Effects of Age and Salt

Blood pressure response to chronic high salt intake and kinetics of red blood cell Na and K(Rb) transport were studied in salt-sensitive (DS) and salt-resistant (DR) Dahl rats fed a high salt diet (8% NaCl) for 7 weeks from the fifth (young), 12th (adult), or 23rd (old) week of age. The kinetics of ouabain-sensitive Rb uptake and Na extrusion were determined in Na media as a function of both intracellular Na (Na,, 2-8 mmol/1 cells) and extracellular Rb (Rb0). In addition, the kinetics of furosemide-sensitive Rb + uptake (related to Rb0) and the magnitude of the Na and Rb leaks were assessed. High salt intake induced hypertension in young and adult but not in old DS rats although red blood cell Na was slightly increased in all age groups of DS rats fed a high salt diet The kinetic parameters of the Na-K pump were similar in DS and DR rats fed a low salt diet Ouabain-sensitive transport rates were not suppressed in erythrocytes of salt hypertensive Dahl rats. Maximal velocities of the Na-K pump (related to Na,) decreased significantly with age in all groups except in DS rats fed a high salt diet This was compensated by an age-dependent increase in the affinity for Na, so that no substantial differences in transport rates between young and old rats were seen at physiological cell Na and plasma K levels. The maximal velocity of furosemide-sensitive Rb uptake rose with age in all groups without changes in the affinity for Rb0. High salt intake increased its maximal activity only in DS rats. The Rb leak was higher in DS relative to DR rats irrespective of salt intake, age, or blood pressure. The Na leak was elevated in DS rats in which it was augmented by high salt intake. Salt hypertension was, however, not associated with a significant increase of the Na leak, which was responsible for most alterations of cell Na content (Hypertension 1990;15:612-627)