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Article

Food Intake Abolishes the Response of Rat Jejunal Na⁺,K⁺-ATPase to Dopamine¹

Institute of Pharmacology and Therapeutics, Faculty of Medicine, 4200 Porto, Portugal

²To whom correspondence should be addressed.

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 µmol/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 µmol/L) did not inhibit enzyme activity. The B_max value for binding of [³H]-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.

KEY WORDS: • dopamine • jejunum • rats • Na⁺,K⁺-ATPase • food intake

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