Neonatal exposure of male rats to estradiol benzoate causes rete testis dilation and backflow impairment of spermatogenesis

Male animal sterilization: history, current practices, and potential methods for replacing castration

Sterilization and castration have been synonyms for thousands of years. Making an animal sterile meant to render them incapable of producing offspring. Castration or the physical removal of the testes was discovered to be the most simple but reliable method for managing reproduction and sexual behavior in the male. Today, there continues to be global utilization of castration in domestic animals. More than six hundred million pigs are castrated every year, and surgical removal of testes in dogs and cats is a routine practice in veterinary medicine. However, modern biological research has extended the meaning of sterilization to include methods that spare testis removal and involve a variety of options, from chemical castration and immunocastration to various methods of vasectomy. This review begins with the history of sterilization, showing a direct link between its practice in man and animals. Then, it traces the evolution of concepts for inducing sterility, where research has overlapped with basic studies of reproductive hormones and the discovery of testicular toxicants, some of which serve as sterilizing agents in rodent pests. Finally, the most recent efforts to use the immune system and gene editing to block hormonal stimulation of testis function are discussed. As we respond to the crisis of animal overpopulation and strive for better animal welfare, these novel methods provide optimism for replacing surgical castration in some species.

Imprinting and Reproductive Health: A Toxicological Perspective

This overview discusses the role of imprinting in the development of an organism, and how exposure to environmental chemicals during fetal development leads to the physiological and biochemical changes that can have adverse lifelong effects on the health of the offspring. There has been a recent upsurge in the use of chemical products in everyday life. These chemicals include industrial byproducts, pesticides, dietary supplements, and pharmaceutical products. They mimic the natural estrogens and bind to estradiol receptors. Consequently, they reduce the number of receptors available for ligand binding. This leads to a faulty signaling in the neuroendocrine system during the critical developmental process of 'imprinting'. Imprinting causes structural and organizational differentiation in male and female reproductive organs, sexual behavior, bone mineral density, and the metabolism of exogenous and endogenous chemical substances. Several studies conducted on animal models and epidemiological studies provide profound evidence that altered imprinting causes various developmental and reproductive abnormalities and other diseases in humans. Altered metabolism can be measured by various endpoints such as the profile of cytochrome P-450 enzymes (CYP450's), xenobiotic metabolite levels, and DNA adducts. The importance of imprinting in the potentiation or attenuation of toxic chemicals is discussed.

Expression patterns of sex steroid receptors in developing mesonephros of the male mouse: three-dimensional analysis

The androgen pathway via androgen receptor (AR) has received the most attention for development of male reproductive tracts. The estrogen pathway through estrogen receptor (ESR1) is also a major contributor to rete testis and efferent duct formation, but the role of progesterone via progesterone receptor (PGR) has largely been overlooked. Expression patterns of these receptors in the mesonephric tubules (MTs) and Wolffian duct (WD), which differentiate into the efferent ductules and epididymis, respectively, remain unclear because of the difficulty in distinguishing each region of the tracts. This study investigated AR, ESR1, and PGR expressions in the murine mesonephros using three-dimensional (3-D) reconstruction. The receptors were localized in serial paraffin sections of the mouse testis and mesonephros by immunohistochemistry on embryonic days (E) 12.5, 15.5, and 18.5. Specific regions of the developing MTs and WD were determined by 3-D reconstruction using Amira software. AR was found first in the specific portion of the MTs near the MT-rete junction at E12.5, and the epithelial expression showed increasing strength from cranial to the caudal regions. Epithelial expression of ESR1 was found in the cranial WD and MTs near the WD first at E15.5. PGR was weakly positive only in the MTs and cranial WD starting on E15.5. This 3-D analysis suggests that gonadal androgen acts first on the MTs near the MT-rete junction but that estrogen is the first to influence MTs near the WD, while potential PGR activity is delayed and limited to the epithelium.

Anatomy, Endocrine Regulation, and Embryonic Development of the Rete Testis

Reproduction in males requires the transfer of spermatozoa from testis tubules via the rete system to the efferent ductules, epididymis, and vas deferens. The rete therefore forms an essential bridging system between the testis and excurrent ducts. Yet the embryonic origin and molecular regulation of rete testis development is poorly understood. This review examines the anatomy, endocrine control, and development of the mammalian rete testis, focusing on recent findings on its molecular regulation, identifying gaps in our knowledge, and identifying areas for future research. The rete testis develops in close association with Sertoli cells of the seminiferous cords, although unique molecular markers are sparce. Most recently, modern molecular approaches such as global RNA-seq have revealed the transcriptional signature of rete cell precursors, pointing to at least a partial common origin with Sertoli cells. In the mouse, genes involved in Sertoli cell development or maintenance, such as Sox9, Wt1, Sf1, and Dmrt1, are also expressed in cells of the rete system. Rete progenitor cells also express unique markers, such as Pax8, E-cadherin, and keratin 8. These must directly or indirectly regulate the physical joining of testis tubules to the efferent duct system and confer other physiological functions of the rete. The application of technologies such as single-cell RNA-seq will clarify the origin and developmental trajectory of this essential component of the male reproductive tract.

