Modifications of reproductive organs in male rats influenced prenatally or pre- and postnatally by an "antiandrogenic" steroid (Cyproterone)

Endocrine and morphological perspectives in testicular descent

Before sexual differentiation occurs at seven weeks, the urological ridges develop in the embryo. These contain the primitive gonads, the mesonephros (embryonic kidneys) and the paired Wolffian (mesonephric) ducts, along with the Müllerian (paramesonephric) ducts. The fundamental mechanism of fetal sexual development was elucidated by Alfred Jost and is determined by the development of the gonad: where testes form in response to the testis-determining gene, and the male testicular hormones cause development of the male phenotype. If ovaries develop or the gonads are absent, female secondary sex characteristics are produced. Recently, the cloning of the putative human testis-determining gene on the Y-chromosome was reported. Assuming this is the true controller of testicular development, an understanding of the initiation of sexual differentiation at the genetic level should emerge in the near future. Of great importance will be the isolation of the testis-determining gene product and identification of other genes that it regulates.

Scanning electron microscopy shows inhibited gubernacular development in relation to undescended testes in oestrogen-treated mice

The morphological relationship between transabdominal testicular descent and the 'swelling reaction' of the gubernaculum was investigated in oestrogen-treated fetal mice by using scanning electron microscopy (scanning EM). In addition, flutamide was also administered to pregnant mice to determine whether androgens cause gubernacular growth and transabdominal testicular descent in offspring. In oestrogen-treated fetal mice, scanning EM showed that both the gubernacular 'swelling reaction' and transabdominal testicular descent were inhibited, in addition to inhibition of Müllerian duct regression. The gubernaculum showed a flat, thin bulb (widest diameter 0.25 +/- 0.04 mm) and an elongated cord (1.28 +/- 0.41 mm) after oestrogen treatment in utero, which was significantly different in appearance from that in normal control mice (width 0.44 mm +/- 0.06 mm, p < 0.001; length 0.27 +/- 0.19 mm, p < 0.0001). However, flutamide-treated mice showed much more normal gubernacular enlargement and transabdominal testicular descent. The width of the gubernacular bulb after flutamide exposure was 0.44 +/- 0.05 mm, which was comparable to that in control animals; the length of the intra-abdominal gubernaculum (0.44 +/- 0.15 mm) was slightly longer than in controls (p < 0.02). These results suggest that both the swelling reaction of the gubernaculum and transabdominal testicular migration are blocked by prenatal exposure to oestrogen. However, oestrogen exposure of the fetus does not block the swelling reaction of the gubernaculum by acting as an antiandrogen.

Does sinus vaginal epithelium persist in the adult mouse vagina?

It generally is held that the murine vagina develops from the urogenital sinus and the lower portion of the Müllerian ducts and that both endodermally derived sinus epithelium and mesodermally derived Müllerian epithelium contribute to the adult vagina. We tested Müllerian and urogenital sinus-derived vaginal epithelia for their ability to differentiate in response to various hormonal conditions and compared these responses to those of the in situ vagina. Tissue recombinants were prepared with 0-day Müllerian-derived vaginal epithelium and vaginal mesenchyme. Similarly, tissue recombinants containing urogenital sinus-derived vaginal epithelium were prepared with either 0-day sinus vaginal epithelium or 16-day fetal urogenital sinus epithelium and vaginal mesenchyme. Müllerian- or sinus-derived vaginal mesenchyme was used to construct the tissue recombinants; however, the source of the mesenchyme had no influence on the results. Tissue recombinants were grafted to the renal capsule of female mice, allowed to develop for 1 month, and exposed to various hormonal treatments. In diethylstilbestrol-treated hosts, all tissue recombinants regardless of the source of the epithelium were lined by a cornified epithelium. In contrast, only in tissue recombinants containing mesodermally derived Müllerian vaginal epithelium did the epithelium mucify in response to progesterone plus estrogen or become atrophic in ovariectomized hosts. These are the same epithelial modifications seen in the hosts' vagina. Tissue recombinants containing endodermally derived urogenital sinus epithelium or sinus vaginal epithelium and grafts of intact urogenital sinus maintained a stratified squamous noncornified epithelium in both ovariectomized and progesterone plus estrogen-treated hosts. Furthermore, in tissue recombinants containing Müllerian vaginal epithelium and vaginal mesenchyme, estrogen induced a slightly higher epithelial labeling index than in tissue recombinants containing urogenital sinus epithelium or sinus vaginal epithelium. The epithelial labeling index was the same regardless of the source of the vaginal mesenchyme. These results indicate that Müllerian-derived and sinus-derived vaginal epithelia are not equivalent and suggest that Müllerian vaginal epithelium displaces sinus vaginal epithelium during postnatal development. The replacement may result in part from a slight but consistently higher proliferation rate in Müllerian versus sinus vaginal epithelium.

