Transdifferentiation of adult rat stem Leydig cells into prostatic and uterine epithelium, but not epidermis

Stem Leydig cells (SLCs), precursors of testicular Leydig cells that secrete testosterone required for male sexual differentiation, spermatogenesis, and fertility, were recently identified in rat testes. Various types of stem cells have shown the ability to differentiate into other tissues, but there is no information on the plasticity of adult rat SLCs (rSLCs). This study investigated the ability of rSLCs to transdifferentiate into cell types from all three germ layers-prostatic epithelium (endoderm), uterine epithelium (mesoderm), and epidermis (ectoderm)-under the influence of inductive mesenchyme from fetal and neonatal tissues. To differentiate rSLCs into cells of other lineages, mesenchyme from green fluorescent protein (GFP)-expressing mice was used. Tissue recombinants of urogenital sinus mesenchyme (a potent prostate inducer) and rSLCs grafted into adult male hosts formed ductal structures resembling prostate after 5 weeks. Prostate epithelium was of rSLC origin as determined by absence of GFP expression, and expressed characteristic markers of prostatic epithelium. Similarly, uterine mesenchyme + rSLCs tissue recombinants contained a simple columnar epithelium that was histologically similar to normal uterine epithelium and expressed typical uterine epithelial markers, but was of rSLC origin. In contrast, epidermal tissue was absent in fetal dermis + rSLCs recombinants, suggesting rSLCs did not form skin epithelium. Thus, rSLCs can transdifferentiate into uterine and prostatic epithelium, mesodermal, and endodermal derivatives, respectively, but they may have a limited transdifferentiation potential, as shown by their inability to form epidermis, an ectodermal derivative.

Estrogen receptor alpha mediates estrogen-inducible abnormalities in the developing penis

Previously, we reported an association between estrogen receptor-alpha (ERalpha) upregulation and detrimental effects of neonatal diethylstilbestrol (DES) exposure in the rat penis. The objective of this study was to employ the ERalpha knockout (ERalphaKO) mouse model to test the hypothesis that ERalpha mediates DES effects in the developing penis. ERalphaKO and wild-type C57BL/6 mice received oil or DES at a dose of 0.2 microg/pup per day (0.1 mg/kg) on alternate days from postnatal days 2 to 12. Fertility was tested at 80-240 days of age and tissues were examined at 96-255 days of age. DES caused malformation of the os penis, significant reductions in penile length, diameter, and weight, accumulation of fat cells in the corpora cavernosa penis, and significant reductions in weight of the bulbospongiosus and levator ani muscles in wild-type mice. Conversely, ERalphaKO mice treated with DES developed none of the above abnormalities. While nine out of ten male mice sired pups in the wild-type/control group, none did in the wild-type/DES group. ERalphaKO mice, despite normal penile development, are inherently infertile. Both plasma and intratesticular testosterone levels were unaltered in the DES-treated wild-type or DES-treated ERalphaKO mice when compared with controls, although testosterone concentration was much higher in the ERalphaKO mice. Hence, the resistance of ERalphaKO mice to developing penile abnormalities provides unequivocal evidence of an obligatory role for ERalpha in mediating the harmful effects of neonatal DES exposure in the developing penis.

