Reduced Sperm Production Research Articles

Male age influences the pregnancy rates on ICSI cycles with epididymal spermatozoa

Aging influence over female fertility has been shown by many epidemiological studies, but less is know about male. However, sperm DNA fragmentation increases with age, and male age constitute an important risk factor for conceiving failure by assisted reproduction. Intracytoplasmic sperm injection (ICSI) allows men with reduced sperm production to reproduce. Patients with obstructive azoospermia can also be benefited as percutaneous epididymal sperm aspiration (PESA). Men who underwent vasectomy are a suitable model for studying age effect, as spermatogenesis is usually preserved.

Adverse Effects of 5-Aza-2′-Deoxycytidine on Spermatogenesis Include Reduced Sperm Function and Selective Inhibition of de Novo DNA Methylation

The anticancer agent, 5-aza-2'-deoxycytidine (5-azaCdR, decitabine), causes DNA hypomethylation and a robust, dose-dependent disruption of spermatogenesis. Previously, we have shown that altered testicular histology and reduced sperm production in 5-azaCdR-treated animals is associated with decreased global sperm DNA methylation and an increase in infertility and/or a decreased ability to support preimplantation embryonic development. The goal of this study was to determine potential contributors to 5-azaCdR-mediated infertility including alterations in sperm motility, fertilization ability, early embryo development, and sequence-specific DNA methylation. We find that although 5-azaCdR-treatment adversely affected sperm motility and the survival of sired embryos to the blastocyst stage, the major contributor to infertility was a marked (56-70%) decrease in fertilization ability. Sperm DNA methylation was investigated using Southern blot, restriction landmark genomic scanning, and quantitative analysis of DNA methylation by real-time polymerase chain reaction. Interestingly, hypomethylation was restricted to genomic loci that have been previously determined to acquire methylation during spermatogenesis, demonstrating that 5-azaCdR selectively inhibits de novo methylation activity. Similar to previous studies, we show that mice that are heterozygous for a nonfunctional Dnmt1 gene are partially protected against the deleterious effects of 5-azaCdR; however, methylation levels are not restored in these mice, suggesting that adverse effects are due to another mechanism(s) in addition to DNA hypomethylation. These results demonstrate that clinically relevant doses of 5-azaCdR specifically impair de novo methylation activity in male germ cells; however, genotype-specific differences in drug responses suggest that adverse reproductive outcomes are mainly mediated by the cytotoxic properties of the drug.

Diesel exhaust particles disturb gene expression in mouse testis

Inhalation of diesel exhaust particles (DEP) has been found to reduce sperm production. There is a possibility that DEP exposure elicits changes in gene expression in testis. To identify the alteration of gene expression resulting from DEP exposure, we constructed subtracted cDNA libraries from mouse testis using the suppression subtractive hybridization method. We isolated 16 candidate clones whose expression levels changed after exposure. Some of these candidates were highly similar to known testis-specific genes. Some of the clones also seemed to correlate with spermatogenesis. Northern blot analysis revealed that DEP exposure changed the expression levels of several clones in a dose-dependent manner. For example, the expression of clone R8, which was very similar to human XRRA1, increased by 2.3-fold in testis after DEP exposure. On the other hand, the expressions of long-chain acyl-CoA synthetase 6 (Acsl6) and serine/threonine kinase 35 reduced by 0.3-fold. These results indicated that some constituents of DEP alter gene expression in the testis.

Influence of endocrine disruptors on human male fertility

It has been suggested that during the past five decades human sperm counts have declined and the incidence of testicular cancer, hypospadias and cryptorchidism has increased. Furthermore, geographical differences, with respect to these markers of male reproductive function, have been reported. According to a recent hypothesis, all these abnormalities of the male genital system do have a common cause, namely exposure to endocrine disruptors affecting the male in early fetal life. Reduced sperm production as well as congenital abnormalities of male genitalia can be evoked in laboratory animals by exposing them to chemicals with endocrine-disrupting effect, and in humans similar effects have been seen following accidental exposures to very high concentrations of these environmental toxicants. However, the evidence for association between levels of exposure found in the general population and serious adverse effects on male reproduction, including fertility, is still lacking. A recent European Union-supported study, on the effect of persistent organohalogen pollutants on human reproduction, failed to show any correlation between post-natal exposure levels and fertility. Future studies will reveal whether prenatal exposure does more strongly affect male fertility and whether genetic predisposition regulates the susceptibility of an individual to the adverse effects of endocrine disruptors.

