Quantitative restoration of advanced spermatogenic cells in adult male rats made azoospermic by active immunization against luteinizing hormone or gonadotropin-releasing hormone

Biologically relevant reductions in fetal testosterone and Insl3 induced by in utero exposure to high levels of di-isononyl phthalate (DINP) in male rats

Some phthalate esters alter male rat reproductive development during sexual differentiation by interfering with fetal testis maturation resulting in reduced Leydig Cell synthesis of testosterone and insulin-like 3 (Insl3) hormones. Gene transcripts associated with steroid hormone and cholesterol transport, and cholesterol synthesis and lipid metabolism also are reduced. These alterations cause permanent malformations of hormone-dependent tissues, sperm production and fertility in male offspring; effects known as the "Phthalate Syndrome." We have shown that administration of a high dose of 750 mg diisononyl phthalate (750 mg/kg/d DINP) during sex differentiation reduced fetal testis testosterone production (T Prod), testis gene expression and induced a low incidence of reproductive malformations in male rat offspring. In the current study we administered DINP at even higher dose levels (1.0 and 1.5 g/kg/d) from gestational day (GD) 14 to postnatal (PND) 3 to determine if these effects were dose related and if the magnitude of the effects could be predicted from a statistical model of fetal testosterone production (T Prod) and Insl3 mRNA levels. These models were previously developed using dipentyl phthalate (DPeP) data from fetal T Prod and postnatal studies. We found that the severity of the demasculinizing effects on the androgen-dependent organs and gubernaculum by DINP were accurately predicted from the statistical models of fetal T prod and Insl3 mRNA, respectively. Taken together, our results indicate that reductions fetal T prod and Insl3 predict the severity of demasculinizing effects in utero exposure to the phthalates DINP and DPeP regardless of potency.

Revisiting the gonadotropic regulation of mammalian spermatogenesis: evolving lessons during the past decade

Spermatogenesis is a multi-step process of male germ cell (Gc) division and differentiation which occurs in the seminiferous tubules of the testes under the regulation of gonadotropins - Follicle Stimulating Hormone (FSH) and Luteinising hormone (LH). It is a highly coordinated event regulated by the surrounding somatic testicular cells such as the Sertoli cells (Sc), Leydig cells (Lc), and Peritubular myoid cells (PTc). FSH targets Sc and supports the expansion and differentiation of pre-meiotic Gc, whereas, LH operates via Lc to produce Testosterone (T), the testicular androgen. T acts on all somatic cells e.g.- Lc, PTc and Sc, and promotes the blood-testis barrier (BTB) formation, completion of Gc meiosis, and spermiation. Studies with hypophysectomised or chemically ablated animal models and hypogonadal (hpg) mice supplemented with gonadotropins to genetically manipulated mouse models have revealed the selective and synergistic role(s) of hormones in regulating male fertility. We here have briefly summarized the present concept of hormonal control of spermatogenesis in rodents and primates. We also have highlighted some of the key critical questions yet to be answered in the field of male reproductive health which might have potential implications for infertility and contraceptive research in the future.

Macrophages Contribute to the Spermatogonial Niche in the Adult Testis

The testis produces sperm throughout the male reproductive lifespan by balancing self-renewal and differentiation of spermatogonial stem cells (SSCs). Part of the SSC niche is thought to lie outside the seminiferous tubules of the testis; however, specific interstitial components of the niche that regulate spermatogonial divisions and differentiation remain undefined. We identified distinct populations of testicular macrophages, one of which lies on the surface of seminiferous tubules, in close apposition to areas of tubules enriched for undifferentiated spermatogonia. These macrophages express spermatogonial proliferation- and differentiation-inducing factors, such as colony-stimulating factor 1 (CSF1) and enzymes involved in retinoic acid (RA) biosynthesis. We show that transient depletion of macrophages leads to a disruption in spermatogonial differentiation. These findings reveal an unexpected role for macrophages in the spermatogonial niche in the testis and raise the possibility that macrophages play previously unappreciated roles in stem/progenitor cell regulation in other tissues.

Recovery of lead-induced suppressed reproduction in male rats by testosterone

The objective of the present study was to investigate the effects of testosterone in recuperation of lead-induced suppressed reproduction in adult male rats. Lead acetate was administered orally to adult male rats (95 ± 5 days) at dosage level of 0.05 and 0.15% for 55 days through drinking water and injected intraperitoneally with either testoviron depot at a dose of 4.16 mg kg(-1) body weight or vehicle alone on days 1, 7 and 14 respectively. At the end of treatment, control and treated males were cohabited with untreated normal-cycling females. After cohabitation for 5 days, all the male rats were killed and weights of reproductive organs were determined. Significant increase in the indices of testis, epididymis, seminal vesicles, vas deferens and prostate glands was observed in testosterone (T)-treated rats when compared to those of lead-exposed rats. Testosterone treatment significantly increased epididymal sperm count, motile spermatozoa, viable spermatozoa and HOS tail-coiled spermatozoa and also the activity levels of testicular 3β- and 17β-hydroxysteroid dehydrogenases when compared to those of lead-exposed males. From the results, it can be hypothesised that supplementation of testosterone mitigated lead-induced suppressed reproduction in male rats.

Endocrine control of spermatogenesis: Role of FSH and LH/ testosterone

Evaluation of testicular functions (production of sperm and androgens) is an important aspect of preclinical safety assessment and testicular toxicity is comparatively far more common than ovarian toxicity. This chapter focuses (1) on the histological sequelae of disturbed reproductive endocrinology in rat, dog and nonhuman primates and (2) provides a review of our current understanding of the roles of gonadotropins and androgens. The response of the rodent testis to endocrine disturbances is clearly different from that of dog and primates with different germ cell types and spermatogenic stages being affected initially and also that the end-stage spermatogenic involution is more pronounced in dog and primates compared to rodents. Luteinizing hormone (LH)/testosterone and follicle-stimulating hormone (FSH) are the pivotal endocrine factors controlling testicular functions. The relative importance of either hormone is somewhat different between rodents and primates. Generally, however, both LH/testosterone and FSH are necessary for quantitatively normal spermatogenesis, at least in non-seasonal species.