The phytoestrogen genistein suppresses cell-mediated immunity in mice

The soy phytoestrogen, genistein, induces thymic atrophy when administered to ovariectomized mice by injection or in the diet. Injected genistein also causes decreased humoral immunity, but the effects of genistein on cell-mediated immunity have not been addressed. Here we examined effects of injected and dietary genistein on cell-mediated immune responses. Female C57BL/6 mice (25- to 27-days-old) were ovariectomized, then placed on phytoestrogen-free feed 5 days later. Seven days after ovariectomy, they were given daily subcutaneous injections of either dimethylsulfoxide (DMSO) or genistein (8, 20, 80 mg/kg) for 28 days; some mice were given 80 mg/kg genistein plus the anti-estrogen ICI 182,780 (5 mg/kg/week). Cell-mediated immune response was tested by analyzing the delayed-type hypersensitivity (DTH) response to a hapten, 4-hydroxy-3-nitrophenyl acetyl succinimide (NP-O-SU), at the end of treatment. Reversibility of the effects of genistein was tested by measuring the DTH response in mice that were given genistein (20 or 80 mg/kg) for 28 days, then allowed to recover for 28 days. To determine if dietary genistein could affect cell-mediated immunity, mice ovariectomized as above were fed genistein at 0, 1000 or 1500 parts per million (ppm) for 28 days. There was a 46-67% decrease in the DTH response in the footpads of mice injected with 8-80 mg/kg genistein compared with controls (P<0.05 vs control for all treatment groups); these effects were reversible. On histopathological examination of the feet, there was decreased cell infiltration in genistein-treated animals compared with controls, and the numbers of CD4(+) and CD8(+) T cells in popliteal lymph nodes were reduced. The effects of genistein are mediated through both estrogen receptor (ER) and non-ER pathways, as the anti-estrogen ICI 182,780 only partially blocked the effects of genistein on the DTH response. Dietary genistein (1000 or 1500 ppm) decreased cell-mediated immunity while producing serum genistein concentrations in the physiological range for humans under certain nutritional conditions. Further work is needed to determine if dietary genistein and phytoestrogen exposure can produce effects on cell-mediated immunity in humans or other animals under various nutritional conditions.

Effect of ovariectomy on adipose tissue of mice in the absence of estrogen receptor alpha (ERalpha): a potential role for estrogen receptor beta (ERbeta)

Adipose tissue deposition is highly responsive to estrogen; ovariectomy increases adipose deposition, and estrogen replacement reverses this. Estrogen receptor alpha (ERalpha) plays a major role in adipose tissue. ERalpha knockout (alphaERKO) mice show an increase in adipose tissue of over a 100 % compared to wild-type mice. However, alphaERKO mice undergo a 10-fold increase in 17beta-estradiol (E2), and persistent or even increased signaling through ERbeta could be a factor in obesity of alphaERKO mice. To test the hypothesis that ERbeta plays a role in adipose tissue, adult female alphaERKO mice were ovariectomized or sham-ovariectomized and fed a phytoestrogen-free diet. Ovariectomized mice were treated with vehicle or E2, and bodyweights and food consumption were measured. Mice were killed after 28 days and inguinal and parametrial fat pads collected. Sham-ovariectomized alphaERKO mice had increased body weight, ovariectomized alphaERKO mice showed a 6 % decrease, and E2 replacement restored body weight to sham levels. Fat pads of ovariectomized alphaERKO mice showed 45 % and 16 % decreases in weight and adipocyte circumference, respectively, compared to sham-ovariectomized or E2-replaced ovariectomized alphaERKO mice. Ovariectomized alphaERKO mice showed a trend towards decreased feed consumption that did not reach significance. Blood glucose levels were lower both before and after glucose injection in ovariectomized compared to sham alphaERKO mice, and E2 treatment reversed this. Insulin levels following glucose challenge were lower in ovariectomized compared to sham-ovariectomized alphaERKO mice, indicating that ovariectomy ameliorated the glucose intolerance and insulin resistance in alphaERKO mice. Immunohistochemical analysis revealed strong staining for ERbeta in adipose tissue. These observations indicate that removing E2/ERbeta signaling in alphaERKO mice by ovariectomy decreases body and fat-pad weights and adipocyte size, while improving insulin and glucose metabolism. ERbeta mediated effects on adipose tissue are opposite those of ERalpha, although E2 effects on adipose tissue are predominately through ERalpha.

Epithelial-stromal tissue interaction in paramesonephric (Müllerian) epithelial differentiation

During organogenesis, the middle to caudal portion of Müllerian epithelium differentiates into uterine and vaginal epithelia in females. Functional differentiation of uterine and vaginal epithelia occurs in adulthood, and is regulated by 17beta-estradiol (E(2)) and progesterone. In this report, the roles of mesenchyme/stroma in differentiation of uterine and vaginal epithelia were studied in tissue recombination experiments. At birth, Müllerian epithelium was negative for uterine and vaginal epithelial markers. Tissue recombinant experiments showed that uterine and vaginal gene expression patterns were induced in neonatal Müllerian epithelium by the respective mesenchymes. Differentiated adult uterine and vaginal epithelia did not change their original gene expression in response to heterotypic mesenchymal induction. In the adult vagina, E(2) induced expression of involucrin, a CCAAT/enhancer-binding protein beta and cytokeratin 1 via estrogen receptor alpha (ERalpha). Tissue recombination experiments with wild-type and ERalpha knockout mice demonstrated that epithelial gene expression is regulated by E(2) via epithelial-stromal tissue interactions. Uterine/vaginal heterotypic tissue recombinations demonstrated that functional differentiation of uterine and vaginal epithelia required organ-specific stromal factors. In contrast, stromal signals regulating epithelial proliferation appeared to be nonspecific in the uterus and vagina.

