Endocrine and paracrine control of sperm production in stallions

Effects of insulin-like growth factor-1 on the proliferation and apoptosis of stallion testicular cells under normal and heat stress culture conditions

This study investigated the effect of heat stress on stallion testicular cells (TCs) and the effect of insulin-like growth factor (IGF)-1 on TC viability, proliferation, and apoptosis, including different stages of germ cells. TCs were divided into control or treatment groups with 0.01, 0.1, 1, 10, and 100 ng/mL of recombinant human IGF-1 (rhIGF-1) for 24 h at 34 °C and 37 °C. The population and viability were measured before and after treatment. The effects of rhIGF-1 on TC viability, proliferation, and apoptosis were determined using RT-qPCR. Proliferating cell nuclear antigen (PCNA) and marker of proliferation Ki-67 (MKI-67) were used as proliferation markers. Myeloid leukemia-1 (MCL-1) was used as an antiapoptotic marker. BCL2 antagonist/killer-1 (BAK-1) was used as a proapoptotic marker. The relative abundance of mRNA transcript of undifferentiated cell transcription factor 1 (UTF-1), protein gene product 9.5 (PGP9.5), and deleted in azoospermia-like (DAZL), was measured for spermatogenesis progression. TCs treated with 1 ng/mL rhIGF-1 at 34 °C exhibited the highest viability. Significant upregulation of the relative abundance of mRNA transcript of PCNA, MKI-67, and MCL-1 was observed in treated TCs compared with untreated TCs; however, BAK-1 was significantly downregulated in treated TCs. Germ cells treated with 1 ng/mL rhIGF-1 exhibited the highest relative abundance of mRNA transcript of UTF-1 and DAZL, whereas TCs exposed to 0.1 ng/mL showed the highest PGP9.5 level. These data confirm that heat stress in stallions decreases TC viability. These findings may help identify a basal IGF-1 level for TC proliferation and apoptosis during heat stress-induced testicular degeneration in stallions.

Effect of platelet-rich plasma (PRP) on post-thaw quality, kinematics and in vivo fertility of fertile and subfertile buffalo (Bubalus bubalis) spermatozoa

This study investigated the effect of adding platelet-rich plasma (PRP) in semen extender prior cryopreservation on post-thaw quality, kinematics, and in vivo fertility of fertile and subfertile buffalo spermatozoa. Eleven buffalo bulls were classified based on their conception rate (CR) into fertile (n = 8, CR > 55%) and subfertile (n = 3, CR < 35%) groups. Ejaculates were collected with artificial vagina, pooled, and dispensed into 6 aliquots, diluted with Tris-egg yolk-glycerol extender supplemented with different proportions of PRP [0% (control), 5%, 10%, 15%, 20%, and 25%] followed by cryopreservation using standard procedures. Post-thaw sperm quality, kinematics, antioxidant activity, cryosurvival rate, and in vivo fertility were compared between fertile and subfertile groups and among proportions of PRP within each group. The results showed that 15% PRP greatly (P < 0.001) improved sperm characteristics, average path velocity, and curvilinear velocity of the subfertile group. Interestingly, 5%, 10%, and 15% PRP greatly (P < 0.001) reduced malondialdehyde content and improved enzymatic (glutathione peroxidase and superoxide dismutase) and total antioxidant capacity in fertile and subfertile groups. However, these three proportions of PRP significantly (P < 0.001) improved the cryosurvival rate of the subfertile group; only 15% PRP greatly improved CR of subfertile (60.83% vs. 34.17%) animals to be comparable with that of fertile ones treated with 5 (59.17%) and 10% (60.83%) PRP. In conclusion, adding 15% PRP to semen extender before cryopreservation is recommended to improve post-thaw quality, antioxidant activity, and in vivo fertility of buffalo semen particularly of the subfertile animals.