Influence of Exposure to Benzo[a]pyrene on Mice Testicular Germ Cells during Spermatogenesis

The objective of this study was to assess the toxicological effect of exposure to benzo(a)pyrene, B[a]P, on germ cells during spermatogenesis. Mice were exposed to B[a]P at 1, 10, 50, and 100 mg/kg/day for 30 days via oral ingestion. Germ cells, including spermatogonia, spermatocytes, pachytene spermatocytes, and round spermatids, were recovered from testes of mice exposed to B[a]P, while mature spermatozoa were isolated from vas deferens. Reproductive organs were collected and weighed. Apoptotic response of germ cells and mature spermatozoa were qualified using the terminal deoxynucleotidyl transferase mediated deoxy-UTP nick end labeling (TUNEL) assay. B[a]P exposure at ≤10 mg/kg/day for 30 days did not significantly alter concentrations of germ cells and mature spermatozoa and apoptotic response in germ cells and mature spermatozoa. Exposure to B[a]P at 50 and 100 mg/kg/day induced testicular atrophy and yielded a significant reduction in the concentrations of spermatogonia, spermatocytes, pachytene spermatocytes, and round spermatid cells as compared with the control. Also, mature spermatozoa experienced decreased concentrations and viability. B[a]P-exposed mice experienced a significant increase in apoptotic germ cells as compared to the control mice. However, the mice dose concentrations were not relevant for comparison to human exposure.

Simultaneous quantification of steroids in rat intratesticular fluid by HPLC-isotope dilution tandem mass spectrometry

An isotope dilution mass spectrometry method has been developed for the simultaneous measurement of picolinoyl derivatives of testosterone (T), dihydrotestosterone (DHT), 17β-estradiol (E(2)), and 5α-androstan-3α,17β-diol (3α-diol) in rat intratesticular fluid. The method uses reversed-phase high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry. Following derivatization of 10-μL samples of testicular fluid with picolinoyl chloride hydrochloride, the samples were purified by solid phase extraction before analysis. The accuracy of the method was satisfactory for the 4 analytes at 3 concentrations, and both inter- and intraday reproducibility were satisfactory for T, DHT, and E(2). Measurements of intratesticular T concentrations in a group of 8 untreated adult rats by this method correlated well with measurements of the same samples by radioimmunoassay. As in men, there was considerable rat-to-rat variability in T concentration, despite the fact that the rats were inbred. Although its levels were more than an order of magnitude lower than those of T, DHT was measured reliably in all 8 intratesticular fluid samples. DHT concentration also varied from rat to rat and was highly correlated with T levels. The levels of E(2) and 3α-diol also were measurable. The availability of a sensitive method by which to measure steroids accurately and rapidly in the small volumes of intratesticular fluid obtainable from individual rats will make it possible to examine the effects, over time, of such perturbations as hormone and drug administration and environmental toxicant exposures on the intratesticular hormonal environment of exposed individual males and thereby to begin to understand differences in response between individuals.

Male infertility and the androgen receptor: molecular, clinical and therapeutic aspects

Idiopathic male infertility has previously been diagnosed imprecisely, and has been treated using regimes that are not based on a clear understanding of the underlying pathophysiology; however, this is gradually changing, and a more rational approach is being adopted. Testosterone and its metabolite, DHT, is allimportant for the maintenance of sperm production and this has led us to examine the AR for causes of male infertility. Some, but not all, androgen-binding studies have indicated that in a certain proportion of cases of male infertility, defective androgen binding occurs. The cloning of the AR gene allowed for a more rigorous examination of the molecular pathogenesis which turned out to be both subtle and heterogeneous. Genetic screening of a large group of men with defective spermatogenesis has indicated that up to 30% of infertile males could have variations in the androgenicity of their AR caused by polymorphisms in the length of the polyglutamine tract. Substitutions of the AR in the LBD and the DBD can also lead to reduced AR function and male infertility. In this regard, it is interesting to note that depressed spermatogenesis and prostate cancer represent opposite ends of the spectrum of AR action (Figure 6). Although empirical treatment of AR mutants in some cases has been shown to restore normal AR function and to improve spermatogenesis, a fully rational basis of treatment has to be based on an understanding of the crystallographic structure of the AR LBD. A full understanding could lead to the construction and the administration of ‘designer’ androgen analogues to treat male infertility caused by mutations of the AR gene.

Preclinical characterization of a (S)-N-(4-cyano-3-trifluoromethyl-phenyl)-3-(3-fluoro, 4-chlorophenoxy)-2-hydroxy-2-methyl-propanamide: a selective androgen receptor modulator for hormonal male contraception

The pharmacologic effects of (S)-N-(4-cyano-3-trifluoromethyl-phenyl)-3-(3-fluoro, 4-chlorophenoxy)-2-hydroxy-2-methyl-propanamide (S-23) were characterized in male rats as an animal model of hormonal male contraception. S-23 showed high binding affinity (inhibitory constant = 1.7 +/- 0.2 nm) and was identified as a full agonist in vitro. In castrated male rats, the ED50 of S-23 in the prostate and levator ani muscle was 0.43 and 0.079 mg/d, respectively. In intact male rats treated for 14 d, S-23 alone suppressed LH levels by greater than 50% at doses greater than 0.1 mg/d, with corresponding decreases in the size of the prostate but increases in the size of levator ani muscle. In intact male rats treated for up to 10 wk with S-23 and estradiol benzoate (EB; necessary to maintain sexual behavior in rats), S-23 showed biphasic effects on androgenic tissues and spermatogenesis by suppressing serum concentrations of LH and FSH. EB alone showed no effect on spermatogenesis. In the EB + S-23 (0.1 mg/d) group, four of six animals showed no sperm in the testis and zero pregnancies (none of six) in mating trials. After termination of treatment, infertility was fully reversible, with a 100% pregnancy rate observed after 100 d of recovery. S-23 increased bone mineral density and lean mass but reduced fat mass in a dose-dependent manner. This is the first study to show that a selective androgen receptor modulator combined with EB is an effective and reversible regimen for hormonal male contraception in rats. The beneficial effects of S-23 on the muscle, tissue selectivity, and favorable pharmacokinetic properties make it a strong candidate for use in oral male contraception.