Estrogens and development of the rete testis, efferent ductules, epididymis and vas deferens

Estrogen has always been considered the female hormone and testosterone the male hormone. However, estrogen's presence in the testis and deleterious effects of estrogen treatment during development have been known for nearly 90 years, long before estrogen receptors (ESRs) were discovered. Eventually it was learned that testes actually synthesize high levels of estradiol (E2) and sequester high concentrations in the reproductive tract lumen, which seems contradictory to the overwhelming number of studies showing reproductive pathology following exogenous estrogen exposures. For too long, the developmental pathology of estrogen has dominated our thinking, even resulting in the "estrogen hypothesis" as related to the testicular dysgenesis syndrome. However, these early studies and the development of an Esr1 knockout mouse led to a deluge of research into estrogen's potential role in and disruption of development and function of the male reproductive system. What is new is that estrogen action in the male cannot be divorced from that of androgen. This paper presents what is known about components of the estrogen pathway, including its synthesis and target receptors, and the need to achieve a balance between androgen- and estrogen-action in male reproductive tract differentiation and adult functions. The review focuses on what is known regarding development of the male reproductive tract, from the rete testis to the vas deferens, and examines the expression of estrogen receptors and presence of aromatase in the male reproductive system, traces the evidence provided by estrogen-associated knockout and transgenic animal models and discusses the effects of fetal and postnatal exposures to estrogens. Hopefully, there will be enough here to stimulate discussions and new investigations of the androgen:estrogen balance that seems to be essential for development of the male reproductive tract.

Evaluation of an in vitro mouse testis organ culture system for assessing male reproductive toxicity

BACKGROUND

Development of an in vitro system capable of producing mature sperm remains a challenging goal, with only few successes reported. Such a system, could be used to test agents for potential toxicity to the male reproductive system; to explore this, we exposed immature mouse testis fragments in culture to ethinylestradiol (EE), a well-known testicular toxicant in vivo.

METHODS

Testis fragments from postnatal day 5 mice were cultured in Albumax I medium. After 24 hr of culture, fragments were treated with 0.01, 0.1 or 1 nM EE, then harvested after 20 days in culture and examined for histology or gene expression measures by quantitative PCR.

RESULTS

There was substantial variability between fragments in the degree of spermatogenesis observed. The percentage of seminiferous tubules containing any dead germ cells increased as a result of EE exposure in a dose dependent fashion. This was accompanied with a decreased percentage of tubules with round spermatids. Expression of estrogen receptor 1, cytochrome P450, family 11, subfamily a, and polypeptide 1 also was reduced, depending on the dose.

CONCLUSION

These gene expression changes in the testis fragments are similar to those seen after animals have been exposed to EE. Gene expression changes in testis fragments are encouraging, but the variability across samples will need to be reduced for this in vitro system to become a generally applicable method for assessing testicular toxicants.

Perspectives in Pediatric Pathology, Chapter 11. Testicular Pathology of Hamartomatous Origin

The term hamartoma was coined by Albrecht in 1904 from the Greek μαρτ-άνω, to go wrong [ 1 ]. Hamartoma is currently used to name nonneoplastic lesions composed of disorganized tissue indigenous to the site where it is found. In the testis, this refers to abnormal/excessive development of structures that usually form part of the gonadal parenchyma, epididymis, or spermatic cord. We include the following as hamartomatous lesions of the testis and sperm excretory ducts: cystic dysplasia of the rete testis, rete testis hamartomas, fetal gonadoblastoid testicular dysplasia (FGTD), Sertoli cell nodules, tubular hamartomas, congenital testicular and epididymal lymphangiectasis, and smooth muscle hyperplasia of paratesticular structures. These hamartomas are always benign, but their importance resides in their association with specific disorders, or as markers of complex syndromes.

The increase in the number of spines on the gonadotropin-releasing hormone neuron across pubertal development in rats

The onset of puberty is initiated by an increase in the release of the gonadotropin-releasing hormone (GnRH) from GnRH neurons in the hypothalamus. However, the precise mechanism that leads to the activation of GnRH neurons at puberty remains controversial. Spines are small protrusions on the surface of dendrites that normally receive excitatory inputs. In this study, we analyzed the number and morphology of spines on GnRH neurons to investigate changes in synaptic inputs across puberty in rats. For morphological estimation, we measured the diameter of the head (DH) of each spine and classified them into small-type (DH < 0.65 μm), large-type (DH > 0.65 μm) and giant-type (DH > 0.9 μm). The greatest number of spines was observed at the proximal dendrite within 50 μm of the soma. At the soma and proximal dendrite, the number of spines was greater in adults than in juveniles in both male and female individuals. Classification of spines revealed that the increase in spine number was due to increases in large- and giant-type spines. To further explore the relationship between spines on GnRH neurons and pubertal development, we next analyzed adult rats neonatally exposed to estradiol benzoate, in which puberty onset and reproductive functions are disrupted. We found a decrease in the number of all types of spines. These results suggest that GnRH neurons become to receive more and greater excitatory inputs on the soma and proximal dendrites as a result of the changes that occur at puberty and that alteration to spines plays a pivotal role in normal pubertal development.

Disruption of estrogen receptor signaling and similar pathways in the efferent ductules and initial segment of the epididymis

Seminiferous tubular atrophy may involve indirectly the disruption of estrogen receptor-α (ESR1) function in efferent ductules of the testis. ESR1 helps to maintain fluid resorption by the ductal epithelium and the inhibition or stimulation of this activity in rodent species will lead to fluid accumulation in the lumen. If not resolved, the abnormal buildup of fluid in the head of the epididymis and efferent ductules becomes a serious problem for the testis, as it leads to an increase in testis weight, tubular dilation and seminiferous epithelial degeneration, as well as testicular atrophy. The same sequence of pathogenesis occurs if the efferent ductule lumen becomes occluded. This review provides an introduction to the role of estrogen in the male reproductive tract but focuses on the various overlapping mechanisms that could induce efferent ductule dysfunction and fluid backpressure histopathology. Although efferent ductules are difficult to find, their inclusion in routine histological evaluations is recommended, as morphological images of these delicate tubules may be essential for understanding the mechanism of testicular injury, especially if dilations are observed in the rete testis and/or seminiferous tubules.

