Defective renal handling of water in the rat with a portacaval shunt.

Male rats with a portacaval anastomosis, placed in metabolic cages excreted twice as much urine as unoperated control rats. After subcutaneous injection of one unit of pitressin tannate in oil, the rats on average exhibited a 27% reduction in fluid intake and a 37% reduction in urine volume. Nevertheless the rats still excreted 60% more urine than control rats. Fluid restriction resulted in a reduction in urine volume and an increase in urine osmolality in both groups of rats. Shunted rats, however, continued to excrete 49 ml.kg.(-1)24h-1, while drinking only 43 ml.kg.(-1)24h-1. Owing to the negative water balance plasma osmolality rose by 22 mosm/kg H2O. Two weeks after portacaval anastomosis arterial prostaglandin-E concentrations were 412 ng/1, compared to 158 ng/1 in control rats. The results are consistent with the idea, that the shunt induced diuresis may be due to the renal effects of prostaglandin-E.