Potential roles of matrix metalloproteinases and characteristics of ovarian development in neonatal guinea pigs

Influences of non‐nutritive sweeteners on ovarian and uterine expression of T1R2 and T1R3 in peripubertal female guinea pigs

The underlying mechanism of taste receptor type 1 subunit 2 (T1R2) and taste receptor type 1 subunit 3 (T1R3) in the hormonal and reproductive system is still elusive. A low or a high dose of sweetness equivalent to that sodium saccharin (SS, 1.5 or 7.5 mM) and rebaudioside A (RA, 0.5 or 2.5 mM) was administered to young female guinea pigs for 28 consecutive days from the age of 28 days. Our results indicated that the sweet taste receptor subunit T1R2 was markedly expressed in the ovary and uterus of guinea pigs, whereas the T1R3 protein was expressed at a lower level. We elucidated that low-dose (1.5 mM) SS increased body and ovary weight associated with elevated ovarian expression of T1R2 in guinea pigs, unlike the high-dose (7.5 mM) SS, which suppressed the ovarian expression of T1R2 and resulted in certain adverse effects on ovarian and uterine morphology. Furthermore, high-dose (2.5 mM) RA increased the number of corpus luteum and elevated uterine expression of T1R2, whereas low-dose (0.5 mM) RA induced increased secretion of serum progesterone. Therefore, our findings suggest that we should pay more attention to the potential adverse effects, including increases in ovary weight, morphology changes, and increased progesterone that result from the dose-dependent regulation of T1R2 by non-nutritive sweeteners (NNS) in the ovaries and uteri of peripubertal females.

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.