Smad8 is involvement in follicular development via the regulation of granulosa cell growth and steroidogenesis in mice

Background:SMAD family proteins(SMADs)are crucial transcription factors downstream of transforming growth factor beta(TGF-ß)/SMAD signaling pathways that have been reported to play a pivotal role in mammalian reproduction.However,the role of SMAD family member 8(SMAD8,also known as SMAD9),a member of the SMAD family,in mammalian reproduction remains unclear.Methods:We employed RNA interference techniques to knock down Smad8 expression in mouse granulosa cells(GCs)to investigate the effects of Smad8 on GC growth and steroidogenesis.Results:Our findings revealed a significant decrease in the proliferative capacity and a substantial increase in the apoptosis rate of GCs after transfection with Smad8-siRNA for 48 h.Subsequent hormone assays demonstrated a significant decrease in estradiol(E2)levels,whereas progesterone(P4)remained unchanged.Further mechanistic analysis showed that the mRNA expression of proliferating cell nuclear antigen(Pcna),Cyclin D2,cell cycle-dependent kinase 4(Cdk4),B-cell lymphoma-2(Bcl-2),estrogen receptor(Er),luteinizing hormone receptor(Lhr)and cytochrome P450 family 19 subfamily A member 1(Cyp19a1)significantly decreased.Conversely,the mRNA of cysteine aspartate proteinase 3(Caspase 3)significantly increased,wheras Bcl2-associated X(Bax),folliclestimulating hormone receptor(Fshr)and cytochrome P450 family 11 subfamily A member 1(Cyp11a1)remained unchanged compared to the controls.Conclusion:This study indicates that Smad8 knockdown inhibits cell proliferation,promotes apoptosis,reduces Er and Lhr transcription,and decreases E2 production in mouse GCs.These findings suggest that Smad8 may serve as a novel genetic marker for mammalian reproduction.

Cox7a2 mediates steroidogenesis in TM3 mouse Leydig cells

Aim： To investigate the regulatory function of Cox7a2 on steroidogenesis and the mechanism involved in TM3 mouse Leydig cells. Methods： The cDNA of Cox7a2 was cloned from TM3 mouse Leydig cells. It was subcloned to pDsRed- Express-N 1 and transfected back into TM3 mouse Leydig cells for Cox7a2 overexpression by transient gene transfection. Steroidogenesis affected by overexpressed Cox7a2 was studied by ELISA. To elicit the mechanism of this effect, expression of steroidogenic acute regulatory （STAR） protein and reactive oxygen species （ROS） were examined by Western blot and fluorometer, respectively. Results： The cDNA of Cox7a2 （249 bp） was cloned from Leydig cells and confirmed by DNA sequencing. After constructed pDsRed-Express-N1-Cox7a2 was transfected back into TM3 mouse Leydig cells, Cox7a2 inhibited not only luteinizing hormone （LH）-induced secretion of testosterone but also the expression of StAR protein. At the same time, Cox7a2 increased the activity of ROS in TM3 mouse Leydig cells. Conclusion： Cox7a2 inhibited LH-induced StAR protein expression, and consequent testosterone production, at least in part, by increasing ROS activity in TM3 mouse Leydig cells.

Gonadotrophin-releasing hormone-Ⅰ and -Ⅱ stimulate steroidogenesis in prepubertal murine Leydig cells in vitro

Aim： To study the effect and mechanism of gonadotrophin-releasing hormone （GnRH） on murine Leydig cell steroidogenesis. Methods： Purified murine Leydig cells were treated with GnRH-Ⅰ and -Ⅱ agonists, and testosterone production and steroidogenic enzyme expressions were determined. Results： GnRH-Ⅰ and -Ⅱ agonists significantly stimulated murine Leydig cell steroidogenesis 60%-80% in a dose- and time-dependent manner （P 〈 0.05）. The mRNA expressions of steroidogenic acute regulatory （STAR） protein, P450scc, 3β-hydroxysteroid dehydrogenase （HSD）, but not 17β-hydroxylase or 17β-HSD, were significantly stimulated by both GnRH agonists with a 1.5- to 3-fold increase （P 〈 0.05）. However, only 3β-HSD protein expression was induced by both GnRH agonists, with a 1.6- to 2-fold increase （P 〈 0.05）. Conclusion： GnRH directly stimulated murine Leydig cell steroidogenesis by activating 3β-HSD enzyme expression.