Functions of somatic cells for spermatogenesis in stallions

Spermatogenesis and testis development are highly structured physiological processes responsible for post-pubertal fertility in stallions. Spermatogenesis comprises spermatocytogenesis, meiosis, and spermiogenesis. Although germ cell degeneration is a continuous process, its effects are more pronounced during spermatocytogenesis and meiosis. The productivity and efficiency of spermatogenesis are directly linked to pubertal development, degenerated germ cell populations, aging, nutrition, and season of the year in stallions. The multiplex interplay of germ cells with somatic cells, endocrine and paracrine factors, growth factors, and signaling molecules contributes to the regulation of spermatogenesis. A cell-to-cell communication within the testes of these factors is a fundamental requirement of normal spermatogenesis. A noteworthy development has been made recently on discovering the effects of different somatic cells including Leydig, Sertoli, and peritubular myoid cells on manipulation the fate of spermatogonial stem cells. In this review, we discuss the self-renewal, differentiation, and apoptotic roles of somatic cells and the relationship between somatic and germ cells during normal spermatogenesis. We also summarize the roles of different growth factors, their paracrine/endocrine/autocrine pathways, and the different cytokines associated with spermatogenesis. Furthermore, we highlight important matters for further studies on the regulation of spermatogenesis. This review presents an insight into the mechanism of spermatogenesis, and helpful in developing better understanding of the functions of somatic cells, particularly in stallions and would offer new research goals for developing curative techniques to address infertility/subfertility in stallions.

Serum Insulin-like Growth Factor-1 Is a Biomarker of Testosterone Production and Intact Acrosome in Asian Elephants (Elephas maximus)

Simple Summary

In Thailand, the low fertility rate of Asian elephants has been identified. Factors contributing to poor semen quality in the elephants are not fully understood. Insulin-like growth factor-1 (IGF-1) is related to male infertility. It plays an essential role in testicular development by stimulating cell proliferation, differentiation, and steroidogenesis. In addition, there is increasing evidence that IGF-1 plays a critical role in spermatogenesis. This may be conducive to finding the causes of poor sperm quality in Asian elephants (Elephas maximus). In the present study, we investigated the relationships among serum IGF-1, serum testosterone level, and semen parameters in seven elephant bulls. The findings suggest that serum IGF-1 concentration is likely to predict sperm quality like acrosome integrity. The further mechanism by which IGF-1 affects sperm quality requires further investigation.

Abstract

The objective of this study was to find relationships among serum IGF-1, serum testosterone, seminal plasma IGF-1 concentrations and semen parameters in Asian elephants (Elephas maximus). A total of 17 ejaculates (one to three ejaculates/bull) were collected from seven captive elephant bulls by performing rectal massage. Before each ejaculation, blood samples were obtained for serum IGF-1 and testosterone assays. Subsequently, the semen characteristics of each ejaculate were evaluated. Mean serum IGF-1 concentration of elephant bulls was estimated as 326.3 ± 114.6 ng/mL (median, 286.2 ng/mL; range, 167.4–542.7 ng/mL). An increase in serum IGF-1 concentration was found to correlate with the percentage of spermatozoa with intact acrosomes. In addition, IGF-1 concentration was positively correlated with testosterone level. However, seminal IGF-1 concentrations could not be detected. In conclusion, our findings suggest that serum IGF-1 concentration is likely a biomarker of normal testicular functions, particularly spermatogenesis in elephants. Moreover, this commercial IGF-1 ELISA is eligible for analyzing serum IGF-1 concentration in Asian elephants.

Kisspeptin and its Effect on Mammalian Spermatogensis

BACKGROUND

Kisspeptin and its receptor, GPR54, are regarded as key regulators of and catalysts for male puberty onset, and also fundamental gatekeepers of spermatogenesis in mammals. Consequently, the loss function of kisspeptin or GPR54 leads to a symptom of Hypogonadotropic Hypogonadism (HH) in human and HH accompanied by lower gonadotrophic hormone levels, smaller testes, impaired spermatogenesis and abnormal sexual maturation in mice. Besides its well-recognized functions in hypothalamus before and during puberty, accumulating data strongly support kisspeptin production in testis, and participation in somatic and germ cell development and sperm functions as well. This review aims to summarize recent findings regarding kisspeptin activity in the testes and sperm function.

METHODS

We undertook a keyword search of peer-reviewed research literature including data from in vivo and in vitro studies in humans and genetically modified animal models to identify the roles of kisspeptins in male reproduction.

