Release of Growth Hormone from Purified Somatotrophs: Interrelation between Ca++and Adenosine 3′,5′-Monophosphate*

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Abstract
CAMP is thought to be an essential intracellular mediator in the release of GH from somatotrophs. Ca++ is required in the incubation medium to elicit GH release iin vitro. We have carried out studies using a purified preparation of rat somatotrophs to see whether the Ca++ requirement precedes or follows the accumulation of cAMP induced by prostaglandin E2 (which increases adenylate cyclase activity) and 3-isobutyl-lmethylxanthine (a phosphodiesterase inhibitor). Incubation of somatotrophs in low Ca++ medium (μm) abolished the release of GH induced by the two secretagogues, while the increase in intracellular cAMP was actually augmented. Thus, Ca++ is required in the incubation medium to express the action of intracellular cAMP. (Endocrinology106: 764, 1980)