- The renal handling of water by SBH and SBN rats was evaluated under basal conditions and following various intervention procedures. During 17 weeks of unrestricted water intake, SBH rats drank less water and excreted less urine with a higher osmolality than SBN. The differences in urine volume and osmolality persisted during 2 weeks of paired water intake. Acute water loading elicited comparable dilution of the urine in the two strains. Water deprivation for 48 h resulted in a marked rise in urine osmolality, which tended to be higher in SBN. Administration of exogenous vasopressin in water loaded animals caused a similar rise in urine osmolality. Papillary solute and urea content was higher in SBH than in SBN, but comparable in water loaded animals. The results show that although SBH differ from SBN rats in the handling of water under basal conditions, their renal diluting and concentrating capacity is comparable at extreme conditions. GFR and RBF were equal in both strains. The data suggest that SBH rats have increased renal water reabsorption as compared to SBN, which may be mediated by ADH, PG or other mechanisms. This characteristic may be related to their propensity to develop hypertension.