Fasting enhances alpha(1)-adrenoceptor-mediated effects on jejunal epithelial transport in 20-day-old rats

• Type: Other Publications
• Date: 1999

Authors

lucas-teixeira, v (Author) Other; vieiua-coelho, ma (Author) Other; serrao, mp (Author) Other; soares-da-silva, p (Author) FMUP

Scientific classification

FOS: Medical and Health sciences > Health sciences

Other information

Authenticus ID: P-000-YWN

Abstract (EN): This study examined the effect of food deprivation on the jejunal response to ¿2-adrenoceptor activation in young (20-d-old) and adult (60-d-old) rats, using short-circuit (l(sc)) measurements in the absence or presence of furosemide (1 mmol/L). The effect of ¿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 I(sc) with similar half-maximal effective concentration (EC50; 12.3 ± 1.1 vs. 9.6 ± 1.1 nmol/L) and maximal effect (E(max); 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 I(sc) in fed and food-deprived rats was markedly (P < 0.05) attenuated by furosemide (1 mmol/L). E(max) 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 I(sc) 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 K(D) 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 ¿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 ¿2-adrenoceptors.

Language: English

Type (Professor's evaluation): Scientific