www.elsevier.comrlocateranireprosci
Deteriorating trends in male reproduction:
idiopathic or environmental?
D.N. Rao Veeramachaneni
)Animal Reproduction and Biotechnology Laboratory, Department of Physiology, College of Veterinary Medicine and Biomedical Sciences, Colorado State UniÕersity, Fort Collins, CO 80523-1683, USA
Abstract
Recent reports portend deterioration in male reproductive health in several human populations. Similar trends might exist in domestic animals, but data are not available because of the inherent nature of animal husbandry practices — culling of the reproductively inefficient food- and fiber-producing animals at an early age. Although the causes for this deterioration are unknown, a variety of endocrine-mimicking environmental pollutants have been implicated. Data for relevant laboratory animal models exposed to several classes of suspect chemicals indicate that a variety of chemicals ubiquitously present in the environment can disrupt normal reproductive phenomena in the male at exposure rates encountered in nature. Data are presented for occurrence of cryp-torchidism, carcinoma in situ of the testis, acrosomal malformations, and impaired sexual function
Ž .
following in utero andror postnatal exposures to pesticides e.g., DDT and vinclozolin ,
high-Ž .
volume industrial chemicals e.g., alkylphenols and phthalates , and commonly occurring organic
Ž
and inorganic chemical contaminants in drinking water e.g., chemical mixtures and water
.
disinfection byproducts . These observations are discussed in the context of similar, so-called idiopathic conditions encountered in stallions.q2000 Elsevier Science B.V. All rights reserved.
Keywords: Testicular carcinoma in situ; Intratubular germ cell neoplasia; Acrosomal dysgenesis; Sexual
dysfunction; Chemical contaminants; Environmental pollutants
1. Introduction
Ž
Recent studies of human populations in several countries Carlsen et al., 1992, Auger
.
et al., 1995 showed that the incidence of abnormalities of male genitalia is on the rise
)Correspondence author. Tel.:q1-970-491-1769r1770; fax:q1-970-491-3557.
Ž .
E-mail address: rao@cvmbs.colostate.edu D.N. Rao Veeramachaneni .
0378-4320r00r$ - see front matterq2000 Elsevier Science B.V. All rights reserved. Ž .
and that the quality of semen has declined over the past 50 years. Although other reports
ŽFisch et al., 1996; Paulsen et al., 1996 revealed no downward trend in semen quality,.
the subjects involved in these studies represented a limited geographic area. Another meta-analysis of data involving bulls, boars, and rams also did not find any decline in
Ž .
sperm counts over the last 60 years Setchell, 1997 . Whether test populations of these farm animal species already had been selected for their reproductive efficiency, or if there was any decline in the quality of sperm is not known. Although data for many animal species might be compiled, this would likely have limited value because of non-standard conditions of evaluation, particularly collection of semen in a manner precluding estimation of daily sperm production.
The incidence of testicular cancer, the most frequent malignancy in young men, also has increased three- to four-fold during the past 50 years in several human populations,
Ž .
particularly in the Western world Adami et al., 1994; Bosl and Motzer, 1997 .
Ž .
Likewise, epidemiologic data Laumann et al., 1999 , together with increased demand for clinical services to correct erectile dysfunction, indicate that sexual dysfunction in human populations is more prevalent than previously thought. Similar trends might also exist in domestic animals, but data are not available largely because of the inherent nature of animal husbandry practices — culling of the reproductively inefficient food-and fiber-producing animals at an early age. The implications of these data for human populations have caused great concern. The relatively short time period during which these changes have occurred in human populations has been inferred as evidence that the cause is environmental rather than genetic.
Many chemicals in the environment, including some pharmaceutical compounds, are capable of mimicking the inherent actions of reproductive hormones and, hence, have the ability to disrupt the neuroendocrine system or function of the gonads directly. Estrogens or estrogen-like chemicals have been implicated as the causative agents for cryptorchidism, testicular cancer, or other testicular abnormalities and declining sperm
Ž .
counts Sharpe and Skakkebaek, 1993; Toppari et al., 1996 . There is convincing evidence that a variety of compounds with endocrine-mimicking characteristics — pesticides, alkylphenols, phthalates, disinfection byproducts of water purification, com-mon chemical contaminants, phytoestrogens and estrogenic mycotoxins — are found in
Ž
packaged foods, drinking water, lakes, and oceans Colborn et al., 1993; Jobling et al.,
.
