone in arteriovenous anastomoses during anesthesia. J Appl Physiol 1993; 22:782–9.

27.

Heyck

. Pathogenesis of migraine. Res Clin Stud Headache 1969; 22:1–28.

28.

Saxena

Schamhardt

Forsyth

Loeve

. Computer programs for the radioactive microsphere technique. Determination of regional blood flows and other haemodynamic variables in different experimental circumstances. Comput Programs Biomed 1980; 22:63–84.

29.

Saxena

Verdouw

. Redistribution by 5-hydroxytryptamine of carotid arterial blood at the expense of arteriovenous anastomotic blood flow. J Physiol (Lond) 1982; 22:501–20.

30.

Baile

Nelems

Schulzer

Pare

. Measurement of regional bronchial arterial blood flow and bronchovascular resistance in dogs. J Appl Physiol 1982; 22:1044–9.

31.

Pauwels

. Pharmacological properties of a putative 5-HT_1B/D receptor antagonist GR127935. CNS Drug Rev 1996; 22:415–28.

32.

Skingle

Beattie

Scopes

DIT

Starkey

Connor

Feniuk

Tyers

. GR127935: a potent and selective 5-HT_1D receptor antagonist. Behav Brain Res 1996; 22:157–61.

33.

De Vries

Apaydin

Villalón

Heiligers

JPC

Saxena

. Interactions of GR127935, a 5-HT_1B/D receptor ligand, with functional 5-HT receptors. Naunyn-Schmiedeberg's Arch Pharmacol 1997; 22:423–30.

34.

Steel

RGD

Torrie

. Principles and Procedures of Statistics. A Biomedical Approach, 2nd edn. Tokyo: McGraw-Hill Kogakusha, 1980.

35.

Willems

De Vries

Heiligers

JPC

Saxena

. Porcine carotid vascular effects of eletriptan (UK-116,044): a new 5-HT_1B/1D receptor agonist with anti-migraine activity. Naunyn Schmiedebergs Arch Pharmacol 1998; 22:212–9.

36.

De Vries

Willems

Heiligers

JPC

Villalón

Saxena

. Constriction of porcine carotid arteriovenous anastomoses as indicator of antimigraine activity: the role of 5-HT_1B/1D receptors as well as unidentified receptors. In: Edvinsson

, editor. Migraine and Headache Pathophysiology. London: Martin Dunitz, 1998:119–32.

37.

De Vries

Villalón

Heiligers

JPC

Saxena

. Characterisation of 5-HT receptors mediating constriction of porcine carotid arteriovenous anastomoses; involvement of 5-HT_1B/1D and novel receptors. Br J Pharmacol 1998; 22:1561–70.

38.

Schoeffter

Hoyer

. 5-Hydroxytryptamine (5-HT)-induced endothelium-dependent relaxation of pig coronary arteries is mediated by 5-HT receptors similar to the 5-HT_1D receptor subtype. J Pharmacol Exp Ther 1990; 22:387–95.

39.

Gupta

. An endothelial 5-HT receptor that mediates relaxation in guinea-pig isolated jugular vein resembles the 5-HT_1D subtype. Br J Pharmacol 1992; 22:703–9.

40.

Glusa

Richter

. Endothelium-dependent relaxation of porcine pulmonary arteries via 5-HT_1C-like receptors. Naunyn-Schmiedeberg's Arch Pharmacol 1993; 22:471–7.

41.

Den Boer

Somers

JEA

Saxena

. Comparative effects of the antimigraine drugs sumatriptan and ergotamine on the distribution of cardiac output in anaesthetised pigs. Cephalalgia 1992; 22:205–13.

42.

Cambridge

Whiting

Butterfield

. 5-Carboxamidotryptamine induced renal vasoconstriction in the dog. In: Fozard

Saxena

Serotonin: Molecular Biology, Receptors, and Functional Effects. Basel: Birkhäuser Verlag, 1991:282–8.

43.

Granier

Gossen

Vandenhende

. Safety, pharmacokinatics and efficacy of intravenous LY334370. Cephalalgia 2000; 22:351–2.

44.

Roon

KI.

New 5-HT₁ agonists in migraine, clinical efficacy and mechanisms. Leiden: Department of Neurology, Leiden University Medical Centre, 2000::174.

Effects of Donitriptan on Carotid Haemodynamics and Cardiac Output Distribution in Anaesthetized Pigs

Abstract

Keywords

Introduction

Materials and methods

General

Distribution of carotid blood flow

Distribution of cardiac output

Experimental protocol

Data presentation and statistical analysis

Drugs

Results

Carotid blood flow experiments

Systemic haemodynamics and arterio-jugular venous oxygen saturation difference

Carotid haemodynamics

Cardiac output experiments

Systemic haemodynamics

Regional haemodynamics

Discussion

Heart rate and blood pressure

Carotid haemodynamics

Cardiac output and regional haemodynamics

Therapeutic implications

Footnotes

Acknowledgements

References