Hypovolaemia inhibits acid-induced alkaline transport in the rat duodenum via an alpha-2 adrenergic mechanism.

Acid exposure of the duodenal mucosa is a well-known stimulant of the mucosal alkaline secretion. We have previously reported that a minor blood loss inhibits this secretory increment via activation of the splanchnic nerves. In the present study the pharmacological characteristics of the splanchnic neural inhibition of the alkaline secretion were investigated. Duodenal HCO3- secretion was measured by in-situ titration in chloralose-anaesthetized rats. Exposure of the duodenal mucosa to hydrochloric acid (0.01 M, 5 min) increased the secretion by approximately 60%. A 10% decrease in blood volume simultaneously to the luminal acidification abolished the secretory increase, as previously reported. Treatment with either guanethidine or yohimbine blocked the bleeding-induced inhibition of the secretion after acid-exposure. Neither prazosin nor propranolol did prevent such hypovolaemia-induced inhibition of duodenal alkaline secretion. The present results suggest that the splanchnic neural inhibition of acid-induced duodenal HCO3- secretion is mediated via adrenergic nerve fibres and alpha-2 adrenoceptors.