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.
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