Cortisol inhibition of growth hormone-releasing hormone-stimulated growth hormone release from cultured sheep pituitary cells.

Cortisol inhibits growth hormone (GH) release in short-term culture and is stimulatory in long-term cultures of rat and human pituitary cells. This study sought to determine the in vitro effects of cortisol on GH release and the signal transduction pathways mediating the effects of cortisol on GH release from cultured ovine somatotrophs. Pituitary cells were dispersed with collagenase and placed in culture medium for 4 days. The data indicate that cortisol inhibited growth hormone-releasing hormone (GHRH)-stimulated GH release by at least 2 h. In short-term culture GHRH-, forskolin- and dibutyryl cyclic AMP-stimulated GH release were inhibited by cortisol, suggesting an effect distal to the membrane and involving a protein kinase A (PKA)-dependent pathway. GH release initiated by KCl was inhibited by cortisol, but GH release caused by the calcium ionophore A23187 was unaffected. This suggests a possible action of cortisol on the calcium channels. The inhibition by cortisol of the calcium-dependent secretion of GH release appeared to play a smaller role in mediating cortisol inhibition of GH release than that seen with PKA. Attempts to overcome cortisol inhibition of GH release using puromycin, arachidonic acid or pertussis toxin were unsuccessful. Since cortisol inhibition of GH release does not occur via the mechanisms found in other cell types, cortisol inhibition of pituitary cell secretions appears to be cell-specific rather than utilizing a single inhibitory mechanism. The majority of cortisol actions on the somatotroph appear to act at a site distal to the production of cyclic AMP.(ABSTRACT TRUNCATED AT 250 WORDS)