132 A NEW APPROACH TO ASSESS OVARIAN STRUCTURES IN LIVE RABBITS: SURGICAL TRANSLOCATION AND ULTRASOUND BIOMICROSCOPY

Abstract

For the purpose of determining factors associated with ovulation induction in rabbits, there is a need to examine the ovaries in a serial fashion. To this end, a study was designed to develop an approach that would permit serial evaluation of ovarian structures in vivo using ultrasound biomicroscopy (UBM) while preserving ovarian function in rabbits. The use of UBM has enabled characterisation of ovarian dynamics in live mice and has recently been validated for assessing structures in excised rabbit ovaries (Cervantes et al. 2011 Reprod. Fertil. Dev. 23, 183–184). However, acoustic impedance of the body wall prevented acquisition of high-quality ovarian images in vivo by transabdominal UBM in rabbits. Female New Zealand White rabbits (5 months old; n = 12) underwent surgical ovarian translocation. Each ovary was exteriorized through a lateral flank incision on the respective sides, without compromising vascular supply. The mesovarium at each pole of the ovary was transfixed to the muscle layers of the abdominal wall to keep the ovary in a subcutaneous position. Finally, the subcutaneous and skin layers were closed. No postoperative complications were observed. The surgical site was allowed to heal for 2 weeks and the skin sutures were removed before UBM was attempted. The rabbits were wrapped in a towel for restraint without sedation. Acoustic gel was applied to the shaved skin over the translocated ovary and ovarian structures were imaged transcutaneously by UBM using a 25-MHz transducer on 3 consecutive days. Both ovaries were clearly distinguished in all 12 rabbits during each examination. Antral follicles ranging from 0.6 to 3.1 mm were detected and the number of follicles ≥0.6 mm per pair of ovaries ranged from 7 to 18. Data were analysed by one-way ANOVA. The number and diameter of follicles ≥0.6 mm per rabbit did not differ among the 3 examinations (mean ± s.e.m.; 11.0 ± 0.82, 11.8 ± 0.85 and 12.3 ± 0.75 follicles and 1.3 ± 0.07, 1.3 ± 0.07 and 1.4 ± 0.07 mm, respectively). However, follicles ≥2 mm in diameter were detected in 3 out of 12 rabbits on the first and second days and in 5 out of 12 rabbits on the third day. One or more corpora lutea were detected in the same 2 rabbits (2/12) during each of the 3 examination days. Two months after surgery, ovarian structures were clearly discernible by UBM in 11 of 24 translocated ovaries. Image deterioration was attributed to the attenuation of sound waves associated with increased skin thickness and growth of subcutaneous fat and connective tissue around the ovary, assessed at necropsy. In summary, translocated ovaries continued to function in their new location and transcutaneous UBM permitted serial visualisation of ovarian structures in live rabbits. Therefore, this new approach provides a nonterminal alternative for repetitive examination of rabbit ovaries and is particularly appropriate for experiments involving factors associated with ovulation induction in rabbits. This research was supported by the Natural Sciences and Engineering Research Council of Canada.