Signature Lesion:

The rete testis and efferent ductules can appear dilated, as if the lumens were greatly expanded with excess fluid or the accumulation of sperm. Because the efferent ductules resorb most of the fluid arriving from the rete testis lumen, one of two mechanisms is likely to be involved: a) reduced fluid uptake, which has been caused by the disruption in estrogen receptor signaling or associated pathways; or b) an increased rate of fluid resorption, which results in luminal occlusion. Both mechanisms can lead to a temporary increase in testicular weight, tubular dilation and atrophy of the seminiferous tubules.

Differential expression of aromatase, estrogen receptor alpha and 17β-HSD associated with the processes of total testicular regression and recrudescence in the bat Myotis nigricans (Chiroptera: Vespertilionidae)

Despite the worldwide distribution and many unique reproductive adaptations that bats present, many aspects of their reproductive hormonal regulation have not been adequately studied, especially in species that presented patterns of total testicular regression. Thus, this study aimed to evaluate the testicular expression of 17β-HSD type 1, aromatase and ERα in the bat Myotis nigricans, during the four periods of its reproductive cycle. Immunoreactivity for ERα was detected only in the cytoplasm of elongated spermatids and in the nuclei of spermatogonia and Sertoli cells. Expression of aromatase was observed in round and elongated spermatids and in Sertoli and Leydig cells. Immunoreactivity for 17β-HSD was restricted to the cytoplasm of Leydig cells. The three expression patterns varied significantly during the four periods of the reproductive cycle. Expression of ERα and aromatase in spermatids was continuous, while expression of ERα in spermatogonia occurred only in initial types (Ap). Expression of ERα and aromatase in Sertoli cells varied, with expression only in periods of spermatogenetic activities; and the same variation was observed for the expression of aromatase and 17β-HSD in Leydig cells. We, therefore, propose that the processes of total testicular regression and posterior recrudescence suffered by M. nigricans from September to January in the northwest of the São Paulo State of Brazil, are directly regulated by testosterone and estrogen. This occurs via the production of testosterone by 17β-HSD, its conversion into estrogen by aromatase, and activation/deactivation of Sertoli cells' AR and spermatogonia's ERα.

Morphological comparison of the testis and efferent ductules between wild-type and estrogen receptor alpha knockout mice during postnatal development

Estrogen and the estrogen receptor (ER)alpha play an important role in the male reproductive tract and in fertility. Previous studies demonstrated that disruption of ERalpha function resulted in abnormal morphology of the testis and efferent ductules (EDs) of adult mice. However, the effect of a lack of a functional ERalpha during early postnatal development has not been determined. The present study is an evaluation of morphological changes effected by a lack of ERalpha in the male reproductive tract during the postnatal period. Age-equivalent wild-type and ERalpha knockout (alphaERKO) mice at 10, 18, 35 and 60 days of age after birth were used for morphological comparison of the testes and ED. Light microscopic examination of the testes of the alphaERKO mouse revealed a dramatic dilation of the rete testis as early as 10 days of age, premature lumen formation, reduced epithelial height and greatly dilated lumen of seminiferous tubules as early as 18 days of age. The proximal ED of the alphaERKO mouse showed lumen dilation, reduction of epithelial height and a decrease of nuclear height as early as 10 days of age. Similar, but somewhat less severe, morphological abnormalities were observed in the distal ED of the alphaERKO mouse. These results indicate that a lack of functional ERalpha leads to morphological changes of the testis and ED of the early postnatal developing mouse. Based on these observations, we conclude that ERalpha plays an important role in normal development of the testis and ED, not only during adulthood but also during the entire postnatal period and presumably during fetal development.

Neonatal estrogenic effects upon the male rat pituitary: early gonadotrophin attenuation precedes long-term recovery

Neonatal exposure to potent estrogenic compounds can affect multiple components of the male reproductive system causing impaired development of the epithelium and overgrowth of stromal tissue in the epididymis, vas deferens, seminal vesicles, and prostate. However, very little is known about the direct effects of estrogenic compounds on the anterior pituitary gland. In this study we have investigated the effects of neonatal estrogenic exposure upon the anterior pituitary. Both the early- and late-stage effects of exposure to a synthetic estrogenic agent, diethylstilbestrol (DES), upon pituitary gonadotroph cell function were assessed. We administered either a high dose (10 microg) or a low dose (0.1 microg) of DES to male rats during their neonatal period (P2-12). Gonadotroph function, cell number and morphology shortly after DES treatment (P18) and during adulthood (P90) were assessed. At P18 there was a significant decrease in follicle stimulating hormone (FSH) immunoreactivity in the pituitary gonadotroph cells in the high DES dose treated rats compared to control animals. No significant change in luteinizing hormone (LH) was observed at either DES dose. In adulthood (P90), there was no significant difference in FSH or LH gonadotroph immunoreactivity between control rats and any dose of DES-treated rats. Therefore, despite acute and selective ablation of FSH expression the gonadotrophs were able to recover in adulthood, suggesting that perinatal estrogenic exposure was only temporarily deleterious.

Recovery of suppressed male reproduction in mice exposed to progesterone during embryonic development by testosterone

The present study aimed to examine whether transplacental exposure to progesterone caused male reproductive abnormalities and whether the changes can be reversed after testosterone administration. Progesterone was injected to mice on day 1, 3, and 7 of pregnancy. The male pups (F1 generation) were allowed to grow for 50 days and assessed for reproductive performance. Gestational exposure to progesterone (7 mg/kg body weight) resulted in significant body weight gain with a decrease in reproductive tissue indices in mice. Total sperm count, viable sperm, and motile sperm decreased in experimental mice. Hypo-osmotic swelling test revealed that experimental mice sperm membrane integrity was severely altered. The activity levels of testicular steroidogenic marker enzymes (hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase cluster (HSD3B) and hydroxysteroid (17-beta) dehydrogenase 1 (HSD17B)) decreased significantly in mice exposed to progesterone during embryonic development when compared with the controls. The levels of serum testosterone decreased with an increase in serum FSH and LH in mice exposed to progesterone during embryonic development. Prenatal exposure to progesterone caused significant reduction in the number of spermatozoa and increase in the lumen of seminiferous tubule. The experimental mice that cohabited with normal females showed fertility reduction. Administration of testosterone (4.16 mg/kg body weight) on postnatal day 20, 30, and 40 to progesterone-exposed prenates resulted in recovery of progesterone-induced suppressed male reproduction. It is suggested that the impairment of male reproduction in mice exposed to progesterone during embryonic development could be mediated through the inhibition of testosterone production. These results also indicate thatin uteroexposure to progesterone affects male reproduction and that supplementation of testosterone restores the suppressed male reproduction.

