Effects of nifedipine on the renal vascular responses and blood pressure responses to norepinephrine and angiotensin II in the anesthetized rabbit.

Effects of a Ca-antagonist, nifedipine, on renal vascular responses and systemic pressor responses to angiotensin II and norepinephrine were studied in anesthetized rabbits. The changes of renal blood flow were estimated by an electromagnetic flowmeter. After the intravenous administration of nifedipine (50 micrograms/kg), mean blood pressure decreased from 116 +/- 3.1 mmHg to 102 +/- 3.4 mmHg (p less than 0.001). Renal vascular responses to angiotensin II were attenuated significantly after the administration of nifedipine, but not changed to norepinephrine. Pressor responses to angiotensin II at a low dose were significantly diminished after the administration of nifedipine (p less than 0.05), whereas it had no effect at higher doses. Nifedipine tended to suppress the increase in arterial pressure induced by norepinephrine, but the changes were not statistically significant. These results suggest that calcium influx in the vascular smooth muscle cells is not likely to be a common pathway in the vasoconstrictor reaction to angiotensin II and norepinephrine in anesthetized rabbit.