1995 . Surprisingly, in spite of an ominous potential for catastrophic health hazards,
Ž .
there is little information on long-term consequences in adult life of exposure to endocrine-disrupting chemicals in utero or during infancy. In most cases of reproductive dysfunction, because the cause and effect are separated by a long interval, it is impossible to ascribe a current clinical condition to an etiologic agent or event that impacted many years earlier and thus the existing condition commonly would be labeled as idiopathic.
Our laboratory is studying whether some common perturbations of the male reproduc-tive system or sperm are truly idiopathic or sequelae to developmental exposure to common environmental pollutants. Some of these experimental paradigms in laboratory animals vis-a-vis clinical cases of stallions manifesting perturbed reproductive phenom-
`
2. Carcinoma in situ of the testis
Ž . Ž .
Skakkebaek 1972 first coined the term ‘‘carcinoma in situ’’ CIS of the testis to describe atypical intratubular germ cells in humans that were shown to later result in testicular germ cell tumors. Since germ cell tumors are not true carcinomas, a variety of names including testicular intraepithelial neoplasia and testicular intratubular germ cell neoplasia also have been suggested. It is widely accepted that CIS cells are present in a testis many years before clinical manifestation of a tumor. Although it is not definitively known which differentiating germ cell type undergoes this neoplastic transformation,
Ž
there is evidence that the CIS cell is a gonocyte with stem cell potential Skakkebaek,
.
1998 . Whether all gonocytes are fully differentiated into spermatogonia neonatally, or if a few remain undifferentiated in the adult is uncertain. While the cause and pathogenesis
Ž
of such transformation into CIS are not known, occurrence of CIS cells Bettocchi et al.,
.
1994; Moller and Skakkebaek, 1999 in infertile men indicates that male subfertility and testicular cancer share common etiological factors. Estrogenic xenobiotics that are
Ž .
present as natural constituents of the environment phytoestrogens and fungal products
Ž .
or as synthetic byproducts chlorinated hydrocarbons and alkylphenols are considered to be the most likely factors involved in these phenomena. However, a major factor limiting verification of this hypothesis or study of pathogenesis of testicular germ cell
Ž
tumors has been lack of an animal model Rajpert-De Meyts and Skakkebaek, 1993;
.
Looijenga and Oosterhuis, 1999 .
We were the first to document atypical germ cells resembling CIS cells of human
Ž
testis in an 8-year-old, subfertile, unilaterally cryptorchid stallion Veeramachaneni and
. Ž
Sawyer, 1998 and a 3-year-old, infertile, rabbit Veeramachaneni and VandeWoude,
.
1999 . In both cases, these cells were found in association with a developing intratubular seminoma directly linking them to CIS — a first observation for any animal species. The etiological factors in these two spontaneous cases are unknown.
We induced similar lesions in rabbits under controlled conditions by exposing them
Ž . X
to octylphenol in utero Veeramachaneni and Palmer, unpublished or to p, p
-Ž .
DDTrDDE in utero and during infancy Veeramachaneni et al., 1999 or to zeranol
Ž .
during infancy Veeramachaneni and Amann, 1994 . Octylphenol, an estrogenic chemi-cal, is commonly used in a variety of industrial applications including cosmetics, detergents, lubricants, etc.; p, pX
-DDT, an androgen receptor antagonist with a half-life of ;50 years, still is being used as an insecticide in several countries, although it is
banned in Western countries; zearalenones, found in moldy cereal grains, can be food-borne, and their synthetic metabolites, such as zeranol, are commercially used as growth promotants in meat-producing animals. Although the incidence varied, develop-mental exposures to these chemicals resulted in undescended testes, which manifested
Ž .
CIS cell-like lesions Fig. 1 . While CIS-like atypical cells were also found occasionally
Ž .
in scrotal testes Fig. 2 of animals exposed to these agents, they were predominant in undescended testes. To verify if abdominal location of the testis was a major factor in
Ž
the development of CIS, we surgically induced cryptorchidism in rabbit pups not
. Ž
exposed to chemicals before the testes transcended the inguinal canal VandeWoude et
.
al., 1999 and evaluated histopathological features of testes at 6 months of age
Ž . Ž .
animals were either unaffected gonocytes Fig. 3 or spermatogonia Fig. 4 similar to those normally present in neonatal or adolescent testes. Germ cell differentiation did not progress beyond the spermatogonial stage, as is common for the cryptorchid condition. No cellular atypia was evident in surgically induced cryptorchidism. This indicates that
Ž .
