Asian Pacific Journal of Reproduction

189-194

Authors: Sulagna Dutta, Pallav Sengupta, Suriyani Muhamad

Male reproductive functions are mediated by different hormones whose orchestrations remain a major research interest. The ‘master’ regulator hormonal axis is the hypothalamo- pituitary-gonadal/testicular axis which is led by the pulsatile release of hypothalamic gonadotropin-releasing hormone. This, in turn, stimulates the anterior pituitary trophic hormones, the luteinizing hormone and follicle-stimulating hormone. Luteinizing hormone and follicle-stimulating hormone act upon the testicular cells, the Leydig cells for steroidogenesis and Sertoli cells to aid spermatogenesis, respectively. This primary axis is influenced by an array of other testicular hormones, metabolic hormones, and different regulatory factors. These hormonal crosstalks influence the intricate testicular functions, sexual behavior and semen quality in men. Given the growing concern in the last few decades over the increasing prevalence of male subfertility and/or infertility mostly in terms of deteriorating semen quality, it is required to find its underlying mechanisms. In this regard, the endocrine regulation of testicular functions is of prime importance in the determination of semen quality and sperm functions. This review article aims to present a concise updated overview on the mechanism by which the key hormones integrate the male reproductive functions and maintain the semen quality.

203-210

Authors: Ahmed Alahmar, Sulagna Dutta, Pallav Sengupta

Thyroid hormones have been well studied for its relevance to male reproduction in the last few decades. They are considered as essential regulators of male reproductive functions and play vital roles in male gonadal developments. Hyperthyroidism and hypothyroidism both affect testicular functions and influence neuroendocrine regulations over reproductive functions via the crosstalk between the hypothalamic-pituitary-thyroid axis and the hypothalamic-pituitary-gonadal axis. The alterations in the male reproductive hormonal milieu by thyroid hormones may lead to reduced testosterone levels and deterioration of semen quality. However, there are very few reports on the direct effects of thyroid disorders upon testicular functions and semen quality. This article aims to review the available literature to present a concise updated concept on the regulation of male reproductive functions by the thyroid hormones, and the possible mechanism by which thyroid dysfunctions affects testicular functions.

220-226

Authors: Pallav Sengupta, Koushik Bhattacharya, Sulagna Dutta

The global scenario reveals that the recent trend of deterioration of male fertility parameters parallels the growing prevalence of obesity. Over the last few decades, substantial research evidence has surfaced that aid understanding of the mechanisms by which body energy homeostasis is associated with reproductive functions. In this regard, leptin, an adipocyte- derived hormone, finds utmost relevance for its versatile physiological functions especially in metabolism as well as in the regulation of reproductive functions. Since leptin receptors are found to be highly expressed in several structures, both centrally and peripherally, it has been hypothesized that leptin may affect reproductive functions either via the hypothalamic-pituitary-gonadal axis or may also directly act upon gonadal tissues. Its roles, particularly during puberty and reproduction, are well documented. However, the exact mechanisms of leptin actions upon the gonadotropin-releasing hormone neurons to induce physiological changes of puberty and reproduction need further research. Leptin is proven as an essential hormone required for normal reproductive functions, but when leptin levels exceed the physiological limit, it may adversely affect the testicular processes. Leptin can serve as a potential link between obesity and male infertility, as it has been shown that poor male reproductive parameters such as low sperm count, testicular oxidative stress, high rate of morphological abnormalities in sperm, positively correlate with increased levels of leptin in obese men. Therefore, the present review article aims to provide a better understanding of the updated views on the functions of leptin and mechanisms of leptin actions on male reproduction.

233-238

Authors: Pallav Sengupta, Sulagna Dutta, Maiza Tusimin, Ivan Rolland Karkada

Orexins (or hypocretins) are hypothalamic neuropeptides with a multitude of physiological functions. They occur in two known forms, namely, orexin A and orexin B with a common precursor, preproorexin. The orexin receptors (orexin 1R and orexin 2R) belong to the Family of G-protein coupled receptors. The primary function of the orexin system, i.e. the orexins, their receptors and associated neuronal circuitries, perhaps is to increase spontaneous physical activity and food intake, thereby promoting an increase in energy expenditure. Reports suggest that orexins may be the key brain components to mediate the mechanism of obesity resistance. Recent research also has thrown lights upon a significant role of orexins, especially orexin A, in regulation of male reproductive functions owing to their receptor expressions in vital testicular cells, such as Leydig cells, Sertoli cells as well as spermatozoa at different developmental stages, even in the epididymis and penis. Moreover, orexins have been reported to greatly influence gonadotropin-releasing hormone neurons and their secretions to regulate reproductive functions via modulation of the hypothalamic-pituitary-gonadal axis. Evidence thus implicates participation of orexins in steroidogenesis, spermatogenesis, transportation and maturation of sperm as well as in the control of penile function. However, further research is required in this direction to elucidate the mechanisms by which orexins play a role in different testicular functions and effect of orexins on semen quality.

244-250

Authors: Sulagna Dutta, Pallav Sengupta, Anupam Biswas

Adiponectin is an adipokine that has the highest plasma concentration among all other adipokines. It is a white adipose tissue secretion essential for the regulation of energy metabolism owing to its antiatherogenic insulin-resistance, and anti-inflammatory properties. Studies have put forth that adiponectin is a potent endocrine regulator with mechanisms relating energy balance with reproductive function in different species, including humans. The two adiponectin receptors, AdipoR1 and AdipoR2 have been found to be expressed in the prime regulatory axis of reproduction, the hypothalamic-pituitary-gonadal axis. The activation of adiponectin receptors has been shown to regulate the secretion and gene expressions of kisspeptin, gonadotropin-releasing hormone and gonadotropins. Adiponectin finds relevance in the regulations of most of the vital testicular functions, such as steroidogenesis, germ cell proliferation and their coordinated apoptosis, as well as in modulation of testicular redox status and oxidative stress. Since metabolic syndrome and their associations with male infertility have been gaining immense research interest, adiponectin seems to be one of the important mediators of metabolic syndrome-induced male reproductive dysfunctions. This article aims to review the patterns of adiponectin expression in the male reproductive tissues and the mechanism by which adiponectin modulates male reproductive functions.