Effect of different beta-adrenergic agonists on the intestinal absorption of galactose and phenylalanine

Nutrient transport across the mammalian small intestine is regulated by sev eral factors, including intrinsic and extrinsic neural pathways, paracrine modulators, circulating hormones and luminal agents. Because beta-adrenocep tors seem to regulate gastrointestinal functions such as bicarbonate and ac id secretion, intestinal motility and gastrointestinal mucosal blood flow, we have investigated the effects of different beta-adrenergic agonists on n utrient absorption by the rat jejunum in-vitro. When intestinal everted sacs were used the beta(2)-agonist salbutamol had n o effect either on galactose uptake by the tissue or mucosal-to-serosal flu x whereas mixed beta(1)- and beta(2)-agonists (isoproterenol and orciprenal ine) and beta(3)-agonists (BRL 35135, Trecadrine, ICI 198157 and ZD 7114) i nhibited galactose uptake and transfer of D-galactose from the mucosal-to-s erosal media across the intestinal wall (although the inhibiting effects of isoproterenol and Trecadrine were not statistically significant). In intes tinal everted rings both Trecadrine and BRL 35135 clearly reduced galactose uptake, the effect being a result of inhibition of the phlorizin-sensitive component. Total uptake of phenylalanine by the intestinal rings was also reduced by those beta(3)-adrenergic agonists. These results suggest that beta(1)- and beta(3)-adrenergic receptors could be involved in the regulation of intestinal active transport of sugars and amino acids.