RESULTS

A plethora of studies detail the role of kisspeptins and GPR54 in mammalian spermatogenesis in vivo and in vitro. This review identified recent findings regarding the kisspeptin system in male gonads, and regulation of kisspeptin in testicular physiology and male reproductive defects and disorders.

CONCLUSION

The findings of this review confirm the importance role of kisspeptins in male fertility. Understanding their biphasic roles in testis may help to consider kisspeptins as potential pharmacological targets for treating human infertility.

Dexamethasone downregulates expression of several genes encoding orphan nuclear receptors that are important to steroidogenesis in stallion testes

Glucocorticoids impair testosterone synthesis by an unknown mechanism. Stallions treated with the synthetic glucocorticoid dexamethasone had testes collected at 6 or 12 hours postinjection. The testicular expression of selected genes encoding nuclear receptors and steroidogenic enzymes was measured. At 6 hours, dexamethasone treatment decreased levels of NR0B2, NR4A1, NR5A1, and NR5A2 messenger RNAs (mRNAs) and NR5A2 mRNA levels remained depressed at 12 hours. In contrast, dexamethasone increased levels of NFKBIA mRNA at both time points. At 6 hours, dexamethasone did not alter levels of NR0B1, NR2F1, NR2F2, NR3C1, CYP11A1, CYP17A1, CYP19A1, DHCR24, GSTA3, HSD3B2, HSD17B3, LHCGR, or STAR mRNAs. In primary cultures of Leydig cells, 10 ^-9 and 10 ^-7 M dexamethasone decreased levels of NR4A1 and NR5A1 mRNAs and increased those of NFKBIA mRNA. Our discovery that dexamethasone downregulates NR4A1, NR5A1, and NR5A2 genes, known to be important for testicular functions, may be part of the mechanism by which glucocorticoids acutely decreases testosterone.

Safety evaluation of Bon-santé cleanser® polyherbal in male Wistar rats: Further investigations on androgenic and toxicological profile

BACKGROUND

The global increase in acceptance and use of herbal remedies in recent times is still accompanied with poor knowledge of their potential adverse effects and the toxicological implications of their use are underestimated.

METHODS

Bon-santé Cleanser® (BSC), a polyherbal containing Anogeissus leiocarpus, Terminalia ivorensis, Massularia acuminate and Macuna pruriens, is an "energizer and hormone booster". We assessed the effect of BSC on reproductive function after administration for 60 days in male Wistar rats. Rats (150-300 g) were assigned into four groups of 8/group. Control received distilled water (10 ml/kg) while other groups received BSC 250, 500 and 1000 mg/kg/day p.o. respectively. Animals were euthanized by cervical dislocation and samples collected for analysis.

RESULTS

BSC (250 mg/kg) elevated (p < 0.05) follicle stimulating hormone and luteinizing hormone levels respectively. BSC decreased sperm motility and the live-dead ratio at 1000 mg/kg and reduced reproductive hormone at 500 mg/kg and 1000 mg/kg respectively. BSC at 500 mg/kg increased (p < 0.05, F = 3.18-13.21) testicular reduced glutathione level (50.3%) and catalase (43.7%) but not activities of superoxide dismutase, glutathione S-transferase, and malondialdehyde level. Further, BSC influenced Mg, Zn, Cu, P, Mn, Ni and Fe levels (p < 0.05). BSC (1000 mg/kg) decreased testis weight (p < 0.05) and induced mild inflammation characterized by atrophic tubules.

CONCLUSION

Overall, our data suggest BSC at low doses may increase reproductive hormones regulated by FSH and LH as observed in this study. However, BSC administration should be done with caution as it may induce reproductive toxicity in large doses.

