The effect of PMSG treatment on the ovarian histomorphometry of prepubertal rabbits

The study aimed to determine the effect of pregnant mare serum gonadotropin (PMSG) administration on ovarian immunohistomrphology and follicular growth in prepubertal female rabbits (Oryctolagus cuniculus). Sixteen animals, aged 75±5 days, were equally assigned into two groups, each containing eight animals. Animals in the control group were administered with normal saline (1 ml), while the treatment group received a single intramuscular injection of PMSG (100 IU). After 72 hours, the animals were euthanized, and their ovaries were dissected. Ovarian sections were stained with hematoxylin and eosin to determine ovarian features, follicle measurements, and classifications. The estrogen receptor beta (ERs-β) expression pattern was recognized by immunohistochemical staining. The diameter of the secondary, preantral, and antral follicles was significantly greater (P<0.05) than the control group. Interestingly, the matured large-sized follicles were exclusively detected in the treated group. However, relative to control, the proportion of preantral and antral follicles was significantly increased (P<0.001). In contrast, PMSG triggered a substantial reduction (P<0.001) in the percentage of secondary follicles. The control group demonstrated an intense expression of ERs-β in the nuclei of granulosa cells of preantral follicles, stroma, theca, and epithelial cells. However, in the treated group, the staining pattern of ERs-β was largely decreased in the growing and antral follicles. Collectively, a single PMSG treatment effectively induced ovarian hyperstimulation in prepubertal rabbits, significantly increasing the size and number of developing follicles. Further research is necessary to understand the marked decrease in ERs-β expression triggered by PMSG treatment.