Role of the aryl hydrocarbon receptor in the development of control and 2,3,7,8-tetrachlorodibenzo-p-dioxin-exposed male mice

Experiments were conducted to determine the role of the aryl hydrocarbon receptor (AhR) in the development of control and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-exposed C57Bl/6 male mice. Male and female mice heterozygous for the AhR (Ahr+/-) were mated, and pregnant females were dosed orally on gestation day 13 with corn oil vehicle or TCDD (5 microg/kg). Pups were necropsied on postnatal day (PND) 21, 35, and 90. Comparison of vehicle-exposed wild-type (Ahr+/+) pups with vehicle-exposed AhR knockout (AhRKO; Ahr-/-) pups confirmed and extended previous reports that development of the liver, heart, spleen, thymus, and kidney is affected by absence of the AhR. Lung, submandibular gland, testis, and epididymis weights were also affected, indicating that the AhR plays a role in normal development of these organs as well. The presence or absence of the AhR had no effect on the incidence of hydronephrosis, daily sperm production, or cauda epididymal sperm numbers in vehicle-exposed mice. TCDD caused numerous effects in wild-type mice that were absent in AhRKO mice; specifically, hydronephrosis, increases in relative liver and heart weight, decreases in absolute heart and lung weight, and decreases in absolute and relative thymus, submandibular gland, epididymis, and testis weight. In several cases, TCDD produced one effect in wild-type mice (reductions in body weight and absolute thymus, submandibular gland, and epididymis weight on PND 21; and reductions in absolute and relative submandibular gland and absolute testis weight on PND 35) but caused the opposite effect in AhRKO mice. In yet other cases (reduced relative spleen weight on PND 21 and reductions in absolute and relative thymus weight on PND 35), TCDD produced similar effects in wildtype and AhRKO mice. There were also cases in which TCDD significantly affected AhRKO mice without significantly altering the same endpoint in wild-type mice; absolute liver, lung, and kidney weight were increased and relative submandibular gland weight was decreased on PND 21; relative heart weight was reduced and absolute lung weight increased on PND 35; and relative liver weight was decreased on PND 90. Although many effects of TCDD required the presence of the AhR, these results provide evidence either for multiple forms of the AhR in mice (one or more of which are still present in AhRKO mice), or for AhR-independent effects of low-level TCDD exposure.

The role of estrogen and estrogen receptor-alpha in male adipose tissue

Males and females both express estrogen receptor (ER) in white adipose tissue (WAT), and estrogens appear to play an important role in regulating WAT in females. However, the role of ER in male WAT was unclear. In this review, we describe our work, which used wild type (WT) and ERalpha-knockout (alphaERKO) male and female mice to determine the role of ERalpha in regulating WAT and brown adipose tissue (BAT). There were progressive increases in WAT with advancing age in alphaERKO compared with WT males; weights of various WAT depots in alphaERKO males were increased by more than 100% compared with WT controls during adulthood. Conversely, BAT weight was similar in alphaERKO and WT males at all ages. Adipocyte areas and numbers were also increased in WAT from alphaERKO compared with WT males. Compared with WT controls, alphaERKO females also had increases in WAT. The alphaERKO mice also had insulin resistance and impaired glucose tolerance, similar to humans lacking ERalpha or aromatase. The obesity in alphaERKO males appeared to involve decreased energy expenditure rather than hyperphagia. In summary, ERalpha absence causes adipocyte hyperplasia and hypertrophy in WAT, but not BAT, and is accompanied by insulin resistance and glucose intolerance in both males and females. These results are the first evidence that the estrogen/ERalpha signaling system is critical in female and male WAT deposition, and may have clinical implications.

