Involvement of alpha-2 adrenergic receptor subtypes in hyperglycemia.

Alpha-2 adrenoceptor stimulation induces in the mouse a hyperglycemic response which is accompanied by a concomitant inhibition of insulin secretion. To test the possibility that one of the postulated subtypes of alpha-2 adrenoceptors is preferentially implicated in this response, we compared the interaction of several drugs with known selectivity toward alpha-2A or alpha-2B adrenoceptor subtypes in our model. The alpha-2A preferential agonist oxymetazoline induced in the mouse a hyperglycemic response similar to that of the nonselective alpha-2 adrenoceptor agonist UK 14.304. This hyperglycemic response to oxymetazoline was accompanied by a concomitant inhibition of insulin release. Both the effect on glycemic level and the inhibition of insulin release by oxymetazoline were antagonized by the alpha-2 adrenoceptor antagonist idazoxan. The alpha-2B preferential antagonists ARC-239, prazosin or chlorpromazine failed to block the modifications in both glycemic and insulin levels induced by alpha-2 adrenoceptor stimulation. The nonselective antagonists rauwolscine, yohimbine, WY 26703, phentolamine and corynanthine, as well as the receptor antagonists with alpha-2A selectivity like WB 4101, idazoxan and tolazoline, dose-dependently antagonized both the glycemic and the insulin responses to UK 14.304. A positive correlation was obtained between the potencies of these drugs in antagonizing the hyperglycemic response to UK 14.304 and their affinities for alpha-2A adrenergic receptors (r = 0.918, P less than .001) but no correlation was obtained with their affinities for alpha-2B adrenergic receptors (r = 0.048, P = N.S.)(ABSTRACT TRUNCATED AT 250 WORDS)