Changes in nitric oxide, carbon monoxide, hydrogen sulfide and male reproductive hormones in response to chronic restraint stress in rats

Gasotrasmitters are endogenously synthesized gaseous molecules that are engaged in cellular physiological and pathological processes. Stress influences various physiological aspects of an organism and amends a normal system's functions, including those of the reproductive system. This study aims to investigate the effect of long-term exposure to restraint stress on the male reproductive system as well as the possible impact of stress on the levels of nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S), and the expression of their producing-enzymes. In this study, rats were subjected to the restraint condition for 2 h per day and 7 days per week for 8 consecutive weeks. The results revealed decreases in the serum levels of kisspeptin-1(Kiss-1), gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone and dehydroepiandrosterone sulfate (DHEA-s); however, corticosterone, gonadotropin-inhibitory hormone (GnIH), estradiol (E2) and prolactin levels increased following restraint stress. The mRNA expression levels of NO synthases (NOSs); neuronal NOS (nNOS), inducible NOS (iNOS) and H2S synthases; cystathionine-gamma-lyase- (CSE), 3-mercaptopyruvate-sulfurtransferase- (3MST) and CO-producing enzyme; heme oxygenase-2 (HO-2) were upregulated in the hypothalamus of restraint rats. Testicular mRNA expression levels of endothelial NOS (eNOS), nNOS, HO-1 and HO-2 were upregulated whereas cystathionine beta-synthase (CBS), CSE and 3MST expression levels were downregulated following restraint stress. Concentrations of NO increased in the testes but decreased in the semen of restraint rats. On the contrary, CO levels were reduced in the testes while they were elevated in the semen, whereas H2S concentrations decreased in both testes and semen of restraint rats. Concentrations of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX), as well as total antioxidant capacity (TAC) rose in the testes, while they declined in the semen of the restraint group. Restraint stress decreases the levels of reactive oxygen species (ROS) and malondialdehyde (MDA) in the testes while increasing them in the semen. Collectively, restraint stress negatively impacts male reproductive functions and modulates gasotransmitters producing-enzymes expression in the hypothalamus and testes.