RENAL EFFECTS OF NIFEDIPINE AND CAPTOPRIL IN PATIENTS WITH ESSENTIAL-HYPERTENSION AND REDUCED RENAL RESERVE

In this study we investigated the short-term effects of calcium channel blockers and angiotensin-converting enzyme inhibitors on renal hemodynamics and the urinary excretion of proteins with different relative mass in subjects with mild to moderate essential hypertension and apparently normal glomerular filtration rate but reduced renal functional reserve. Sixteen subjects underwent the following four treatments: (1) low-protein meal (0.2 g protein/kg body wt), (2) high-protein meal (1.3 g protein/kg body wt), (3) high-protein meal plus oral nifedipine (20 mg), and (4) high-protein meal plus oral captopril (50 mg). Two urine samples were obtained after meals. Blood samples were drawn at the midpoint of each 120-minute urine collection period. Urine and serum were tested for total protein, immunoglobulin G, albumin, alpha(1)-microglobulin, retinol binding protein, and beta(2)-microglobulin. Glomerular filtration rate and renal plasma flow were assessed by iothalamate and p-aminohippuric clearance, respectively. Compared with the high-protein meal alone, nifedipine elicited a dear-cut increase in the urinary excretion of total protein (+60%, P<.01), immunoglobulin G (+58%, P<.01), albumin (+25%, P<.05), retinol binding protein (+47%, P<.05), and beta(2)-microglobulin (+52%, P<.05); captopril decreased the urinary excretion rate of immunoglobulin G (-26%, P<.05), albumin (-22%, P<.05), and beta(2)-microglobulin (-34%, P<.05). The ratio between the clearances of immunoglobulin G and albumin was higher after nifedipine (+21%, P<.01) and unchanged after captopril (-9%, P=NS) compared with the high-protein meal alone. Glomerular filtration rate and renal plasma flow were higher after nifedipine (+10%, P<.05 and +9%, P<.05, respectively) and lower after captopril(-2%, P<.05 and -9%, P=NS, respectively) than after the high-protein meal alone. Thus, single doses of nifedipine, preceding a protein load in the form of a meat meal, raise both glomerular filtration rate and renal plasma flow and increase urinary protein excretion rate. Changes in both glomerular selectivity and tubular reabsorption seem to account for increased proteinuria.