Effects of dietary salt on erythrocyte and renal Na,K-ATPase activity in Dahl salt-sensitive and salt-resistant rats

This study was designed to investigate the effects of dietary salt and potassium supplementation on blood pressure and the Na,K-ATPase activity in erythrocytes and renal cortex from Dahl salt-sensitive (DS) and salt-resistant (DR) rats. Rats were fed diets containing low salt (0.4%), high salt (7%) or high salt plus potassium-citrate (K-citrate, 3%) from 5 to 10 weeks of age or from 15 to 20 weeks of age. The systolic blood pressure of DS rats measured by the tail-cuff method was significantly increased by feeding the high salt or high salt plus K-citrate diets compared with rats fed the low salt diet at both ages. The DR rats remained normotensive regardless of the dietary salt level. Supplementation of the high salt diet with K-citrate attenuated elevation of blood pressure in DS rats. The sodium content of red blood cells of DS rats fed the high salt diet was increased whereas that of DR rats fed the same diet remained unchanged. The erythrocyte Na,K-ATPase activity was not altered at 10 weeks of age by dietary salt in both strains of rats. But at 20 weeks of age, the erythrocyte enzyme activity was suppressed in DS rats fed the high salt diet and was significantly lower compared with that in DR rats fed the same diet. The renal cortex microsomal enzyme activity was decreased in both of 10-week and 20-week old DS rats fed the high salt diet. The renal cortex enzyme activity in DR rats was not changed by dietary salt levels and consequently was greater than that of DS rats when fed the high salt diet. The renal cortex Na,K-ATPase activity of DS rats was negatively correlated to blood pressure. These results suggest that the permeability of cell membrane in DS rats is increased when fed the high salt diet and consequent increases in cell sodium concentration together with suppressed Na,K-pump activity are involved in the progressive increase in blood pressure.