Dexamethasone acutely down-regulates genes involved in steroidogenesis in stallion testes

In rodents, livestock and primate species, a single dose of the synthetic glucocorticoid dexamethasone acutely lowers testosterone biosynthesis. To determine the mechanism of decreased testosterone biosynthesis, stallions were treated with 0.1mg/kg dexamethasone 12h prior to castration. Dexamethasone decreased serum concentrations of testosterone by 60% compared to saline-treated control stallions. Transcriptome analyses (microarrays, northern blots and quantitative PCR) of testes discovered that dexamethasone treatment decreased concentrations of glucocorticoid receptor alpha (NR3C1), alpha actinin 4 (ACTN4), luteinizing hormone receptor (LHCGR), squalene epoxidase (SQLE), 24-dehydrocholesterol reductase (DHCR24), glutathione S-transferase A3 (GSTA3) and aromatase (CYP19A1) mRNAs. Dexamethasone increased concentrations of NFkB inhibitor A (NFKBIA) mRNA in testes. SQLE, DHCR24 and GSTA3 mRNAs were predominantly expressed by Leydig cells. In man and livestock, the GSTA3 protein provides a major 3-ketosteroid isomerase activity: conversion of Δ(5)-androstenedione to Δ(4)-androstenedione, the immediate precursor of testosterone. Consistent with the decrease in GSTA3 mRNA, dexamethasone decreased the 3-ketosteroid isomerase activity in testicular extracts. In conclusion, dexamethasone acutely decreased the expression of genes involved in hormone signaling (NR3C1, ACTN4 and LHCGR), cholesterol synthesis (SQLE and DHCR24) and steroidogenesis (GSTA3 and CYP19A1) along with testosterone production. This is the first report of dexamethasone down-regulating expression of the GSTA3 gene and a very late step in testosterone biosynthesis. Elucidation of the molecular mechanisms involved may lead to new approaches to modulate androgen regulation of the physiology of humans and livestock in health and disease.

Insulin receptor substrate 2 is required for testicular development

Insulin receptor substrate (IRS) proteins are key mediators of insulin and insulin-like growth factor (IGF) signalling. In mice, deletion of Irs1 is associated with profound growth retardation and increased longevity whereas Irs2-deficiency causes diabetes and female infertility. Clinical studies suggest that diabetes and obesity diminish male fertility. However, the role of IRS proteins in male reproduction is unknown. We observed that testis weight is reduced by 45% in Irs2-deficient mice as compared with control males. The weight of these organs in Irs1(-/-) males was similar to controls; however, since Irs1-deficient mice are 50% smaller, testis weight:body weight was increased in this model. Neonatal Irs2(-/-) mice also exhibited reduced testicular size, suggesting that impairments in this model occur during development. Histological examination of testicular cross sections from Irs2(-/-) mice revealed normal cellular associations without obvious abnormalities in the seminiferous epithelium. Reduced testicular weight was associated with fewer Sertoli cells, spermatogonia, spermatocytes, elongated spermatids, and epididymal spermatozoa. However, Leydig cell number and the concentration of serum testosterone were equivalent between Irs2-deficient and control males. Testicular weight was reduced similarly in non-diabetic and diabetic Irs2(-/-) mice, indicating that hyperglycemia does not compound the effects of Irs2 deletion on impaired testis development. Expression of Irs1, Irs3, and Irs4 was comparable between experimental groups. Collectively, our results demonstrate that IRS2 plays a critical role in testicular development, potentially by mediating IGF1 signalling during embryonic and early postnatal development.

Use of a deslorelin implant for influencing sex hormones and male behaviour in a stallion - Case report

This case report describes the use of a subcutaneously applied 4.7-mg deslorelin acetate implant in a three-year-old Arabian crossbred stallion showing unwanted strong male behaviour. Following deslorelin acetate implantation the stallion showed a short transitional increase in male behaviour. A 'gelding-like' behaviour was noted 15 days (D15) after treatment. The horse was surgically castrated at the owners request at D52 after treatment. Serum testosterone, oestradiol-17β and oestrone sulphate values decreased after deslorelin acetate implantation, but serum LH and FSH levels remained unchanged. Histopathological analysis of both testes and sperm analysis revealed a reduced spermatogenesis at D52. The testicular volume decreased after treatment. The use of a subcutaneously applied deslorelin acetate implant might be a promising tool to change the behaviour of aggressive stallions.