Effects of Low Concentrations of Di-(2-ethylhexyl) and Mono-(2-ethylhexyl) Phthalate on Steroidogenesis Pathways and Apoptosis in the Murine Leydig Tumor Cell Line MLTC-1

The aim of this study was to evaluate the effects of low concentrations of DEHP and MEHP on steroidogenesis in a murine Leydig tumor cell line （MLTC-1） in vitro. The result of flow cytometry analysis revealed that the proportion of apoptotic cells was significantly increased after the exposure to DEHP. All three genes （P450scc, P450c17, and 38HSD） under study showed an increased expression following exposure to DEHP or MEHP, although some insignificant inhibitory effects appeared in the 10μmol/L treatment group as compared with the controls. It was also found that DEHP or MEHP stimulated INSL3 mRNA and protein especially in the 0.001 μmol/L treatment group. Testosterone secretions were stimulated after the exposure to DEHP or MEHP. Alterations of steroidogenic enzymes and INSL3 in MLTC-1 cells might be involved in the biphasic effects of DEHP/MEHP on androgen production.

Interaction between porcine granulosa and thecal cells in steroidogenesis in an amnion dual chamber culture system

Objective: To study the interaction between granulosa and thecal cel1s in steroidogenesis in an am-nion dual chamber in comparison with the cellulose dual chamber.Method: A dual chamber culture system was designed and prepared with amnion membrane from human term placenta. The isolated porcine granulosa and thecal cells were grown on both sides of the amnion membrane, with granulosa cells in the inner chamber and thecal cells in the outer chamber. The concentrations of estradiol (E,), progesterone (P) and testosterone (T) in the culture media were mea-sured by radioimmunoassay.Results: The growth of both cells and their steroidogenic function were more active in amnion dual chamber system than in cellulose dual chamber system: (1) more T produced by thecal cells in the outer chamber, passing into inner chamber through the amnion membrane. T was used by granulosa cells as the substrate of aromatization, so that granulosa cells produced more E2 (up to 2 435 pmol/L); (2) the production of P (52. 5 μmol/L) and T (10. 2μmol/L) by granulosa cells cultured in the amnion mem-brane dual chamber system were also higher.Conclusions:The dual chamber system made of amnion mpmbrane showed better effect in studying steroidogenesis than with cellulose dual chamber system, and can be used as a model for studying paracrine regulatory interaction between granulosa and thecal cells in vitro.

Effects of Fenvalerate on Steroidogenesis in Cultured Rat Granulosa Cells

Objective This study was designed to examine the in vitro effects of fenvalerate on steroid production and steroidogenic enzymes mRNA expression level in rat granulosa cells. Methods Using primary cultured rat granulosa cells (rGCs) as model, fenvalerate of various concentrations (0, 1, 5, 25, 125, 625 μmol/L) was added to the medium for 24 h. In some cases, optimal concentrations of 22(R)-hydroxycholesterol (25 μmol/L), Follicle stimulating hormone (FSH, 2 mg/L), or 8-Bromo-cAMP (1 mmol/L) were provided. Concentrations of 17β-estradiol(E2) and progesterone (P4) in the medium from the same culture wells were measured by RIA and the steroidogenic enzyme mRNA level was quantified by semi-quantitative RT-PCR. Results Fenvalerate decreased both P4 and E2 production in a dose-dependent manner while it could significantly stimulate rGCs proliferation. This inhibition was stronger in the presence of FSH. Furthermore, it could not be reversed by 22(R)-hydroxycholesterol or 8-Bromo-cAMP. RT-PCR revealed that fenvalerate had no significant effect on 3β-HSD, but could increase the P450scc mRNA level. In addition, 17β-HSD mRNA level was dramatically reduced with the increase of fenvalerate dose after 24 h treatment. Conclusion Fenvalerate inhibits both P4 and E2 production in rGCs. These results support the view that fenvalerate is considered as a kind of endocrine-disrupting chemicals. The mechanism of its disruption may involve the effects on steroidogenesis signaling cascades and/or steroidogenic enzyme’s activity.

