Stimulating effect of .ALPHA.-adrenoceptor agonists on isoproterenol-induced amylase release in rat parotid tissue.

Abstract

Isoproterenol(ISO)-induced amylase release from rat parotid slices was increased by the addition of methoxamine to either a normal or a Ca-free medium. The potentiating effect of methoxamine was completely blocked by the addition of phentolamine, whether or not the slices were incubated in the normal or the Ca-free medium; and the effect also disappeared after prolonged preincubation (60 min) of the slices in the Ca-free medium. Both verapamil and procaine reduced methoxamine-induced amylase release, but only verpamil blocked the stimulating effect of methoxamine in the normal medium. ISO-induced accumulation of cAMP in the slices was unaffected by methoxamine or phenylephrine. The potentiating effect of methoxamine on ISO-induced amylase release may be independent of the presence of extracellular Ca, and the increased accumulation of cAMP in the tissue is unnecessary.