Effect of feeding fescue seed containing ergot alkaloid toxins on stallion spermatogenesis and sperm cells

The cellular effects of tall fescue grass-associated toxic ergot alkaloids on stallion sperm and colt testicular tissue were evaluated. This was a continuation of an initial experiment where the effects of toxic ergot alkaloids on the stallion spermiogram were investigated. The only spermiogram parameter in exposed stallions that was affected by the toxic ergot alkaloids was a decreased gel-free volume of the ejaculate. This study examined the effect of toxic ergot alkaloids on chilling and freezing of the stallion sperm cells. The effect of toxic ergot alkaloids on chilled extended sperm cells for 48 h at 5°C was to make the sperm cells less likely to undergo a calcium ionophore-induced acrosome reaction. The toxic ergot alkaloids had no effect on the freezability of sperm cells. However, if yearling colts were fed toxic ergot alkaloids, then the cytological analysis of meiotic chromosome synapsis revealed a significant increase in the proportion of pachytene spermatocytes showing unpaired sex chromosomes compared to control spermatocytes. There was little effect of ergot alkaloids on adult stallions, but there might be a significant effect on yearling colts.

PGF(2α), LH, testosterone, oestrone sulphate, and cortisol plasma concentrations around sexual stimulation in jackass

Many hormones are involved in the regulation of male reproductive functions, controlling sexual behavior, and influencing sexual arousal, the onset of erection and ejaculation, and the post-ejaculatory detumescence. The aims of this study were to analyze the plasma concentrations of 15-ketodihydro-PGF(2α) (PGFM), LH, testosterone (T), oestrone sulphate (OS), and cortisol (C) in relation to sexual stimulation and to evaluate the possible correlations among circulating hormones and between hormones and semen characteristics in the donkey stallion. Thirteen sexually experienced Martina Franca jackass of proven fertility were enrolled and semen was collected through an artificial vagina. Plasma samples were collected at 12, 9, 6 and 3 min before oestrous jenny exposure, at the first erection in the mating arena in the presence of an oestrous jenny, during ejaculation, at dismounting, 3, 6, 9 and 12 min after ejaculation in box, and then every 10 min during the following 50 min. PGFM showed an increasing trend with significant differences between the pre-ejaculatory and post-ejaculatory period, suggesting a role of this hormone in the control of ejaculation. LH showed a significantly higher concentration at ejaculation compared to last samples, while T showed significantly higher levels at erection, ejaculation and dismounting, probably for its influence on these processes and on sexual behavior. Finally, OS did not show any difference in the period of observation, while C presented a significant increase only 22 minutes after erection. The only hormonal correlation found was a positive one between LH and T at erection and dismounting, while T and OS were positively correlated with total and progressive motility, respectively.

Expression of Neuropeptide Y gene in mouse testes during testicular development

AIM

To elucidate the distribution and regulation of Neuropeptide Y (NPY) gene expression in testes under physiological and pathophysiological conditions, such as testicular development, fasting and experimental cryptorchidism.

METHODS

In the first experiment, C57BL/6J male mice at the ages of 3 days as well as 2, 3, 5 and 8 weeks were used. In the second and third experiments, adult C57BL/6J male mice were subjected to fasting for 48 h and experimental cryptorchidism for 72 h. The NPY transcripts were detected by isotopic in situ hybridization histochemistry.

RESULTS

The NPY transcripts were exclusively expressed in the interstitial cells regardless of the age groups and experimental conditions. The NPY mRNA levels were found to increase significantly with age (from the neonatal to prepubertal period [P<0.01] and from the prepubetal to postpubertal period [P<0.01]). Food deprivation for 48 h resulted in a significant increase in the NPY mRNA levels in the arcuate nucleus of the hypothalamus (P<0.01), but not in the testes. Experimental cryptorchidism for 72 h failed to regulate the NPY gene expression in the testes.

CONCLUSION

NPY gene expression is distributed in Leydig cells and increases in line with testicular development. The regulation of testicular NPY is different from that of hypothalamic NPY.

