Tumor promoters enhance basal and growth hormone releasing factor stimulated cyclic AMP levels in anterior pituitary cells

Tumor promoters, such as phorbol esters and teleocidin, amplified the ability of growth hormone releasing factor to increase pituitary cyclic AMP levels. This effect of tumor promoters was concentration-dependent, could be observed in 5 minutes, and was over by 4 hours. Inactive tumor promoters (i.e., 4-alpha-didecanoate) had no effect on this sytem, whereas a synthetic diacylglycerol (i.e., 1-oleoly-2-acetyl glycerol), mimicked the action of tumor promoters. Due to the known stimulation of protein kinase C by both tumor promoters and diacylglycerols, we suggest that this calcium and phospholipid dependent protein kinase C can enhance the ability of the growth hormone releasing factor receptor to activate the cyclic AMP generating system.