Sage Journals: Discover world-class research

Abstract

It has been proposed that prostaglandin E₂ (PGE₂) is released from astrocytic endfeet to dilate parenchymal arterioles through activation of prostanoid (EP₄) receptors during neurovascular coupling. However, the direct effects of PGE₂ on isolated parenchymal arterioles have not been tested. Here, we examined the effects of PGE₂ on the diameter of isolated pressurized parenchymal arterioles from rat and mouse brain. Contrary to the prevailing assumption, we found that PGE₂ (0.1, 1, and 5 μmol/L) constricted rather than dilated parenchymal arterioles. Vasoconstriction to PGE₂ was prevented by inhibitors of EP₁ receptors. These results strongly argue against a direct role of PGE₂ on arterioles during neurovascular coupling.

Keywords

astrocytes brain parenchymal arterioles neurovascular coupling

INTRODUCTION

Local blood flow is regulated by neuronal activity so as to match changes in the metabolic demand of brain tissue with the supply of oxygen and glucose, a process that is critical to maintain cerebral homeostasis and to prevent the development of ischemic conditions. This linkage between neuronal activity and cerebral blood flow, termed as neurovascular coupling or functional hyperemia,¹ is rapid (seconds) and occurs at the level of the cerebral microcirculation within the brain parenchyma. Local increases in cerebral blood flow are mediated by dilation of parenchymal arterioles,² which, unlike surface cerebral arteries (pial arteries), are encased by astrocytic processes (‘endfeet’).¹

Recent evidence indicates that information about neuronal activity is communicated to (1) surface arterioles via astrocytic processes comprising the glia limitans and to (2) parenchymal arterioles through elevation of astrocytic Ca²⁺ and the subsequent engagement of Ca²⁺-dependent vasodilatory pathways in astrocytic endfeet.^1,3 Two potential Ca²⁺-dependent astrocytic endfoot targets in particular have received considerable research attention: large-conductance, Ca²⁺-sensitive K⁺ (BK) channels, which deliver K⁺ into the restricted perivascular space and dilate vessels by activating strong inwardly rectifying K⁺ channels,^4–6 and phospholipase A₂,^3,7 which produces arachidonic acid through the hydrolysis of membrane lipids.

Prostaglandin E2 (PGE₂), a metabolite of arachidonic acid produced by the action of cyclooxygenase (COX), has been proposed as a major mediator of neurovascular coupling.⁸ A role for PGE₂ in neurovascular coupling has largely been inferred from studies on the effects of COX inhibitors on neurally evoked vasodilation in brain slices.⁸ However, some studies have found no effect of COX inhibition on neurovascular coupling in brain slices,⁶ and others have attributed the reduction of functional hyperemia by COX inhibition to effects on COX2 in neurons.⁹ Moreover, whether COX is even expressed in astrocytes has been called into question.¹⁰

In theory, PGE₂ could act as a vasodilator or constrictor depending on the nature of the member of the G protein-coupled prostanoid (EP) receptor family. The G_s-coupled EP₄ receptor signals through the cyclic adenosine monophosphatedependent protein kinase (PKA) pathway, which is associated with dilation. Whereas the EP₁ subtype is thought to couple to G_q-type α subunits and mediates an increase in intracellular Ca²⁺, consistent with a role in constriction. EP₃, a subtype with promiscuous G protein-coupling propensity, has also been linked to elevation of intracellular Ca²⁺ and thus might mediate a contractile response to PGE₂.

A critical test for the potential involvement of PGE₂ in neurovascular coupling is the demonstration that PGE₂ directly dilates isolated parenchymal arterioles. This evidence is currently lacking. In contrast, external K⁺, also posited as a mediator of neurovascular coupling, has been shown to be a potent, rapid, reversible dilator of parenchymal arterioles.^4–6 Here, we tested the effects of PGE₂ on the diameter of isolated pressurized parenchymal arterioles from rat and mouse brain. Contrary to expectation, we found that PGE₂ constricted rather than dilated parenchymal arterioles.

MATERIALS AND METHODS

Animals

All experimental protocols used in this study were in accord with institutional guidelines approved by the Institutional Animal Care and Use Committee of the University of Vermont. Male C57BL6 mice and male Sprague-Dawley rats were used. Animals (aged 3 to 4 months) were euthanized by intraperitoneal injection of sodium pentobarbital (mouse: 100 mg/kg; rat: 150 mg/kg) followed by rapid decapitation.

