Glomerular hyperfiltration and hypertension induced by extensive loss of renal parenchyma are suspected to accelerate progression of renal failure. Amino acid infusion or protein ingestion also modify renal hemodynamics and increase glomerular filtration rate (GFR). This phenomenon was used to study the influence of two commonly used antihypertensive agents, captopril and nifedipine, on renal hemodynamics at rest and during glomerular hyperfiltration. Thirteen healthy volunteers were studied on three separate days (days A, B, and C) in random sequence: inulin and p-amino hippurate (PAH) clearance were measured first under glucose infusion and afterwards under stimulation by amino acid infusion (0.35 mmol/kg/min; 4 mg/kg/min). Day A served as a control, where no medication was given. On day B, 10 mg nifedipine, and on day C, 25 mg captopril, were administered orally before study. Without premedication (= day A, control) GFR increased from 108.0 +/- 6.9 mL/min (SEM) to 131.7 +/- 7.0 mL/min (P less than 0.05). On day B (nifedipine), GFR before stimulation by amino acids was already elevated to 121.8 +/- 4.2 mL/min (P less than 0.05 compared with day A) and increased to 132.6 +/- 6.3 mL/min with infusion of amino acids, thus to the same range as on day A without medication. On day C, after captopril, GFR did not increase with infusion of amino acids (from 112.5 +/- 7.2 to 117.3 +/- 6.3 mL/min). Our results indicate the calcium channel antagonist nifedipine and the angiotensin-converting enzyme (ACE) inhibitor captopril differ in their effect on intrarenal hemodynamic parameters. Nifedipine induces hyperfiltration at rest and allows maximal hyperfiltration to develop under amino acid infusion.(ABSTRACT TRUNCATED AT 250 WORDS)