The Interaction of α- and β-Adrenergic Agonists on Amylase Release from Parotid Glands of Euthyroid and Hypothyroid Rats

The interaction between alpha- and beta-adrenergic agonists was examined with respect to amylase release from rat parotid glands. The effect of hypothyroid status on this interaction was also compared with that in euthyroid rats. Both methoxamine and clonidine potentiated isoproterenol-induced amylase release from parotid glands of eu- and hypothyroid rats, but the alpha 2-adrenoceptor-mediated response disappeared in the hypothyroid rats. Dibutyryl cyclic AMP, a second messenger of beta-adrenergic agonists, also showed essentially the same results as those of isoproterenol, but potentiation of dibutyryl cyclic AMP-induced amylase release with alpha-adrenergic agonists was mediated through only alpha 1-adrenoceptors in both groups. Calcium ion plays an important role in the interaction between alpha- and beta-adrenergic agonists. These results suggest that the potentiating effect of alpha-adrenergic agonists may be mediated at least in part through an unknown mechanism at the step distal to cyclic AMP formation in both eu- and hypothyroid rats.