Induction of follicular luteinization by equine chorionic gonadotropin in cyclic guinea pigs

Combined treatment with cysteamine and leukemia inhibitory factor promotes guinea pig oocyte meiosis in vitro

The guinea pig is an excellent but underused animal model due to its reproductive biology, which poses difficulties in inducing superovulation, embryo manipulation in vitro, and embryo transfer. We examined the effects of cysteamine (Cys), leukemia inhibitory factor (LIF), and Y27632 on guinea pig oocyte in vitro maturation (IVM). Cumulus-oocyte complexes were collected from antral follicles and classified into three different types before IVM. Among type I oocytes, maturation rates to metaphase II (MII) were similar in basal maturation medium and medium supplemented with Cys or LIF (39.5-40.9%), but combined Cys and LIF treatment increased the MII rate to 61.8%. Supplementation with Y27632 alone or in combination with Cys and LIF dramatically reduced the MII rate (27.7-29.7%). Similar trends were observed for type II oocytes, although their overall MII rate was lower than that of type I oocytes. The MII rate was higher among oocytes collected from 2-month-old guinea pigs compared with those from 4-month-old guinea pigs (56.5 vs. 44.8%). The optimal IVM duration was 24 h (52.5%), as 36 or 48 h of IVM reduced the MII rate (32.8-42.5%). Furthermore, Y27632 reduced the presence of microfilaments in oocytes. These findings indicate that combined supplementation of maturation medium with Cys and LIF, but not Y27632, improves the maturation efficiency of guinea pig oocytes. This study provides an important scientific basis for further efforts toward guinea pig in vitro fertilization, cloning, and gene editing by establishing an animal model for human reproduction and related diseases.

Expression of matrix metalloproteinases and ovarian morphological changes in androgenized cyclic female guinea pigs

This study was conducted to investigate expression of matrix metalloproteinases (MMPs) and ovarian morphological changes in androgenized cyclic female guinea pigs. Adult cyclic female guinea pigs were injected daily for 28 days with medium doses of testosterone propionate (TP; 1 mg/100g), high doses of TP (2 mg/100g), or saline (control). Serum concentrations of testosterone, estradiol (E2), and progesterone (P4) were measured. Histologic sections of ovaries were stained with hematoxylin-eosin and by immunohistochemistry. Expressions of steroidogenic acute regulatory protein, proliferating cell nuclear antigen, and MMP-2 and MMP-9 in the ovary were characterized by immunohistochemistry. After 28 days of TP injection, serum testosterone concentrations were increased dose-dependently. An appropriate dosage of TP could induce permanent anovulation in guinea pigs, making them a potential model for human polycystic ovary syndrome. MMP-2 and MMP-9 are jointly involved in the growth and atresia of ovarian follicles in cyclic guinea pigs. Increased numbers of atretic antral follicles in the ovary might be associated with the observed high expression of MMP-2 in androgenized cyclic guinea pigs.