Altered prostate growth and daily sperm production in male mice exposed prenatally to subclinical doses of 17alpha-ethinyl oestradiol

Approximately 2 million women in the USA and Europe continue taking oral contraceptives each year during undetected pregnancy due primarily to non-compliance and also to individual variation in sensitivity to hormones in the contraceptives. Prenatal exposure to oral contraceptives containing 17alpha-ethinyl oestradiol (EE) has generally not been associated with an increased incidence of externally observable malformations at birth. The purpose of this study was to assess effects on reproductive organs in adult male mice that had been exposed during gestation day 0 through 17 (equivalent to gestation week 16 in humans) to clinically relevant (approximately 0.5 microg/kg/day) and lower doses of EE. Doses used in this study ranged from 0.002 to 2 microg/kg/day. By 5 months of age, prostate weight was significantly (P < 0.05) higher than controls in most treatment groups of EE (0.02-2 microg/kg). Prostatic androgen receptor populations were significantly elevated only in the 0.02 microg/kg group, suggesting different mechanisms for the increase in prostate weight at different doses. Daily sperm production (DSP) and DSP per gramme of testis were reduced in all treatment groups during adolescence, but not later in adulthood. These findings are consistent with prior studies showing that prenatal exposure of mice to very low doses of a number of oestrogenic chemicals can alter the adult male reproductive system without causing gross external malformations.

Paracrine mechanisms of mouse mammary ductal growth

Ductal growth during puberty is stimulated by estrogens, which elicit their effects via specific estrogen receptors, ER alpha and ER beta. Analysis of mice with targeted disruption of ER alpha or ER beta has emphasized the importance of ER alpha in mammary gland development. In the mouse mammary gland, ER alpha are expressed in both epithelial and stromal cells (Kurita and Cunha, unpublished), which raises the possibility that the growth and morphogenetic effects of estrogen could be mediated via either epithelial or stromal ER. The aim of this paper is to review the role of epithelial versus stromal ER in mammary ductal-alveolar growth to assess the importance of paracrine mechanisms.

Regulation of progesterone receptors and decidualization in uterine stroma of the estrogen receptor-alpha knockout mouse

Regulation of progesterone receptor (PR) in uterine stroma (endometrial stroma plus myometrium) by estrogen was investigated in estrogen receptor-alpha (ERalpha) knockout (alphaERKO) mice. 17 beta-Estradiol (E(2)) increased PR levels in uterine stroma of ovariectomized alphaERKO mice, and ICI 182 780 (ICI) inhibited this E(2)-induced PR expression. Estrogen receptor-beta(ER beta) was detected in both uterine epithelium and stroma of wild-type and alphaERKO mice by immunohistochemistry. In organ cultures of alphaERKO uterus, both E(2) and diethylstilbestrol induced stromal PR, and ICI inhibited this induction. These findings suggest that estrogen induces stromal PR via ERbeta in alphaERKO uterus. However, this process is not mediated exclusively by ERbeta+, because in ERbeta knockout mice, which express ERalpha, PR was up-regulated by E(2) in uterine stroma. In both wild-type and alphaERKO mice, progesterone and mechanical traumatization were essential and sufficient to induce decidual cells, even though E(2) and ERalpha were also required for increase in uterine weight. Progesterone receptor was strongly expressed in decidual cells in alphaERKO mice, and ICI did not inhibit decidualization or PR expression. This study suggests that up-regulation of PR in endometrial stroma is mediated through at least three mechanisms: 1) classical estrogen signaling through ERalpha, 2) estrogen signaling through ERbeta, and 3) as a result of mechanical stimulation plus progesterone, which induces stromal cells to differentiate into decidual cells. Each of these pathways can function independently of the others.

Increased adipose tissue in male and female estrogen receptor-alpha knockout mice

