INTRACEREBRAL ADRENOCEPTOR AGONISTS INFLUENCE RAT DUODENAL MUCOSAL BICARBONATE SECRETION

We have studied the effects of intracerebral administration of selecti ve alpha-adrenergic agonists on duodenal bicarbonate secretion. Duoden um free of Brunner's glands was cannulated in situ in anaesthetised ra ts, and bicarbonate secretion into the luminal reperfusate was continu ously titrated by pH stat. Infusion of the alpha(1)-selective adrenoce ptor agonist, phenylephrine (1,000-2,500 mu g . kg(-1). h(-1)), into a lateral brain ventricle increased (P < 0.01) duodenal bicarbonate sec retion. Pretreatment with prazosin, an alpha(1)-antagonist, significan tly (P < 0.01) reduced the stimulatory effect when infused into the la teral ventricle (30 mu g . kg(-1). h(-1)), but not when administered i ntravenously (1,000 mu g . kg(-1). h(-1)). Hexamethonium (10 mg . kg(- 1). h(-1) iv) abolished stimulation, whereas cervical vagotomy, epidur al blockade, and naloxone were each without effect. Vasopressin, vasop ressin antagonists, and oxytocin did not affect basal secretion. Intra cerebroventricular administration of the alpha(2)-adrenoceptor agonist , clonidine (1,000 mu g . kg(-1). h(-1)), in contrast to alpha(1)-rece ptor activation, decreased (P < 0.01) the secretion. Thus central nerv ous adrenoceptors influence duodenal mucosal bicarbonate secretion, an d alpha(1)-adrenoceptor stimulation may provide protection against lum inal acid. This potent stimulation was not mediated by the vagal nerve s, spinal cord pathways, or the release of beta-endorphin but involves nicotinic, possibly enteric nervous transmission.