Changes in spermatogenesis and endocrine function in the ram testis due to irradiation and active immunization against luteinizing hormone-releasing hormone

Spermatogonial stem cell transplantation is a technique that has potential in livestock to enhance genetic gain and generate transgenic offspring through the male germ line. A means for depletion of endogenous germ cells in a recipient's seminiferous tubules is necessary for this technology to be applied. The objectives of this study were to evaluate several methods for depletion of endogenous germ cells in the testes of adult rams and to evaluate ultrasound-guided injections into the rete testes as a means for infusing a suspension into the seminiferous tubules. Sixteen adult rams were randomly divided into 4 treatment groups (n = 4 per group). Treatments consisted of active immunization against LHRH (IMM), localized testicular irradiation (IR), LHRH immunization + irradiation (IMM+IR), and untreated control. Serial bleedings were conducted pretreatment and monthly after treatment for 4 mo, at which time all rams were castrated. Both IMM and IMM+IR rams received exogenous gonadotropin in the form of Perganol weekly for 8 wk before castration to bypass the immunization. All rams also received an ultrasound-guided injection of PBS containing 0.4% trypan blue into the rete testis of one testicle before castration. Rams receiving IMM and IMM+IR treatments had higher (P < 0.05) average percentages of seminiferous tubule cross sections with depleted germ cells compared with controls. Serum testosterone was decreased (P < 0.05) in IMM and IMM+IR rams 1 mo after treatment and throughout the remainder of the study compared with controls and IR rams, which were not different from each other. Serum inhibin concentration was unchanged in all rams following treatment indicating that Sertoli cell function was unaltered. A greater (P < 0.05) average percentage of the total testicular area could be filled with the trypan blue solution by rete testis injection in IMM and IMM+IR rams. These data demonstrate the depletion of endogenous germ cells in adult ram testes without alteration of Sertoli cell viability and function that have potential as methods for preparing recipient animals for germ cell transplantation.

Insights into male germ cell apoptosis due to depletion of gonadotropins caused by GnRH antagonists

The role of pituitary gonadotropins in the regulation of spermatogenesis has been unequivocally demonstrated, although, the precise mechanism of this regulation is not clearly understood. Previous studies have shown that specific immunoneutralization of LH/testosterone caused apoptotic cell death of meiotic and post-meiotic germ cells while that of FSH resulted in similar death of meiotic cells. In the present study, the death process of germ cells has been characterized by depleting both FSH and testosterone by administering two different potent GnRH antagonists, Cetrorelix and Acyline to both rats and mice. Pro-survival factors like Bcl-2 and Bcl-x/l were unaltered in germ cells due to GnRH antagonist treatment, although a significant increase in several pro-apoptotic markers including Fas and Bax were evident at both protein and RNA levels. This culminated in cytochrome C release from mitochondria and eventually increase in the activity of caspase-8 and caspase-3. These data suggest that both extrinsic and intrinsic apoptotic death pathways are operative in the germ cells death following decrease in FSH and testosterone levels. Multiple injections of GnRH antagonist resulted in complete disappearance of germ cells except the spermatogonial cells and discontinuation of the treatment resulted in full recovery of spermatogenesis. In conclusion our present data suggest that the principal role of FSH and testosterone is to maintain spermatogenic homeostasis by inhibiting death signals for the germ cells.

Deficiency of Growth Hormone Receptor Does Not Affect Male Reproduction in Dwarf Chickens

Sex-linked dwarf chickens caused by the mutation of the growth hormone receptor gene are characterized by normal growth hormone (GH), very low insulin-like growth factor I (IGF-I) level in the blood, and reduced growth. It has been demonstrated that the sex-linked dwarfing gene has negative effects on female reproduction. In the current study, dwarf cocks and their phenotypic normal siblings were used to investigate the effects of dwarf gene on male reproduction. Dwarf cocks grew slower than the normal cocks did, and at 20 wk of age, their BW were 36.4% smaller. However, all parameters for semen quality, including volume, sperm concentration, viability, mobility, pH, and percentage of abnormal sperms, examined at 30 wk of age showed no significant difference between normal and dwarf cocks. The fertility of dwarf cocks was 95.2%, and the normal was 92.4%. The concentrations of GH and IGF-I in serum and seminal plasma were measured with RIA and ELISA, respectively. The serum GH in the dwarf cocks was significantly higher than their normal siblings (P < 0.05), whereas the serum IGF-I in the dwarf cocks was very low. However, the concentration of seminal IGF-I in dwarf cocks was similar to that of their normal siblings, indicating that IGF-I might be produced and acted independently in testis. In conclusion, the deficiency in GH receptor did not affect the male reproduction in dwarf chickens, and the fertility of dwarf cocks could be satisfactory for production when artificial insemination was adopted.

The androgen microenvironment of the human testis and hormonal control of spermatogenesis

It is well established for both rat and man that the total testosterone concentration within the testis is far higher than that in serum. We know for the rat that intratesticular testosterone can be reduced by 50-60% without an adverse effect on spermatogenesis but that the required intratesticular testosterone concentration is still 10-fold greater than serum testosterone concentration. This kind of information, if available for the human, could prove invaluable for understanding and treating select men with infertility and in the development of male hormonal contraceptives. Unfortunately, we know little about the androgen content of intratesticular fluid within the human testis and nothing about the relationship between intratesticular androgens and human spermatogenesis. Using a newly developed minimally invasive technique for repetitive testicular sampling, our recent studies of the human have demonstrated that, as in the rat, there is a gradient between the concentration of testosterone in serum and within the testis; intratesticular testosterone levels were found to be 100-fold higher than serum testosterone levels in normal men. Using liquid chromatography tandem mass spectroscopy, we have shown that intratesticular 5alpha-dihydrotestosterone (DHT) levels are only 2% that of testosterone and, thus, despite greater affinity for the androgen receptor, intratesticular DHT is not significant in normal men. In order to assess how much of the testosterone within the human testis is bioactive, we adapted a highly sensitive recombinant protein mammalian cell-based bioassay to measure androgen bioactivity. The androgen bioactivity in the normal human testis is roughly two-thirds that of the total testosterone measurable by radioimmunoassay, despite the fact that the concentrations of the major androgen-binding proteins (sex hormone-binding globulin- and androgen-binding protein) are insufficient to account for this difference. This finding suggests that androgens may bind to other, as-yet-unknown molecules in the human testis. How, or if, this relates to spermatogenesis in the rat, or to man-to-man differences in the response to hormonal contraceptives, is not clear. We do not yet know how much testosterone is required within the human testis to either maintain or restore quantitatively normal spermatogenesis because, as yet, experimental studies comparable to those performed in the rat have not been feasible for the human.

