Influence of a Decrease in Blood Viscosity on Arterial Pressure in Normotensive and Spontaneously Hypertensive Rats.

We investigated the effect of a decrease in blood viscosity on the mean BP during isovolumic hemodilution and vasodilating activity of the endothelium in normotensive Wistar rats and spontaneously hypertensive rats (SHR). Blood viscosity was reduced by isovolumic hemodilution (replacement of 10% of circulating blood with an equal volume of plasma). Hemodilution caused the same reduction in blood viscosity by 16% in both groups of rats. In Wistar rats, a decrease in blood viscosity did not significantly change in the mean BP; no significant correlations between blood viscosity and mean BP were observed before and after hemodilution. In SHR, a decrease in blood viscosity led to a significant decrease in the mean BP by 18%. Correlations were found between the mean BP and blood viscosity in SHR before (r=0.63; p=0.028) and after (r=0.71; p=0.009) isovolumic hemodilution. In SHR, a decrease in the index of vasodilating activity of the endothelium due to a decrease in the vasodilatory response to intravenous administration of the endothelium-dependent vasodilator acetylcholine was revealed. In SHR, BP passively follows the change, in this case, the decrease in blood viscosity, which attests to impaired BP regulation in response to changes in shear stress on the vascular endothelium caused by the development of endothelial dysfunction in hypertensive animals.