The study investigated the effects of intravenous infusion of atrial natriuretic peptide (human ANP 99-126) on renal function and central hemodynamics after coronary artery bypass grafting (CABG), and the ability of ANP to reverse the acute nephrotoxic effects of cyclosporine after heart transplantation. Ten patients with an EF > 0.5 and normal renal function were studied 2 to 4 hours after CABG surgery. Furthermore, six heart transplant recipients receiving cyclosporine for immunosuppression who developed renal dysfunction 2 to 4 days after transplantation were studied. Standard urinary clearance of 51Cr-EDTA and PAH was used to study the effects of ANP on glomerular filtration rate (GFR) and renal blood flow (RBF). Baseline measurements were first performed during two 30-minute periods. Incremental infusion rates of ANP were then administered for three consecutive 30-minute periods (25, 50, and 100 ng/kg/min), followed by two 30-minute post-ANP control periods. Marked increases in urinary flow (UF), GFR, filtration fraction (FF), and fractional urinary excretion of Na+ were observed in the CABG patients with increasing doses of ANP, while RBF was unchanged. Mean arterial pressure decreased by around 15% at the highest ANP dose. In the heart transplant recipients, baseline GFR was markedly reduced compared to pretransplantation values (-65%). UF, GFR, and RBF increased 240%, 69%, and 53%, respectively, while renal vascular resistance decreased 45% during the highest dose of ANP infused. At this ANP dose level, circulating ANP concentrations were sixfold to eightfold higher than the preinfusion control level.(ABSTRACT TRUNCATED AT 250 WORDS)