Inhibition by central alpha-2 adrenergic mechanism of thyrotropin-releasing hormone-induced gastric acid secretion in the rat.

Influences of central alpha-2 adrenergic agonists on thyrotropin-releasing hormone (TRH)-stimulated gastric acid secretion were examined in the perfused stomach of anesthetized rats. Clonidine, an alpha-2 adrenergic agonist, given subcutaneously or intracerebroventricularly inhibited the gastric acid secretion stimulated by intracerebroventricular TRH. Intracerebroventricular injection of norepinephrine tended to reduce the acid secretion, while phenylephrine, serotonin and quipazine (serotonin agonist) did not influence the acid secretion. Subcutaneous clonidine enhanced the acid secretion peripherally stimulated by electrical vagus stimulation. The inhibitory effect of clonidine on TRH-induced acid secretion was reversed by yohimbine, an alpha-2 adrenergic antagonist, and phentolamine. In conclusion, the present study suggests that the central alpha-2 adrenergic receptor system participates in the TRH-mediated central nervous system control of gastric acid secretion in anesthetized rats.