Pressurized Parenchymal Arterioles

After euthanasia, the brain was removed and placed into 4°C MOPS-buffered saline. Parenchymal arterioles, arising from the M1 region of the middle cerebral artery and perfusing the neocortex, were dissected. Precapillary arteriolar segments were then cannulated on glass micropipettes with one end occluded in an organ chamber (University of Vermont Instrumentation and Model Facility) and pressurized using an arteriograph system (Living Systems Instrumentation, Inc., Burlington, VT, USA). Parenchymal arterioles were pressurized to 40 mm Hg and superfused (4 mL/min) with prewarmed (35°C to 37°C), gassed (5% CO₂, 20% O₂, 75% N₂) artificial cerebrospinal fluid (aCSF) for at least 1 hour. Only viable parenchymal arterioles, defined as those that developed pressure-induced myogenic tone greater than 20%, were used in subsequent experiments (Supplementary Figure 1A). The average percentage of tone was 36.6 ± 3.4% (n = 20) and 38.1 ± 2.3% (n = 23) in parenchymal arterioles from rat and mouse, respectively. Endothelial function was tested by assessing the vasodilator response to NS309 (1 μmol/L), an activator of endothelial small- (SK) and intermediate (IK)-conductance Ca²⁺-activated K⁺ channels. Drugs were applied by addition to the superfusate. Vessel internal diameter was continuously monitored using a CCD camera and edge-detection software (IonOptix, Milton, MA, USA). Maximal dilation was obtained in nominally Ca²⁺ -free aCSF (0 μmol/L [Ca²⁺]o, 5 mmol/L EGTA).

Figure 1.

(A–D) Rat and mouse parenchymal arterioles (PA) constrict in response to prostaglandin E₂ (PGE₂). (A) Recording of the internal diameter of a pressurized (40 mm Hg) rat parenchymal arteriole during the perfusion of PGE₂ (0.1, 1, and 5 μmol/L), added noncumulatively. (B) Summary data (means ± SEMs) showing changes in luminal diameter expressed as percentages relative to baseline diameter; the number of experiments is indicated in parentheses (**P < 0.01, NS indicates nonsignificant). (C) Recordings of the internal diameter of pressurized (40 mm Hg) mouse parenchymal arterioles during the perfusion of PGE₂ (1 μmol/L) with and without EP receptor inhibitors. Upper trace: nonselective EP₁, EP₂, and EP₃ receptor antagonist AH6809 (10 μmol/L). Bottom trace: selective EP₁ antagonist SC51322 (1 μmol/L). Both nonselective inhibition of EP_1–3 receptors and specific inhibition of EP₁ completely prevented PGE₂-induced vasoconstriction in mouse parenchymal arterioles. Adenosine (10 μmol/L; top trace) and NS309 (1 μmol/L; bottom trace) were included as positive controls. (D) Summary data (means ± SEMs) showing change in luminal diameter; the number of experiment is indicated in parentheses (**P < 0.01, ***P < 0.001). (E, F) Prostacyclin (PGI₂) dilates mouse parenchymal arterioles. (E) Typical recordings of the internal diameter of pressurized (40 mm Hg) parenchymal arterioles during the perfusion of PGI₂ (1, 3, and 10 μmol/L), added noncumulatively. (F) Summary data (means ± SEMs) showing change in luminal diameter induced by adenosine with and without A_2A receptor antagonist ZM241385 and PGI₂; the number of experiments is indicated in parentheses (*P < 0.05, **P < 0.01, NS indicates nonsignificant).

Solutions

The composition of MOPS-buffered saline (in mmol/L) was 135 NaCl, 5 KCl, 1 KH₂PO₄, 1 MgSO₄, 2.5 CaCl₂, 5 D-glucose, 3 MOPS, 0.02 EDTA, 2 pyruvate, bovine serum albumin (10 mg/mL), pH 7.3 at 4°C. The composition of aCSF (in mmol/L) was 125 NaCl, 3 KCl, 26 NaHCO₃, 1.25 NaH₂PO₄, 1 MgCl₂, 4 D-glucose, 2 CaCl₂; pH was 7.3 when aerated with 5% CO₂.

