Role of the renin-angiotensin system on the renal functional reserve in renal transplant recipients.

To determine the renal functional reserve in renal transplant recipients, we measured the glomerular filtration rate by inulin clearance and the renal plasma flow by PAH clearance before and during an amino acid infusion (Totamine, 6 to 8 mg/kg/min for 90 to 120 min) in 18 transplanted patients with stable renal function. To test the role of the renin-angiotensin system on the renal functional reserve, we performed a crossover placebo-controlled randomized trial of acute blockade of the renin-angiotensin system by injection of perindoprilat (2 mg i.v.), an inhibitor of angiotensin converting enzyme before amino acid infusion, each patient being studied twice at seven day intervals. Amino acid infusion induced a time-dependent increase in the glomerular filtration rate (P = 0.04), whether or not the renin-angiotensin system was blocked. Maximal increases were from 49.1 +/- 4.1 to 58.9 +/- 5.4, mean +/- SE (18.5%), in control conditions and from 52.4 +/- 5.6 to 62.1 +/- 5.5 ml/min/1.73 m2 (19.7%) after perindoprilat. The increase in glomerular filtration rate was less pronounced in patients taking cyclosporin A than in patients treated with steroid and azathioprine. Amino acid infusion also induced a significant and time-dependent increase (15.2 to 20.2%) in the renal plasma flow (P < 0.01) whether or not perindoprilat had been given. Furthermore, perindoprilat alone increased renal plasma flow by 13.6%, and this effect seemed additive with that of amino acids. Perindoprilat injection decreased filtration fraction (from 0.20 +/- 0.01 to 0.19 +/- 0.01). This parameter returned to basal values after amino acid infusion (0.20 +/- 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)