Effect of Different β-Adrenergic Agonists on the Intestinal Absorption of Galactose and Phenylalanine

Abstract

Abstract Nutrient transport across the mammalian small intestine is regulated by several factors, including intrinsic and extrinsic neural pathways, paracrine modulators, circulating hormones and luminal agents. Because β-adrenoceptors seem to regulate gastrointestinal functions such as bicarbonate and acid secretion, intestinal motility and gastrointestinal mucosal blood flow, we have investigated the effects of different β-adrenergic agonists on nutrient absorption by the rat jejunum in-vitro. When intestinal everted sacs were used the β2-agonist salbutamol had no effect either on galactose uptake by the tissue or mucosal-to-serosal flux whereas mixed β1- and β2-agonists (isoproterenol and orciprenaline) and β3-agonists (BRL 35135, Trecadrine, ICI 198157 and ZD 7114) inhibited galactose uptake and transfer of D-galactose from the mucosal-to-serosal media across the intestinal wall (although the inhibiting effects of isoproterenol and Trecadrine were not statistically significant). In intestinal 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 β3-adrenergic agonists. These results suggest that β1 and β3-adrenergic receptors could be involved in the regulation of intestinal active transport of sugars and amino acids.