Release of growth hormone from purified somatotrophs: role of adenosine 3',5'-monophosphate and guanosine 3',5'-monophosphate.

Studies were carried out to simultaneously measure cAMP and cGMP accumulation and GH release from acutely dispersed purified somatotrophs obtained from rat adenohypophyses. cAMP accumulation was dramatically increased by both prostaglandin E2 (10(-6) M) and 3-isobutyl-1-methylxanthine (a phosphodiesterase inhibitor, 0.5 mM) within 1 min of their addition, while there was a delay of 8--16 min before a significant increase in GH release was seen. SRIF (100, 10, or 1 ng/ml) completely blocked the stimulated release of GH. SRIF also consistently decreased the elevation of cAMP induced by the two secretagogues, but this decrease was small and not always significant. cGMP was unmeasurable (less than 0.02 fmol/1000 cells) in all of our experiments, while basal cAMP levels were about 1 fmol/1000 cells. We conclude that cAMP plays a role in the intracellular mechanisms governing GH release and that SRIF primarily acts subsequent to cAMP elevation, with a possible secondard or minor action on cAMP formation.