Gonadotropin Surge Alone Was Not Sufficient to Up-Regulate Matrix Metalloproteinases Within Ovulatory Sized Bovine Follicles.

Abstract

Control of follicular maturation and ovulation is necessary for assisted reproductive technologies. This study examined the ability of an induced gonadotropin surge to up-regulate matrix metalloproteinase (MMP) expression before or after prostaglandin F2a (PGF) induced luteolysis (high or low circulating progesterone [P4], respectively). Non-pregnant, non-lactating beef cows were detected in standing estrus (d 0). In a 2 × 2 factorial design cows either did (+) or did not (−) receive an injection of PGF on d 8 of the estrous cycle and subsequently did (+) or did not (−) receive an injection of GnRH (6.2 ± 1.0 h after the PGF). Therefore, the treatments were as follows: main effects + PGF vs - PGF and + GnRH vs - GnRH with interactions of the main effects being; 1) - PGF/- GnRH (high P4 and no gonadotropin surge; n = 3), 2) - PGF/+ GnRH (high P4 and an induced gonadotropin surge; n = 5), 3) + PGF/- GnRH (low P4 and no gonadotropin surge; n = 4), and 4) + PGF/+ GnRH (low P4 and an induced gonadotropin surge; n = 6). Dominant follicles were measured and granulosa cells were collected by ultrasound guided follicle aspiration (27.3 ± 1.1 h after PGF, 19.5 ± 0.7 h after GnRH). Blood samples were collected at PGF and at follicular aspiration. Total cellular RNA was extracted from all granulosa cells and relative mRNA abundance was determined by real-time RT-PCR and corrected for ubiquitin and GAPDH. There was a PGF by time interaction on concentrations of progesterone (P < 0.01) with concentrations increasing (P = 0.01) from d 8 to d 9 among - PGF cows, but decreasing (P < 0.001) among + PGF cows. There tended (P = 0.07) to be a GnRH by time interaction on concentrations of progesterone, with concentrations among - GnRH cows similar (P = 0.31) between d 8 and d 9 but concentrations among + GnRH cows tended to decrease (P = 0.09) from d 8 to d 9. Follicle size did not differ between treatments (P = 0.48) and did not influence expression of MMP-2 (P = 0.92), tissue plasminogen activator (tPA; P = 0.51), or urokinase plasminogen activator receptor (uPAR; P = 0.32). There was no effect of PGF (P = 0.30) or GnRH (P = 0.26), but there tended (P = 0.10) to be a PGF by GnRH interaction on expression of MMP-2. Expression was decreased (P = 0.05) among + PGF/- GnRH cows (1.7 ± 1.2) compared to + PGF/+ GnRH cows (5.1 ± 1.0) and tended (P = 0.10) to be decreased compared to - PGF/- GnRH cows (5.0 ± 1.4). Expression of MMP-2 did not differ (P > 0.62) between + PGF/+ GnRH, - PGF/- GnRH, or - PGF/- GnRH cows (4.3 ± 1.1). Expression of tPA was not influenced by PGF (P = 0.30), but there was an effect of GnRH (P = 0.05) and there tended to be a PGF by GnRH interaction (P = 0.08). Expression of tPA was increased (P = 0.05) in + GnRH cows (6.8 ± 1.4) compared to - GnRH cows (1.9 ± 1.8). Expression was also increased in + PGF/+ GnRH (10.2 ± 1.9) compared to + PGF/- GnRH (P < 0.01; 1.0 ± 2.4), - PGF/+ GnRH (P = 0.03; 3.3 ± 2.1), and - PGF/- GnRH (P = 0.04; 2.8 ± 2.7). Expression of tPA did not differ (P > 0.47) between - PGF/- GnRH, - PGF/+ GnRH, and + PGF/- GnRH. There was no effect of PGF (P = 0.31) or GnRH (P = 0.41), and no PGF by GnRH interaction (P = 0.19) on expression of uPAR. In summary, induction of luteolysis without induction of a gonadotropin surge decreased expression of MMP-2, but induction of luteolysis was necessary to increase expression of tPA following an induced gonadotropin surge.