Activin A and equine chorionic gonadotropin recover reproductive dysfunction induced by neonatal exposure to an estrogenic endocrine disruptor in adult male mice

We aimed to elucidate the mechanism of action of estrogenic endocrine disruptors and the rescue of reproductive function, particularly the responsiveness of testes to eCG and/or activin A (ACT) after establishing reproductive disorders. Newborn male mice (n = 29) were randomly divided into an untreated group and three treatment groups that received diethylstilbestrol (DES; 100 mug per animal) subcutaneously on Postnatal Day 3 to establish reproductive disorders and daily treatment with PBS (controls: DES + PBS), eCG (eCG group: DES + eCG), or eCG + ACT (eCG + ACT group: DES + eCG + ACT) at 6-8 wk of age prior to mating. After treatment, the controls showed diminished Leydig cells in the testes and thin germ cell layers containing pyknotic germ cells and multinucleated cells. In the eCG and eCG + ACT groups, spermatids and Leydig cells increased markedly. The immunoexpression of androgen receptors in the eCG group and steroidogenic acute regulatory (STAR) protein in the eCG and eCG + ACT groups recovered to approximately the levels in the untreated group; plasma LH and testosterone levels also increased relative to those in the controls. In addition, the cell proliferation index, which is estimated from 5-bromo-2'-deoxyuridine immunoexpression in spermatogonia, increased significantly under eCG treatment, and even more with eCG + ACT. However, the numbers of germ and Leydig cells decreased at 12 wk of age. Thus, ACT and eCG help the testes to recover from the dysfunction induced by neonatal DES administration. Furthermore, the permanent male reproductive disorder induced by neonatal exposure to estrogenic agents may be more likely to result from dysfunction of the hypothalamic-pituitary axis than from dysfunction of the lower reproductive organs.

Adult-only exposure of male rats to a diet of high phytoestrogen content increases apoptosis of meiotic and post-meiotic germ cells

Apoptosis plays a critical role in regulating sperm production. Removal of androgens and gonadotropins, or estrogen administration induces germ cell apoptosis. It is hypothesized that dietary phytoestrogens increase apoptosis of developing germ cells, decreasing sperm production. This study aimed to test this in rats fed a high phytoestrogen diet only during adulthood. Male Wistar rats used in this study were offspring of females maintained on a low phytoestrogen diet prior to conception through to weaning. After weaning, juveniles were fed the same low phytoestrogen diet into adulthood. A cohort of males were transferred to a high phytoestrogen diet for 24 days and subsequently testes were collected from all animals. In the high phytoestrogen fed group, homogenization-resistant sperm counts were significantly decreased, as were epididymal sperm counts. Morphometric analysis determined round and elongated spermatid volumes to be significantly decreased, but seminiferous tubule lumen diameters to be significantly increased. TUNEL analysis determined that apoptosis of spermatocytes and round spermatids was significantly greater in the high phytoestrogen fed rats. Neither plasma gonadotropin concentrations nor testicular testosterone were altered. In conclusion, exposure of the adult male rat to a high phytoestrogen diet disrupts spermatogenesis, increasing germ cell apoptosis. This effect is independent of the hypothalamo–pituitary–testicular axis and is likely due to disruption of estrogen’s actions in the testis.

Defective Reproductive Organ Morphology and Function in Domestic Rooster Embryonically Exposed to o,p′-DDT or Ethynylestradiol1

Environmental pollutants with estrogenic activity have a potential to disrupt estrogen-dependent developmental processes. The objective of this study was to investigate if embryonic exposure to the environmental estrogens o,p'-DDT (1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2,2-trichloroethane; 37, 75, 150 or 300 microg/g egg) and EE2 (17alpha-ethynyl estradiol; 60 ng/g egg) affects the reproductive system in domestic roosters. Following egg injection on Embryonic Day 4, the newly hatched chicks were sexed by cloacal inspection. A skewed phenotypic sex ratio with overrepresentation of chicks deemed as females was observed in the groups exposed to the three highest doses of o,p'-DDT but not in the EE2-exposed group. Normal sex ratios were observed in all groups at adulthood. However, a cloacal deformation seemed to remain in the adult roosters, causing an abnormal semen flow upon semen collection. Semen yield was significantly reduced in both o,p'-DDT-exposed and EE2- exposed birds, whereas semen quality was unaffected. When killed, deformations of the left testis were found in all treatment groups. Image analysis revealed a reduced seminiferous tubular area in the roosters exposed to the two highest doses of o,p'-DDT. Embryonic exposure to o,p'-DDT caused decreased comb weight and right-spur diameter, while EE2 only affected right-spur diameter. In conclusion, this study shows that embryonic exposure to estrogenic compounds can induce permanent effects in male birds. The effects of the two studied compounds were partly similar but o,p'-DDT also induced alterations not seen in the EE2-treated birds.

The antiestrogen ICI 182,780 induces early effects on the adult male mouse reproductive tract and long-term decreased fertility without testicular atrophy

BACKGROUND

Estrogen receptors (ER) have important physiological roles in both the female and male reproductive systems. Previous studies using the estrogen receptor-alpha knockout mouse (alphaERKO) or antiestrogen treatment in adult rodents have shown that ERalpha is essential for normal function of the male reproductive tract. In the present study, time-response effects of the antiestrogen ICI 182,780 were determined to better understand ERalpha function in the adult male.

