Glucose uptake via SGLT-1 is stimulated by β2-adrenoceptors in the ruminal epithelium of sheep

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 mumol/L C-14- 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 mumol/L). Serosal preincubation with 100 mumol/L epinephrine increased (P < 0.05) the phlorizin-sensitive glucose uptake in the absence and presence of indomethacin (10 mumol/L). The effect of epinephrine was simulated by P(100 mumol/L isoproterenol) and beta(2)-receptor agonists (10 mumol/L terbutaline), as well as by direct stimulation of adenylyl cyclase (10 mumol/L forskolin). The serosal addition of methoxamine, clonidine, dobutamine or BRL 37344 had no effect. Inhibition of protein kinase A with 2 mumol/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.