PARENT SESSION
Corpus Luteum

IGF-I STIMULATION OF STEROIDOGENESIS IN PORCINE LUTEAL CELLS INVOLVES PI-3-KINASE.

Ge, Zhaoping¹, Hedgpeth, Vickie¹, Gadsby, John¹, ¹

ABSTRACT- The Insulin-like Growth Factor-I (IGF-I) system is believed to play an important role in control of porcine corpus luteum development and function. Previously, we have shown that mRNAs and proteins of IGF-I, IGF type I receptor and IGFBPs 2-5 are expressed in the CL. In addition, we have shown that IGF-I stimulates porcine luteal progesterone secretion both in vitro and in vivo. This study was designated to investigate the signal transduction pathway(s) mediating the stimulatory actions of IGF-I on steroidogenesis in the porcine CL. CLs were collected on day 7 of the estrous cycle, enzyme dissociated and large luteal isolated cells by elutriation (note: large luteal cells are the predominant target cell for IGF-I). Large luteal cells (50,000 cells per well) were cultured for 24 hours in M199 containing 0.1% BSA, 40 ng/ml hydrocortisone and 50 g/ml (cholesterol) porcine LDL, with or without IGF-I (100 ng/ml) and in the presence or absence of inhibitors of the IGF-I signal transduction pathways: the PI-3-kinase pathway inhibitor wortmannin (100nM), or the MAP kinase pathway inhibitor PD98059 (50 M). Progesterone concentration in conditioned media was analyzed by RIA. IGF-I increased progesterone secretion in the porcine luteal cells significantly (127% ± 4.1%; p< 0.05 versus control, n=12). Wortmannin (107% ± 1.4%; NS versus control) significantly blocked the stimulatory effects of IGF-I on luteal progesterone secretion, whereas PD98059 had no effect (127% ± 3.1%; p< 0.05 versus control, n=4). We tentatively conclude that IGF-I′s stimulatory effects on porcine luteal cell steroidogenesis are mediated via the PI-3-kinase pathway. Supported by USDA 98-35203-6283.

KEY WORDS: pig, corpus luteum, IGF, signal transduction