Stimulation of pituitary cAMP accumulation by human pancreatic GH-releasing factor-(1-44)

This study seeks to determine whether hpGRF-(1-44) stimulates pituitary growth hormone (GH) secretion and cAMP accumulation in a manner that is consistent with the concept of cAMP as an intracellular mediator of GH release. Addition of 10 nM hpGRF-(1-44) to rat anterior pituitary cell cultures stimulated a rapid elevation of intracellular cAMP that preceded or coincided with increases in GH and cAMP secretion. A dose-related increase in GH and cAMP release and in intracellular cAMP accumulation was observed in response to increasing concentrations of hpGRF-(1-44). Stimulation of cAMP accumulation and release, however, occurred over a hpGRF-(1-44) concentration range that was approximately one order of magnitude higher than required for dose-related GH release. Simultaneous addition of 0.05 nM hpGRF-(1-44) and 0.2, 0.5, or 1.0 mM 3-isobutyl-1-methylxanthine (MIX) to the cultures resulted in a significant potentiation of intracellular cAMP accumulation and release. Potentiation of GH release was not observed, however, probably due to attainment of maximal or near maximal GH release by MIX alone. The addition of increasing doses of exogenous N6-O2'-dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP) to cell cultures resulted in a dose-related increase in GH secretion. The results of this study are consistent with the concept of cAMP as a second messenger for hpGRF-(1-44) in stimulating GH release. Additionally, a novel method for cAMP extraction that utilizes trifluoroacetic acid is described.