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