METHODS

Adult male mice, 30 days old, were injected subcutaneously with ICI 182,780 (5 mg) once per week for 17 weeks. Tissues were fixed by vascular perfusion to study the time responses from day 2 to 125 post treatment.

RESULTS

No difference was seen in body weight due to treatment. Testis weight was decreased 18% on day 59 and 21.4% on day 125. Other significant treatment-related effects included the following: 1) dilation of rete testis and efferent ductule lumen; 2) decreased height of the rete testis and efferent ductule epithelium; 3) decreased height of the supranuclear epithelial cytoplasm in efferent ductules; 4) decreased height of the efferent ductule epithelial microvilli, particularly in the proximal ductules; 5) decrease in the PAS-positive granules and endocytotic vesicles in nonciliated epithelial cells of efferent ductules; 6) capping and vesiculation of narrow cells in the initial segment of the epididymis; 7) accumulation of PAS-positive granules in apical cells of the caput epididymis; 8) increase in lysosomal granules in clear cells of the corpus and cauda epididymis; 9) limited induction of atrophic seminiferous tubules and abnormal spermatogenesis; and 10) decreases in the concentration of cauda sperm, progressive sperm motility and decreased fertility.

CONCLUSIONS

Antiestrogen treatment of the pubertal male mouse resulted in reproductive effects similar to those observed in the alphaERKO mouse as early as day 4; however, testis weight did not increase substantially and total atrophy was not observed with extended treatment.

Neonatal coadministration of testosterone with diethylstilbestrol prevents diethylstilbestrol induction of most reproductive tract abnormalities in male rats

The primary purpose of this study was to evaluate whether the coadministration of testosterone (TE; 200 micro g) with 10 micro g of diethylstilbestrol (DES) between days 2 and 12 postnatally could prevent the adverse gross reproductive tract changes and associated loss of androgen receptor (AR) expression induced by DES treatment alone. Various endpoints (rete testis area, efferent duct lumen area, epithelial cell height of efferent ducts, and vas deferens) were quantified to check for the abnormal changes that have been shown to occur after neonatal treatment with a high dose (10 micro g) of DES. Additionally, DES induction of an aberrant pattern of estrogen receptor alpha (ER-alpha) immunoexpression in the vas deferens and seminal vesicles was evaluated. The coadministration of DES with TE prevented the induction of all but one of the abnormalities induced by DES treatment on its own, coincident with the restoration of normal/supranormal TE levels and normal immunoexpression of the AR and ER-alpha in the tissues studied. The exception was DES-induced lumenal distension of the efferent ducts, which was only partially prevented by the coadministration of DES with TE. These evaluations were made on day 18, but the described abnormalities were already somewhat evident by day 8 in DES-treated animals. It was therefore tested whether a delay of TE replacement until days 8-12 was still able to reverse the abnormalities already induced by DES treatment alone. A delayed treatment with TE reversed the adverse changes in epithelial cell height and in ER-alpha and AR immunoexpression in the same tissues by day 18; however, rete testis overgrowth was only partially prevented, and efferent duct distension was not prevented at all. These results provide further evidence that DES-induced disorders of reproductive tract development in the male result from a disturbance of the androgen-estrogen balance rather than from estrogen action alone.

Neonatal estrogen exposure of male rats alters reproductive functions at adulthood

The effects of neonatal exposure to different doses of diethylstilbestrol (DES) on the reproductive functions of male rats at adulthood were evaluated. Sprague-Dawley rats (5-8/group) received sc injections of 25 microl olive oil containing DES (Sigma Chemical Co., St. Louis, MO) at a dose of 10 microg, 1 microg, 100 ng, 10 ng, or 1 ng per rat on alternate days from Postnatal Days 2-12. Control animals received olive oil only. All animals were allowed to develop until 83-91 days of age; however, when they were 70 to 80 days old, four male rats each from the 10 microg, 1 microg, 100 ng, and control groups were cohabited with untreated 60- to 70-day-old females (1:1) for 12 days. At the end of cohabitation, both mated and unmated male rats were weighed, and blood and tissue samples were collected and processed. Results revealed that although sperm motility patterns and sperm morphology were adversely affected in the 10- microg group, other reproductive parameters, including 1). daily sperm production (DSP)/testis; 2). absolute and relative weights of the testis, epididymis, and seminal vesicle; and 3). sperm numbers in both regions of the epididymis declined significantly in a dose-dependent manner in the 10- and 1- microg groups. Conversely, in the <1- microg groups, none of these parameters (except DSP/testis and weight of the epididymis in the 100-ng group, and sperm numbers in the epididymis of the 100- and 10-ng groups) was different from controls. Generally, plasma testosterone levels decreased in the 10- and 1- microg groups, FSH level increased in the 10-microg group, and prolactin and LH levels were unaltered. In the fertility study, although each male in the 1-microg, 100-ng, and control groups produced a copulatory plug and impregnated a female, none could do so in the 10-microg group. The mean number of pups per litter was reduced to eight in the 1-microg group, in contrast to 15 each in the 100-ng and control groups. In conclusion, exposure of neonatal male rats to DES altered sperm motility patterns, sperm fertility (as evident from the reduced number of pups in the 1-microg group), and sexual behavior (as evident from the absence of copulatory plugs in the 10-microg group) and reduced weights of reproductive organs, DSP/testis, and sperm numbers in the epididymis. Whether these alterations/reductions persist in older rats (6-8 mo of age) is under investigation.