Inhibitory actions of mibefradil on steroidogenesis in mouse Leydig cells： involvement of Ca^2＋ entry via the T-type Ca^2＋ channel

Intracellular cAMP and Ca^2＋ are involved in the regulation of steroidogenic activity in Leydig cells, which coordinate responses to luteinizing hormone （LH） and human ehorionic gonadotropin （hCG）. However, the identification of Ca^2＋ entry implicated in Leydig cell steroidogenesis is not well defined. The objective of this study was to identify the type of Ca^2＋ channel that affects Leydig cell steroidogenesis. In vitro steroidogenesis in the freshly dissociated Leydig cells of mice was induced by hCG incubation. The effects of mibefradil （a putative T-type Ca^2＋ channel blocker） on steroidogenesis were assessed using reverse transcription （RT）-polymerase chain reaction analysis for the steroidogenic acute regulatory protein （STAR） mRNA expression and testosterone production using radioimmunoassay. In the presence of 1.0 mmol L-1 extracellular Ca^2＋, hCG at 1 to 100 IU noticeably elevated both StAR mRNA level and testosterone secretion （P 〈 0.05）, and the stimulatory effects of hCG were markedly diminished by mibefradil in a dose-dependent manner （P 〈 0.05）. Moreover; the hCG-induced increase in testosterone production was completely removed when external Ca^2＋ was omitted, implying that Ca entry is needed for hCG-induced steroidogenesis. Furthermore, a patch-clamp study revealed the presence of mibefradil-sensitive Ca^24- currents seen at a concentration range that nearly paralleled those inhibiting steroidogenesis. Collectively, Our data provide evidence that hCG-stimulated steroidogenesis is mediated at least in part by Ca^2＋ entry carried out by the T-type Ca^2＋ channel in the Leydig cells of mice.

Oleic acid reduces steroidogenesis by changing the lipid type stored in lipid droplets of ovarian granulosa cells

Background:Oleic acid is an abundant free fatty acid present in livestock that are in a negative energy-balance state,and it may have detrimental effects on female reproduction and fertility.Oleic acid induces lipid accumulation in bovine granulosa cells,which leads to a foam cell-like morphology and reduced steroidogenesis.However,why oleic acid increases lipid accumulation but decreases steroidogenesis remains unclear.This study focused on oleic acid’s effects on lipid type and steroidogenesis.Results:Oleic acid increased the lipid accumulation in a concentration-dependent manner and mainly increased the triglyceride level and decreased the cholesterol ester level.Oleic acid also led to a decline in estradiol and progesterone production in porcine granulosa cells in vitro.In addition,oleic acid up-regulated the expression of CD36 and diacylglycerol acyltransferase 2,but down-regulated the expression of 3-hydroxy-3-methylglutarylcoenzyme A reductase,scavenger receptor class B member 1 and acetyl-Coenzyme A acetyltransferase 2,as well as steroidogenesis-related genes,including cytochrome P450 family 11 subfamily A member 1,cytochrome P450family 19 subfamily A member 1 and 3 as well as steroidogenic acute regulatory protein at the mRNA and protein levels.An oleic acid-rich diet also enhanced the triglyceride levels and reduced the cholesterol levels in ovarian tissues of female mice,which resulted in lower estradiol levels than in control-fed mice.Compared with the control,decreases in estrus days and the numbers of antral follicles and corpora lutea,as well as an increase in the numbers of the atretic follicles,were found in the oleic acid-fed female mice.Conclusions:Oleic acid changed the lipid type stored in lipid droplets of ovarian granulosa cells,and led to a decrease in steroidogenesis.These results improve our understanding of fertility decline in livestock that are in a negative energy-balance state.