Ž .
In another experiment using rabbits Higuchi et al., 1999 , we found that dibutylph-thalate, following in utero exposure during the later half of gestation, caused unde-scended testes, ambiguous genitalia, hypospadias, regressed prostate, and missing bul-bourethral glands. Similar effects were observed in male rats following gestational
Ž
andror lactational exposures to dibutyl- and diethylhexyl phthalates Mylchreest et al.,
.
1998; Gray et al., 1999 . Phthalates are utilized as plasticizers to produce polymeric materials. Environmental contamination and exposure occur when phthalates leach out of plastic products. Due to high-volume production and usage, phthalate esters are distributed globally and are potentially ubiquitous pollutants.
Cryptorchidism occurs in humans and many species of animals including dogs, pigs, and horses. CIS has been associated with the coexistence or a history of testicular
Ž
maldescent in 20% to 30% of human cases Berthelsen et al., 1982; Loy and
Dieck-.
mann, 1993 . We have examined, by light and transmission electron microscopy, undescended testes of 41 stallions aged 1 to 8 years and found atypical germ cells and
Ž
CIS-like lesions in eight; a 20% incidence Veeramachaneni, Hendrickson and Sawyer,
.
unpublished . In three of these eight stallions, CIS cells were found coincident with beginning seminomatous lesions!
Migration and descent of the testes, differentiation of germ cells and specialized somatic cells, and initiation and maintenance of spermatogenesis require trophic and regulatory hormones. Any imbalance in the hormonal milieu, caused by endogenous or exogenous factors, will alter these processes. While some exogenous agents cause abnormal transformation of differentiating germ cells in addition to interfering with normal testicular descent, others might only cause cryptorchidism without affecting stem cell differentiation. Could these lesions in stallions be sequelae of exposure to pollutants early in life? Perhaps these animals were unknowingly exposed at critical periods of development to endocrine-mimicking chemicals similar to the ones we tested in rabbits.
Fig. 1. A CIS cell, transformed gonocyte, from the undescended testis of a 6-month-old Dutch-Belted rabbit
Ž
exposed in utero to octylphenol 150 mgrkg body weight; administerd orally on alternate days between
.
gestation days 15 and 30 . Note the size, irregular nuclear contours, chromatin clumps, and cytoplasmic inclusions including glycogen granules and lipid droplets characteristic of germ cell neoplasia. Scale bar
Ž
represents 1 mm for ease of comparison, all micrographs are photographed and printed at the same
.
magnification .
Fig. 2. An atypical germ cell, probably a spermatogonium, from the scrotal testis of a 6-month-old
Ž
Dutch-Belted rabbit exposed to octylphenol. Scale bar represents 1 mm for ease of comparison, all
.
micrographs are photographed and printed at the same magnification .
Fig. 3. A normal gonocyte from the abdominal testis of a 6-month-old Dutch-Belted rabbit in which testicular descent was prevented surgically at 3 weeks of age. Note that gonocytes are not normally found in postnatal scrotal testes, particularly in neopubertal animals. Compare this cell with that in Fig. 1. Scale bar represents 1
Ž .
mm for ease of comparison, all micrographs are photographed and printed at the same magnification .
Fig. 4. An unaffected spermatogonium from the abdominal testis of a surgically induced cryptorchid
Ž
6-month-old Dutch-Belted rabbit. Compare this with Fig. 2. Scale bar represents 1 mm for ease of
.
3. Acrosomal dysgenesis
It is well established that the acrosome of a mammalian spermatozoon plays a pivotal role in unassisted fertilization of an oocyte and that any defect in formation or function of the acrosome results in subfertilityrsterility. Using light and transmission electron microscopic procedures to evaluate equine spermatozoa as a part of breeding soundness
Ž .
acrosomal malformations in subfertile or sterile stallions. During the last 3 years, we
Ž .
evaluated semen collected from 55 subfertile stallions: Of these, 52 95% had acroso-mal vesiculation, acrosoacroso-mal dysplasia resulting in nuclear invasion, acrosomes shared between two or more sperm, and occasionally aplasia or complete lack of an acrosome
ŽVeeramachaneni, Moeller, and Sawyer, unpublished . Thirteen of the 52 stallions were.
evaluated multiple times over a period of 6 to 30 months during which time they consistently manifested these same lesions. Although a few of these stallions were from Europe, most originated from various regions of the USA. Because it is impossible to make a definitive association with a probable cause based on recent clinical history, the etiology behind acrosomal dysgenesis in these otherwise valuable stallions remains unknown.
