The rabbit as an animal model for the study of ovulation-inducing factor

Abstract

Ovulation–inducing factor (OIF) is a seminal plasma protein that has been found in the ejaculate of different species. Evidence suggests that OIF and its function may be conserved among species. Our general objective was to develop a rabbit model for the study of OIF in seminal plasma. In the first study, we conducted two experiments to validate the use of ultrasound biomicroscopy as a method for assessing ovarian structures in rabbits, and to develop a method that permits serial noninvasive repetitive ultrasound evaluation of ovarian structures in vivo in rabbits. In Experiment 1, the number and size of follicles ≥ 0.6 mm and corpora lutea (CL) detected by ultrasound biomicroscopy (UBM) ex situ were correlated with those detected by histology in each pair of ovaries from 4 female New Zealand White rabbits (5-5.5 months old) given an ovulation-inducing treatment. In Experiment 2, we translocated the ovaries of female New Zealand white rabbits (n=12; 5 months old) to a subcutaneous position in order to develop a method that permits serial UBM evaluation of ovarian structures in vivo in rabbits. Results showed strong correlations (P < 0.05) between UBM and histology in all the ovarian variables evaluated in Experiment 1, and also showed that ovarian structures are easily identified using UBM in vivo in the rabbits submitted to the surgical approach performed in Experiment 2. In the second study, we conducted two experiments to test the hypothesis that llama and rabbit seminal plasma elicits a surge of LH release and is responsible for inducing ovulation in rabbits. In Experiment 1, we compared the effect of an intramuscular administration of saline, GnRH, llama or rabbit seminal plasma in female New Zealand White rabbits (n=4-6 per group, 5.5 months old) that were group-housed. In Experiment 2, we compared the effects of the same treatments in rabbits (n=5-7 per group, 5.5 months old) that were individually caged. Ovulation and CL formation occurred in most rabbits regardless of the treatment given when animals were group housed, while rabbits given similar treatment but individually housed did not ovulate. In the GnRH group, a surge in plasma LH concentrations was observed in all the rabbits, followed by CL formation and an increase in plasma progesterone concentrations. In summary, we developed a rabbit model for the study of OIF, where ovarian structures can be evaluated in vivo by UBM. Results did not support the hypothesis that OIF in seminal plasma elicits ovulation in rabbits. Further studies are needed to determine the effects of dose and route of administration of seminal plasma in rabbits.