Abstract

The effect of a single oral dose of 10 mg of the calcium antagonist felodipine or placebo was investigated in 10 cyclosporin-treated renal transplant recipients before, during, and after an acute intravenous infusion of cyclosporin in a randomised, single-blind cross-over study. Renal plasma flow (RPF), glomerular filtration rate (GFR), renal tubular sodium and water handling as judged by the lithium clearance technique, and plasma concentrations of angiotensin II (AngII), aldosterone (Aldo), atrial natriuretic factor (ANF), and arginine vasopressin (AVP) were measured. Both RPF and GFR increased after felodipine (mean increase: RPF, 38.7%; GFR, 16.2%; P less than 0.01 for both) in spite of a significant decrease in both systolic and diastolic blood pressure (mean decrease 10.6% and 16.0% respectively, P less than 0.02 for both). Estimated by the lithium clearance technique felodipine induced a decrease in fractional reabsorption in the proximal tubules (mean 72.0% vs 63.0%, P less than 0.01), an increase in proximal output of fluid (mean 11.0 ml/min vs 16.0 ml/min, P less than 0.01), and a decrease in distal fractional reabsorption of sodium (mean 90.5% vs 83.9%, P less than 0.05) resulting in a significant natriuresis and diuresis. Ang II, Aldo, ANF, or AVP did not change. Intravenous infusion of cyclosporin per se did not influence any of the parameters. It is concluded that a single dose of felodipine in cyclosporin treated renal transplant recipients has beneficial effects on blood pressure, renal haemodynamics, and renal tubular sodium and water handling, which seems to compensate for some of the adverse effects of cyclosporin. It is suggested that these effects result from a direct vasodilatation and an effect on proximal tubular function.