Pregnancy-associated plasma protein-A and insulin-like growth factor binding protein mRNAs in granulosa cells of dominant and subordinate follicles of preovulatory cattle

To determine if (1) levels of pregnancy-associated plasma protein-A (PAPP-A) mRNA and insulin-like growth factor binding protein (IGFBP) (-2, -3, -4 and -5) mRNAs differ between the dominant and subordinate follicles during the follicular phase of an estrous cycle, and (2) these differences are associated with differences in follicular fluid (FFL) concentrations of steroids (estradiol, androstenedione, and progesterone), total and free IGF-I, or IGFBPs, estrous cycles of non-lactating Holstein dairy cows (n = 16) were synchronized with two injections of prostaglandin (PGF2α) 11 days apart. Granulosa cells and FFL were collected either 24 h or 48 h after the second injection of PGF2α. FFL from dominant follicles had lower concentrations of progesterone (P < 0.08) and higher concentrations of estradiol (P < 0.05), androstenedione (P < 0.0001), estradiol:progesterone ratio (P < 0.0001), free IGF-I (P < 0.0001), and calculated percentage free IGF-I (P < 0.01) than large subordinate follicles. Levels of IGFBP-2, -4, and -5 in FFL were 3.0- (P < 0.05), 2.4- (P < 0.06), and 3.4-fold (P < 0.05) greater, respectively, in subordinate than in dominant follicles. IGFBP-3, IGFBP-4 and PAPP-A mRNA expression and IGF-II concentration did not differ (P > 0.10) between dominant or subordinate follicles. Levels of IGFBP-2 and -5 mRNA were severalfold greater (P < 0.05) in subordinate than dominant follicles. IGFBP-5 mRNA in granulosa cells decreased (P < 0.05) 62% to 92%, between 24 h and 48 h post-PGF2α. We conclude that decreased levels of IGFBP-2 and -5 mRNA in granulosa cells may contribute to the decrease in FFL IGFBP-2 and -5 protein levels of preovulatory dominant follicles, and that changes in granulosa cell IGFBP-3 and -4 mRNA and PAPP-A mRNA levels do not occur during final preovulatory follicular development in cattle.