Drugs

Stock solutions of PGE₂ (10 mmol/L in dimethyl sulfoxide) were prepared from powder each day of the experiment or stored at −20°C for < 1 month, and were protected from exposure to light in accordance with recommendations of the suppliers. During experiments, PGE₂ was superfused immediately after dissolution in aCSF or dilution from dimethyl sulfoxide stock solutions to prevent PGA₂ formation from PGE₂ dehydration.

Prostaglandin E₂ was purchased from different suppliers (Enzo Life Sciences, Farmingdale, NY, USA; Sigma-Aldrich, St Louis, MO, USA; and Tocris Bioscience, Ellisville, MO, USA). No significant differences were observed among the responses to PGE₂ from the different vendors in parenchymal arteriolar diameter recording experiments. Prostacyclin (PGI₂) was purchased from Enzo Life Sciences. ZM241385 and SC51322 were purchased from Tocris Bioscience. AH6809 and adenosine were purchased from Sigma-Aldrich.

Data Analysis and Statistics

Changes in arteriolar diameter were calculated as percent change from baseline (change in diameter/initial diameter). Data are expressed as means ± SEMs. Differences between two groups were analyzed using Student's t-test. Statistical significance was tested at the 95% (P < 0.05) confidence level.

RESULTS

Prostaglandin E₂ Constricts Pressurized Parenchymal Arterioles Although PGE₂ released from astrocytes has been proposed as a major mediator of neurovascular coupling, whether PGE₂ actually dilates parenchymal arterioles has not been experimentally determined. To test this directly, we assessed the effects of different concentrations of PGE₂ on the diameter of isolated parenchymal arterioles, preconstricted by elevation of intravascular pressure to a physiologic level (40 mm Hg). Surprisingly, rather than inducing dilation, PGE₂ constricted cerebral parenchymal arterioles from rat (Figures 1A and 1B) and mouse (Figures 1C to 1E) in a concentration-dependent manner. Prostaglandin E₂ (1 μmol/L) constricted rat and mouse parenchymal arterioles by 18.6 ± 3% (n = 11) and 16.5 ± 2% (n = 21), respectively.

In mouse, vasoconstriction induced by PGE₂ (1 μmol/L) was significantly higher at an intraluminal pressure of 20 mm Hg, than at 80 mm Hg (25.8 ± 2% versus 10.8 ± 1%, n = 7, Supplementary Figures 1B and C). Superfusing mouse parenchymal arterioles with aCSF gassed with 5% CO₂, 10% O₂, 85% N₂ to lower the oxygen tension had no effect on the constriction to 1 μol/L PGE₂. The constriction measured in 10% O₂ (17.1 ± 2.6%, n = 7) was very similar to the above-mentioned value in 20% oxygen. Thus, we have found that PGE₂ invariably constricted parenchymal arterioles over a range of test conditions. Under these same test conditions, NS309, a synthetic activator of endothelial SK and IK channels, always dilated the parenchymal arterioles (Figures 1A and 1C), indicating that their dilator capacity was not impacted by the test conditions employed.

Prostaglandin E₂-Induced Constriction of Pressurized Parenchymal Arterioles is Mediated by EP₁ Receptors

In studies of newborn and adult pigs, an assessment of PGE₂ receptor subtypes along with measurements of the effects of PGE₂ on IP₃ and cyclic adenosine monophosphate production suggests a predominant expression of EP₁ with lesser levels of EP₃ in adult brain microvessels.¹¹ In mouse parenchymal arterioles, we found that vasoconstriction to PGE₂ (1 μmol/L) was inhibited by the prostanoid receptor antagonist AH6809 (10 μmol/L), which does not discriminate among EP₁, EP₂, and EP₃ receptors (Figures 1C and 1D).¹² SC51322 (1 μmol/L), a selective antagonist of the EP₁ receptor,¹² completely inhibited the constriction to PGE₂ (Figures 1C and 1D), indicating that PGE₂ acts through EP₁ receptors to constrict parenchymal arterioles. This is consistent with the likely coupling of EP₁ receptors to G proteins of the G_q class, which typically mediate the contractile response to vasoconstrictor agonists. Prostaglandin E₂ did not cause vasodilation in the presence of AH6809 or SC51322.