Increased male mating rate in Drosophila is associated with Wolbachia infection

The maternally inherited bacterium Wolbachia pipientis infects 25-75% of arthropods and manipulates host reproduction to improve its transmission. One way Wolbachia achieves this is by inducing cytoplasmic incompatibility (CI), where crosses between infected males and uninfected females are inviable. Infected males suffer reduced fertility through CI and reduced sperm production. However, Wolbachia induce lower levels of CI in nonvirgin males. We examined the impact of Wolbachia on mating behaviour in male Drosophila melanogaster and D. simulans, which display varying levels of CI, and show that infected males mate at a higher rate than uninfected males in both species. This may serve to increase the spread of Wolbachia, or alternatively, may be a behavioural adaptation employed by males to reduce the level of CI. Mating at high rate restores reproductive compatibility with uninfected females resulting in higher male reproductive success thus promoting male promiscuity. Increased male mating rates also have implications for the transmission of Wolbachia.

Testicular maturation of Oligosarcus hepsetus (Cuvier) (Actinopterygii, Characidae) in a brazilian tropical reservoir

Six reproductive classes of male Oligosarcus hepsetus (Cuvier, 1829), a medium-sized carnivorous Characiform species, are described based on macroscopic and histological techniques. A total of 175 individuals were caught monthly between April 2001 and June 2002 in the Lajes Reservoir, Brazil, one of the largest impoundment areas in the state of Rio de Janeiro. The reproductive classes were based upon changes in the testicular morphology and stages of germinative cells, i.e., resting, early maturing, late maturing, mature, partially spent and totally spent. Fish in the resting class showed testes with spermatogonia and spermatocytes along the wall of seminal lobules, while spermatids were present in the lumina of the lobules. During early maturing, active spermatogenesis occurs throughout the testis; in the late maturing and mature classes, the lobules are swollen with sperm that are typical of fish in breeding condition. Spent testes presented seminal lobules with residual spermatozoa, coinciding with decreasing GSI and greatly reduced sperm production. Overall, the testicular morphology and class of maturity development of O. hepsetus in the Lajes reservoir did not differ significantly from those of closely related species in other lentic environments. Lower GSI values in the oligotrophic Lajes reservoir than in other eutrophic natural lakes suggest that this species may be modifying this aspect of its reproductive strategy in response to the artificial environment.

Rhox: A New Homeobox Gene Cluster

Homeobox genes encode transcription factors notable for their ability to regulate embryogenesis. Here, we report the discovery of a cluster of 12 related homeobox genes on the X chromosome expressed in male and female reproductive tissues in adult mice. These reproductive homeobox on the X chromosome (Rhox) genes are expressed in a cell type-specific manner; several are hormonally regulated, and their expression pattern during postnatal testis development corresponds to their chromosomal position. Most of the Rhox genes are expressed in Sertoli cells, the nurse cells in direct contact with developing male germ cells, suggesting that they regulate the expression of somatic-cell gene products critical for germ cell development. In support of this, targeted disruption of Rhox5 increased male germ cell apoptosis and reduced sperm production, sperm motility, and fertility. Identification of this family of homeobox genes provides an opportunity to study colinear gene regulation and the transcriptional control of reproduction.

Collaboration of homologous recombination and nonhomologous end-joining factors for the survival and integrity of mice and cells.