Interestingly, we have also observed acrosomal malformations identical to those
Ž . Ž
found in the 52 subfertile stallions in: 1 rabbits exposed in utero to octylphenol Figs.
. Ž .
5–8 ; 2 rabbits exposed in utero and during infancy to a mixture of common chemical
w
contaminants in drinking water viz., arsenic, lead, chromium, benzene, chloroform, phenol, and trichloroethylene, which are most frequent contaminants in ground water
x Ž . Ž .
near industrial sites in the USA Veeramachaneni et al., 1995 ; 3 rats exposed
Ž . Ž .
postnatally to trichloroethylene Veeramachaneni, unpublished ; 4 rats exposed to
Ž . Ž .
dibromoacetic acid, a water disinfection byproduct Linder et al., 1997 ; and 5 rabbits
Ž
exposed in utero and throughout postnatal life to dibromoacetic acid Veeramachaneni,
.
unpublished . Also, exposure to cadmium has been implicated in abnormal acrosomal
Ž
function, i.e., reduced mannose receptor expression and acrosome exocytosis Benoff et
.
al., 1997 . While other causes such as genetic factors cannot be ruled out, it is very likely that the 52 stallions in question had been exposed to one or more of these contaminants present in feed andror drinking water. Therefore, it appears that exposure
Fig. 5. Two round spermatids in golgi phase sharing a common golgi apparatus. Transmission electron micrograph of a section from scrotal testis of a 6-month-old, octylphenol-exposed rabbit depicting acrosomal dysgenesis. Scale bar represents 1mm.
Fig. 6. Two spermatids sharing a developing acrosome. Note the irregular orientationrspread of the acrosomal
Ž .
cap arrows . This results in two disoriented sperm heads conjoined by a common acrosome as seen in Fig. 8. Large arrow points to acrosomal granule and arrowheads point to ends of the acrosomal cap. Transmission electron micrograph of a section from scrotal testis of a 6-month-old, octylphenol-exposed rabbit depicting acrosomal dysgenesis. Scale bar represents 1mm.
Ž .
Fig. 7. Condensing or elongating spermatids. As the spermatids sharing a common acrosome arrow condense, the acrosomal matrix surrounds both nuclei resulting in the development of two spermatozoa as a single unit. In this process, the acrosome sometimes invades nucleus resulting in nuclear as well as acrosomal malformations as seen in Fig. 8. Transmission electron micrograph of a section from scrotal testis of a 6-month-old, octylphenol-exposed rabbit depicting acrosomal dysgenesis. Scale bar represents 1mm.
Ž .
Fig. 8. Acrosomal malformations: acrosomal vesiculation arrow head , acrosomal dysplasia resulting in
Ž . Ž
invasion of the nucleus arrow , and shared, dysplastic acrosome between two elongated spermatids open
.
to one or more of these insidious pollutants during critical periods of development can cause lasting and irreversible effects on spermatogenesis.
4. Sexual dysfunction
Inability to copulate is a major cause of functional sterility and a major reason for
Ž .
culling domestic animals; it had been documented by the 1930s Lagerlof, 1936 . It is very difficult to pinpoint the causes for impaired sexual functionrcapacity since they can vary widely from physical to psychogenic factors. However, a few examples of how environmental pollutants affect sexual interest and capacity will be presented to illustrate how common pollutants, even at low, environmentally relevant concentrations, can alter these processes. These observations were recorded in an as-observed manner rather than during ethological studies.
Male rabbits exposed in utero andror during infancy to a mixture of common
Ž .
chemical contaminants in drinking water same mixture as described above , or to
Ž . Ž
disinfection byproducts of water purification dibromoacetic acid or to vinclozolin a
. Ž
fungicide widely used in European agriculture and horticulture were studied
Veera-.
machaneni et al., 1995; Veeramachaneni, unpublished . Several treated animals, but no control animal, failed to show any sexual interest in the female or failed to ejaculate. These observations might indicate that developmental exposure to certain chemicals can permanently alter sexual behaviorrcapacity in adult life.
