Factors influencing pituitary glycogen metabolism and gonadotropic hormone release. I. Luteinizing hormone releasing hormone

The mechanism of release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the rat anterior pituitary by LH releasing hormone (LH RH) was further evaluated by studies on pituitary glycogen metabolism and its relation to the hormone release mechanism in vitro. Pituitary glycogen content and the activity levels of its 2 major regulatory enzymes, glycogen synthetase and glycogen phosphorylase, were analyzed after exposure to different doses of synthetic LH RH in vitro. Less than 5 ng of LH RH induced within minutes a maximum glycogenolytic response with an increase in the proportion of pituitary phosphorylase in the more active a form and a decrease in pituitary glycogen. Exogenous N⁶,O²' dibutyryl cyclic AMP (10 millimol) with theophylline (1 millimol) mimicked the effect of LH RH. 15 ng of LH RH also induced a significant release of LH and FSH into the medium during 4 hr of incubation. These results suggest that pituitary glycogen may be a source of the energy required for the hypothalamic hypophysiotropic hormone release mechanism.