Homologous recombination (HR) and nonhomologous end-joining (NHEJ) are mechanistically distinct DNA repair pathways that contribute substantially to double-strand break (DSB) repair in mammalian cells. We have combined mutations in factors from both repair pathways, the HR protein Rad54 and the DNA-end-binding factor Ku80, which has a role in NHEJ. Rad54(-/-)Ku80(-/-) mice were severely compromised in their survival, such that fewer double mutants were born than expected, and only a small proportion of those born reached adulthood. However, double-mutant mice died at lower frequency from tumors than Ku80 single mutant mice, likely as a result of rapid demise at a young age from other causes. When challenged with an exogenous DNA damaging agent, ionizing radiation, double-mutant mice were exquisitely sensitive to low doses. Tissues and cells from double-mutant mice also showed indications of spontaneous DNA damage. Testes from some Rad54(-/-)Ku80(-/-) mice displayed enhanced apoptosis and reduced sperm production, and embryonic fibroblasts from Rad54(-/-)Ku80(-/-) animals accumulated foci of gamma-H2AX, a marker for DSBs. The substantially increased DNA damage response in the double mutants implies a cooperation of the two DSB repair pathways for survival and genomic integrity in the animal.

Follow-up study of adolescents exposed to di(2-ethylhexyl) phthalate (DEHP) as neonates on extracorporeal membrane oxygenation (ECMO) support.

Di(2-ethylhexyl) phthalate (DEHP) is used to make polyvinyl chloride (PVC) plastic tubing soft and flexible. Animal data show that adverse effects of DEHP exposure may include reduced fertility, reduced sperm production in males, and ovarian dysfunction in females. Known treatments that involve high DEHP exposures are blood exchange transfusions, extracorporeal membrane oxygenation (ECMO), and cardiovascular surgery. Although potential exposure to DEHP in ECMO patients is significant, the exposure has not been associated with short-term toxicity. To evaluate long-term toxicity, we undertook a study of neonatal ECMO survivors to assess their onset of puberty and sexual maturity. We evaluated 13 male and 6 female subjects at 14–16 years of age who had undergone ECMO as neonates. All subjects had a complete physical examination including measurements for height, weight, head circumference, and pubertal assessment by Tanner staging. The testicular volume and the phallic length were measured in male participants. Laboratory tests included thyroid, liver, and renal function as well as measurements of luteinizing hormone, follicle-stimulating hormone, testosterone for males, and estradiol for females. Except for one patient with Marfan syndrome, the rest had normal growth percentile for age and sex. All had normal values for thyroid, liver, and renal functions. Sexual hormones were appropriate for the stage of pubertal maturity. Our results indicate that adolescents exposed to significant quantities of DEHP as neonates showed no significant adverse effects on their physical growth and pubertal maturity. Thyroid, liver, renal, and male and female gonadal functions tested were within normal range for age and sex distribution.

Cyclin A1 protein shows haplo-insufficiency for normal fertility in male mice.

In higher eukaryotes, the cyclins constitute a family of proteins involved in progression through the cell cycle. The cyclin A1 gene (Ccna1) is expressed during meiosis and is required for spermatogenesis. Targeted disruption of the Ccna1 gene with a LacZ reporter gene has allowed us to study the expression pattern of this gene in more detail. We have confirmed expression in mouse pre-meiotic spermatocytes and also detected expression in the accessory olfactory bulb, hippocampus and amygdala of the adult brain. We have also found that the amount of cyclin A1 protein influences the fertility of male mice and its action is modulated by genetic background. On an outbred genetic background (129S6/SvEv x MF1), Ccna1 (tm1Col) -/- animals are sterile due to spermatogenic arrest prior to the first meiotic division while Ccna1 (tm1Col) +/- mice show reduced sperm production and fertility. This is even more pronounced on an inbred genetic background (129S6/SvEv) where Ccna1 (tm1Col) +/- male mice are sterile due to a severe reduction in the total number of sperm.

