Glucose Uptake via SGLT-1 Is Stimulated by β2-Adrenoceptors in the Ruminal Epithelium of Sheep

Abstract

Glucose absorption via the sodium glucose-linked transporter (SGLT)-1, decreases the glucose concentration in the ruminant forestomach and may ameliorate or prevent ruminal lactic acidosis. Because acidotic ruminants show increased sympathetic activity, the possibility of adrenergic modulation of SGLT-1 was investigated. Glucose uptake into ovine ruminal epithelia was measured in Ussing chambers after the addition of 200 micromol/L (14)C-labeled glucose to the mucosal solution. Glucose uptake decreased (P < 0.05) by >50% in comparison with control after mucosal addition of the SGLT-1 inhibitor, phlorizin (100 micromol/L). Serosal preincubation with 100 micromol/L epinephrine increased (P < 0.05) the phlorizin-sensitive glucose uptake in the absence and presence of indomethacin (10 micromol/L). The effect of epinephrine was simulated by beta- (100 micromol/L isoproterenol) and beta(2)-receptor agonists (10 micromol/L terbutaline), as well as by direct stimulation of adenylyl cyclase (10 micromol/L forskolin). The serosal addition of methoxamine, clonidine, dobutamine or BRL 37344 had no effect. Inhibition of protein kinase A with 2 micromol/L H 89 completely abolished the stimulation of glucose uptake by epinephrine. We conclude that ruminal SGLT-1 can be stimulated via beta(2)-dependent generation of cyclic adenosine monophosphate.