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 micromol/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 micromol/L) did not inhibit enzyme activity. The B(max) value for binding of [(3)H]-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.
Lucas-Teixeira
V
V
Institute of Pharmacology and Therapeutics, Faculty of Medicine, 4200 Porto, Portugal.
Vieira-Coelho
M A
MA
Soares-Da-Silva
P
P
D000821:Animal Feed; D000818:Animals; D001552:Benzazepines / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism / Q000494:pharmacology*; D018492:Dopamine Antagonists / Q000378:metabolism; D004435:Eating / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism; D007583:Jejunum / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D008297:Male; D008892:Milk; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D001552:Benzazepines; D018492:Dopamine Antagonists; D000254:Sodium-Potassium-Exchanging ATPase; D004298:Dopamine