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

Department of Physiology, Queen's University Kingston, Ontario, Canada K7L3N6

Address requests for reprints to: Dr. J. Kraicer, Department of Physiology, Abramsky Hall, Queen's University, Kingston, Ontario,Canada K7L 3N6.

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 (<85 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. (Endocrinology 106: 764, 1980)

Footnotes

^* This work was supported by the MRC of Canada (Grant MT-1634) and the School of Graduate Studies and Research, Queen's University.

Received May 7, 1979.