Evaluation of relative role of LH and FSH in restoration of spermatogenesis using ethanedimethylsulphonate-treated adult rats

Spermatogenesis is a complex process, and previous studies have clearly established the role for testosterone in its maintenance. However, the role of FSH remains controversial, although several lines of evidence suggest its importance in initiation of spermatogenesis. In the present study, the relative roles of FSH and LH have been evaluated using specific antisera capable of neutralizing endogenous hormones in adult male rats following ethanedimethylsulphonate (EDS) treatment. Restoration of spermatogenesis in EDS-treated rats was monitored following FSH or LH deprivation by histological analysis and flow cytometry. Deprivation of FSH resulted in a reduction of seminiferous tubule diameter and spermatogonial number, which was much more drastic than that observed following LH deprivation. More importantly, FSH deprivation was associated with a significant reduction in the number of pachytene spermatocytes. These results provide evidence for a definite role for FSH in regulation of spermatogenesis, in addition to confirming the role of LH in spermatogenesis via testosterone.

Nuclear factor-kappaB activates transcription of the androgen receptor gene in Sertoli cells isolated from testes of adult rats

The androgen receptor (AR) in Sertoli cells mediates the actions of testosterone on spermatogenesis. However, the transcription factors responsible for AR gene regulation in Sertoli cells remain unknown. In this study, we determined that nuclear factor-kappaB (NF-kappaB) regulates transcription of AR in primary cultures of Sertoli cells isolated from testes of adult rats. Electrophoretic mobility shift and antibody supershift assays with nuclear extracts prepared from Sertoli cells identified two binding sites, termed kappaB1 at -491/-482 bp and kappaB2 at -574/-565 bp, upstream of the transcription start site of the AR gene that bind the NF-kappaB subunits, p50 and p65. DNAse I footprint analyses showed that binding of the p50 NF-kappaB subunit protected the same regions on the rat AR promoter. Analyses of AR promoter-luciferase reporter gene activity after transfection of primary cultures of Sertoli cells demonstrated that mutation of the kappaB2 site or combined mutation of the kappaB1 and kappaB2 sites reduced activity by 40%. Preferential binding of the transcriptionally active p65/p50 heterodimer to the kappaB2 site rather than to the kappaB1 site supported these observations. Overexpression of the NF-kappaB p65 and p50 subunits in Sertoli cells increased activity from the wild-type AR promoter and the promoter with mutation of the kappaB1 site, but not the kappaB2 site. Activity was further stimulated by CBP (CREB binding protein), a coactivator of p65 transcriptional activity. Taken together, our data show that NF-kappaB is an activator of AR gene transcription in Sertoli cells and may be an important determinant of androgen activity during spermatogenesis.

Hormones: what the testis really sees

Various barriers in the testis may prevent hormones from readily reaching the cells they are supposed to stimulate, especially the hydrophilic hormones from the pituitary. For example, LH must pass through or between the endothelial cells lining the blood vessels to reach the surface of the Leydig cells, and FSH has the additional barrier of the peritubular myoid cells before it reaches the Sertoli cells. The specialised junctions between pairs of Sertoli cells would severely restrict the passage of peptides from blood to the luminal fluid and therefore to the cells inside this barrier, such as the later spermatocytes and spermatids. There is evidence in the literature that radioactively labelled LH does not pass readily into the testis from the blood, and the concentration of native LH in the interstitial extracellular fluid surrounding the Leydig cells in rats is only about one-fifth of that in blood plasma. Furthermore, after injection with LHRH, there are large rises in LH in the blood within 15 min, at which time the Leydig cells have already responded by increasing their content of testosterone, but with no significant change in the concentration of LH in the interstitial extracellular fluid. Either the Leydig cells respond to very small changes in LH, or the testicular endothelial cells in some way mediate the response of the Leydig cells to LH, for which there is now some evidence from co-cultures of endothelial and Leydig cells. The lipophilic steroid hormones, such as testosterone, which are produced by the Leydig cells, have actions within the seminiferous tubules in the testis but also in other parts of the body. They should pass more readily through cells than the hydrophilic peptides; however, the concentration of testosterone in the fluid inside the seminiferous tubules is less than in the interstitial extracellular fluid in the testis, especially after stimulation by LH released after injection of LHRH and despite the presence inside the tubules of high concentrations of an androgen-binding protein. The concentration of testosterone in testicular venous blood does not rise to the same extent as that in the interstitial extracellular fluid, suggesting that there may also be some restriction to movement of the steroid across the endothelium. There is a very poor correlation between the concentrations of testosterone in fluids from the various compartments of the testis and in peripheral blood plasma. Determination of the testosterone concentration in the whole testis is also probably of little predictive value, because the high concentrations of lipid in the Leydig cells would tend to concentrate testosterone there, and hormones inside these cells are unlikely to have any direct effect on other cells in the testis. The best predictor of testosterone concentrations around cells in the testis is the level of testosterone in testicular venous blood, the collection of which for testosterone analysis is a reasonably simple procedure in experimental animals and should be substituted for tissue sampling. There seems to be no simple way of determining the concentrations of peptide hormones in the vicinity of the testicular cells.

