Effect of the calcium antagonists felodipine and nimodipine on cortical blood flow in the spontaneously hypertensive rat.

: We studied the effect of the dihydropyridine calcium antagonists felodipine nimodipine on perfusion of the cerebral cortex in the spontaneously hypertensive rat (SHR). Nimodipine and felodipine were infused in equipotent doses in chloralose-anaesthetized SHR. During the infusion of a low and an intermediate dose of felodipine, mean arterial blood pressure was lowered to 90.5 +/- 1.5 and 67.1 +/- 2.9% of the control level. The nimodipine infusion lowered mean arterial pressure to 85.7 +/- 2.0 and 59.7 +/- 2.4% of the control level. At these pressures, cortical perfusion as measured by a laser Doppler flow technique increased to 123.5 +/- 6.9 and 130 +/- 5.4% of the control level during the felodipine infusion and to 114.0 +/- 1.6 and 122.3 +/- 3.2% of the control level during the nimodipine infusion. When these results were compared by covariance analysis of variance, felodipine induced a significantly greater change in cortical perfusion. At the highest dose of felodipine and nimodipine there was no significant difference in cortical perfusion between the two drugs. The administration of felodipine induced a decrease in cerebrovascular autoregulation. However, this impairment of cerebrovascular autoregulation is not likely to trigger cerebral hypoperfusion. Thus, for a mean arterial pressure of 55 mmHg, the laser Doppler-measured cortical flow was, if anything, elevated after felodipine administration.