Intrauterine bisphenol A exposure leads to stimulatory effects on Sertoli cell number in rats

Using the optical disector for quantifying cell numbers, we investigated whether oral treatment of rats on days 6-21 of gestation with the weakly estrogenic bisphenol A (BPA, 0.1 or 50 mg/kg) or the highly estrogenic ethinyl estradiol (EE, 0.02 mg/kg) alters testicular histology, in those offspring 9-12 month of age. Since production of male germ cells depends on Sertoli cell number, possible changes in that parameter were investigated using unbiased stereology. Spermatogenesis was qualitatively normal in all groups. BPA increases Sertoli cell number per organ but not when expressed as per gram testis. EE did not affect cell number per organ but did affect numbers on a per gram testis basis due to a lowered testis weight. In contrast to the lowering of Sertoli cell numbers that might have been expected according to the estrogen hypothesis, intrauterine administration of these xenoestrogens in fact resulted in minor increases in Sertoli cell numbers and had no qualitative effect on spermatogenesis.

Development of the blood-testis barrier in the mouse is delayed by neonatally administered diethylstilbestrol but not by beta-estradiol 3-benzoate

A group of newborn mice were treated with 1 micro g dose-1 individual-1 of diethylstilbestrol (DES) on alternate days, from days 1 to 11 postnatally. Another group of mice were treated similarly with 125 ng dose-1 individual-1 of beta-estradiol 3-benzoate (E2B). The testes were sequentially examined up to 84 days of age using light and electron microscopy. Spermatogenic cells in the DES-treated mice differentiated normally from birth until 17 days of age, when they differentiated into pachytene spermatocytes and remained at this meiotic prophase for the next 10 days approximately. The cells then began to differentiate further, ultimately forming spermatozoa by 49 days of age. Confocal and electron microscopy showed that the blood-testis barrier did not form until 28 days of age in the DES-treated mice, and a delay in the functional maturation of this structure, as the blood-testis barrier, was confirmed by intercellular tracer experiments. The arrest of spermatogenesis at the meiotic prophase may have been attributable to the DES-induced defective formation of the blood-testis barrier. No delay of the blood-testis barrier formation was detected in the E2B-treated mice. Thus, DES and E2B, both of which are known as potent oestrogenic compounds, had different effects on the Sertoli cells.

Decreased sperm number and motile activity on the F1 offspring maternally exposed to butyl p-hydroxybenzoic acid (butyl paraben)

Butyl p-hydroxybenzoic acid (butyl paraben, BP) is widely used as a preservative in food and cosmetic products. Routledge et al showed that BP is weakly estrogenic in both in vitro and in vivo (rat uterotrophic) analyses. We investigated whether maternal exposures to BP during gestation and lactation periods affected the development of the reproductive organs of the F1 offspring. Pregnant Sprague-Dawley rats were injected subcutaneously with 100 or 200 mg/kg of BP from gestation day (GD) 6 to postnatal day (PND) 20. In the group exposed to 200 mg/kg of BP, the proportion of pups born alive and the proportion of pups surviving to weaning were decreased. The body weights of female offspring were significantly decreased at PND 49. The weights of testes, seminal vesicles and prostate glands were significantly decreased in rats exposed to 100 mg/kg of BP on PND 49. In contrast, the weights of female reproductive organs were not affected by BP. The sperm count and the sperm motile activity in the epididymis were significantly decreased at doses of 100 and 200 mg/kg of BP. In accordance with the sperm count in the epididymis, the number of round spermatids and elongated spermatids in the seminiferous tubule (stage VII) were significantly decreased by BP. Testicular expression of estrogen receptor (ER)-alpha and ER-beta mRNA was significantly increased in 200 mg/kg of BP treated group at PND 90. Taken together, these results indicated that maternal exposure of BP might have adverse effects on the F1 male offspring.

Neonatal low- and high-dose exposure to estradiol benzoate in the male rat: II. Effects on male puberty and the reproductive tract

Environmental contaminants with estrogenic properties have been cause for heightened concern about their possible role in inducing adverse health effects. Brief exposure of rodents to high doses of natural estrogens early in life results in permanent alterations of the male reproductive tissues, but the question of whether environmentally relevant doses can cause the same effects remains controversial. The current project was designed to determine the dose-response relationship between neonatal estradiol exposure and the development of the male reproductive tract in the rat. Neonatal male Sprague-Dawley (SD) and Fisher 344 (F344) rats were exposed to beta-estradiol-3-benzoate (EB) at concentrations ranging from 0.015 microg/kg body weight (BW) to 15.0 mg/kg BW and 0.15 microg/kg BW to 1.5 mg/kg BW, respectively. Results showed an inverted U-shaped dose-response profile for testis and epididymis weights in 35-day-old SD rats, with increased organ sizes at the low-dose end of the treatment. This effect was transient and was not sustained into adulthood. Increased hepatic testosterone hydroxylase activities in low-dose animals suggest an advancement of puberty as the cause for increased reproductive organ weights. On postnatal day (PND) 90, a stimulatory low-dose response to EB was present in SD rat testicular and epididymal weights, however at one order of magnitude lower dose than that seen on PND 35, suggesting a separate effect. All SD male reproductive tract organs and serum hormones showed a permanent inhibitory response to high doses of neonatal EB. F344 rats exhibited greater estrogen sensitivity on PND 90. Despite this heightened responsiveness, F344 rats did not exhibit a low-dose effect for any endpoint. These low-dose responses to estradiol are organ and strain specific.

Mechanisms of estrogen action

Our appreciation of the physiological functions of estrogens and the mechanisms through which estrogens bring about these functions has changed during the past decade. Just as transgenic mice were produced in which estrogen receptors had been inactivated and we thought that we were about to understand the role of estrogen receptors in physiology and pathology, it was found that there was not one but two distinct and functional estrogen receptors, now called ER alpha and ER beta. Transgenic mice in which each of the receptors or both the receptors are inactive have revealed a much broader role for estrogens in the body than was previously thought. This decade also saw the description of a male patient who had no functional ER alpha and whose continued bone growth clearly revealed an important function of estrogen in men. The importance of estrogen in both males and females was also demonstrated in the laboratory in transgenic mice in which the aromatase gene was inactivated. Finally, crystal structures of the estrogen receptors with agonists and antagonists have revealed much about how ligand binding influences receptor conformation and how this conformation influences interaction of the receptor with coactivators or corepressors and hence determines cellular response to ligands.

