Disparate effects of intracisternal RX 77368 and ODT8-SS on gastric acid and serotonin release: role of adrenal catecholamines.

Intracisternal injection of the thyrotropin releasing hormone (TRH) analogue RX 77368 (100 ng) or the somatostatin analogue ODT8-SS (1 microgram) produced an 82% and 101% increase in gastric acid secretion in 2 h pylorus-ligated rats. In contrast, dissimilar effects were produced by intracisternal injection of these peptides on the secretion of serotonin into the gastric lumen. Intracisternal RX 77368 (100 ng) produced a 496% increase in intraluminal serotonin release, while in contrast, intracisternal ODT8-SS (1 microgram) produced a 78% inhibition in intraluminal serotonin release. Bilateral adrenalectomy reversed the stimulatory effect of intracisternal RX 77368 (100 ng) on serotonin, but not acid release. The data reveal a difference in the ability of the two peptides, which act as gastric secretagogues, to produce intraluminal acid and serotonin release, and suggest that combined activation of the vagus and the adrenal gland are important in mediating basal and RX 77368-stimulated serotonin release into the gastric lumen. In particular, differential effects on adrenal catecholamine release are implicated in the divergent effects of the two peptides.