Verapamil alters the relationship between renal perfusion pressure and glomerular filtration rate and renin release: the mechanism of the antihypertensive effect.

The renal hemodynamic and renin release responses to verapamil were analyzed in order to determine if the antihypertensive action of the calcium entry blocker could be due to its renal effects. Hemodynamic and renin release measurements were compared in a control group of anesthetized rabbits (N = 9) and in a group of rabbits given verapamil (N = 10) (200 micrograms/kg i.v. initially, 4 micrograms/kg/min thereafter) starting 30 min before data collection. Measurements were made over a range of controlled renal perfusion pressure from 100 to 40 mm Hg. The renal blood flow (RBF) at 100 mm Hg of the verapamil-treated group was 18% greater than (p less than 0.02) that of the control group, while the glomerular filtration rate (GFR) was 51% greater than (p less than 0.001) that of the control group. RBF and GFR autoregulation was highly effective in the control group down to 80 mm Hg, but both variables were poorly regulated in the verapamil group. The filtration fraction of the treated group was 36.9 +/- 1.5% versus 28.5 +/- 1.6% in the control group (p less than 0.003) at 100 mm Hg, and the filtration fraction of the treated group remained significantly greater down to 40 mm Hg. Renin release rates of the two groups were similar at the 100 mm Hg pressure level, but the increase in release due to the progressive reduction in perfusion pressure was significantly greater in the treated group than in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)