Estrogen and spermatogenesis

Although it has been known for many years that estrogen administration has deleterious effects on male fertility, data from transgenic mice deficient in estrogen receptors or aromatase point to an essential physiological role for estrogen in male fertility. This review summarizes the current knowledge on the localization of estrogen receptors and aromatase in the testis in an effort to understand the likely sites of estrogen action. The review also discusses the many studies that have used models employing the administration of estrogenic substances to show that male fertility is responsive to estrogen, thus providing a mechanism by which inappropriate exposure to estrogenic substances may cause adverse effects on spermatogenesis and male fertility. The reproductive phenotypes of mice deficient in estrogen receptors alpha and/or beta and aromatase are also compared to evaluate the physiological role of estrogen in male fertility. The review focuses on the effects of estrogen administration or deprivation, primarily in rodents, on the hypothalamo-pituitary-testis axis, testicular function (including Leydig cell, Sertoli cell, and germ cell development and function), and in the development and function of the efferent ductules and epididymis. The requirement for estrogen in normal male sexual behavior is also reviewed, along with the somewhat limited data on the fertility of men who lack either the capacity to produce or respond to estrogen. This review highlights the ability of exogenous estrogen exposure to perturb spermatogenesis and male fertility, as well as the emerging physiological role of estrogens in male fertility, suggesting that, in this local context, estrogenic substances should also be considered "male hormones."

Effects of neonatal exposure to a high-dose p-tert-octylphenol on the male reproductive tract in rats

Time-course alterations in morphological changes of the reproductive tract including spermatogenesis as well as pituitary and gonadal hormones, reproductive ability, and the size of the sexually dimorphic nucleus of the preoptic area (SDN-POA) were investigated in male rats neonatally exposed to 100 mg/kg p-tert-octylphenol (OP) subcutaneously. OP treatment affected hormone levels of follicle stimulating hormone (FSH) and testosterone, reproductive organ weights and sperm counts. Slightly depressed FSH levels at prepuberty and prolonged suppression of testosterone till 7 weeks of age were observed as two hormonal alterations. The lasting reduction in testosterone appeared to be associated with growth inhibition of male reproductive organs such as the testis, prostate and epididymis, these demonstrating low organ weights compared with those of age-matched controls till 7 weeks of age. The FSH concentrations after puberty showed a rise to values equal to or higher than those of the control group, suggesting recovery of maturation of the reproductive tract. No morphological abnormalities, even with morphometric stage analysis of spermatogenesis, were detected in the male reproductive tract throughout the study. Size of the SDN-POA and reproductive ability was comparable to those in controls. At the termination (18 weeks of age), however, a reduction in the sperm count in the epididymis of OP-treated animals demonstrated a possibility that the male reproductive system might be still affected by neonatal exposure to OP. The results observed demonstrate that neonatal exposure to a high-dose OP exerts estrogenic action directly or indirectly, resulting in slight but prolonged impairment of the male reproductive tract. The suppression of FSH caused by modulation of the hypothalamus-pituitary control system may be the trigger for the impairment, while the possibility of direct estrogenic action of OP is not ruled out. Our results also indicate that more sensitive endpoints should be established to detect the effects of neonatal exposure to estrogens or estrogenic compounds on the male reproductive tract.

Suppression of spermatogenesis for cell transplantation in adult mice

Spermatogenesis occurs within the testis of adult males by a complex and very well organized process. Breakthroughs in techniques such as cryopreservation and culture of spermatogenic cells and the maturation of these cells in exogenous testes after transplantation renewed the interest in this process. Transplantation of spermatogenic cells from a donor to a recipient animal needs a preparatory step that consists in the elimination of the endogenous population of spermatogenic cells. The most common method used to empty the seminiferous tubules is the treatment with busulfan (1,4-butanediol dimethanesulfonate). Busulfan partially eliminates stem cells because of its alkylating nature, but a residual component of stem cells survives the treatment and competes in the regeneration of the testis with transplanted cells. Estradiol has also been used as an agent that causes a delay in the process of spermatogenesis by altering its hormonal stimulation, although it does not affect the spermatogonia population. Therefore, we have tested different treatments with busulfan, estradiol benzoate, and also an agonist of the chorionic gonadotrophin-releasing hormone, leuprolide acetate, for the inhibition of endogenous spermatogenesis. We have found that a combination of estradiol, busulfan, and leuprolide can destroy the population of endogenous spermatogenic cells without altering Sertoli cells and maintains the optimal environment needed to allow the development of transplanted cells.

Comparative effects of neonatal exposure of male rats to potent and weak (environmental) estrogens on spermatogenesis at puberty and the relationship to adult testis size and fertility: evidence for stimulatory effects of low estrogen levels

