The influence of antihypertensive therapy on cerebral autoregulation in aged hypertensive rats.

Cerebrovascular responses to hemorrhage induced hypotension were tested in aged (24 month) spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) after ten weeks of antihypertensive drug or sham treatment. Antihypertensive drug treatment consisted of 1 mg/kg/day minoxidil, 4 mg/kg/day hydralazine and 4 mg/kg/day propranolol given in the drinking water. Antihypertensive therapy produced a 30% decrease in systolic blood pressure in aged SHR to levels not significantly different from sham treated WKY. Cerebral blood flow (CBF), measured under control conditions using ketamine anesthesia, was not significantly different between sham and drug treated SHR and WKY. Cerebral oxygen metabolic rate (CMRO2) was significantly decreased in drug treated SHR and WKY compared to sham treated rats. Lowering blood pressure to a level between 80 and 95 torr produced no significant change in CBF or CMRO2 in sham or drug treated WKY or antihypertensive treated SHR, but a produced a significant decrease it both CBF and CMRO2 in sham treated SHR. Decreasing mean blood pressure to 50-60 torr produced a significant decrease in CBF but not CMRO2 in both WKY treatment groups and in hypertensive treated SHR, but again in sham treated SHR both CBF ana CMRO2 were significantly decreased. These results indicate that aged hypertensive rats are unable to maintain CBF or CMRO2 under even moderate hypotensive test conditions, and that cerebral autoregulation can be improved with antihypertensive therapy.