Effects of selective alpha 1 and alpha 2 adrenoceptor active drugs on 86Rb+ efflux from pieces of rat parotid gland.

Minute pieces of rat parotid gland were used in studies of adrenergic regulation of K+ efflux using 86Rb+ as a probe for K+. Noradrenaline induced a concentration-dependent RB+ efflux, whereas the beta 1-selective agonist prenalterol was without effect. On the other hand, the beta 2-selective drug, terbutaline, at high concentrations displayed a small enhancement of Rb+-secretion. The selective alpha 1-adrenoceptor drug, phenylephrine, was as potent as noradrenaline, whereas the alpha 2-agonist clonidine had only a small effect. The noradrenaline-induced Rb+-efflux was effectively inhibited in the presence of prazosin, an alpha 1-blocker, whereas the alpha 2-antagonist, yohimbine, was roughly 50 times less potent. The results suggest that catecholamine-induced K+-secretion from the rat parotid gland is mediated via activation of post-synaptic alpha-adrenoceptors of the alpha 1-subtype.