This study investigated whether neonatal exposure of male rats to estrogenic compounds altered pubertal spermatogenesis (days 18 and 25) and whether the changes observed resulted in long-term changes in testis size, mating, or fertility (days 90-100). Rats were treated neonatally with a range of doses (0.01-10 microg) of diethylstilbestrol (DES; administered on alternate days from days 2-12), a high dose of octylphenol (OP; 2 mg administered daily from days 2-12) or bisphenol A (Bis-A; 0.5 mg administered daily from days 2-12), or vehicle, while maintained on a standard soy-containing diet. The effect on the same parameters of rearing control animals on a soy-free diet was also assessed as was the effect of administering such animals genistein (4 mg/kg/day daily from days 2-18). Testis weight, seminiferous tubule lumen formation, the germ cell apoptotic index (apoptotic/viable germ cell nuclear volume), and spermatocyte nuclear volume per unit Sertoli cell nuclear volume were used to characterize pubertal spermatogenesis. Compared with (soy-fed) controls, DES administration caused dose-dependent retardation of pubertal spermatogenesis on day 18, as evidenced by decreases in testis weight, lumen formation, and spermatocyte nuclear volume per unit Sertoli cell and elevation of the germ cell apoptotic index. However, the two lowest doses of DES (0.1 and 0.01 microg) significantly increased spermatocyte nuclear volume per unit Sertoli cell. Similarly, treatment with either OP or Bis-A significantly advanced this and some of the other aspects of pubertal spermatogenesis. Maintenance of control animals on a soy-free diet also significantly advanced lumen formation and spermatocyte nuclear volume per unit Sertoli cell compared with controls fed a soy-containing diet. Administration of genistein reversed the stimulatory effects of a soy-free diet and significantly retarded most measures of pubertal spermatogenesis. In general, plasma FSH levels in the treatment groups changed in parallel to the spermatogenic changes (reduced when pubertal spermatogenesis retarded, increased when pubertal spermatogenesis advanced). By day 25, although the changes in FSH levels largely persisted, all of the stimulatory effects on spermatogenesis seen on day 18 in the various treatment groups were no longer evident. In adulthood, testis weight was decreased dose dependently in rats treated neonatally with DES, but only the lowest dose group (0.01 microg) showed evidence of mating (3 of 6) and normal fertility (3 litters). Animals treated neonatally with OP or Bis-A had normal or increased (Bis-A) testis weights and exhibited reasonably normal mating/fertility. Animals fed a soy-free diet had significantly larger testes than controls fed a soy-containing diet, and this difference was confirmed in a much larger study of more than 24 litters, which also showed a significant decrease in plasma FSH levels and a significant increase in body weight in the males kept on a soy-free diet. Neonatal treatment with genistein did not alter adult testis weight, and although most males exhibited normal mating and fertility, a minority did not mate or were infertile. It is concluded that 1) neonatal exposure of rats to low levels of estrogens can advance the first wave of spermatogenesis at puberty, although it is unclear whether this is due to direct effects of the estrogen or to associated elevation of FSH levels; 2) the effect of high doses of OP and Bis-A on these processes is essentially benign; and 3) the presence or absence of soy or genistein in the diet has significant short-term (pubertal spermatogenesis) and long-term (body weight, testis size, FSH levels, and possibly mating) effects on males.

Permanent effects of neonatal estrogen exposure in rats on reproductive hormone levels, Sertoli cell number, and the efficiency of spermatogenesis in adulthood

This study aimed to identify the mechanism(s) for impairment of spermatogenesis in adulthood in rats treated neonatally with estrogens. Rats were treated (days 2-12) with 10, 1, or 0.1 microg diethylstilbestrol (DES), 10 microg ethinyl estradiol (EE), 10 mg/kg of a GnRH antagonist (GnRHa), or vehicle and killed in adulthood. DES/EE caused dose-dependent reductions in testis weight, total germ cell volume per testis, and Sertoli cell volume per testis. Sertoli cell number at 18 days of age in DES-treated rats was reduced dose dependently. GnRHa treatment caused changes in these parameters similar to those in rats treated with 10 microg DES. Plasma FSH levels were elevated (P < 0.001) to similar levels in all treatment groups regardless of differences in Sertoli cell number and levels of inhibin B; the latter reflected Sertoli cell number, but levels were disproportionately reduced in animals treated with high doses of DES/EE. Neonatal estrogen treatment, but not GnRHa, caused dose-dependent reductions (40-80%) in plasma testosterone levels in adulthood, but did not alter LH levels. Preliminary evidence suggests that the decrease in testosterone levels in estrogen-treated rats is not due to reduced Leydig cell volume per testis. GnRHa-treated rats exhibited a significant increase in germ cell volume per Sertoli cell and a reduction in germ cell apoptosis, probably because of the raised FSH levels. Despite similar raised FSH levels, rats treated with DES (10 or 1 microg) or EE (10 microg) had reduced germ cell volume/Sertoli cell and increased germ cell apoptosis, especially when compared with GnRHa-treated animals. The latter changes were associated with an increase in lumen size per testis, indicative of impaired fluid resorption from the efferent ducts, resulting in fluid accumulation in the testis. Rats treated neonatally with 0.1 microg DES showed reduced germ cell apoptosis comparable to that in GnRHa-treated animals. The changes in apoptotic rate among treatment groups occurred across all stages of the spermatogenic cycle. It is concluded that 1) neonatal estrogen treatment results in dose-dependent alterations in Sertoli cell numbers, germ cell volume, efficiency of spermatogenesis, and germ cell apoptosis in adulthood; 2) the relatively poor spermatogenesis in estrogen-treated animals is most likely due to altered testis fluid dynamics and/or altered Sertoli cell function; 3) as indicated by FSH (LH) and testosterone levels, the hypothalamic-pituitary axis and Leydig cells are probably more sensitive than the Sertoli cells to reprogramming by estrogens neonatally; and 4) elevated FSH levels in adulthood may improve the efficiency of spermatogenesis.

'Paracrine' control of spermatogenesis

Spermatogenesis is a remarkably complex but precise process yielding highly differentiated haploid germ cells from diploid stem cells. Although many factors have been implicated in the paracrine control of spermatogenesis, functional proof is only available for a few regulators. Among those are androgens, growth factors and stem cell factor. Cell- and organ-specific genetargeting will provide important insights into the relevance of local factors controlling male gametogenesis. As testicular communication frequently occurs between rather remote cells and compartments, it is proposed that the term 'local' rather than 'paracrine' mediators/factors should be used, since the latter term refers to communication amongst neighbouring cells (and mainly via diffusion).