Effect of Epidermal Growth Factor on Follicular Development and Steroidogenesis in Perfused Rat Ovary

The effect of epidermal growth factor(EGF) on follicular development and steroidogenesis was investigated using an in vitro perfused immature rat ovary model. Type 3a and type 3b follicles were counted in the sections of perfused ovaries. To determine action of EGF on amortize activity, effect of testosterone(10-5 M) plus EGF(10 ng/ml) and that of testosterone(10-5 M) alone were compared. EGF(10 ng/ml) significantly increased the number of both types of follicles. At time-course experiment, EGF(10 ng/ml) did not enhance the number of both types of follicles after 10 hr perfusion, but significantly augmented it after perfusion of 20 hrs. EGF(10 ng/m) also stimulated progesterone production. There was no significant difference in estradiol level when ovaries were treated with EGF alone. The addition of testosterone significantly increased estradiol production. EGF inhibited testosterone-derived ovary estradiol production. These results suggest that EGF induces development of the primordial and primary follicles and plays an important role in controlling development by regulating function of granulosa cells.

Adiponectin orchestrates testosterone suppression in biological pathways

This current review highlights adiponectin engagement with AdipoR1 and AdipoR2 which subsequently triggers pathways such as AMPK,PPARα,and MAPK,thereby modulating testicular steroidogenesis.Adiponectin's actions on Leydig and adrenal cells inhibit androgen secretion by suppressing the steroidogenic acute regulatory protein(StAR).Given that StAR facilitates cholesterol to testosterone conversion,AMPK inhibits this process by modulating cholesterol transport and suppressing StAR expression through multiple avenues.Furthermore,adiponectin-induced PPARαactivation impedes mitochondrial cholesterol influx,further modulating androgen biosynthesis.The suppressive influence of PPARαon steroidogenic genes,notably StAR,is evident.Collectively,adiponectin signalling predominantly attenuates androgen production,ensuring metabolic and reproductive equilibrium.Imbalances,as seen in conditions like hypogonadism and obesity-related infertility,highlight their crucial roles and potential clinical interventions for reproductive disorders.

Effect of interrupted endogenous BMP/Smad signaling on growth and steroidogenesis of porcine granulosa cells

Bone morphogenetic proteins(BMPs) play a critical role in the growth and steroidogenesis of granulosa cells(GCs).BMP signals act through membrane-bound heteromeric serine/threonine kinase receptors.Upon ligand binding,BMPs activate intracellular Smad proteins and regulate growth and apoptosis in various cell types.The objective of this study was to demonstrate the effects of BMP/Smad signal on growth and steroidogenesis of porcine GCs.A strategy of RNA interference(RNAi)-mediated 'gene silencing' of Smad4,a core molecule mediating the intracellular BMP/Smad signal transduction pathways,was used to interrupt endogenous BMP/Smad signaling.Results indicate that Smad4-small interfering RNA(siRNA) caused specific inhibition of Smad4 mRNA and protein expression after transfection.Interrupted endogenous BMP/Smad signaling significantly inhibited growth,and induced apoptosis of porcine GCs,while decreasing estradiol production.In addition,interrupted BMP/Smad signaling significantly(P<0.05) changed the expression of Cyclin D2,CDK4,Bcl-2,and Cyp19a1.These findings provide new insights into how BMP/Smad signaling regulates the growth and steroidogenesis of porcine GCs.

Development and organisation of gonadal steroidogenesis in bony fishes - A review

Gonadal steroidogenesis is pivotal to synchronize various reproductive stages including sexual development,growth and maturation.In all vertebrates including teleost,steroidogenesis is triggered by the mobilization of cholesterol by steroidogenic acute regulatory protein from outer to inner mitochondrial membrane.Thereafter,the entire process occurs in endoplasmic reticulum or mitochondria wherein various steroidogenic enzyme genes play a crucial role.The onset of steroidogenesis during sexual development in teleost is essentially regulated by differential expression of several transcription as well as steroidogenesis-related factors.More specifically,the role of dmrt,sox9,sox3,other sox forms,ad4bp/sf-1,wt-1,foxl2,ftz-f1,gata4,gsdf,Activator protein-1,fgfs and growth factors and steroidogenic enzymes such as cytochrome P450aromatase(cyp19a1),hydroxysteroid 3β-dehydrogenase(hsd3b),hydroxysteroid 17β-dehydrogenase(hsd17b)have been well characterised.Recently,the role of pax2,THO complex(thoc),pentraxin(ptx)and few signalling molecules like wnt4/5 regulating teleostean steroidogenesis has been reported.In females,cyp19a1 appears to be critical as it converts androgens to estrogens during ovarian differentiation which suggests that estradiol-17βis indispensable for the event.Unlike females,males do not depend on testosterone for testicular determination,yet has a major role along with 11-ketotestosterone in testicular development and growth when compared to early testicular differentiation.In males,onset of sex determining or testis-related genes seems most essential.Considering these,the regulation of steroidogenesis is virtually critical at later stages.In view of this,several steroidogenic motifs pertaining to transcriptional regulation have been analysed in teleost,yet far below than the reports on mammals.In this context,the regulatory influence on HHG axis plays a critical role in teleost.Further,multiple gonadotropin-releasing hormones and duality of gonadotropins play a differential role in gonadal function.As for steroidogenic pathway,the synthesis of sex steroids predominantly usesΔ4,however,Δ5 pathway was also evident.The next aspect is shift in steroidogenesis that usually occurs in the maturing follicles during final oocyte maturation,yet such a mechanism is not clear in males.The review highlights the interactions of steroidogenic enzyme gene regulation in terms of HHG axis and other important transcription factors that are involved in the regulatory pathways as well as the influence of environmental and dietary factors by comparing both sexes to present a holistic view on steroidogenesis onset and organisation during gametogenesis in teleost.

