VASOPRESSIN IS INVOLVED IN RENAL EFFECTS OF HIGH-PROTEIN DIET - STUDY IN HOMOZYGOUS BRATTLEBORO RATS

The present study was designed to test the possible role of vasopressin in the renal response to dietary protein. This possiblity was suggested by the similarity of effects on renal function and morphology of chronic high-protein intake and chronic stimulation of urine concentration. Adult male Brattleboro rats, genetically unable to produce vasopressin, were fed high-protein (32% casein = HP, n = 8) or low-protein (10% casein = LP, n = 9) diet for 7 wk. Renal function was evaluated by clearance techniques based on 24-h urine collections in metabolic cages. The response to a single injection of the vasopressin analogue 1-desamino-8-D-arginine vasopressin (DDAVP) was also tested. Kidney weight and height of the different renal zones were assessed at the end of the study. HP diet increased urea excretion nearly sevenfold. Water intake increased by 57% (P < 0.001) and urine flow rate by 71% (P < 0.01). Urine osmolality rose from 104 to 181 mosmol/kgH2O (P < 0.001). At variance with what occurs in rats with endogenous vasopressin (Sprague-Dawley; Bouby, N., et al. Kidney Int 34: 4-12, 1988), HP diet increased creatinine clearance per unit body weight by only 14% and did not change free water clearance, renal mass, and height of inner stripe of outer medulla. However, the rise in urine osmolality and drop in free water clearance after DDAVP were significantly greater in HP- than in LP-fed Brattleboro rats. These results show 1) that vasopressin is necessary for the full manifestation of the protein-induced changes in renal function and morphology and 2) that the well-known influence of dietary proteins and urea on water economy is strictly dependent on vasopressin.