EXPRESSION OF IGF-I MESSENGER-RNA IN THE OVINE OVARY

IGF-I has been implicated as a local and/or systemic regulator of ovar ian function by acting alone or as an amplifier of the actions of gona dotrophins, thereby influencing follicular growth and ovulation. In th e sheep it is uncertain as to whether IGF-I can fulfil an autocrine or paracrine role, since mRNA expression and peptide synthesis have not previously been demonstrated. Using in situ hybridization with ovine a nd human riboprobes, IGF-I mRNA was found in all major steroidogenic c ell types of the sheep ovary, namely the granulosa, theca and luteal c ells and, to a lesser extent, the stroma. IGF-I mRNA was found to be e xpressed in the granulosa and thecal cells of early antral follicles a nd thereafter in these cell types as the follicles increased in diamet er. Evidence for IGF-I mRNA expression in preantral follicles could no t be demonstrated. No obvious differences in the levels of expression were observed in ovaries recovered during the luteal phase, follicular phase, anoestrus or after exogenous FSH treatment. IGF-I expression w as confirmed by Northern blotting and PCR. These findings are consiste nt with the notion that IGF-I may have an autocrine or paracrine role in enhancing ovarian function in the sheep.