[Diuresis, renal plasma flow and glomerular filtration in conscious and anesthetized sheep: the effects of a diet deficient in proteins].

Determinations of renal plasma flow (RPF), glomerular filtration rate (GFR) and urine flow in sheep fed low protein diets have yielded controversial data. In the present experiment, 8 sheep were fed a regular diet and another 6 received a low protein ration. Water intake and urine output were measured over 10 days. RPF and GFR were determined on 2 consecutive days. The latter determinations were repeated on 5 anaesthetized animals (sodium thiopental) in each group. An important increase in water intake (58%) and urine output (98%) was observed in the sheep on the low protein diet. In these animals, blood urea averaged 0.1 g/l. Urine output was greater (with a lower osmolarity) when the blood urea level was the lowest. RPF and GFR were significantly lower in the sheep on the low protein diet (RPF: 13.5 versus 28.1 ml/min/kg in the control animals; GFR: 1.61 versus 4.01 ml/min/kg); no relationship could be established with the blood urea level. The only effect of the anaesthesia was a reduction in RPF, of the same magnitude in both groups of sheep (about 35%). In conclusion, when sheep are fed a low protein diet, the volume of plasma processed through the kidney is decreased. In the present experiment, the increased urine flow and the lowered urinary osmolarity indicate an impaired renal concentrating ability. Barbiturate anaesthesia does not affect this phenomenon.