Food intake abolishes the response of rat jejunal Na+,K+-ATPase to dopamine

The aim of the present study was to evaluate whether the sensitivity of jejunal Na+,K+-ATPase to inhibition by dopamine (DA) in young rats is related to the type of food (breast milk vs. solid) or reflects a developmental adaptation. When 18-d-old rats were separated from their dams and fed solid food (the same used to feed adult rats) for 2 d, intestinal Na+,K+-ATPase activity was significantly greater than that of breast-fed pups of the same age (20 d) (127 +/- 8 vs. 52 +/- 4 nmol Pi . mg protein(-1) . min(-1); P < 0.05). Activity in rats fed solid food was insensitive to inhibition by 1 mu mol/L DA. Na+ ,K+-ATPase activity in 60-d-old rats (117.4 +/- 4.2 nmol Pi . mg protein(-1) . min(-1)) was also higher (P < 0.05) than in breast-fed rats, and DA (1 mu mol/L) did not inhibit enzyme activity. The B-max value for binding of [H-3]-Sch 23390 in 20-d-old breast-fed rats did not differ from that in age-matched rats fed a solid food for 2 d and or that in 60-d-old rats. Levels of DA, but not L-3,4-dihydroxyphenylalanine and amine metabolites, in the jejunal mucosa of 20-d-old rats that had eaten solid food for 2 d were 60% lower than in age-matched rats, breast-fed rats, and not different from those in the jejunal mucosa of 60-d-old rats fed the solid food. We conclude that in adult rats, in contrast to in young rats, DA does not inhibit jejunal Na+,K+-ATPase activity, and food intake in young rats plays an important role in the development of the insensitivity of Na+,K+-ATPase activity to DA.