5. Conclusion
Experimental evidence strongly indicates that many chemical pollutants in the environment can permanently alter reproductive function in male laboratory animals at doses likely encountered by domestic animals. Use of a relevant laboratory animal model, such as the rabbit, that facilitates longitudinal seminal evaluation and monitoring of the sexual capacity is imperative to delineate cause and effect relationships in many so-called idiopathic clinical conditions in males. The causative factors for the conditions such as cryptorchidism, testicular carcinoma in situ, and poor seminal quality described here for stallions are unknown and the evidence to date is limited to a few unrelated studies with rabbits and rats. Nevertheless, based on the morphological findings pre-sented herein, the effects of some environmental pollutants appear to have a common thread across several animal species including humans. Given the impact of this global phenomenon, more studies focusing on the areas of mechanisms of action of endocrine-mimicking chemicals, pathogenesis of reproductive anomalies resulting from exposure to these chemicals, and environmental remediation are obligatory.
Acknowledgements
L.E. Gray, C. Awoniyi, F. Pau, and R. Amann for insightful discussions and collabora-tive efforts in various projects. This work was supported by USEPA grant R826131-01-0, USEPA contract CR826465-01-0, and the College Research Council and the Department of Physiology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University.
References
Adami, H.O., Bergstrom, R., Mohner, M., Zatonski, W., Storm, H., Ekbom, A., Tretli, S., Teppo, L., Zeigler, H., Rahu, M., Gurevicius, R., Stengrevics, A., 1994. Testicular cancer in nine Northern European countries. Int. J. Cancer 59, 33–38.
Auger, J., Kunstmann, J.M., Czyglik, F., Jouannet, P., 1995. Decline in semen quality among fertile men in paris during the past 20 years. N. Engl. J. Med. 332, 281–285.
Benoff, S., Hurley, I.R., Barcia, M., Mandel, F.S., Cooper, G.W., Hershlag, A., 1997. A potential role for cadmium in the etiology of varicocele-associated infertility. Fertil. Steril. 67, 336–347.
Berthelsen, J.G., Skakkebaek, N.E., von der Maase, H., Sorensen, B.L., Mogensen, P., 1982. Screening for carcinoma in situ of the contralateral testis in patients with germinal testicular cancer. Br. Med. J. 285, 1683–1686.
Bettocchi, C., Coker, C.B., Deacon, J., Parkinson, C., Pryor, J.P., 1994. A review of testicular intratubular
Ž .
germ cell neoplasia in infertile men. J. Androl. 15, 14S–16S, Suppl. .
Bosl, G.J., Motzer, R.J., 1997. Testicular germ-cell cancer. N. Engl. J. Med. 337, 242–253.
Carlsen, E., Giwercman, A., Keiding, N., Skakkebaek, N.E., 1992. Evidence for decreasing quality of semen during past 50 years. Br. Med. J. 305, 609–613.
Colborn, T., vom Saal, F.S., Soto, A.M., 1993. Developmental effects of endocrine-disrupting chemicals in wildlife and humans. Environ. Health Perspect. 101, 378–384.
Fisch, H., Goluboff, E.T., Olson, J.H., Feldshuh, J., Broder, S.J., Barad, D.H., 1996. Semen analyses in 1,283 men from the United States over a 25-year period: no decline in quality. Fertil. Steril. 65, 1009–1014. Gray, L.E. Jr., Wolf, C., Lambright, C., Mann, P., Price, M., Cooper, R.L., Ostby, J., 1999. Administration of
Ž
potentially antiandrogenic pesticides procymidone, linuron, iprodione, chlozolinate, p,p’-DDE, and
keto-. Ž
conazole and toxic substances dibutyl- and diethylhexyl phthalate, PCB 169, and ethane dimethane
.
sulfonate during sexual differentiation produces diverse profiles of reproductive malformations in the male rat. Toxicol. Ind. Health 15, 94–118.
Higuchi, T.T., Kane, C.M., Palmer, J.S., Veeramachaneni, D.N.R., 1999. Developmental effects of dibutyl
Ž . Ž .
phthalate in frogs and rabbits. Biol. Reprod. 60 Suppl 1 , 153, Abstr. .
Jobling, S., Reynolds, T., White, R., Parker, M.R., Sumpter, J.P., 1995. A variety of environmentally persistent chemicals, including some phthalate plasticizers, are weakly estrogenic. Environ. Health Perspect. 103, 582–587.
