Interactions of Insulin-like Growth Factors and Estradiol in Rat Pituitary Gonadotrophs

Insulin-like growth factors are involved in the regulation of gonadotropin secretion. Insulin-like growth factor I (IGF-I) has an augmenting effect on gonodotropin-releasing hormone (GnRH)-induced luteinizing hormone (LH) release from female rat gonadotrophs that is facilitated by estradiol. To identify the underlying mechanisms, we investigated whether IGF-I influences total LH pool and the production of intracellular inositol phosphate. In another series of experiments we tested whether IGF-II and estradiol affect LH release of gonadotrophs. Pituitary cells were incubated with 100 pM IGF-I and/or 100 pM estradiol for 24 h. They were stimulated, partially in the presence of Wortmannin, an inhibitor of phosphoinositide 3-kinase, with 330 pM GnRH for 3 h. Subsequently, total LH pool (released and remaining hormone content in lysed cells) in cultures was measured. Intracellular inositol trisphosphate of ! T3-1 cells, a gonadotrope cell line, treated with estradiol and IGF-I as described before and stimul...