Alterations of Kiss 1 receptor, GnRH receptor and nuclear receptors of the hypothalamo-pituitary-ovarian axis following low dose bisphenol-A exposure in Wistar rats

Abstract

Bisphenol A is a chemical used primarily as a monomer in the production of polycarbonate plastics and epoxy resins. It is a synthetic chemical compound that is produced in billions of pounds annually, and tagged as an endocrine disruptor. Bisphenol A is a high production synthetic chemical compound that is used in the production of many consumables and equipments of daily consumption and use by man. Growing interest in possible health threats posed by endocrine disrupting chemicals (bisphenol-A inclusive), as these substances are in our environment, food, and many consumer products. Therefore, this study aims to determine bisphenol-A effects on the hypothalamo-pituitary-ovarian axis, and role of melatonin in this regard. Forty-two Wistar rats were bred, grouped into 7, with each group consisting of 6 rats. Experimental groups were administered low and high doses of bisphenol-A and melatonin, starting from day 19, and was continued for 7 weeks orally. They were left to develop into full adults and were sacrificed on day 120±4 days. Blood samples, hypothalamus, pituitary and ovarian tissues were excised for biochemical and tissue antioxidants assays as well as genetic studies. Results show elevated gonadotropin and androgen levels. There was disruption of reactive oxygen species in the ovarian tissues, as well as alterations in the expression of genes that regulate reproduction at the hypothalamus and pituitary levels. Conclusion of early exposure to bisphenol-A is associated with prolonged duration of disruption of reproductive functions in female Wistar rats, which persist long after cessation of the exposure. Melatonin antioxidant effects give some promising outturns against bisphenol-A induced toxicities.

Keywords: Bisphenol A; Endocrine disruptors; Hypothalamo-pituitary-ovarian axis; Melatonin; Reproduction.

Fig. 1

Showing the plasma levels of anti-mullerian hormone (AMH) (A), follicle stimulating hormone (FSH) (B), luteinizing hormone (LH) (C), progesterone (D), estradiol (E), and testosterone (F) following prenatal exposures to normal saline (NS), vehicle control (VC), 10 mg/kg melatonin (MEL), 25 mg/kg bisphenol-A (BPA) (LBP-A), 25 mg/kg BPA+10 mg/kg melatonin (LBP-A+MEL), 50 mg/kg BPA (HBP-A) and 50 mg/kg BPA+10 mg/kg melatonin (HBP-A+MEL). Values are presented as mean±standard error of mean. Asterisk indicates significant increase from all or specific groups (*P<0.05).

Fig. 2

Showing the ovarian levels of (A) superoxide dismutase (SOD), (B) nitric oxide synthase (NOS), (C) glutathione peroxidase (GPx), and (D) uridine 5’-diphospho (UDP) following exposures to normal saline (NS), vehicle control (VC), 10 mg/kg melatonin (MEL), 25 mg/kg bisphenol-A (BPA) (LBP-A), 25 mg/kg BPA+10 mg/kg melatonin (LBP-A+MEL), 50 mg/kg BPA (HBP-A), and 50 mg/kg BPA+10 mg/kg melatonin (HBP-A+MEL). Values are presented as mean±standard error of mean. Asterisks indicate significant differences at *P<0.05, **P<0.01, and ***P<0.001, respectively from all or specific groups.

Fig. 3

Showing the expression of Kiss 1 (A), GnRH mRNA (B), GnRH receptor (GnRHr) (C), estrogen receptor (EsR) (D), androgen receptor (AR) (E), and anti-mullerian hormone (AMH) (F) following exposures to normal saline (NS), vehicle control (VC), 10 mg/kg melatonin (MEL), 25 mg/kg bisphenol-A (BPA) (LBP-A), 25 mg/kg BPA+10 mg/kg melatonin (LBP-A+MEL), 50 mg/kg BPA (HBP-A), and 50 mg/kg BPA+10 mg/kg melatonin (HBP-A+MEL). Values are presented as mean±standard error of mean. Asterisks indicate significant differences at *P<0.05, **P<0.01, and ***P<0.001, respectively from all or specific groups.

Fig. 4

Showing (A) representative photomicrographs of the ovaries (H&E, ×40) and (B) follicular count following prenatal exposures to normal saline (NS), vehicle control (VC), 10 mg/kg melatonin (MEL), 25 mg/kg bisphenol-A (BPA) (LBP-A), 25 mg/kg BPA+10 mg/kg melatonin (LBP-A+MEL), 50 mg/kg BPA (HBP-A), and 50 mg/kg BPA+10 mg/kg melatonin (HBP-A+MEL). Values are presented as mean±standard error of mean. *Significant decrease from the control; ^aSignificant decrease from the vehicle control group. CL, corpus luteum; CTR, control.

Fig. 5

Showing the (A) ovarian histoarchitecture (H&E, ×100) and (B) follicle count in adolescent rats exposed to normal saline (NS) is the control group (CTR), vehicle control (VC), 10 mg/kg melatonin (MEL), 25 mg/kg bisphenol-A (BPA), 25 mg/kg BPA+MEL, 50 mg/kg BPA, and 50 mg/kg BPA+MEL. AF, antral follicles; AT, atretic follicles; CL, corpus luteum; FD, follicular degeneration; PA, preantral; PF, primary follicle.