Human Pancreatic Tumor Growth Hormone (GH)-Releasing Factor and Cyclic Adenosine 3′,5′-Monophosphate Evoke GH Release from Anterior Pituitary Cells: The Effects of Pertussis Toxin, Cholera Toxin, Forskolin, and Cycloheximide*

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Abstract
Both synthetic human pancreatic tumor GH [growth hormone]-releasing factor (hpGRF) and prostaglandin E2 (PGE2) rapidly stimulate cellular cAMP accumulation in and GH release from primary cultures of rat anterior pituitary cells. SRIF [somatostatin] inhibits both of these actions. A 1 h treatment with the protein synthesis inhibitor cycloheximide potentiates hpGRF-induced cAMP accumulation for hours and GH release for the 1st hour. A rapidly turning over protein tonically mutes the degree of hpGRF-stimulated cAMP accumulation. Pretreatment of the cells with pertussis toxin amplifies hpGRF- and PGE2- stimulated cAMP levels and GH release; pertussis toxin also attenuates the ability of SRIF to affect these variables. An inhibitory coupling protein contributes to these events. Cholera toxin and forskolin are also potent stimulators of cAMP accumulation and GH release. The hpGRF-evoked GH release and the inhibitory action of SRIF are closely correlated with the cAMP-generating system.