REGULATION OF STEROIDOGENESIS OF INFANT AND ADULT RHESUS MONKEY GRANULOSA CELLS in vitro

The present studies have demonstrated that infant monkey granulosa cells, like the adult ones, have the potential of responding markedly in vitro to human FSH, cyclic-AMP and forskolin, resulting in the increase of progesterone and estrogen production. Exogenous hCG was also capable of increasing FSH-stimulated progesterone biosynthesis in both infant and adult granulosa cells, but did not stimultate the infant granulosa cells to secrete estrogen. Addition of a synthetic estrogen, diethylstilestrol, to the culture of monkey granulosa cells enhanced the FSH-stimulated progesterone and estrogen production. The esteroidogenesis of monkey granulosa cells was also dramatically stimulated by a gonadotropin-releasing hormone agonist. Monkey granulosa cells, unlike the other animal cells, secrete measurable amount of estrogen in the absence of androgen substrate. The findings reported here are significant in regard to understanding of the mechanism of hormonal regulation of primate ovarian function.

Effects of Bushen Tiaochong Recipe (补肾调冲方) Containing Serum on Ovarian Granulosa Cell Proliferation,Steroidogenesis and Associated Gene Expression in Rats

Objective： To observe the effect of Bushen Tiaochong Recipe （补肾调冲方, BSTCR） on rats＇ ovarian granulosa cell （GC） proliferation, steroidogenesis and follicle-stimulating hormone receptor （FSHR）, and insulin-like growth factor-1 （IGF-1） mRNA expression using serum pharmacological method. Methods： Rats＇ GCs were incubated with 10% blank serum （as negative control group）, follicle- stimulating hormone （FSH）-containing serum （S-FSH, as positive control group）, or BSTCR （in different dosages） containing serum （S-BSTCR, as the BSTCR groups） for 48 h. ^3H-TdR incorporation was then performed; DNA was measured to analyze the distribution of GCs in the cell cycle and their proliferation index （PI） using a flow cytometer; estradiol （E2） and progesterone （P） content in the culture fluid were examined by radioimmunoassay; and levels of FSHR and IGF-1 mRNA expression in GCs were measured by real-time RT-PCR. Results： A dose-dependent increase of ^3H-TdR incorporation in GC was shown in the BSTCR groups. Cells in Go/G1 phase had markedly less, while those in S phase had a significantly higher increase in the BSTCR groups compared with the negative control group. A high value of PI was also shown in the BSTCR groups, especially in the high dose group where the influence of cell proliferation was stronger than that in the positive control group. The levels of E2 and P in the BSTCR groups of all dosages were significantly higher than those in the negative control group, and did not show any significant difference compared with those in the positive control group. Levels of FSHR and IGF-1 mRNA expression in the BSTCR groups increased in a dose-dependent manner at levels higher than those in the negative control group. Conclusion： S-BSTCR can obviously stimulate the proliferation and steroidogenesis of ovarian GCs.It is speculated that BSTCR could play a regulatory action on ovarian function through two different pathways of endocrine and autocrine by promoting FSHR and IGF-1 mRNA expression.