The Vasodilator Adenylyl Cyclase-Protein Kinase Pathway is Intact in Parenchymal Arterioles

It has been proposed that PGE₂, acting through G_s-coupled receptors (e.g., EP₄), stimulates the adenylyl cyclase-PKA pathway to dilate parenchymal arterioles.⁸ To confirm that the adenylyl cyclase-PKA pathway is operational in parenchymal arterioles, we tested the effects of the endogenous agents, adenosine and PGI₂, which have been shown to relax smooth muscle through this mechanism. Both adenosine and prostacyclin caused rapid and reversible dilation of parenchymal arterioles (Figures 1C, Figures 1E, and 1F). Vasodilation to adenosine was prevented by preincubation with the adenosine A_2A receptor antagonist ZM241385 (Figure 1D).

Prostaglandin E₂ Constricts Pressurized Mouse Pial Arterioles Previous studies have investigated the effects of PGE₂ in isolated cerebral arteries from different species (Supplementary Table 1), the majority of which have shown vasoconstriction. Arteries from guinea pig, dog, pig, and baboon constrict in response to PGE₂, whereas feline pial arteries display weak relaxation at lower concentrations and contraction at higher concentrations of PGE₂. Studies using rat, rabbit, and postmortem human cerebral arteries have reached very divergent conclusions (Supplementary Table 1). In tests of PGE₂ (0.1 and 1 μmol/L) on middle and posterior cerebral arteries from adult mice, we observed only vasoconstriction (Supplementary Figures 1D and E).

DISCUSSION

A number of studies have proposed that astrocyte-derived PGE₂ makes a major contribution to functional hyperemia.⁸ According to this model, PGE₂, generated via a Ca²⁺-dependent mechanism through the action of astrocytic endfoot COX1 on phospholipase A₂-derived arachidonic acid, is released from astrocytes and activates receptors on vascular smooth muscle cells, presumably G_s-coupled EP₄ receptors, to promote arteriolar dilation. Much of the evidence for this mechanism comes from inhibitor-based studies using brain slice preparations in which Ca²⁺ elevation in astrocytes is induced directly through application of a metabotropic glutamate receptor agonist or indirectly through electrical field stimulation of neurons, after which the effects of COX inhibitors on arteriolar dilation are measured. These studies have yielded mixed results.^6,7

Several neurovascular coupling agents have been proposed including prostaglandins, epoxyeicosatrienoic acids, adenosine, oxygen, nitric oxide, H⁺, and K⁺.^1,8 Although mechanisms of functional hyperemia may vary substantially between regions of the brain, one absolute criterion that a putative ‘gliotransmitter’ must satisfy, if it is to couple neuronal activation to vasodilation, is a demonstrated ability to dilate isolated arterioles. Adenosine, prostacyclin, and external H⁺ and K^+4,5,13 are potent vasodilators that induce a rapid dilation when directly applied to isolated arterioles, and therefore fulfill this requirement. Prostaglandin E₂ does not. Although the remote possibility that an unknown vasoconstrictor is released from remnant endfoot membranes in response to PGE₂ cannot be formally excluded, we consider this highly unlikely given that pial arteries, which lack endfeet also constrict to PGE₂ (Supplementary Figures 1D and E) and no dilation was observed in parenchymal arterioles in the presence of an EP₁ blocker (Figure 1). Therefore, our results clearly indicate that PGE₂ does not dilate cerebral parenchymal arterioles (Figure 1), which are critical to neurovascular coupling, but instead causes vasoconstriction through activation of EP₁ receptors.