Testosterone regulates FGF-2 expression during testis maturation by an IRES-dependent translational mechanism

Spermatogenesis is a complex process involving cell proliferation, differentiation, and apoptosis. Fibroblast growth factor 2 (FGF-2) is involved in testicular function, but its role in spermatogenesis has not been fully documented. The control of FGF-2 expression particularly occurs at the translational level, by an internal ribosome entry site (IRES)-dependent mechanism driving the use of alternative initiation codons. To study IRES activity regulation in vivo, we have developed transgenic mice expressing a bicistronic construct coding for two luciferase genes. Here, we show that the FGF-2 IRES is age-dependently activated in mouse testis, whereas EMCV and c-myc IRESs are not. Real-time PCR confirms that this regulation is translational. By using immunohistological techniques, we demonstrate that FGF-2 IRES stimulation occurs in adult, but not in immature, type-A spermatogonias. This is correlated with activation of endogenous FGF-2 expression in spermatogonia; whereas FGF-2 mRNA transcription is known to decrease in adult testis. Interestingly, the FGF-2 IRES activation is triggered by testosterone and is partially inhibited by siRNA directed against the androgen receptor. Two-dimensional analysis of proteins bound to the FGF-2 mRNA 5'UTR after UV cross-linking reveals that testosterone treatment correlates with the binding of several proteins. These data suggest a paracrine loop where IRES-dependent FGF-2 expression, stimulated by Sertoli cells in response to testosterone produced by Leydig cells, would in turn activate Leydig function and testosterone production. In addition, nuclear FGF-2 isoforms could be involved in an intracrine function of FGF-2 in the start of spermatogenesis, mitosis, or meiosis initiation. This report demonstrates that mRNA translation regulation by an IRES-dependent mechanism participates in a physiological process.

A comparison of the effects of equine luteinizing hormone (eLH), equine growth hormone (eGH) and human recombinant insulin-like growth factor (hrIGF-I) on steroid production in cultured equine Leydig cells during sexual maturation

There are several hormones and local testicular factors involved in the initiation and control of steroidogenesis and spermatogenesis during puberty. GH and its mediator, IGF-I, increase substantially during puberty, and in addition to LH, these growth-promoting hormones can have direct effects upon testicular function. The objective of this work was to investigate the effects of eLH, eGH and hrIGF-I upon Leydig cells derived from testes of colts and stallions representing different stages of development. Testes were obtained from 48 light horse colts and stallions at the time of routine castration, horses were categorized according to age group (prepubertal, pubertal and postpubertal) and a Leydig cell enriched preparation was utilized for cell culture. Cells derived from all 48 horses were treated with doses of eLH, and a subset of 21 horses received doses of eGH and hrIGF-I. Cells were plated at a concentration of 1 x 10(6) cells/ml and incubated for 24 h at 32 degrees C. Production of testosterone and estradiol was measured by validated RIA. Leydig cells from prepubertal colts secreted greater basal amounts of testosterone but lesser basal amounts of estradiol compared with the other age groups (p < 0.001). Pubertal stallions exhibited the greatest relative response to eLH (p < 0.05). Neither eGH nor hrIGF-I elicited a steroidogenic response over baseline concentrations in any of the three age groups.

Modulating reproductive activity in stallions: A review

Situations in which suppression or stimulation of reproductive activity in stallions has been attempted, or is desired, include resolution of the equine arteritis virus 'shedding' state, induction of testicular descent in inguinal cryptorchids, and the improvement of sperm production capacity and/or semen quality in sub-fertile stallions. However, the most common reason for wanting to modulate reproductive activity in a stallion is to alter the expression of sexual behaviour. In the case of intact stallions used for competitive or recreational purposes, the overt expression of sexual or aggressive behaviour can be distracting for both animal and owner and, in some cases, dangerous to all concerned. By the same token, a breeding stallion that displays little interest in mounting a mare/phantom, or is slow to achieve erection and/or ejaculation, can be extremely frustrating. This paper reviews the major pharmacological agents reported to usefully modify reproductive activity in stallions, and outlines their pros and cons when compared to training, management or surgical alternatives.

