We examined renal responses to a pharmacological dosage of human atrial natriuretic peptide (hANP) and the potential interference of nifedipine administration with the effects of hANP on kidney function in healthy subjects and normoglycemic patients with type 1 diabetes mellitus. Ten healthy volunteers (age, 28 +/- 1 years) and ten patients (age, 33 +/- 2 years; diabetes duration; 14 +/- 3 years; HbAI 7.2% +/- 0.2%) were studied. According to a double-blind, randomized, placebo-controlled trial design, three experiments were performed in each subject using the double-dummy technique: placebo only, hANP only, and nifedipine + hANP. As i.v. bolus injection 100 micrograms hANP was given; nifedipine was applied buccally, at a dose of 10 mg 90 min before and at a dose of 5 mg together with hANP injection. At base-line and in the placebo only experiment, patients did not differ from controls. In the hANP only experiment, in both groups hANP resulted in increased urinary volume and both sodium and chloride excretion (P less than 0.05 vs placebo only experiment). In patients, hANP-induced increase in electrolyte excretion was greater than in controls (P less than 0.05). In the nifedipine + hANP experiment, hANP-induced changes in renal indexes were enhanced in controls (P less than 0.05 vs hANP only experiment) but not in patients. Thus, diuretic response to nifedipine + hANP in patients was decreased in comparison with controls (P less than 0.05). In patients, however, nifedipine administration decreased the hANP-induced increase in urinary albumin excretion (P less than 0.05 vs hANP only experiment). Creatinine clearance was uninfluenced throughout the experiments.(ABSTRACT TRUNCATED AT 250 WORDS)