Latent effects of pesticides and toxic substances on sexual differentiation of rodents

In humans and rodents, exposure to hormonally active chemicals during sex differentiation can produce morphological pseudohermaphrodism (Schardein, 1993; Gray, 1992). For example, hormonally active drugs like DES (estrogenic), Danazol (androgenic), and progestins cause urogenital malformations in the reproductive tracts of humans and rodents. The current discussion will present new information on the effects of toxic chemicals and pesticides that act on reproductive development via novel mechanisms, including germ cell toxicity, antiandrogenicity, and Ah-receptor binding. Information will be presented that describes how exposure during critical stages of life to synthetic chemicals present in our environment, such as benzidine-based dyes, antiandrogenic fungicides, 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD), and PCB congener 169, result in abnormal rodent sex differentiation. In rodents, perinatal exposure to fetal germ cell toxicants reduced the reproductive potential of female, and permanently reduced sperm production in male progeny. Phenotypic sex differentiation, however, was unaffected by these germ cell toxicants. In contrast, antiandrogenic drugs and fungicides induced profound alterations in phenotypic sex differentiation. Effects such as hypospadias, ectopic testes, vaginal pouches, agenesis of the ventral prostate, and nipple retention in male rats were observed commonly. Although these antiandrogens induced no permanent effects in female progeny, another class of chemicals, the Ah-receptor mediated toxicants, did reduce fertility in both male and female rat offspring. Cauda epididymal sperm numbers were reduced permanently in TCDD-exposed male rat and hamster progeny, and female progeny displayed malformations of the external genitalia. Other toxicants produced dramatic alterations of sex differentiation (uterus unicornis, agenesis of the vas and epididymis, and undescended testes), via mechanisms that have not been characterized yet. Since these adult/pubertal alterations resulted from gestational and/or neonatal exposures, future studies should include a comprehensive assessment of reproductive function after perinatal exposure because the developing animal is extremely sensitive to toxicants during sex differentiation, and many of the effects are difficult to detect until late in life.

Testicular feminization: a model for testicular descent in mice and men

The position of the testis was determined in patients and mice with the testicular feminization (TFM) syndrome, to answer the question, do androgens cause testicular descent? In 16 children with complete or partial TFM syndrome with androgen insensitivity, plus two children with a deficiency of androgen secretion, the testes were at or beyond the internal inguinal ring in 35 out of 36 instances. In male mice with TFM, the testes had descended normally to the internal ring by the time of birth but further descent was absent. These observations suggest testicular descent is a two-stage process comprising transabdominal and transinguinal phases. The first phase is not controlled by androgen, and hence is normal in TFM; by contrast the second phase is androgen-dependent, and absent in TFM. It is speculated that the first phase may be regulated by Müllerian Inhibiting Substance, although this is unproven. Because testicular descent in TFM can be separated into two stages, the TFM mouse should prove a useful model for studying the hormonal control of descent of the testis.

The dual origin of vaginal epithelium

The absence of the cranial three-fifths of the vaginae of male mice carrying the gene, Testicular Feminization, provides strong support for the view that vaginal epithelium is of dual origin, the cranial three-fifths being of Mullerian in origin and the caudal two-fifths being derived from the urogenital sinus.