Assessment of ovarian follicular dynamics and folliculogenesis associated endocrine profiles following gonadotropin stimulation in the bonnet monkey

We evaluated ovarian follicular dynamics in bonnet monkeys by employing trans-abdominal ultrasonography. Following the administration of human follicle stimulating hormone (hFSH) and/or human menopausal gonadotropin (hMG), multiple follicular development was assessed and their numbers, size and growth profiles were monitored. The ultrasonograms showed that the follicular antrum appeared distinctly anechoic with well-defined hyperechoic borders. Depending on the type, quantity (12.5-25 IU), and duration (6-9 days) of hormones administered, the number of developing follicles was 2-12 per ovary with their lowest diameter being 2 mm. With continued hormone administration, their numbers and diameters increased; which were more pronounced in animals administered with hFSH than with hMG, with follicles of 6-8 mm. Interestingly, human chorionic gonadotropin (hCG) injection (2000-3000 IU), when follicles acquiring >6-8 mm sizes, induced the maximum expansion of antral follicles with sizes reaching up to 14 mm. On days 3-5 post-hCG, the ultrasonograms showed loosely demarcated multiple hypoechoic structures and well-demarcated hyperechoic structures with anechoic/hypoechoic cores corresponding to unruptured luteinized follicles and corpora lutea, respectively. On day 4 post-hCG, there was a substantial reduction in the number of antral follicles. In stimulated animals, follicular growth, ovulation, and formation of luteal structures were accompanied by corresponding physiological changes in the serum estradiol and progesterone profiles. These findings, for the first time, showed that ultrasonographic imaging approach is useful for precise monitoring of temporal changes in follicular developmental dynamics and to time the hCG induced ovulation in the bonnet monkey.