Expression and subcellular localization of the μ-opioid receptor in equine spermatozoa: evidence for its functional role

The development of fertilizing ability in sperm cells is associated with changes in the plasma membrane. However, to date the exact nature of sequentially activated primary receptors and channels and the signal transduction pathways derived from these remains elusive. We analyzed the expression and localization of the μ-opioid receptossr in equine spermatozoa. A transcript corresponding to the third extracellular loop that selectively binds μ agonists was amplified, sequenced and compared with the known sequences in humans, rats and cattle. The amplification product showed a high degree of nucleotide conservation. By immunofluorescence, μ-opioid receptor labeling was found on the sperm head and on the tail and disappeared in the acrosomal region of acrosome-reacted sperm cells. Immunoblotting revealed two bands of 50 and 65 kDa. Effects of the opioid antagonist naloxone on motility and on viability and capacitation/acrosome reaction were investigated by computer-assisted sperm analysis and Hoechst 33258/chlortetracycline (H258/CTC) staining. Progressive motility was significantly reduced after 3 h incubation in 10−3M naloxone (P< 0.05), whereas it increased significantly after 5 h in 10−8M naloxone (P< 0.05). Sperm velocity at 5 h was significantly reduced by the addition of 10−3M naloxone (P< 0.05), but increased significantly in the presence of 10−8M (P< 0.001). Curvilinear velocity and amplitude of lateral head displacement in spermatozoa incubated in the presence of naloxone were not indicative of hyperactivation. H258/CTC staining showed that 10−8M naloxone significantly stimulated capacitation (P< 0.01) after 3 h. However, it had no effect on sperm cell viability and acrosomal status. Overall, this study provides the first evidence that the μ-opioid receptor is expressed in equine spermatozoa and that naloxone significantly affects motility and capacitation.

Influence of exogenous GnRH on sexual behavior and frozen/thawed semen viability in stallions during the non-breeding season

Twelve fertile stallions were divided into two groups, either receiving gonadotropin-releasing hormone (GnRH) (n = 6) or Placebo (n = 6). Based on the history of frozen/thawed semen characteristics three stallions within each group were assigned as being "good freezers" [GnRH (+); Placebo (+)] and three stallions were assigned as being "poor freezers" [GnRH (-); Placebo (-)]. The study was performed as a "blinded" investigation and stallions were treated twice daily by an intramuscular injection of 1 ml GnRH (Buserelin), 50 microg) or Placebo. The experiment was divided into three time periods. Period A (pre-treatment) was performed between 16 November and 20 December; Period B (treatment) was performed during 6 weeks between 21 December and 31 January; and Period C (post-treatment) was performed between 1 February and 12 February. Semen was collected every Monday, Wednesday, Friday, and analysed for motion characteristics by the use of a computerized semen analyser, and sperm morphology immediately after collection. The spermatozoa were cryopreserved, stored in liquid nitrogen, and evaluated for motility (computer assisted semen analysis), membrane integrity (carboxyfluoresceine diacetate (CFDA) combined with propidium-iodide (PI), CFDA/PI), viability and sperm morphology (Eosine-Nigrosine, EN), and osmotic reactivity (hypo-osmotic swelling test, HOS) following thawing in a water bath. The viability of spermatozoa was expressed as the difference between pre-freeze and post-thaw values. A libido score of 1-4, the number of mounts on the phantom before ejaculation, and ejaculation latency were used to evaluate the stallions sexual behavior. Effect of treatment was analysed by comparing time intervals within groups as well as comparing groups within time intervals using SAS statistics software. GnRH treatment decreased the number of mounts before ejaculation (GnRH (total): 2.5 +/- 1.14 versus 1.8 +/- 1.06, P < 0.05), and shortened ejaculation latency. Cessation of treatment increased ejaculation latency in the GnRH group (4.7 +/- 4.98 min versus 7.2+/-7.88min, P<0.05). With the exception of libido score all parameters of sexual behavior were superior in the GnRH (+) group compared to the Placebo (-) group during the treatment period (P < 0.05). GnRH administration increased progressive motility (GnRH (+): 30.7 +/- 10.74% versus 38.4 +/- 15.1%, P < 0.05; GnRH (total): 24.9 +/- 11.80% versus 31.9 +/- 14.68%, P < 0.05), membrane intact spermatozoa CFDA/PI (GnRH (-): 16.8 +/- 7.17% versus 26.2 +/- 7.02%, P < 0.05; GnRH (total): 23.1 +/- 12.33% versus 29.5 +/- 10.77%, P < 0.05) and HOS positive spermatozoa (GnRH (+): 33.2 +/- 11.29% versus 42.2 +/- 10.36%, P < 0.05; GnRH (total): 32.9 +/- 10.23% versus 40.1 +/- 10.30%, P < 0.05) of frozen/thawed spermatozoa. Following cessation of treatment, the viability of frozen/thawed spermatozoa decreased. GnRH treated stallions had lower losses of live stained spermatozoa (EN) compared to the Placebo group (GnRH (total): 17.6 +/- 4.77 versus Placebo (total): 27.2 +/- 5.44, P < 0.05). This was particularly observed in the "poor freezer" group (GnRH (-): 16.6 +/- 4.35 versus Placebo (-): 31.3 +/- 5.87; P < 0.05). In conclusion, exogenous GnRH was shown to improve sexual behavior and increase the quality of frozen/thawed spermatozoa in fertile stallions during the non-breeding season. Nevertheless, it seems that, although significance was achieved relative to improvement to post-thaw sperm quality, that the "real" change in sperm quality seems negligible in fertile stallions. The mechanism of GnRH effect was not determined but this study may support the possibility of a direct gonadal or epididymal effect of exogenous GnRH in the stallion.