Follicle-stimulating hormone is indispensable for the last spermatogonial mitosis preceding meiosis initiation in newts (Cynops pyrrhogaster)

We previously reported that mammalian FSH induced differentiation of secondary spermatogonia into primary spermatocytes in organ culture of newt testicular fragments, whereas in medium lacking FSH primary spermatocytes never appeared. Here, we investigated why spermatogonia fail to form primary spermatocytes in the absence of FSH. Spermatogonia maintained proliferative activity and viability at about half the level of those cultured in the presence of FSH, progressed into the seventh generation, but became moribund during the G2/M phase. Thus, the eighth generation of spermatogonia never appeared, suggesting that cell death is the chief reason why primary spermatocytes fail to form in the absence of FSH. The presence of Dmc1, a molecular marker for the spermatocyte stage, confirmed our microscopic observations that spermatogonia differentiated into primary spermatocytes in the presence of FSH. Thus, FSH is indispensable for the completion of the last spermatogonial mitosis, a prerequisite for the conversion of germ cells from mitosis to meiosis. Because prolactin induced apoptosis in spermatogonia during the seventh generation, we propose that a checkpoint exists for the initiation of meiosis in the seventh generation whereby spermatogonia enter meiosis when the concentration ratio of FSH to prolactin is high but fail to do so when the ratio is low.

The functional significance of FSH in spermatogenesis and the control of its secretion in male primates

The aim of this review is to provide an integrative analysis of the role of FSH in the control of testicular function in higher primates, including man. Attention is focused on the action of FSH during neonatal development, puberty, and adulthood. Whether FSH is the major determinant of the adult complement of Sertoli cells and whether FSH is obligatory for the initiation, maintenance, and restoration of spermatogenesis is evaluated. The mechanism whereby the circulating concentration of FSH regulates spermatogonial proliferation to dictate the sperm production rate under physiological conditions in the adult is discussed in detail. Inhibin B is the major component of the testicular negative feedback signal governing FSH beta gene expression and FSH secretion, and the evidence for this view is presented. The review concludes with the presentation of a model for the operation of the FSH-inhibin B feedback control system regulating sperm production postpubertally in monkey and man, and with speculation on issues of clinical interest.

Immunoneutralisation of GnRH-I, without cross-reactivity to GnRH-II, in the development of a highly specific anti-fertility vaccine for clinical and veterinary use

In recent years, several forms of gonadotrophin releasing hormone (GnRH) molecules have been isolated from primate brain. These molecules are very similar in sequence and this raises the question of whether previously developed neutralisation vaccines based on GnRH (now termed GnRH-I) would remove other forms of GnRH (namely GnRH-II) as well. As the function of these other molecules has not yet been clearly defined, potential health risks could exist by their ablation. In view of the high sequence homology between the molecules, this paper describes the production of highly specific polyclonal antibodies against GnRH-I and GnRH-II, with negligible cross-reactivity. The ultimate aim of this is to develop an anti-fertility vaccine which does not present any inappropriate side-effects, caused by neutralisation of a GnRH molecule which may or may not be directly involved in reproduction. Several formulations were investigated, based on analogues of the following molecules, conjugated to tetanus toxoid: 1. GnRH-I pGlu-His-Trp-Ser-Try-Gly-Leu-Arg-Pro-Gly-NH2 and 2. GnRH-II pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2. The specificity of the antibodies produced was examined, together with effects on fertility and any inappropriate side-effects. Immunostaining of hypothalamic sections was carried out, using the generated antisera, to determine the regional distribution of GnRH-I and GnRH-II neurones, as well as to further evaluate the specificity of the antibodies.

A novel mutation (N233K) in the transactivating domain and the N756S mutation in the ligand binding domain of the androgen receptor gene are associated with male infertility

OBJECTIVE

Resistance to androgens has been suggested as a possible cause of male infertility. This hypothesis is based mainly on binding studies in genital skin fibroblasts but the molecular evidence is sparse.

DESIGN

Molecular studies of the androgen receptor gene were performed in 10 azoo- or oligozoospermic men, presenting with clinical signs of low androgen activity-poor virilization and high serum LH despite elevated testosterone levels, but without genital malformations.

PATIENTS

Ten men with serum LH >10 IU/l and testosterone >30 nmol/l as well as a low sperm concentration < 20 x 106/ml.

MEASUREMENTS

Genomic DNA was prepared from peripheral leucocytes and PCR-amplification of the coding region of androgen receptor was performed, followed by direct sequencing. Identified mutations were reconstructed by site-directed mutagenesis and the functional properties of the mutants were analysed, using transient expression in COS-1 cells and subsequent transactivation assays. Hormone binding assays were performed in genital skin fibroblasts from the patients.

RESULTS

Two of the 10 men were shown to have a mutation in the androgen receptor gene. Subject 1, who presented with azoospermia, serum testosterone (T) 50 nmol/l and LH 20 IU/l, had a mutation in exon 1, changing amino acid asparagine 233 to lysine (N233K). In fibroblasts cultured from genital skin, the receptor affinity for 5alpha-dihydrotestosterone (DHT) was normal as compared to healthy controls, but the receptor-hormone complex was thermolabile at 42 degrees C. Subject 2 exhibited severe oligozoospermia and a similar endocrine pattern (T = 50 nmol/l and LH = 25 IU/l). He had a mutation in exon 5 changing asparagine 756 to serine (N756S). The affinity for DHT in cultured genital fibroblasts from this patient was reduced. Transactivation was abnormal for both mutants, N233K reaching 46% and N756S 38% of wild type activity when stimulated with 10 nmol/l DHT.

CONCLUSIONS

Androgen receptor mutations may affect sperm production without resulting in genital malformations. Thus, in infertile men with a clinical presentation of poor androgen activity and an endocrine profile compatible with androgen resistance, mutations in the androgen receptor should be taken into consideration.