Ten‐week exposure to treated sewage discharge has relatively minor, variable effects on reproductive behavior and sperm production in goldfish

It is well established that effluent from many sewage treatment plants (STPs) possesses estrogenic properties; however, the biological significance of this estrogenicity to fish reproductive behavior and sperm production is unknown. This study tested the hypothesis that 10-week exposure to a STP effluent with well-established estrogenic properties compromises the reproductive vigor of mature goldfish by decreasing the intensity of their reproductive drive and sperm production. Male goldfish were exposed for 10 weeks to one of four treatments: well water, a solvent control, 50 ng/L estradiol (E2), or undiluted effluent from a major metropolitan STP. Two trials were conducted, one in the winter and one in the summer when the effluent was chlorinated. Exposure to effluent in both the summer and winter trials induced small, but nonsignificant, decreases in the frequency of male spawning behaviors but had no effect on sperm production. Exposure to E2 caused a clear reduction in spawning behavior in one trial while causing reduced sperm production in both trials. We conclude that the effect of effluent exposure from this STP on adult fish is likely to be relatively minor and that the effluent's estrogenic properties may vary over the course of the year.

Great Lakes' contaminants reduce sperm production and fertilizing ability in mice

The long-term effects of Great Lakes' contaminants on male reproductive performance resulting from lactational and dietary exposure were investigated. Female C57BL/6 J mice (F-0) were mated with DBA/2 J male mice to produce B6D2-F1 offspring. Dams (F-0) were fed one of three treatment diets during lactation. The three treatment diets were: (i) diet C, containing lab chow and fish oil; (ii) diet I, containing 60% Iowa carp and 40% lab chow; and (iii) diet G, containing 60% Great Lakes' carp and 40% lab chow. Diet C served as a lab-chow control treatment, while diet I served as a fish-diet control treatment. Diet G contained 2500 µg of polychlorinated biphenyls (PCBs) and 300 µg of 1,1-dichloro-2,2-bis-[p-chlorophenyl]ethylene (4,4′-DDE) per kilogram of feed. The offspring (F-1) were continued on their respective maternal treatment diets from weaning until termination. Greater neonatal mortality and lesser body weights were observed in the F-1 male mice on diet G. Lesser fecundity was observed in one-year-old F-1 male mice on diet G following pairing with non-treated female mice. The sperm concentration of F-1 male mice on diet G was less than 30% of that of mice on diets C and I. The in vitro fertilizing ability of the sperm decreased to 10% of that of mice on the two control diets. Sperm motility, velocity, linearity and amplitude of lateral head (ALH) displacement were also decreased in 15-month-old F-1 male mice on diet G.

Diurnal scrotal skin temperature and semen quality. The Danish First Pregnancy Planner Study Team.

It is well established that heat is associated with reduced sperm production, but the role of physiological variation in temperature has never been scrutinized in humans. We studied diurnal scrotal temperature and markers of male fertility in a population of couples planning their first pregnancy. Sixty men from a cohort of couples who were planning their first pregnancy were included and scrotal skin temperature was monitored during 3 days using a portable data recorder. Working hours and working postures were recorded daily in a questionnaire. Each man provided a fresh semen sample and the couples were followed for six menstrual cycles or until a clinical pregnancy was recognized. The median value of scrotal skin temperature was 33.3 degrees C in the daytime and 34.8 degrees C at night. In periods of sedentary work, the median temperature was on average 0.7 degrees C higher (SE=0.2 degrees C). In addition, scrotal temperature was higher in the daytime, in summer, and in leisure time compared with working hours. Median sperm concentration among men with more than 75% of their daytime readings above 35 degrees C was 33.4 x 10(6)/mL, compared with 91.8 x 10(6)/mL for men with less than half of their readings above 35 degrees C (difference 58.4; 95% CI: 25.9-77.8 x 10(6)/mL). It is concluded that a sedentary position is a significant source of increased scrotal skin temperature, and even moderate and physiological elevation in scrotal skin temperature is associated with a substantially reduced sperm concentration. Sedentary work should be considered as an important potential confounder for reduced sperm count in epidemiological research.

Allocation to Mate Guarding or Increased Sperm Production in a Mediterranean Wrasse.