PARADOXICAL EFFECT OF A GnRH AGONIST ON STEROIDOGENESIS IN CULTURED MONKEY GRANULOSA CELLS

In this study we demonstrate: (i) The GnRH agonist exerts a direct dose-dependet stimulative effect on the aromatase activity and progesterone production in cultured monkey granulosa cells; (ii)the stimulative effect on steroidogenesis can be completely blocked by concomitant treatment with a GnRH antagonist, suggesting that the actions of GnRH are mediated through stringent stereospecific recongnition sites; (iii) in addition to the stimulative effect, the GnRH agonist in the presence of gonadotropins also exerts an inhibitory effect, even though the peptide by itself is more effective in the stimulation of steroidogenesis, and the stimulation of gonadotropin on steroidogenesis could be gradually restored by decreasing the concentration of the GnRH agonist in the culture; and (iv) paradoxical effect can also be observed in the presence of cAMP-inducing agents, suggesting that the inhibitory action of the peptide on gonadotropin-induced steroidogenesis is localized at a step distal to the stringent recognition sites.

Effects of plants and plant products on the testis

For centuries, plants and plant-based products have been used as a valuable and safe natural source of medicines for treating various ailments. The therapeutic potential of most of these plants could be ascribed to their anticancer, antidiabetic, hepatoprotective, cardioprotective, antispasmodic, analgesic and various other pharmacological properties. However, several commonly used plants have been reported to adversely affect male reproductive functions in wildlife and humans. The effects observed with most of the plant and plant-based products have been attributed to the antispermatogenic and/or antisteroidogenic properties of one or more active ingredients. This review discusses the detrimental effects of some of the commonly used plants on various target cells in the testis. A deeper insight into the molecular mechanisms of action of these natural compounds could pave the way for developing therapeutic strategies against their toxicity.

Chronic effect of endosulfan on the testicular functions of rat

Aim: To find out the toxic effect of endosulfan on the testicular function of pubertal rats. Methods: Male rats of pu-bertal age were orally administered endosulfan at a dose of 1.0 mg/kg body weight for 30 days. Twenty-four hours af-ter the last treatment, the rats were sacrificed and the testis, epididymis, seminal vesicles and ventral prostate were re-moved and weighed. A 10 % testicular homogenate was prepared for biochemical estimations. Results: In endosul-fan-treated rats, there were a reduction in the body weight and the weights of testis and accessory sex organs, a de-crease in the testicular lactate and pyruvate activities, and in the testicular DNA and RNA concentrations, whereas thetesticular protein concentration was slightly increased; the specific activity of testicular steroidogenic enzyme, 3β-OH-steroid dehydrogenase and the ascorbic acid level were decreased, which were correlated with a decrease in steroidoge-nesis. The lysosomal enzyme acid phosphatase and brash-border enzyme alkaline phosphatase activities were also de-creased in the testis of treated rats. Conclusion: In pubertal rats, endosulfan treatment inhibits the testicular functions.(Asian J Androl 1999 Dec; 1: 203-206)

Similar causes of various reproductive disorders in early life

During the past few decades, scientific evidence has been accumulated concerning the possible adverse effects of the exposure to environmental chemicals on the well-being of wildlife and human populations. One large and growing group of such compounds of anthropogenic or natural origin is referred to as endocrine-disrupting chemicals （EDCs）, due to their deleterious action on the endocrine system. This concern was first focused on the control of reproductive function particularly in males, but has later been expanded to include all possible endocrine functions. The present review describes the underlying physiology behind the cascade of developmental events that occur during sexual differentiation of males and the specific role of androgen in the masculinization process and proper organogenesis of the external male genitalia. The impact of the genetic background, environmental exposures and lifestyle factors in the etiology of hypospadias, cryptorchidism and testicular cancer are reviewed and the possible role of EDCs in the development of these reproductive disorders is discussed critically. Finally, the possible direct and programming effects of exposures in utero to widely use therapeutic compounds, environmental estrogens and other chemicals on the incidence of reproductive abnormalities and poor semen quality in humans are also highlighted.

Thyroid hormones in male reproduction and infertility

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 functionsvia 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.

Orexins and male reproduction

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 functionsvia 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.