The effects of pre- and postnatal exposure to the nonsteroidal antiandrogen flutamide on testis descent and morphology in the Albino Swiss rat

Exposure of male Albino Swiss rats to the nonsteroidal antiandrogen flutamide during the period from gestational day (d) 10 to birth resulted in feminisation of the external genitalia and the suppression of growth of the male reproductive tract. In adulthood, testes were found to be located in diverse positions. True cryptorchidism occurred in 10% of cases, whereas 50% of testes descended to the scrotum and 40% were located in a suprainguinal ectopic region. Varying degrees of tubule abnormality were seen in the testes of flutamide-treated animals, ranging from completely normal tubules with full spermatogenesis (and the expected frequency of the stages of spermatogenesis) to severely abnormal tubules lined with Sertoli cells only. For each individual testis, the overall severity of tubule damage was strongly correlated with its adult location, with intra-abdominal testes worst affected and scrotally-located testes least; only the latter contained normal tubules. Similarly, intra-abdominal testes were the smallest in weight and contained the least testosterone. By contrast, postnatal treatment of male rats with flutamide from birth to postnatal d 14 did not impair development of the external genitalia, the process of testicular descent or adult spermatogenesis. These findings confirm that androgen blockade during embryonic development interferes with testicular descent but also demonstrate that (1) prenatal flutamide treatment per se has a detrimental effect on adult testis morphology but (2) the degree of abnormality of the testes is strongly influenced by location.

Persistence of infertility in GnRH immunized male rats treated with subdermal implants of dihydrotestosterone (DHT)

Male hormonal contraception has been limited to date because two fundamental requirements have not been concurrently satisfied, these are, consistent and dependable azoospermia and infertility coupled with maintenance of libido. The objective of this study was to determine the extent to which implants of potent androgen (DHT) will restore androgenization and spermatogenesis in hypogonadotropic infertile male rats. Twenty-five sexually mature male rats of proven fertility were actively immunized against gonadotropin releasing hormone (GnRH) to induce azoospermia. After azoospermia was achieved, GnRH immunized rats received subdermal DHT-filled Silastic implants of 2, 4, 6, or 8 cm, or empty implants (n=5/group). Five untreated control rats received empty capsules. Eight weeks later, fertility was evaluated, sperm number was obtained from the testis, and weights of androgen-dependent organs were measured. The results indicate that immunoneutralization of GnRH induced complete azoospermia, and subsequent treatment with DHT implants of 2 or 4 cm for 8 wk restored accessory organ weights, but did not restore spermatogenesis or fertility. In addition, DHT implants of 6 to 8 cm partially restored spermatogenesis, but not fertility. We conclude that low-dose DHT supplementation of GnRH-immunized rats may be a suitable alternate therapy able to maintain androgenization in the face of persistent azoospermia in the rat. This may be an effective model for development of a male contraceptive.

An investigation into the immunogenicity of a GnRH analogue in male rats: a comparison of the toxicity of various adjuvants used in conjunction with GnRH-glycys

Immunization of male Copenhagen Fischer rats with a gonadotrophin releasing hormone (GnRH) analogue, conjugated to PPD resulted in high levels of antibody being produced which disrupted gonadal function in male rats. The antibody reduced serum testosterone levels and subsequently suppressed spermatogenesis. Alternatives to Freund's adjuvant were tested, namely, aluminium hydroxide and non-ionic surfactant vesicles (NISV). The study showed that aluminium hydroxide was as effective as Freund's adjuvant and less toxic, in both BCG and non-BCG primed animals. However, NISV were completely non-toxic and most effective in conjunction with BCG priming. The data obtained showed that NISV have the potential to be used as an alternative to FCA and aluminium hydroxide-based adjuvants.

Differential expression of ornithine decarboxylase, poly(ADP)ribose polymerase, and mitochondrial mRNAs following testosterone administration to hypophysectomized rats

The mRNAs of the nuclear encoded genes, ornithine decarboxylase (ODCase) and poly(ADP)ribose polymerase (PADPRP), and the mitochondrial encoded genes, cytochrome oxidase I and II (COI and COII) and ATPase 6, are differentially expressed during spermatogenesis (Alcivar et al., 1989: Biol Reprod 41:1133; 1989: Dev Biol 135:263; 1991: Biol Reprod 46:201). In this study, we use Northern blotting to examine the steady state levels of ODCase, PADPRP, COI, COII, and ATPase 6 mRNAs in testes of hypophysectomized male rats following testosterone administration. Four weeks after hypophysectomy, rats received 24 cm subcutaneous implants of testosterone-filled polydimethylsiloxane (PDS) and were killed at 3, 7, 14, 28, and 56 days thereafter. After hypophysectomy, the steady state levels for the PADPRP, COI, COII, and ATPase 6 mRNAs were not significantly different from controls, although hypophysectomy caused a 44% loss of preleptotene spermatocytes and an 88% loss of pachytene spermatocytes, the testicular cell types expressing the highest levels of these mRNAs. In contrast, the levels of the two ODCase mRNAs were greatly decreased after hypophysectomy and mirrored the number of germinal cells present in the testis. After testosterone treatment, ODCase mRNA levels remained low 3 days after treatment and gradually increased at days 14, 28, and 56. No major hybridization signal changes in PADPRP, COI, COII, and ATPase mRNA were observed after testosterone treatment. We conclude that the steady state mRNA levels for the housekeeping ODCase gene respond differently after hypophysectomy and testosterone treatment of male rats than the PADPRP and mitochondrial DNA transcripts.

Comparative studies on the effects of specific immunoneutralization of endogenous FSH or LH on testicular germ cell transformations in the adult bonnet monkey (Macaca radiata)

PROBLEM

It is yet to be determined clearly whether the two hormones FSH and T act synergistically in the same cell type--the Sertoli cells--to control overall spermatogenesis or influence independently the transformation of specific germ cell types during spermatogenesis in the adult mammal.

METHOD

Adult male bonnet monkeys specifically deprived of either FSH or LH using immunoneutralization techniques were monitored for changes in testicular germ cell transformation by DNA flow cytometry.

RESULTS

FSH deprivation caused a significant reduction ( > 40%; P < 0.05) in [3H] thymidine incorporation into DNA of proliferating 2C (spermatogonial) cells, a marked inhibition ( > 50%) in the transformation of 2C to primary spermatocytes (4C) and a concomitant, belated reduction (50%) in the formation of round spermatids (1C). In contrast, specific LH/T deprivation led to an immediate arrest in the meiotic transformation of 4C to 1C/HC leading to an effective and significant block ( < 90%; P < 0.01) in sperm production.

CONCLUSION

Thus, LH rather than FSH deprivation has a more pronounced and immediate effect as the former primarily blocks meiosis (4C --> 1C/HC) which controls production of spermatids. These data provide evidence for LH/T and FSH regulating spermatogenic process in the adult primate by primarily acting at specific germ cell transformation steps.