An excellent body of literature exists that examines sperm expenditure when males allocate only to sperm production. However, in many species, males can also allocate energy to behaviors that influence sperm competition. We model whether males in sperm competition should allocate energy to mate guarding or additional sperm production. Mate guarding is predicted to lead to greater reproductive success than increased sperm output, and mate-guarding males are not predicted to alter their allocation to sperm production with increasing sperm competition. Only when mate guarding is ineffective or greatly reduces sperm production are males predicted to allocate to sperm production. In a Mediterranean wrasse Symphodus ocellatus, three male alternative reproductive behaviors coexist. While nesting males and satellites guard mates to decrease sperm competition, sneaker males only compete via sperm production. Sneakers produce four times as much sperm per spawn as either nesting males or satellites. As predicted by the model, mate guarding but not sperm production increased with increased risk of sperm competition in nesting males. We argue that this can be explained by nesting males allocating to mate guarding rather than sperm production. Considering allocation among behaviors that affect sperm competition enhances our ability to explain and to predict sperm allocation patterns.

R-166. Molecular diagnosis of Y chromosome deletions in infertile patients with reduced sperm production

R-166. Molecular diagnosis of Y chromosome deletions in infertile patients with reduced sperm production

Short term pretreatment with medroxyprogesterone and testosterone may potentiate irradiation damage to spermatogenesis in rats

BACKGROUND Hormonal treatments lasting 2–6 months inhibit spermatogenesis in men and have been proposed as germ cell protection against anticancer therapy. Because it is unthinkable to delay anticancer treatments, the authors investigated the protection afforded against irradiation of rats by 22 days of hormonal pretreatment. METHODS Adult Sprague–Dawley rats were assigned to an untreated control group (C) or to one of 5 treatments: medroxyprogesterone acetate plus testosterone only (M), 3 or 5 gray of irradiation (R3 and R5), or hormonal treatment prior to 3 or 5 gray of irradiation (MR3 and MR5). Mating trials were conducted 1, 24, 45, 65, 86, and 109 days after treatment. At 122 days, genital organ weights, testis histology, and epididymal spermatozoa were evaluated. RESULTS Irradiation reduced sperm production and had a clastogenic effect on postmeiotic germ cells. No protective effect of steroid treatment was observed. Moreover, testis weight, tubule diameter, the repopulating index, and the sperm head count decreased more in the MR5 group than in the R5 group. Mating tests showed decreases in positive vaginal smears and fertility at both 45 and 65 days, and an increase in resorption at 109 days. CONCLUSIONS These results indicate that hormonal pretreatment potentiates irradiation damage to germ cells, especially stem cells, as regards survival and genomic alterations, probably because of increased lipoperoxidation of late spermatids. Cancer 1999;85:1313–22. © 1999 American Cancer Society.

Short term pretreatment with medroxyprogesterone and testosterone may potentiate irradiation damage to spermatogenesis in rats

Hormonal treatments lasting 2-6 months inhibit spermatogenesis in men and have been proposed as germ cell protection against anticancer therapy. Because it is unthinkable to delay anticancer treatments, the authors investigated the protection afforded against irradiation of rats by 22 days of hormonal pretreatment. Adult Sprague-Dawley rats were assigned to an untreated control group (C) or to one of 5 treatments: medroxyprogesterone acetate plus testosterone only (M), 3 or 5 gray of irradiation (R3 and R5), or hormonal treatment prior to 3 or 5 gray of irradiation (MR3 and MR5). Mating trials were conducted 1, 24, 45, 65, 86, and 109 days after treatment. At 122 days, genital organ weights, testis histology, and epididymal spermatozoa were evaluated. Irradiation reduced sperm production and had a clastogenic effect on postmeiotic germ cells. No protective effect of steroid treatment was observed. Moreover, testis weight, tubule diameter, the repopulating index, and the sperm head count decreased more in the MR5 group than in the R5 group. Mating tests showed decreases in positive vaginal smears and fertility at both 45 and 65 days, and an increase in resorption at 109 days. These results indicate that hormonal pretreatment potentiates irradiation damage to germ cells, especially stem cells, as regards survival and genomic alterations, probably because of increased lipoperoxidation of late spermatids.

Effects of dietary 17 beta-estradiol exposure on serum hormone concentrations and testicular parameters in male Crl:CD BR rats.

