Responses to renin inhibition in conscious primates

A method for the measurement of renal clearances was adapted in a novel manner to the conscious marmoset. Twenty-four hours before an experiment, animals underwent surgery for placement of both femoral arterial and venous catheters. A catheter was also implanted into the urinary bladder through the abdominal wall. The urinary catheter consisted of two tubes. One tube was connected to a pump, which removed the urine, while the other tube remained open to prevent the formation of a vacuum inside the bladder. Using this technique, we kept renal clearances stable for at least 3 h. All catheters were removed the day after the clearance experiment, and the bladder was reconstructed using microsurgical techniques. The bladder operation did not appear to produce lasting anatomical or functional changes, since the animals were able to void spontaneously and, after 3 mo, the bladder had regained its normal size and shape. Reimplantation of both the vessel and bladder catheters at this time allowed for an additional study of renal clearances within the same animals. Administration of the renin inhibitor CGP 29287 (1 mg/kg) to furosemide-pretreated conscious marmosets lowered blood pressure and increased renal blood flow. Glomerular filtration rate remained unchanged by CGP 29287, leading to a fall in the effective filtration fraction. Urinary volume and urinary sodium excretion also were unchanged by the renin inhibitor. We describe a novel method for the study of renal clearances in a small conscious primate and suggest that the renin-angiotensin system plays an important role in the control of renal function in the sodium-depleted marmoset.