Cyclic AMP increase in canine parotid gland mediated by histamine H₂-receptors

Histamine, 4-meihylhistamine and dimaprit induced a dose-dependent increase in the cyclic AMP content of chopped canine parotid gland in the presence or 3-isobutyl-l-methylxanthine. Metiamide. but not mepyramine, inhibited the effect of these agonists dose-dependently. The cyclic AMP content was also increased by 2-(2-pyridyl)ethylanine. This effect was completely blocked by propranolol. These results indicate that the cyclic AMP response to histamine in canine parotid gland is mediated by H₂ -receptors. Mepyramine enhanced the effect of histamine. However. 2-(2-pyridyl)ethylamine had no significant inhibitory effect on the cyclic AMP response to 4-methylhistaminc. A combination of aminoguanidine and quinacrine potentiated the effect of histamine, though no difference was observed in the histamine concentration of the media with or without these inhibitors when determined at the end of incubation. This suggests that there exist active histamine-metabolizing systems in canine parotid gland.