Nifedipine and Nimodipine: Effect on Blood Pressure and Regional Cerebral Blood Flow in Conscious Normotensive and Hypertensive Rats

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Abstract
The dose-dependent reduction of mean arterial pressure (MAP) in conscious spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) was more pronounced after intravenous nimodipine than nifedipine administration. Nimodipine (5 .mu.g/kg) followed by infusion of 0.75 .mu.g/kg/min lowered the blood pressure by 10% in both normotensive and hypertensive rats; the same dose schedule of nifedipine did not lower MAP. Neither drug altered the regional cerebral blood flow (rCBF) in this dose. After 50 .mu.g/kg nimodipine were administered, followed by 7.5 .mu.g/kg/min nimodipine, MAP dropped 38% in WKY and 46% SHR; corresponding figures for nifedipine were 13 and 17%. In spite of the reduction in MAP and a concomitant decrease in PaCO2, [partial arterial CO2 pressure], rCBF increased significantly in 19 of 23 regions studied after nifedipine and in 15 regions after nimodipine in SHR. The increase in rCBF in WKY was slight and insignificant in most areas. Thus, both calcium entry blockers reduced the cerebrovascular resistance more in SHR than in WKY.

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