Interpretation of the effects of exogenous application of PGE₂ on arteriolar diameter in brain slices or in vivo is potentially complicated by indirect effects on neurons and astrocytes. Our observations are consistent with studies reporting vasoconstriction of cerebral arteries in vivo^14,15 and reduced cerebral blood flow^16,17 in response to PGE₂. Nevertheless, application of PGE₂ has been shown to dilate cerebral arteries^18,19 and parenchymal arterioles in vivo,³ and in neonatal brain slices.⁷ The latter finding could be explained by the observation that EP₂ and EP₄ receptors, which mediate vasodilatory pathways, are predominantly expressed in the early stage of life.^11,20,21 In the adult animal, it has been shown that trigeminal neurons, which innervate pial arteries, release the vasorelaxant calcitonin gene-related peptide in response to PGE₂.^22,23 Depending on experimental conditions, perivascular nerves may or may not be functional—a possible cause of the discrepancies in both in vitro (Supplementary Table 1) and in vivo studies noted above. It should also be borne in mind that other studies have indicated a role for COX2 and PGE₂ in modulating synaptic signaling in neurons.^24,25 Because astrocytes are recruited by synaptic release of glutamate,¹ inhibition of such a mechanism would decrease neurovascular coupling efficiency, a result that could mistakenly be taken as evidence for a direct neurovascular-coupling function of PGE₂. This hypothesis is consistent with the demonstrated contribution of COX2 to functional hyperemia⁹ despite the absence of COX2 expression in astrocytes.¹⁰ Moreover, ablation of the Cox1 gene in mice does not affect functional hyperemia,²⁶ ruling out a contribution of this isoform to PGE₂ production in this context. Accordingly, rather than providing evidence for a role for PGE₂ as an astrocyte-derived agent, the effects of PGE₂ or COX inhibitors in brain slices or in vivo^3,7 may reveal their actions in neurons and synaptic transmission.^9,27 In fact, it is possible that activation of cerebral arteriolar EP₁ receptors and subsequent vasoconstriction may contribute to the neurotoxicity of PGE₂.²⁷

In conclusion, our results provide strong evidence that PGE₂ is not directly involved in neurovascular coupling, and underscore the need to directly test putative neurovascular coupling transmitters on their target arterioles.

DISCLOSURE/CONFLICT OF INTEREST

The authors declare no conflict of interest.

Footnotes

ACKNOWLEDGEMENTS

The authors would like to thank Dr Anne Joutel for her insightful comments on the manuscript.

Notes

Supplementary Information accompanies the paper on the Journal of Cerebral Blood Flow & Metabolism website ()

References

Iadecola

Nedergaard

. Glial regulation of the cerebral microvasculature. Nat Neurosci 2007; 10: 1369–1376.

Fernandez-Klett

Offenhauser

Dirnagl

Priller

Lindauer

. Pericytes in capillaries are contractile in vivo, but arterioles mediate functional hyperemia in the mouse brain. Proc Natl Acad Sci USA 2010; 107: 22290–22295.

Takano

Tian

Peng

Lou

Libionka

Han

. Astrocyte-mediated control of cerebral blood flow. Nat Neurosci 2006; 9: 260–267.

Filosa

Bonev

Straub

Meredith

Wilkerson

Aldrich

. Local potassium signaling couples neuronal activity to vasodilation in the brain. Nat Neurosci 2006; 9: 1397–1403.

Girouard

Bonev

Hannah

Meredith

Aldrich

Nelson

. Astrocytic endfoot Ca2+ and BK channels determine both arteriolar dilation and constriction. Proc Natl Acad Sci USA 2010; 107: 3811–3816.

Koide

Bonev

Nelson

Wellman

. Inversion of neurovascular coupling by subarachnoid blood depends on large-conductance Ca2 +-activated K+ (BK) channels. Proc Natl Acad Sci USA 2012; 109: E1387–E1395.

Zonta

Angulo

Gobbo

Rosengarten

Hossmann

Pozzan

. Neuron-to-astrocyte signaling is central to the dynamic control of brain microcirculation. Nat Neurosci 2003; 6: 43–50.

Attwell

Buchan

Charpak

Lauritzen

Macvicar

Newman

. Glial and neuronal control of brain blood flow. Nature 2010; 468: 232–243.

Niwa

Araki

Morham

Ross

Iadecola

. Cyclooxygenase-2 contributes to functional hyperemia in whisker-barrel cortex. J Neurosci 2000; 20: 763–770.

10.

Lecrux

Toussay

Kocharyan

Fernandes

Neupane

Levesque

. Pyramidal neurons are ‘neurogenic hubs’ in the neurovascular coupling response to whisker stimulation. J Neurosci 2011; 31: 9836–9847.

11.

Varma

Chemtob

. Ontogenic increase in PGE2 and PGF2 alpha receptor density in brain microvessels of pigs. Br J Pharmacol 1994; 112: 59–64.

12.

Abramovitz

Adam

Boie

Carriere

Denis

Godbout

. The utilization of recombinant prostanoid receptors to determine the affinities and selectivities of prostaglandins and related analogs. Biochim Biophys Acta 2000; 1483: 285–293.

