Dihydroergocryptine maintains erythrocyte fluidity in acidotic and hyperosmolar buffer solutions modelling hypoxic and ischemic microcirculation

Abstract

The positive effects of Ergopeptide Alkaloids, particularly Dihydroergotoxine with Dihydroergocryptine (DHEC) as one of the components, on cerebral functions has been known for about three decades. DHEC in particular has multiple biological effects: It is an α-adrenoreceptor blocking agent and an agonist of dopamine receptors and is known as a peripheral and cerebral vasodilator. An anti-aggregative activity has been shown on platelet aggregation induced by adrenaline and collagen as well as on erythrocyte aggregation induced by dextran. It also is a metabolic enhancer, protecting against metabolic stress due to hypoxia and ischemia and it increases the uptake of deoxyglucose and oxygen utilisation in the brain.

We studied the protective effect of DHEC (concentration range 10 nM to 100 μM) on human red blood cell (RBC) rheology in acidotic and hyperosmolar solutions (AHS) modelling the hypoxic and ischemic microcirculation. The microscopic photometric monolayer technique was used to quantify alterations of RBC resting shape, stiffness and relaxation time automatically and time dependently (Elias-c-analyser). The technique is based on changes in light transmission through a RBC monolayer in a flow chamber at controlled shear stresses. A HEPES buffer solution was used as control buffer and an acidotic/hyperosmotic buffer solution (pH 6.8, 380 mosmol/kg) to simulate the metabolic challenge in ischemia. AHS itself hardly altered the RBC discocytic shape. However, it significantly increased RBC stiffness and relaxation time (p<0.001). Both RBC in control buffer and RBC pre-stressed in AHS for 20 minutes were incubated with DHEC at different concentrations within the flow chamber. DHEC-induced stomatocytes appeared dose-dependently in both, control buffer and AHS, within less than 2 minutes. The shape change was reversible after re-incubating in control buffer solution or in AHS not containing DHEC. The AHS induced stiffness and relaxation time increases were partially inhibited when DHEC was added to AHS (p<0.05). Although there was a slight effect of DHEC on RBC in buffer, DHEC was significantly more effective when RBCs were exposed to AHS (p<0.01). From a biophysical point of view the stomatocytic shape change observed might indicate a slight expansion of the cytosolic side of the RBC membrane. This in consequence partially maintain undisturbed spectrin/protein spatial distribution. Inhibition of spectrin-cytosolic interactions, which are altered due to pH shifts in the AHS, leads to maintenance of RBC fluidity. In conclusion DHEC might preserve RBC fluidity in vivo especially in the ischemic and hypoxic region of the pathologic microcirculation. The direction, but not the extent of in vivo effects should be predictable from the in vitro results, since metabolic and physiological effects in in vivo conditions could further enhance the in vitro effects. The RBC stomatocytic shape change observed could be positively correlated with the known vasoactive DHEC effect, acting to improve the blood flow in ischemic regions.