Effects of Levonorgestrel on Reproductive Hormone Levels and Their Receptor Expression in Mongolian Gerbils (Meriones unguiculatus)

Abstract

Abstract:The effects of levonorgestrel (LNG) on serum levels of reproductive hormones and their receptor mRNA expression in the ovary and uterus of Mongolian gerbils were examined. The results show that serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) increased, whereas serum estradiol (E2) and progesterone (P4) decreased profoundly after LNG treatment. LNG down-regulated the mRNA expression of folliclestimulating hormone receptor (FSHR), luteinizing hormone receptor (LHR), estrogen receptor (ER) β and progesterone receptor (PR) in the ovary, and ERα and PR in the uterus of Mongolian gerbils. The down-regulated effects were time-dependent and dose-dependent. LNG had no obvious effects on ERα mRNA expression in the ovary. The findings suggest that LNG impairs reproductive hormone receptor expression at the molecular level in Mongolian gerbils. Also, the two ER subtypes may play different roles in the ovary, and ERβ may not be the predominant ER subtype in the uterus of Mongolian gerbils. The ovary and uterus may be the important sites of action of LNG through its direct progesterone-like effects in Mongolian gerbils.

Effect of progestin on thyroid function in female Wistar rats

“…Acting on the hypothalamicpituitary-gonadal axis, it exerts a strong anti-gonadotropic effect in the hypothalamus, inhibiting ovulation, thickening the uterus, reducing uterine mucus, and inhibiting progesterone secretion. Our findings are consistent with the results of a study on gerbils with a single LNG exposure and SD rats receiving olive oil (0.2 ml/100 g/ day) containing a combination of 1.0 mg ethinylestradiol and 10.0 mg levonorgestrel (30,31). A small randomized controlled trial reported significantly reduced TSH levels in a 12-week trial of oral trace progesterone, 300 mg/d at bedtime, in postmenopausal women (32), which is consistent with our study.…”

“…The low serum progesterone levels in this study indicated that exogenous progestin could directly inhibit progesterone secretion by inhibiting the ovary. Progesterone directly suppresses estrogen and progesterone production by ovarian granulosa cells ( 30 , 31 ). Acting on the hypothalamic-pituitary-gonadal axis, it exerts a strong anti-gonadotropic effect in the hypothalamus, inhibiting ovulation, thickening the uterus, reducing uterine mucus, and inhibiting progesterone secretion.…”