188 EFFECT OF RABBIT SEMINAL PLASMA IN OVULATING RESPONSE

Abstract

The presence of an ovulation-inducing factor (OIF) in the seminal plasma (SP) of several species with spontaneous and induced ovulation, included the rabbit, has been documented. The biochemical identity of OIF in SP remains unknown, but it seems that OIF is a protein (Ratto et al. 2011 Reprod. Biol. Endocrinol. 9, 24). The aim of this study was to determine if the protein present in the rabbit SP could induce ovulation in a dose manner and provoke changes in plasma hormone concentrations [LH and progesterone (P₄)]. Semen was collected from 12 male rabbits using an artificial vagina, pooled, centrifugated at 3000g for 30 min twice and analysed by Bradford method to determine protein concentration that was 7 mg protein mL^–1 of SP. After storage at –80°C, the SP was lyophilized for use at different concentrations. Twenty-four females were synchronized with an i.m. injection of 25 IU of equine chorionic gonadotropin and randomly assigned to 4 groups (n = 6). Forty-eight hours later (day 0) they were given a single i.m. dose of 1) 1 mL of saline solution (SS; negative control), 2) 20 µg of gonadorelin (GnRH; positive control), 3) 1 mL of lyophilized SP diluted in SS containing 7 mg of protein (SP7), 4) 1 mL of lyophilized SP diluted in SS containing 14 mg of protein (SP14). Blood samples for LH measurement were taken every 30 min from 30 min before injection to 2 h after treatment. Blood samples for P₄ measurement were taken every 2 days from Day 0 to Day 6. Hormone determinations were made by enzyme immunoassay. Ovulation rate (OR), number of corpora lutea (CL), follicles higher than 1 mm, and total number of hemorrhagic follicles were determined after euthanasia on Day 7. Statistical analysis was performed by ANOVA. The OR was significantly higher (P < 0.0001) in GnRH than in SS, SP7, and SP14 groups (OR: 100, 0, 0, and 8.3%, respectively). Total number of CL counted in does that ovulated in GnRH and SP14 groups was not different (13.7 ± 0.8 and 9 ± 0.0 CL, respectively; P < 0.0001). No statistical differences were observed between groups on the number of follicles higher than 1 mm (GnRH: 17 ± 2.4; SS: 15 ± 1.6; SP7: 11.7 ± 2.6; SP14: 14.8 ± 0.9) and anovulatory hemorrhagic follicles (GnRH: 2.3 ± 0.9; SS: 0.2 ± 0.2; PS: 1.7 ± 0.8; PS 14: 1.7 ± 1.5). Treatment was followed by a surge in plasma LH concentration beginning 30 min after treatment to 120 min in GnRH group ranging ~75 ng mL^–1, whereas in the other groups it remained at basal levels (around 20 ng mL^–1; P < 0.0001). Plasma P₄ concentrations were significantly increased from Day 2 to 6 (4.7 ± 0.7 to 22.3 ± 3.7 ng mL^–1; P < 0.0001) only in rabbits treated with GnRH. Plasma P₄ concentrations did not vary throughout the experimental period in all OIF-treated rabbits. The present study failed to demonstrate the effect of 3 different dosages of OIF of the rabbit SP on induction of ovulation. More studies are necessary to elucidate if rabbit SP could induce ovulation in rabbit females.

We acknowledge CM and MEC for funding.