EXPRESSION OF THE MESSENGER-RNAS FOR THE INSULIN-LIKE GROWTH-FACTORS AND THEIR BINDING-PROTEINS DURING DEVELOPMENT OF PORCINE OVARIAN FOLLICLES

We examined the expression of the mRNAs for the insulin-like growth fa ctors (IGFs) and two of their binding proteins (BPs), IGFBP-2 and IGFB P-3, in individual follicles of the porcine ovary. Follicular developm ent was synchronized with a progestin (altrenogest). Individual follic les were isolated on days 1, 3, 5 and 7 after progestin withdrawal. No IGFBP-3 mRNA was detected. While IGF-II mRNA was easily detected, the levels of expression did not change. IGF-I and IGFBP-2 mRNAs increase d and decreased, respectively, with follicle development until day 7 w hen IGF-I expression declined. Regression analysis of IGF-I and IGFBP- 2 mRNA expression was performed to assess the relative strength of cor relations with day, diameter and steroid concentrations as covariates. IGFBP-2 MRNA was correlated with both day and diameter (r - -.713 and -.705, respectively, n-24) and neither estrogen (E2) nor progesterone (P4) contributed to the fit. While IGF-I mRNA expression was correlat ed to both day (r - .483) and diameter (r -.587), the strongest predic tor was E2 concentration (r - .694, n-27). In conclusion, the expressi on of IGF-I and IGFBP-2 mRNAs in the ovarian follicle are discordantly regulated during follicular growth and maturation. The observed chang es in these parameters should result in increased bioavailable IGF-1. This supports a pivotal autocrine/paracrine role for these factors dur ing follicle growth and development,