Lagerlof, N., 1936. Sterility in bulls. Vet. Rec. 48, 1159–1173.
Laumann, E.O., Paik, A., Rosen, R.C., 1999. Sexual dysfunction in the United States. Prevalence and predictors. J. Am. Med. Assoc. 281, 537–544.
Linder, R.E., Klinefelter, G.R., Strader, L.F., Veeramachaneni, D.N.R., Roberts, N.L., Suarez, J.D., 1997. Histopathologic changes in the testis of rats exposed to dibromoacetic acid. Reprod. Toxicol. 11, 47–56. Looijenga, L.H.J., Oosterhuis, J.W., 1999. Pathogenesis of testicular germ cell tumours. Rev. Reprod. 4,
90–100.
Ž
Loy, V., Dieckmann, K.P., 1993. Prevalence of contralateral testicular intraepithelial neoplasia carcinoma in
.
situ in patients with testicular germ cell tumour. Eur. Urol. 23, 120–122.
Moller, H., Skakkebaek, N.E., 1999. Risk of testicular cancer in subfertile men: case-control study. Br. Med. J. 318, 559–562.
Paulsen, C.A., Berman, N.G., Wang, C., 1996. Data from men in greater Seattle area reveals no downward trend in semen quality: further evidence that deterioration of semen quality is not geographically uniform. Fertil. Steril. 65, 1015–1020.
Rajpert-De Meyts, E., Skakkebaek, N.E., 1993. The possible role of sex hormones in the development of testicular cancer. Eur. Urol. 23, 54–61.
Setchell, B.P., 1997. Sperm Counts in semen of farm animals 1932–1995. Int. J. Androl. 20, 209–214. Sharpe, R.M., Skakkebaek, N.E., 1993. Are oestrogens involved in falling sperm counts and disorders of the
male reproductive tract? Lancet 341, 1392–1395.
Skakkebaek, N.E., 1972. Possible carcinoma in situ of the testis. Lancet ii, 516–517. Skakkebaek, N.E., 1998. Trends in male reproductive health. Adv. Exp. Med. Biol. 444, 1–4.
Toppari, J., Larsen, J.C., Christiansen, P., Giwercman, A., Grandjean, P., Guillette, L.J. Jr., Jegou, B., Jensen, T.K., Jouannet, P., Keiding, N., Leffers, H., McLachlan, J.A., Meyer, O., Muller, J., Rajpert-De Meyts, E., Scheike, T., Sharpe, R., Sumpter, J., Skakkebaek, N.E., 1996. Male reproductive health and environmental
Ž .
xenoestrogens. Env. Health Perspect. 104 Suppl. 4 , 741–803.
VandeWoude, S., Palmer, J.S., Veeramachaneni, D.N.R., 1999. Surgical induction of cryptorchidism in rabbit pups. Lab. Anim. Sci. 49, 110–113.
Veeramachaneni, D.N.R., Amann, R.P., 1994. Infantile exposure to zeranol causes testicular maldescensus and
Ž .
epididymal adenomyosis in rabbits. Toxicologist 14, 76, Abstr. .
Veeramachaneni, D.N.R., Sawyer, H.R., 1996. Use of semen as biopsy material for assessment of health status of the stallion reproductive tract. In: Veterinary Clinics of North America: Equine Practice on Diagnostic Techniques and Assisted Reproductive Techniques vol. 12 pp. 101–110.
Veeramachaneni, D.N.R., Sawyer, H.R., 1998. Carcinoma in situ and seminoma in equine testis. Acta Pathol. Microbiol. Immunol. Scand. 106, 183–186.
Veeramachaneni, D.N.R., VandeWoude, S., 1999. Interstitial cell tumour and germ cell tumour with carcinoma in situ in rabbit testes. Int. J. Androl. 22, 97–101.
Veeramachaneni, D.N.R., Palmer, J.S., Amann, R.P., 1995. Sexual dysfunction and abnormal acrosomes in rabbits following infantile exposure to a mixture of chemical contaminants in drinking water. Biol. Reprod.
Ž . Ž .
52 Suppl. 1 , 171, Abstr. .
Veeramachaneni, D.N.R., Palmer, J.S., Kane, C.M., Moeller, C.L., Pau, K.-Y.F., 1999. Cryptorchidism induced by exposure to p, pX
-DDTrDDE, but not by surgery, causes carcinoma in situ-like lesions in the
Ž .
