Porcine ovarian cells express messenger ribonucleic acids for the acid-labile subunit and insulin-like growth factor binding protein-3 during follicular and luteal phases of the estrous cycle

It has recently been shown that, in follicular fluid, as in the circulation , insulin-like growth factors (IGFs)-I and -II exist in a ternary complex w ith IGF binding protein-3 (IGFBP-3) and the acid-labile subunit (ALS). The current study was designed to determine whether ovarian follicular and lute al cells could synthesize IGFBP-3 and ALS. Ovaries were collected, during t he follicular and early luteal phases, from mature pigs whose cycles were s ynchronized with PGF2 alpha. We studied IGFBP-3 and ALS messenger RNA (mRNA ) by in situ hybridization. These transcripts were colocalized with aromata se mRNA, a marker of healthy granulosa cells. IGFBP-3 mRNA was equally expr essed in granulosa cells of all growing follicles. In contrast, granulosa c ell ALS mRNA levels were higher (P < 0.05) in preantral and small antral fo llicles than in large antral follicles. In thecal cells, expression of mRNA for IGFBP-3, ALS and cyclin D1 (a marker of cell proliferation) was restri cted to healthy (aromatase- expressing) follicles. In those follicles, thec al expression of IGFBP-3 mRNA was low or absent in preantral follicles but increased (P < 0.05) in antral follicles. Thecal cell ALS transcripts peake d in small antral follicles (P < 0.05) and then declined. In granulosa cell s of atretic follicles, transcripts for aromatase were greatly reduced, whe reas IGFBP-3 mRNA levels remained high. In contrast, ALS transcript levels were greatly reduced in both granulosa (P < 0.05) and thecal cells (P < 0.0 01) of atretic follicles. After ovulation, IGFBP-3 mRNA was moderately expr essed in granulosa luteins but strongly detected in a few theca-derived cel ls and in vascular endothelial cells. This study demonstrates that follicul ar fluid IGFBP-3 and ALS, like the IGFs, originate (at least in part) from the ovary. The ability of follicular cells to synthesize, assemble, and sto re all components of the ternary complex may be critical in determining the bioavailability of follicular IGF-I and -II.