13.

Dabertrand

Nelson

Brayden

. Acidosis dilates brain parenchymal arterioles by conversion of calcium waves to sparks to activate BK channels. Circ Res 2012; 110: 285–294.

14.

Toda

Kawakami

Yoshida

. Constrictor action of oxyhemoglobin in monkey and dog basilar arteries in vivo and in vitro. Am J Physiol 1991; 260(2 Pt 2): H420–H425.

15.

White

Hagen

Morgan

Dawson

Robertson

. Experimental study on the genesis of cerebral vasospasm. Stroke 1975; 6: 52–57.

16.

Pickard

MacDonell

Mackenzie

Harper

. Prostaglandin-induced effects in the primate cerebral circulation. Eur J Pharmacol 1977; 43: 343–351.

17.

White

Hagen

. Cerebrovascular actions of prostaglandins. Pharmacol Ther 1982; 18: 313–331.

18.

Ellis

Wei

Kontos

. Vasodilation of cat cerebral arterioles by prostaglandins D2, E2, G2, and I2. Am J Physiol 1979; 237: H381–H385.

19.

Armstead

Mirro

Busija

Leffler

. Vascular responses to vasopressin are tone-dependent in the cerebral circulation of the newborn pig. Circ Res 1989; 64: 136–144.

20.

Hayashi

Park

Kuehl

. Relaxant and contractile responses to prostaglandins in premature, newborn and adult baboon cerebral arteries. J Pharmacol Exp Ther 1985; 233: 628–635.

21.

Wright

Abran

Bhattacharya

Hou

Bernier

Bouayad

. Prostanoid receptors: ontogeny and implications in vascular physiology. Am J Physiol Regul Integr Comp Physiol 2001; 281: R1343–R1360.

22.

Jenkins

Feniuk

Humphrey

. Characterization of the prostanoid receptor types involved in mediating calcitonin gene-related peptide release from cultured rat trigeminal neurones. Br J Pharmacol 2001; 134: 1296–1302.

23.

Neeb

Hellen

Boehnke

Hoffmann

Schuh-Hofer

Dirnagl

. IL-1 beta stimulates COX-2 dependent PGE(2) synthesis and CGRP release in rat trigeminal ganglia cells. PLoS ONE 2011; 6:e17360.

24.

Sang

Zhang

Marcheselli

Bazan

Chen

. Postsynaptically synthesized prostaglandin E2 (PGE2) modulates hippocampal synaptic transmission via a presynaptic PGE2 EP2 receptor. J Neurosci 2005; 25: 9858–9870.

25.

Clasadonte

Poulain

Hanchate

Corfas

Ojeda

Prevot

. Prostaglandin E2 release from astrocytes triggers gonadotropin-releasing hormone (GnRH) neuron firing via EP2 receptor activation. Proc Natl Acad Sci USA 2011; 108: 16104–16109.

26.

Niwa

Haensel

Ross

Iadecola

. Cyclooxygenase-1 participates in selected vasodilator responses of the cerebral circulation. Circ Res 2001; 88: 600–608.

27.

Andreasson

. Emerging roles of PGE2 receptors in models of neurological disease. Prostaglandins Other Lipid Mediat 2010; 91: 104–112.

Supplementary Material

Please find the following supplemental material available below.

For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.

For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.

0.00 MB

0.29 MB

0.10 MB

Prostaglandin E 2,a Postulated Astrocyte-Derived Neurovascular Coupling Agent,Constricts Rather than Dilates Parenchymal Arterioles

Abstract

Keywords

INTRODUCTION

MATERIALS AND METHODS

Animals

Pressurized Parenchymal Arterioles

Solutions

Drugs

Data Analysis and Statistics

RESULTS

Prostaglandin E2-Induced Constriction of Pressurized Parenchymal Arterioles is Mediated by EP1 Receptors

The Vasodilator Adenylyl Cyclase-Protein Kinase Pathway is Intact in Parenchymal Arterioles

DISCUSSION

DISCLOSURE/CONFLICT OF INTEREST

Footnotes

ACKNOWLEDGEMENTS

Notes

References

Supplementary Material

Prostaglandin E₂-Induced Constriction of Pressurized Parenchymal Arterioles is Mediated by EP₁ Receptors