Haemorheological effects of ketanserin, a selective 5-HT2 receptor antagonist, in aged, spontaneously hypertensive dogs.

The intravenous injection of ketanserin (0.63-0.31-0.16 mg/kg) to aged, spontaneously hypertensive dogs produces a dose- and time-dependent reduction of mean arterial blood pressure. Concomitantly the whole blood viscosity at shear rates between 11.5 to 450 sec-1 is reduced in parallel with the reduction of packed cell volume (PCV), red blood cell (RBC) number and whole blood haemoglobin content. Plasma viscosity and plasma fibrinogen levels are slightly reduced after the highest dose of ketanserin only, while plasma osmolarity is not affected. Packed RBC viscosity and RBC deformability as measured by a filtration technique are not consistently changed by such a treatment. The reduction of PCV, possibly subsequent to plasma volume expansion during whole blood pressure reduction, is the major cause for the decrease in whole blood viscosity. Such a rheological effect of ketanserin may contribute to the reduction of peripheral vascular resistance and the maintenance of microcirculatory flow despite the decrease of capillary perfusion pressure during blood pressure reduction.