Effect of salt intake on jejunal dopamine, Na+,K+-ATPase activity and electrolyte transport.

The present study addresses the question of the relevance of salt intake on jejunal dopamine, Na+,K+-ATPase activity and electrolyte transport. Low salt, but not high salt, intake for 2 weeks increased dopamine levels in the jejunal mucosa accompanied by a marked decrease in L-3,4-dihydroxyphenylalanine tissue levels. By contrast, in rats fasted for 72 h the effect of refeeding for 24 h with a low salt diet failed to change dopamine tissue levels, although it significantly increased those of L-3,4-dihydroxyphenylalanine. By contrast, high salt intake markedly increased the tissue levels of both dopamine and L-3,4-dihydroxyphenylalanine, without changes in dopamine/L-3,4-dihydroxyphenylalanine tissue ratios. Tissue levels of both L-3,4-dihydroxyphenylalanine and dopamine in control conditions (normal salt intake for 2 weeks) were markedly higher (P < 0.05) than in rats submitted to 72 h fasting plus 24 h refeeding. The effect of fasting for 72 h followed by 24 h refeeding was a marked decrease in jejunal Na+,K+-ATPase activity, particularly evident for rats fed a normal salt and high salt diets during the refeeding period. Basal short circuit current was similar in rats fed a normal salt diet for 2 weeks and 24 h, and the type of diet failed to alter basal short circuit current after refeeding with normal, low and high salt diets. On the other hand, the effect of prolonged low salt intake was a marked decrease in jejunal Na+, K+-ATPase activity and basal short circuit current, whereas high salt intake failed to alter enzyme activity and basal short circuit current. In rats fed for 2 weeks a high salt diet ouabain was found to be more potent in reducing jejunal short circuit current than in rats fed normal and low salt diets. The effect of furosemide was more marked in rats fed for 2 weeks high and low salt diets than in animals receiving a normal salt intake. Dopamine (up to 1 micromol L-1) was found not to alter Na+,K+-ATPase and basal short circuit current in jejunal epithelial sheets, in rats fed with normal, low and high salt diets for 2 weeks and 24 h.