The effect of manidipine, a new Ca2+ antagonist, on intrarenal hemodynamics was assessed in essential hypertension and compared with nicardipine, a previously studied Ca2+ antagonist. Identical 2-week studies were repeated before and during the administration of manidipine (10 mg once daily, 2 weeks) in 3 patients with essential hypertension who were given regular- and sodium-restricted diets for 1 week each. The renal function curve (pressure-natriuresis relationship) was drawn by plotting the urinary sodium excretion rate on the y-axis as a function of the systemic mean arterial pressure (MAP) on the x-axis. Assuming that the difference between MAP and the extrapolated x-intercept of the renal function curve represents the effective filtration pressure across the glomerular capillary walls, the intrarenal hemodynamics were calculated (e.g., afferent arteriolar resistance (RA), efferent arteriolar resistance (RE), and glomerular pressure (PG)). During the regular sodium diet, MAP was lowered from 100 +/- 7 to 93 +/- 5 mmHg (p < 0.04) and the effective filtration pressure was lowered from 20 +/- 2 to 10 +/- 3 mmHg (p < 0.05); the renal plasma flow rate (pre: 560 +/- 74 vs. post: 627 +/- 108 mL/min) and glomerular filtration rate (82 +/- 10 vs. 78 +/- 5 mL/min) were not altered. RA remained unchanged (3,800 +/- 700 vs. 3,400 +/- 300 dyn.sec.cm-5; % reduction: 4 +/- 16%) whereas RE was reduced from 4,300 +/- 700 to 3,300 +/- 800 dyn.sec.cm-5 (19 +/- 15%). Thus, PG was lowered from 58 +/- 2 to 50 +/- 2 mmHg (13 +/- 3%), which parallels with the reduction in MAP.(ABSTRACT TRUNCATED AT 250 WORDS)