Hormonal control of spermatogenesis

FSH and testosterone (T) secretion are essential for the successful completion of spermatogenesis. Because there are no receptors for FSH or testosterone on germ cells, there are intermediate steps in this action, the nature of which are unknown. However, as the Sertoli cell contains receptors for both FSH and T, it is likely that these hormones exert their influence on germ cells by modulating Sertoli cell function. Both FSH and T exert synergistic actions on germ cells, but T has a specific action on the later stages of spermatid maturation. FSH, by its ability to stimulate Sertoli cell mitosis during testicular development, can influence the spermatogenic capacity of the adult testis.

Gonadotrophin control of testicular germ cell development

Successful and complete male germ cell development is dependent on the balanced, endocrine interplay of the hypothalamus, the pituitary and the testis. The hypothalamus secretes gonadotrophin-releasing hormone in a pulsatile manner which, in turn, elicits the pulsatile release of the gonadotrophins LH and FSH from the pituitary. Luteinizing hormone stimulates spermatogenesis indirectly via testosterone, whereas FSH acts directly on the seminiferous tubules. The synthesis and release of gonadotrophic hormones is under the feedback control of testosterone. Whether other testicular peptides such as inhibin and activin are also involved is not yet clear. Luteinizing hormone/testosterone and FSH are the prime regulators of germ cell development. On their own, these hormones are capable of exerting clear-cut stimulatory effects on the spermatogenic process. However, the quantitative production of spermatozoa generally requires the presence of both LH/testosterone and FSH. Since receptors for androgens and FSH are confined to the somatic cells of the testis, the trophic effects of these hormones on germ cells must be indirect. However, it is not known as yet precisely which genes/factors mediate the beneficial effects of androgens and FSH on spermatogenesis. The gonadotrophic hormones have been found in a number of isoforms and multiple transcripts of the LH and FSH receptor have been detected. Therefore, the possibility must be considered that certain forms of male infertility could be due to dysfunctional hormones and/or mutated receptors.

Restoration of testicular transferrin, insulin-like growth factor-1 (IGF-1), and spermatogenesis by exogenously administered purified FSH and testosterone in medically hypophysectomized rats

To investigate the relation between testicular transferrin and insulin-like growth factor-1 (IGF-1) secreted by Sertoli cells and the differentiation of germ cells in the rat, testosterone and/or purified FSH was administered to rats medically hypophysectomized by an LH-RH agonist. Spermatogenesis was quantitatively analyzed and concentrations of intratesticular transferrin and IGF-1 were measured by radioimmunoassays. The last step of spermatogenesis was quantitatively restored by combined administration of testosterone and purified FSH. Intratesticular IGF-1 concentrations were significantly increased by combined administration of testosterone and purified FSH. From these observations, it is surmised that IGF-1 may have a stimulatory effect on the last step of spermatogenesis.

Immunoregulation of mammalian fertility

Fertility management is a global issue of agricultural, medical, economic, and social consequence. Although many methods have been devised to both inhibit and assist reproduction, more acceptable alternatives are needed. Regulation by immune intervention is a promising technology as applied to livestock, pets, wildlife, and human beings. Outcome is dictated by site within the reproductive axis that is targeted. Fertility is suppressed by immunization against gonadotropin-releasing hormone, gonadotropins, prostaglandin F2 alpha, oxytocin, gonadotropin receptors, and gamete/embryonic antigens. It also is possible to lyse gonadal cells with ligand-antibody hybrid molecules. Ovulation rates are enhanced by vaccination with inhibin. Antibodies to sex steroid hormones have yielded mixed results. Perhaps recombinant viral vectors can be used to deliver reproductive immunogens. A new and simple technique to generate sustained autoimmune reactions to hormones and cellular antigens entails direct gene transfer into somatic cells. Evolving advances in reproductive immunology and biotechnology should furnish us with novel nonsurgical contraceptives and profertility agents that can be efficiently and safely implemented.

Sensitivity of Sertoli and Leydig cells to xenobiotics in in vitro models

Different chemicals are known to cause testicular damage in the human male and experimental animals. However, the ability to assess the potential and mechanism of action leading to chemically-induced damage in men has been hampered by a lack of good predictive models. Although many of these chemicals were found to impair reproductive capacity in various laboratory animals, only some have caused reproductive damage in men. Mammalian spermatogenesis takes places within the avascular seminiferous tubules of the testis. Specialized tight junctions, which form between adjacent Sertoli cells at the time of puberty, divide the tubular space into the basal and adluminal compartments, and create a "blood-testis" barrier that restricts passage of substances and ions from the circulation. Thus, the completion of meiosis and post-meiotic germ cell differentiation, which take place in the adluminal compartment, are isolated from circulating substances unable to cross the blood-testis barrier. It seems feasible, therefore, that damage to the germ cells induced by testicular toxicants may be mediated through other cells in the testis such as the Sertoli, peritubular, or Leydig cells. A recently developed two-compartment system for culture of testicular cells can simulate, to some degree, the normal physiologic conditions. In principle, Sertoli cells isolated from mammalian testes are cultured on a permeable support (that is millipore filter) between two fluid compartments. They form a highly polarized epithelial layer with characteristic tight junctions that restrict the passage of substances between the two compartments, in analogy to the blood-testis barrier. We believe this system provides an excellent in vitro model for determining the ability of chemicals to: a) alter the permeability of the blood-testis barrier, b) impair the secretory function of Sertoli cells, or c) affect their viability, all of which could indirectly affect the germ cells. We have utilized this system for examining the effects of cadmium chloride (CdCl2) and other toxic substances known to affect the testis. The Leydig cell toxicity was investigated in testicular perfusion system or cultures of isolated Leydig cells.

