Effects of captopril on renal function in healthy uninephrectomized subjects and in healthy control subjects

To study the importance of the renin-angiotensin-II system for renal haemodynamics and sodium and water handling in the adapted remnant kidney in healthy uninephrectomized subjects.

Case-control study.

All subjects were investigated at laboratory C, Department of Medicine and Nephrology, Skejby Hospital.

Fourteen healthy uninephrectomized (Unx) and 14 matched healthy control subjects (Cs).

Captopril, 25 mg orally.

The glomerular filtration rate (GFR) and renal plasma flow (RPF) were measured by the constant infusion clearance technique using 125I-iothalamate and 131I-hippuran as reference substances, tubular function was evaluated by the lithium clearance technique (CLi), urinary flow rate (V), sodium excretion (UNaV), fractional sodium excretion (FENa), mean blood pressure (MBP) and heart rate (HR) were measured by conventional methods and plasma levels of angiotensin II (Ang-II), aldosterone (Aldo), arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) were measured by radioimmunoassay.

In both groups captopril ingestion resulted in a significant decrease in the MBP (Unx: 87.1 to 83.5 and Cs: 86.8 to 83.8 mmHg, median values), filtration fraction (Unx: 24.6 to 22.1 and Cs: 24.1 to 22.5%, median values) and Ang-II (Unx: 10.5 to 7.7 and Cs: 12 to 7.6 pmol-1, median values). Single kidney GFR, V, and CLi were unchanged in both groups. FENa and single kidney RPF were significantly increased in only the Cs group; FENa (Unx: 1.81 to 1.91 and Cs: 1.56 and 1.90%, median values). The plasma level of ANP was significantly decreased in only the Unx group.

The data suggest that sodium handling in the remnant kidney in uninephrectomized subjects could be less sensitive to Ang-II than in healthy control subjects, and that this might be as a result of adaptive changes in the distal parts of the nephron.