MESSENGER-RIBONUCLEIC-ACID FOR INSULIN-LIKE GROWTH FACTORS-I AND FACTORS-II, INSULIN-LIKE GROWTH FACTOR-BINDING PROTEIN-2, GONADOTROPIN RECEPTORS, AND STEROIDOGENIC ENZYMES IN PORCINE FOLLICLES

Several aspects of growth, development, and steroidogenesis in ovarian follicles are controlled by the interaction of insulinlike growth fac tors (IGF-I and IGF-II) and gonadotropins (LH and FSH). The objective of this study was to determine the developmental stage and location at which mRNA for IGF, IGF-finding protein (IGFBP)-2, gonadotropin recep tors, and steroidogenic enzyme genes are expressed within porcine foll icles. Ovaries from pigs on Days 10 (n = 3; midluteal phase) and 19 (n = 3; preovulatory phase) of the estrous cycle were collected, frozen, and sectioned. The mRNA for ICF-I, IGF-II, IGFBP-2, LH receptor, FSH receptor, cytochrome P450 side-chain cleavage (P450(scc)), 3 beta-hydr oxysteroid dehydrogenase (3 beta-HSD), 17 alpha-hydroxylase (P450(17 a lpha)), and aromatase (P450(arom)) were detected by in situ hybridizat ion, and relative amounts were determined by image analysis. Expressio n of mRNA for IGF-I and IGF-II was cell specific (granulosa and theca interna cells, respectively) and increased with follicular size. The I GFBP-2 mRNA was expressed in greater amounts for theca interna cells t han for granulosa cells. The pattern of expression for LH and FSH rece ptors diverged as follicles grew. For LH receptor, mRNA was detected i n the theca interna cells of small antral follicles and in both the th eca interna and granulosa cells of large antral follicles. Amount of L H receptor mRNA increased with follicular diameter. For FSH receptor, mRNA increased as follicles grew to a small antral size. However, FSH receptor mRNA disappeared in large antral follicles on Day 19 of the e strous cycle. Steroidogenic enzyme mRNA for 3 beta-HSD (theca interna cells), P450(scc) (theca interna cells), P450(17 alpha) (theca interna cells), and P450(arom) (granulosa cells) increased with follicular di ameter. In summary, coordinated expression of IGF, IGFBP-2, gonadotrop in receptors, and steroidogenic enzyme mRNA throughout different stage s of follicular development was observed. Changes in mRNA suggested in creased IGF-I and -II action and a switch from FSH to LH dependence in porcine preovulatory follicles.