Anti-LHRH and anti-pituitary gonadotropin vaccines: their development and clinical applications

Active immunization against hormones involved in the regulation of reproduction is a promising approach to immunocontraception. The hypothalamic peptide, LHRH, controls the synthesis and release of the pituitary gonadotropins, LH and FSH, which regulate gonadal steroidogenesis, sperm production, follicular development and ovulation. Immunizing female primates against LHRH or LH induces infertility, but also disrupts the menstrual cycle. Immunization against the beta subunit of the placental hormone, chorionic gonadotropin (hCG), or its fragment prevents pregnancy without interfering with menstrual cycles or ovulation. hCG vaccines have reached the stage of clinical trials. FSH and LHRH have been tested for immunocontraception in male primates. While active as well as passive immunization against FSH reduced spermatogenesis severely, azoospermia could not be achieved consistently. Immunization against LHRH effectively suppressed spermatogenesis in rats and rabbits. Normal sexual behaviour was maintained by concomitant androgen administration. Fertility was restored when antibody titres declined and no adverse effects were observed. A number of LHRH vaccine preparations are being tested in men in several countries, including the United States. Since the LHRH vaccine reduces serum testosterone levels the first clinical studies involve men with prostate cancer. These trials will be followed by immunization of normal men if the antibody response is sufficient and no adverse effects are observed.

Vaccines against fertility

The first evidence for the efficacy of a birth control vaccine in humans is now available from the Phase II trials on the human chorionic gonadotrophin vaccine in India. Several sperm antigens have been identified as potential contraceptive immunogens and zona pellucida antigens have been reported that reversibly control fertility.

Immunoneutralization of gonadotropin-releasing hormone and subsequent treatment with testosterone Silastic implants in rats: an approach toward developing a male contraceptive

STUDY OBJECTIVE

To determine the extent to which increasing doses of exogenous testosterone (T) administered via Silastic implants can restore spermatogenesis and fertility to rats made azoospermic by active immunization against gonadotropin-releasing hormone (GnRH).

DESIGN

Male rats were made azoospermic by active immunization against GnRH. Increasing doses of exogenously administered T (via Silastic implants) were administered for 8 weeks, and testicular sperm concentration and ability to impregnate female rats were evaluated.

SETTING

Reproductive Endocrinology Laboratory, Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, Denver, Colorado.

ANIMALS

Sexually mature male Sprague Dawley rats (SASCO, Omaha, NE).

RESULTS

Suppression of gonadotropins and azoospermia was achieved by actively immunizing rats against GnRH. Testosterone was capable of restoring quantitatively complete spermatogenesis and fertility in GnRH-immunized azoospermic rats. This relationship was dose-dependent, as evidenced by the partial restoration of spermatogenesis and fertility observed in animals replaced with smaller T Silastic implants.

CONCLUSION

Gonadotropin-releasing hormone immunization and T-filled Silastic implants may provide a model to study isolated gonadotropin deficiency and for the development of a reversible male contraceptive.

Reinitiation of spermatogenesis by exogenous gonadotropins in a seasonal breeder, the woodchuck (Marmota monax), during gonadal inactivity

The present study was undertaken (1) to document structural and functional changes in the testes of seasonally breeding woodchuck during active and inactive states of spermatogenesis and (2) to evaluate the ability of exogenous gonadotropins to reinitiate spermatogenesis outside the breeding season. During seasonal gonadal inactivity, there were significant (P less than 0.05) reductions in volumes of several testicular features (testis, seminiferous tubules, tubular lumen, interstitial tissue, individual Leydig cells, Leydig cell nuclei, and Leydig cell cytoplasm) as compared with gonadally active animals. The diameter of the seminiferous tubules was decreased by 26%, and Leydig cell numbers also declined in the regressed testes. These changes were accompanied by a decline in testosterone (T) levels in both plasma and testis, and reduction in epithelial height of accessory reproductive organs. A hormonal regimen was developed that would reinitiate spermatogenesis in captive, sexually quiescent woodchucks. A combination of PMSG and hCG markedly stimulated testicular growth and function and restored spermatogenesis qualitatively. Quantitatively normal spermatogenesis was restored in 2 of 6 treated males. Morphometric analyses revealed substantial increases in seminiferous tubular diameter and in the volume of seminiferous tubules, tubular lumen, total Leydig cells, and individual Leydig cells in the hormone-treated animals. These increased values corresponded to 99, 75, 68, 51, and 200%, respectively, of the values measured in naturally active woodchucks. Leydig cell numbers, however, remained unchanged and approximated only 31% of the number found in naturally active testes. Hormonal stimulation also resulted in a significant rise in serum T as well as in the total content of testicular T, and a marked increase in epithelial height in various accessory reproductive glands. The most effective hormonal protocol for stimulating spermatogenesis was treatment with 12.5 IU of PMSG twice a week for 4 weeks followed by 12.5 IU of PMSG + 25 IU of hCG twice a week for 4 weeks.

Further observations of stage-specific effects seen after short-term hypophysectomy in the rat

Although hypophysectomy has been a popular tool to study the effects of hormone deprivation as well as concomitant or subsequent hormone supplementation, there is relatively little morphological information available on the structural manifestation of pituitary removal on the testis. In the report, changes, in addition to those previously reported after short-term (6 days) hypophysectomy in the rat (Russell and Clermont, 1977), are described. Membrane-bound vacuoles (primarily) appeared within the basal region of the Sertoli cell at approximately the level of Sertoli-Sertoli junctions. In stages VIII through XI elongating spermatids were abnormal and manifested manchette indentation of the nucleus, a variety of other abnormal head shapes, acrosomal breaks and enlargement of the subacrosomal space. These defects were interpreted as the effect of declining hormonal levels in stage VII on spermatids that had survived the stage VII hormone sensitivity known to occur with severe hormone depletion. Abnormalities in the flagellum involving the mitochondrial sheath and fibrous sheath were detected. Preleptotene spermatocytes degenerated and could be identified in the process of doing so near the base of the seminiferous epithelium. The contact of preleptotene spermatocytes with the basal lamina was also significantly reduced. The results show that both Sertoli cell and germ cell abnormalities were present although germ cell abnormalities could be a secondary consequence of lack of appropriate stimulation of the Sertoli cell. Degeneration of basal compartment germ cells shows that germ cells other than those located in the adluminal compartment are vulnerable to hormonal withdrawal. The question of how hormone effects are mediated in the testis at midcycle to produce these effects is discussed.