Journal of Nutrition

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(Journal of Nutrition. 2000;130:2461-2466.)
© 2000 The American Society for Nutritional Sciences

Article

Food Deprivation Increases {alpha}2-Adrenoceptor–Mediated Modulation of Jejunal Epithelial Transport in Young and Adult Rats1

V. Lucas-Teixeira, M. A. Vieira-Coelho, M. P. Serrão and P. Soares-da-Silva2

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

2To whom correspondence should be addressed.

This study examined the effect of food deprivation on the jejunal response to {alpha}2-adrenoceptor activation in young (20-d-old) and adult (60-d-old) rats, using short-circuit (Isc) measurements in the absence or presence of furosemide (1 mmol/L). The effect of {alpha}2-adrenoceptor stimulation by 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK 14,304; 0.3–3000 nmol/L) was a concentration-dependent decrease in Isc with similar half-maximal effective concentration (EC50; 12.3 ± 1.1 vs. 9.6 ± 1.1 nmol/L) and maximal effect (Emax; 70.6 ± 6.9 vs. 80.6 ± 4.5% of reduction) values in adult food-deprived and fed rats. The effect of UK 14,304 on Isc in fed and food-deprived rats was markedly (P < 0.05) attenuated by furosemide (1 mmol/L). Emax values for UK 14,304 in 20-d-old food-deprived rats were higher (P < 0.05) than those observed in fed rats (93.3 ± 3.3 vs. 67.0 ± 11.3% of reduction), without differences in EC50 values. The effect of UK 14,304 on Isc in 20-d-old fed rats was completely abolished by furosemide (1 mmol/L). In food-deprived young rats, the effect of UK 14,304 was also markedly (P < 0.05) antagonized by furosemide, but not completely abolished. Specific [3H]-rauwolscine binding in membranes from jejunal epithelial cells revealed the presence of a single class of binding sites, with an apparent KD in the low nmol/L range. In 20-d-old food-deprived rats, specific [3H]-rauwolscine binding was markedly increased, and this was reversed by refeeding. Na+,K+-ATPase activity in isolated jejunal epithelial cells from 60-d-old fed rats was twice that in 20-d-old fed rats [117 ± 14 vs. 52 ± 5 nmol free inorganic phosphorus/(mg protein·min)]. Food deprivation in adult rats, but not in 20-d-old rats, was accompanied by a significant decrease in Na+,K+-ATPase activity. In both young and adult rats (fed and food-deprived), UK 14,304 did not affect Na+,K+-ATPase activity. In conclusion, food deprivation in 20-d-old rats enhanced the response to {alpha}2-adrenoceptor stimulation. This effect, which depends primarily on the stimulation of a furosemide-sensitive antisecretory mechanism, is suggested to result from increases in the number of jejunal epithelial {alpha}2-adrenoceptors.

KEY WORDS: • rat jejunum • {alpha}2-adrenoceptors • Na+,K+,2Cl--co-transporter • Na+K+-ATPase






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