RESUMEN
Sodium and water balance was determined in two strains of Wistar rats selectively bred for high (hypernatriophilic, HR) or low salt preference (hyponatriophilic, HO) under basal conditions and during sodium deprivation. Male rats from each strain were selected for an average ingestion of 1.5 per cent NaCl solution of more than (HR) or less than (HO) 4 ml 100 g body weight-1 day-l, during a 10-day period. HR rats (N = 17) presented markedly higher sodium intake under basal conditions (2.983 ñ 0.316 mEq 100 g body weight-1 day-l) than HO rats (N = 12; 0.406 ñ 0,076 mEq 100 g body weight-1 day-l; Mann-Whitney test, P<0.01). Water (HR: 8.6 ñ 0.57; HO: 7.7 ñ 0.32 ml 100 g body weight-1 day-1) and sodium balances (HR: 0.936 ñ 0.153; HO: 0.873 ñ 0.078 mEq 100 g body weight-1 day-l) were similar in both strains, despite a higher sodium and total fluid (HR: 16.3 ñ 1.06; HO: 10.8 + 0.49 ml 100 g body weight-1 day-l; P<0.01) ingestion in HR rats. During sodium deprivation HR rats (N = 13) exhibited a sodium balance similar to that of HO rats (N = 13) (HR: -0.159 ñ 0.011; HO: -0.129 ñ 0.019 mEq 100 g body weight-1 day-1), and, in addition, an adequate suppression of natriuresis (HR: O.049 ñ 0.011; HO: 0.026 ñ 0.004 mEq 100 g body weight-1 day-1). These data show that HR rats present hypernatriophilia as a primary trait, since their sodium-conserving mechanisms are intact. Therefore, these rats provide an adequate model to study factors that determine innate sodium preference.