Expression of mRNA encoding insulin-like growth factors I and II and the type 1 IGF receptor in the bovine corpus luteum at defined stages of the oestrous cycle

Previous studies have implicated insulin-like growth factors I and TI (IGF- I and -II), in the regulation of ovarian function. The present study invest igated the localization of mRNA encoding IGF-I and -II and the type 1 IGF r eceptor using in situ hybridization to determine further the roles of the I GFs within the bovine corpus luteum at precise stages of the oestrous cycle . Luteal expression of mRNA encoding IGF-I and -II and the type 1 IGF recep tor was detected throughout the oestrous cycle. The expression of IGF-I mRN A varied significantly during the oestrous cycle. IGF-I mRNA concentrations were significantly higher on day 15 than on day 10, and IGF-I mRNA in the regressing corpus luteum at 48 h after administration of exogenous prostagl andin was significantly greater than in the early or mid-luteal phase (days 5 and 10). Ln contrast, there was no significant effect of day of the oest rous cycle on expression of mRNA for IGF-II and the type 1 IGF receptor in the corpus luteum. Expression of IGF-II mRNA was localized to a subset of s teroidogenic luteal cells and was also associated with cells of the luteal vasculature. mRNA encoding the type 1 IGF receptor was widely expressed in a pattern indicative of expression in large and small luteal cells. These d ata demonstrate that the bovine corpus luteum is a site of IGF production a nd reception throughout the luteal phase. Furthermore, this study highlight s the potential of IGF-II in addition to IGF-I in the autocrine and paracri ne regulation of luteal function.