Introduction

Polycystic Ovary Syndrome (PCOS) is associated with insulin resistance, elevated serum androgen levels, and an increase in the ratio of Luteinizing Hormone (LH) to Follicle-Stimulating Hormone (FSH) [1, 2]. Adiponectin is synthesized in adipose tissue, hypothalamus, and gonads [3, 4]. Deficiency in adiponectin production leads to insulin resistance and disruption in lipid and glucose metabolisms [7, 8]. Serum adiponectin levels in PCOS women are lower than in healthy individuals [8, 10]. L-dopa is a precursor to the neurotransmitters dopamine, epinephrine and norepinephrine [14]. Dopamine and L-dopa inhibit Hypothalamic-Pituitary-Gonadal (HPG) axis activity [15, 16]. PCOS is associated with decreased dopamine release [19]. This study aimed to examine the effects of L-dopa and dopamine receptor antagonists (SCH 23390 as D1 receptor and sulperide as D2 receptor) on LH secretion and relative expression of adiponectin gene in the hypothalamus and ovaries of rats with PCOS induced by 

Materials and Methods

To perform this study, 20 Wistar female rats weighing 180-220 g were used. In order to induce PCOS, the animals received intramuscular injection of Estradiol Valerate (EV) in the estrous stage. 15 PCOS rats were divided into three groups of saline, L-dopa (100 mg/kg), and L-dopa + sulpiride + SCH 23390 (100 mg/kg L-dopa + 10mg/kg sulpiride + 1mg/kg SCH 23390 hydrochloride), and 5 healthy rats received saline as negative control group. In groups receiving antagonist and L-dopa, antagonists were injected 10 minutes before L-dopa injection. The hypothalamus and ovarian samples were isolated and stored at -80°C until RNA extraction. The average serum LH concentration was measured using Radioimmunoassay (RIA). The mean relative expression of adiponectin gene in the ovaries and hypothalamus was calculated using real-time PCR assay and delta-delta CT method ( 2-∆∆Ct formula). The data obtained from this formula were analyzed in SPSS V. 16 software using one-way ANOVA test and the mean data were compared by using Tukey’s post-hoc test. The results were presented as Mean±SD, considering the significance level of P≤0.05.

Results

The results of comparing the mean serum LH concentrations in the negative control and PCOS groups are shown in Table 1.

The mean relative expression of adiponectin gene in the ovaries and hypothalamus of the PCOS control group showed a significant decrease compared to the negative control group (P=0.001 for ovaries and P=0.015 for hypothalamus) (Figure 1).

For the PCOS group received L-dopa only, the mean relative expression of adiponectin gene in the ovaries and hypothalamus increased non-significantly (P=0.924) and significantly (P<0.001), respectively (Figure 1). For the PCOS group received L-dopa, sulpiride, and SCH 23390 hydrochloride simultaneously, the mean relative expression of adiponectin gene in the ovaries and hypothalamus decreased non-significantly (P=0.948) and significantly (P=0.025), respectively (Figure 1).

Discussion

The results of the present study showed that in PCOS rats, serum LH concentrations increased significantly compared to the healthy rats, while the mean relative expression of adiponectin gene in the ovaries and hypothalamus of PCOS rats reduced significantly compared to the healthy rats. The results are consistent with previous research on the extent of adiponectin secretion in humans and rodents with PCOS. Previous studies have shown that the serum adiponectin level is reduced in women with PCOS compared to healthy peers, and PCOS obese women have lower serum levels than non-PICOS obese women [8, 22]. Decreased adiponectin levels in PCOS women may be due to increased production of androgens caused by reduced inhibitory effects of adiponectin on theca cells [23], because hyperandrogenism and obesity have been shown to play an important role in reducing plasma levels of adiponectin and causing insulin resistance, which is a major feature of PCOS [24, 25]. 

L-dopa exerted inhibitory effects on LH secretion and stimulatory effects on adiponectin gene expression in the hypothalamus of PCOS rats; however, it had no stimulatory effects on adiponectin gene expression in the ovaries of PCOS rats. This is consistent with the results of an in-vitro study where researchers examined the effects of dopamine on adipocyte cells incubated in culture, and reported the stimulatory effects of dopamine on adiponectin secretion from these cells [22]. Dopamine receptor antagonists including SCH23390 hydrochloride and sulpiride blocked the inhibitory effects of L-dopa on the LH secretion and its stimulatory effects on the relative expression of the adiponectin gene in the hypothalamus of PCOS rats. Increasing the activity of dopaminergic neurons may be effective in controlling endocrine disorders caused by decreased adiponectin secretion in PCOS patients.

Ethical Considerations

Compliance with ethical guidelines

This study ethically approved in ethics committee of University of Mohaghegh Ardabili (Code: 95-125-1).

Funding

The present paper was extracted from the MSc thesis of the first author, Department of Biology, Faculty of Sciences, University of Mohaghegh Ardabili.

Authors' contributions

All authors contributed in preparing this article.

Conflicts of interest

The authors declared no conflict of interest.

Acknowledgements

The authors would like to thank Deputy of Research and Technology of the Mohaghegh Ardabili University for their financial and non-financial supports. Also thank to Dr. Homayoun Khaz'ali from Shahid Beheshti University for providing the instruments.

 

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