Cerebrovascular and metabolic effects of SNP-induced hypotension in young and aged hypertensive rats

Abstract

Cerebral blood flow (CBF) and cerebral oxygen consumption (CMR(O2)) were measured in young (4 months) and aged (24-26 months) spontaneously hypertensive (SHR) rats and Wistar Kyoto (WKY) controls under control anesthetized conditions (70 per cent N2O, 30 per cent O2) and during hypotension induced with intravenous sodium nitroprusside (SNP) infusions. CBF was measured with radioactive microspheres and cerebral arterial-venous blood O2 measurements were determined from arterial and sagittal sinus blood samples. Arterial blood P(CO2) was maintained at approximately 35 mmHg and body temperature at 37° C. Under control conditions blood pressure was increased in SHR but there was no significant difference in CBF or CMR(O2) between SHR and WKY or young and aged rats. CBF and CMR(O2) were maintained in WKY when mean blood pressure was decreased to 65 mmHg with SNP infusion. CBF was significantly decreased in young and aged hypertensive rats during SNP-induced hypotension. CMR(O2) was also decreased in both young and aged hypertensive animals. These results support previous reports that SNP-induced hypotension will maintain CBF and CMR(O2) in normotensive subjects, but suggest that the direct cerebrovasodilating effects of SNP are moderate and will not reverse the cerebrovascular changes induced by chronic hypertension.