Reproductive considerations: mare and stallion

Functional alterations within the reproductive system and in other supporting systems may limit the reproductive capacity of geriatric patients; however, the age of onset and degree of compromise show wide individual variation. Aging of the hypothalamopituitary-ovarian axis in the mare manifests as delayed entry to the breeding season, prolonged follicular phases, reduced response to ovulation induction, irregular cycles, oocyte defects, increased early embryonic death, and, eventually, persistent anestrus. Aging of the reproductive tract may increase her susceptibility to endometritis, compromise placental formation with long-term effects on the fetus and viability of the resulting foal, increase her risk of ascending placentitis, alter gestation length, and make her more prone to catastrophic rupture of the uterine arteries at the time of parturition. Effects on the stallion are less well documented but include a reduction in sperm output associated with progressive testicular degeneration and potential compromise of libido and mating ability that is often associated with degenerative conditions of the musculoskeletal system.

Insulin-like growth factor-I and insulin-like growth factor binding protein-2 and -5 in equine seminal plasma: association with sperm characteristics and fertility

The objectives of this study were 1) to determine whether insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding proteins (IGFBPs) were present in seminal plasma of stallions; 2) to compare semen parameters (IGF proteins, sperm numbers, morphology, and motility) from stallions at sexual rest (SR) and when sexually active (SA); 3) to compare semen parameters between stallions with high and low seminal plasma IGF-I concentrations; and 4) to examine the relationship between seminal plasma IGF-I concentrations and fertility parameters of stallions. Ejaculates were collected from stallions at SR (n = 51) and SA (n = 46). Concentrations of IGF-I and IGFBP-2 in seminal plasma samples were determined by radioimmunoassay. Presence of IGFBPs in equine seminal plasma was verified using immunoprecipitation and Western ligand blot procedures. IGF-I, IGFBP-2, and IGFBP-5 were present in equine seminal plasma. Concentrations of IGF-I, IGF-I/protein, total IGF-I, IGFBP-2, IGFBP-2/protein, and total IGFBP-2 were not significantly different (P > or = 0.13) in seminal plasma between stallions at either SR or SA. At SR, stallions with higher seminal plasma IGF-I had more total IGFBP-2 per ejaculate (P < 0.01), more morphologically normal sperm (P = 0.05), and higher first-cycle pregnancy rates (P = 0.02). At SA, stallions with higher seminal plasma IGF-I had fewer cycles per pregnancy (P = 0.02). An association of seminal plasma IGF-I concentration with sperm motility, sperm morphology, and pregnancy rates in bred mares suggests that IGF-I may play a role in sperm function.