A 90-day/one-generation reproduction study was conducted in male and female Crl:CD BR rats using dietary levels of 0, 0.05, 2.5, 10, and 50 ppm 17 beta-estradiol. The goals of this study were to set dose levels and evaluate several mechanistic endpoints for inclusion in multigeneration reproduction and combined chronic toxicity/oncogenicity studies with 17 beta-estradiol. In this report we discuss the effects of dietary 17 beta-estradiol exposure on serum hormonal levels and sperm parameters from P1 and F1 male rats. Sperm parameters were also evaluated in recovery P1 and F1 male rats that were fed control diets for 105 and 103 days, respectively, following 97 and 86-94 days of estradiol exposure, respectively. Measurement of Sertoli cell number from F1 male rats was performed to test the hypothesis that in utero exposure to estrogens will decrease Sertoli cell number and sperm production. Other findings from this 90-day/one-generation reproduction study are summarized elsewhere. 17 beta-Estradiol produced a dose-dependent decrease in body weight in P1 male rats at > or = 2.5 ppm and in the F1 male rats at 2.5 ppm. This decrease in body weight was due to a combination or reduced food consumption and food efficiency. In the recovery P1 males, body weight increased in the affected groups, albiet not to control levels, due to food consumption returning to control levels accompanied by an increase in food efficiency. However, in F1 males there was no corresponding rebound in body weight. In the P1 rats, exposure to 17 beta-estradiol decreased testis and epididymis weights in the 10 and 50 ppm groups, while no effects were seen in the P1 2.5 ppm group. In contrast, epididymis weights in the F1 and F1 recovery 2.5 ppm groups were statistically decreased; however, there were no histopathological effects observed. The decreases in testis weights in the P1 generation correlated with histopathologic evidence of interstitial cell atrophy and seminiferous tubule degeneration and reduced sperm production. Correlative changes in the epididymides of P1 rats were characterized by oligospermia or aspermia, the presence of germ cell debris in the lumen of tubules, and atrophy of epididymal tubules. 17 beta-Estradiol decreased testicular spermatid numbers, epididymal sperm numbers, and sperm motility in the P1 males in the 10 and 50 ppm groups, but not in the 2.5 ppm group. Following a 105-day recovery period in the P1 males, all sperm parameters and reproductive organ weights returned to control values except for the epididymal sperm count. Overall, the decline in testicular spermatid and epididymal sperm numbers in the P1 rats correlated with the reduced organ weights and the observed histopathological changes and appeared primarily related to the decrease in serum testosterone levels. In the F1 rats, no significant decreases were noted in the testicular spermatid number but a slight decrease in epididymal sperm number was seen in the 2.5 ppm group, which showed no evidence of recovery. Using morphometric analysis, no change was seen in the number of Sertoli cell nuclei per testis in F1 males. The pattern of hormonal responses seen in this study was characteristic of an estrogen receptor agonist such as 17 beta-estradiol: increased serum prolactin and decreased testosterone, luteinizing hormone, and follicle stimulating hormone levels. The data demonstrate that in utero and postnatal dietary administration of 17 beta-estradiol at levels which increased serum estradiol levels to approximately 400% of control and decreased testosterone levels to 33% of control did not reduce the number of Sertoli cell nuclei per testis.

REDUCED MALE ALLOCATION IN THE PARTHENOGENETIC HERMAPHRODITE DUGESIA POLYCHROA.

Parthenogenetic lineages that arise in a hermaphroditic, sexual population will inherit the male function from their sexual progenitors. Natural selection then acts to reduce male allocation of the parthenogens, freeing resources presumably for the female function. Depending on age and the available genetic variation, one therefore expects to find reduced male allocation in naturally occurring parthenogenetic lineages. We investigated the allocation to sperm production in the hermaphroditic flatworm Dugesia polychroa in three lakes containing a sexual (S), a (pseudogamous) parthenogenetic (P), and a mixed sexual-parthenogenetic population (M). Parthenogenetic lineages from M were assumed to be relatively young due to recurrent origins from the coexisting sexuals, whereas those from P were assumed to be older on biogeographical grounds. As predicted, we found drastically reduced sperm production in parthenogens compared to sexuals, even in the parthenogenetic lineages from M, which may be younger. M parthenogens did not have more testes, but produced more sperm than individuals from the purely parthenogenetic population (P). However, the latter result could not be reproduced with laboratory-raised animals and therefore may be a consequence of different ecological conditions in the different lakes, for example, differences in mating rates. To study the behavioral component of male allocation, copulation frequencies were recorded for sexuals from M and for parthenogens from P. Compared to the drastic reduction in sperm production, copulation frequency was less reduced in parthenogens. This may be a consequence of allosperm limitation in pseudogamous parthenogenetic populations.

