Regulation of gastrin release in the dog by alpha 2-adrenoceptors

1. The purpose of the present study was to analyse the effects of the alpha 2-adrenoceptor agonist medetomidine and the antagonist yohimbine on gastrin release in conscious dogs. 2. Gastrin secretion was investigated under both basal conditions and stimulation by 2-deoxy-D-glucose, food or bombesin. 3. Basal gastrin under fasting conditions was significantly reduced by medetomidine and increased by yohimbine. 4. 2-deoxy-D-glucose-induced gastrin increase was fully inhibited by medetomidine; this effect was antagonized by yohimbine. 5. Medetomidine significantly inhibited food-induced increase in plasma gastrin; under these conditions yohimbine was without effect per se, but significantly antagonized the inhibitory action of medetomidine. 6. Gastrin release induced by bombesin was not affected by medetomidine or yohimbine. 7. These results suggest that alpha 2-adrenoceptors play an inhibitory role under conditions in which gastrin release is mainly mediated through cholinergic and non-cholinergic nervous pathways; in contrast, they do not indicate the presence of alpha 2-adrenoceptors on G cells of the dog stomach.