Cyclic GMP stimulates growth hormone release in rat anterior pituitary cells

In this study, the role of cGMP on growth hormone (GH) release was examined using a static monolayer culture prepared from dispersed rat anterior pituitary cells. Treatment with 8-bromo-cGMP (1 microM to 1 mM) stimulated GH release up to 3.8-fold in a concentration-dependent manner. Elevating cGMP with nitroprusside or the C-type natriuretic peptide was also effective in stimulating GH release. The increase in GH release by cGMP-elevating agents occurred without a concomitant increase in cAMP. Unlike cAMP which increased intracellular Ca2+ concentration, 8-bromo-cGMP caused a small reduction in intracellular Ca2+ concentration. Taken together, these results indicate that i) cGMP appears to be another mechanism that regulates GH release, ii) activation of cytosolic or membranous guanylyl cyclase is equally effective in stimulating GH release; and iii) the cGMP-induced GH release appears to be through a mechanism distinct from that of cAMP.