Effects of charcoal-extracted follicular fluid on reproductive function in postpartum cows

Abstract

In order to determine the role of follicle-stimulating hormone (FSH) on the resumption of ovarian function in cows early postpartum (PP), bovine follicular fluid (FF) was used to selectively suppress concentrations of FSH. Calves were removed from all cows within 24 hr of birth. Follicular fluid that was treated with charcoal to remove steroids (15 ml; n=14) or serum (S) from an ovariectomized cow (15 ml, n=14) was injected i.m. twice daily from days 1 to 10 PP. Blood samples were collected before each injection and frequent samples (every 15 min for 6 hr) taken on days 5 and 10 PP. Eight cows from each group (FF and S) were slaughtered on the morning of day 11 PP and pituitaries and ovaries collected. The remaining cows (n=6) were observed for estrus. Treatment with FF delayed follicular growth (P<0.01), as evidenced by the largest follicle per cow observed at time of slaughter (3.6 ± 0.42 vs 11.5 ± 1.77 mm dia; FF vs S). The intervals from parturition to first estrus (P<0.11) and to first progesterone rise (25.3 ± 1.97 vs 18.0 ± 3.62 d; P<0.06) tended to be delayed by treatment with FF vs S. Many of the cows treated with S ovulated by day 10 PP, they were divided retrospectively into those that had ovulated by (n=9) or after (n=5) day 10 PP for analysis. Cows treated with FF had lower (P<0.05) and less variable (P<0.01) serum FSH concentrations while levels of luteinizing hormone (LH) tended (P<0.08) to be greater on days 5 and 10 PP. Follicular fluid decreased levels of FSH (P<0.001), but not LH (P>0.15), in the samples obtained twice daily compared to S-treated cows that did not ovulate by day 10 PP. Anterior pituitaries were dissociated, and cells from each cow were cultured in order to ascertain whether treatment with FF in vivo would affect gonadotropin secretion in vitro. Estradiol-17β (E) was incubated with pituitary cells to determine the effect of E on gonadotropin secretion from cells of PP cows, and to ascertain whether treatment with FF in vivo and with E in vitro would interact to affect secretion of FSH and LH in culture. After 2 d of incubation, cells were treated with 10 −9 M E or vehicle (1% ethanol). Two days later, cells were treated with gonadotropin-releasing hormone (GnRH) and after 6 hr, medium collected. Injections of FF did not affect GnRH-induced release of FSH or LH from pituitary cells in culture (P>0.20). Incubation with E decreased the release of LH in response to GnRH (P<0.005). There was a greater suppression of GnRH-induced LH release due to E pretreatment in cells from FF-treated cows than in cells from cows treated with S (P<0.03). Thus, treatment with FF decreased FSH concentrations and delayed follicular development and ovulation, even in the presence of elevated or control levels of LH. Therefore, FSH does play a role in folliculogenesis in PP cows. Based on results obtained in vitro, we conclude that E inhibited LH secretion and this phenomenon may be inherent to the PP animal. Even though FF treatment in vivo did not significantly decrease the secretion of FSH or LH in vitro, it did synergize with E resulting in a much greater suppression of LH than with either E or FF alone.