Effects of Dietary 17β-Estradiol Exposure on Serum Hormone Concentrations and Testicular Parameters in Male Crl:CD BR Rats

A 90-day/one-generation reproduction study was conducted in male and female Crl:CD BR rats using dietary levels of 0, 0.05, 2.5, 10, and 50 ppm 17β-estradiol. The goals of this study were to set dose levels and evaluate several mechanistic end- points for inclusion in multigeneration reproduction and com- bined chronic toxicity/oncogenicity studies with 17β-estradiol. In this report we discuss the effects of dietary 17β-estradiol exposure on serum hormonal levels and sperm parameters from P1 and F1 male rats. Sperm parameters were also evaluated in recovery P1 and F1 male rats that were fed control diets for 105 and 103 days, respectively, following 97 and 86–94 days of estradiol exposure, respectively. Measurement of Sertoli cell number from F1 male rats was performed to test the hypothesis that in utero exposure to estrogens will decrease Sertoli cell number and sperm production. Other findings from this 90-day/ one-generation reproduction study are summarized elsewhere. 17β-Estradiol produced a dose-dependent decrease in body weight in P1 male rats at ≥2.5 ppm and in the F1 male rats at 2.5 ppm. This decrease in body weight was due to a combination of reduced food consumption and food efficiency. In the recov- ery P1 males, body weight increased in the affected groups, albiet not to control levels, due to food consumption returning to control levels accompanied by an increase in food efficiency. However, in F1 males there was no corresponding rebound in body weight. In the P1 rats, exposure to 17β-estradiol decreased testis and epididymis weights in the 10 and 50 ppm groups, while no effects were seen in the P1 2.5 ppm group. In contrast, epididymis weights in the F1 and F1 recovery 2.5 ppm groups were statistically decreased; however, there were no histopatho- logical effects observed. The decreases in testis weights in the P, generation correlated with histopathologic evidence of intersti- tial cell atrophy and seminiferous tubule degeneration and reduced sperm production. Correlative changes in the epidid-ymides of P1 rats were characterized by oligospermia or asper-mia, the presence of germ cell debris in the lumen of tubules, and atrophy of epididymal tubules. 17β-Estradiol decreased testicular spermatid numbers, epididymal sperm numbers, and sperm motility in the P1 males in the 10 and 50 ppm groups, but not in the 2.5 ppm group. Following a 105-day recovery period in the P1 males, all sperm parameters and reproductive organ weights returned to control values except for the epididymal sperm count. Overall, the decline in testicular spermatid and epididymal sperm numbers in the P1 rats correlated with the reduced organ weights and the observed histopathological changes and appeared primarily related to the decrease in serum testosterone levels. In the F1 rats, no significant decreases were noted in the testicular spermatid number but a slight decrease in epididymal sperm number was seen in the 2.5 ppm group, which showed no evidence of recovery. Using morphometric analysis, no change was seen in the number of Sertoli cell nuclei per testis in F1 males. The pattern of hormonal responses seen in this study was characteristic of an estrogen receptor agonist such as 17β-estradiol: increased serum prolactin and decreased testosterone, luteinizing hormone, and follicle stimulating hormone levels. The data demonstrate that in utero and postnatal dietary administration of 17β-estradiol at levels which increased serum estradiol levels to approximately 400% of control and decreased testosterone levels to 33% of control did not reduce the number of Sertoli cell nuclei per testis.