Estrogen regulates the amount of white adipose tissue (WAT) in females, but its role in males and whether WAT effects involve estrogen receptor-alpha (ERalpha) or ERbeta were unclear. We analyzed the role of ERalpha in WAT and brown adipose tissue by comparing these tissues in wild-type (WT) and ERalpha-knockout (alphaERKO) male and female mice. Brown adipose tissue weight was similar in alphaERKO and WT males at all ages. Progressive increases in WAT were seen in alphaERKO males with advancing age. Epididymal, perirenal, and inguinal WAT weighed 139-185% more in alphaERKO than in WT males by 270-360 days of age. Epididymal and perirenal adipocyte size was increased 20% in alphaERKO males. Adipocyte number was 82-168% greater in fat pads of alphaERKO vs. WT males. Compared with WT, 90-day-old alphaERKO females had increases in fat pad weights (54-103%), adipocyte size, and number. Both alphaERKO males and females had insulin resistance and impaired glucose tolerance, similar to humans lacking ERalpha or aromatase. Energy intake was equal in WT and alphaERKO males, indicating that obesity was not induced by hyperphagia. In contrast, energy expenditure was reduced by 11% in alphaERKO compared with WT males, indicating that altered energy expenditure may be important for the observed obesity. In summary, ERalpha absence causes adipocyte hyperplasia and hypertrophy, insulin resistance, and glucose intolerance in both sexes. These results are evidence that estrogen/ERalpha signaling is critical in female and male WAT; obesity in alphaERKO males involves a mechanism of reduced energy expenditure rather than increased energy intake.

The differential fate of mesonephric tubular-derived efferent ductules in estrogen receptor-alpha knockout versus wild-type female mice

We investigated mesonephric tubular-derived efferent ductules in female wild-type (WT) and estrogen receptor-alpha knockout (ERalphaKO) mice from late fetal to adult life. On gestational day 17, efferent ductules in both fetal WT and ERalphaKO females were well developed and morphologically similar, although one third the size of the male counterpart. Unexpectedly, efferent ductules with a ciliated epithelium were still present on postnatal day 10 in WT and ERalphaKO females. By day 23, however, marked phenotypic differences occurred in efferent ductules of WT and ERbetaKO vs. ERalphaKO female mice. In the latter, efferent ductules became hypertrophied and dilated, whereas only small tubules remained in WT and ERbetaKO adult mice. The serum testosterone concentrations were similar in 21- to 25-day-old ERalphaKO, heterozygous, and WT female mice, suggesting that increased testosterone was not inducing enlargement of efferent ductules in ERalphaKO females. In conclusion, remnants of efferent ductules persisted in normal adult female mice, although these structures were greatly reduced in size compared with efferent ductules in ERalphaKO female mice. The underlying mechanism inducing hypertrophy and dilation of efferent ductules in ERalphaKO females is not clear, but secretory and/or reabsorptive function of female efferent ductules may involve ERalpha.

Antiestrogenic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in mouse uterus: critical role of the aryl hydrocarbon receptor in stromal tissue

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the role of aryl hydrocarbon receptor (AhR) in estradiol (E(2))-induced uterine epithelial mitogenic activity and secretory protein mRNA expression were determined. Ovariectomized wild-type (wt) and AhR-knockout (AhRKO) mice received oil, E(2), or 5 microg/kg TCDD+E(2). E(2) stimulated similar large increases in the uterine epithelial labeling index (LI) and mRNA abundance for the E(2)-dependent epithelial secretory protein, lactoferrin (LF), in both wt and AhRKO mice. However, uterine epithelial LI and LF mRNA were significantly reduced by TCDD+E(2) in wt but not AhRKO mice. To determine the roles of stromal and epithelial AhR in the TCDD effect, uterine stroma and epithelium from AhRKO and wt mice were enzymatically separated and recombined into four types of tissue recombinants that either contained or lacked AhR in one or more tissue compartments. Tissue recombinants were grafted into nude mice, which were later ovariectomized and given oil, E(2), or TCDD+E(2). Epithelial LI was significantly reduced by TCDD in grafts containing stromal AhR, regardless of epithelial AhR status. However, LI was unaffected by TCDD in grafts lacking stromal AhR, even when epithelial AhR was present. Thus, TCDD inhibits E(2)-induced uterine epithelial mitogenic and secretory activity, and this requires AhR. Anti-proliferative effects of TCDD on uterine epithelia appear to be mediated indirectly through stromal AhR, suggesting that liganded AhR alters epithelial function by disrupting normal E(2)-induced stromal activity. This is the first demonstration that TCDD impairs uterine epithelial function by altering normal stromal-epithelial interactions in vivo.

Normal development of thymus in male and female mice requires estrogen/estrogen receptor-alpha signaling pathway

Estrogen receptors (ERs) are expressed in the thymus of both males and females, but their role in thymic development and function is unclear. To determine whether ERalpha plays a role in thymic function of either males or females, we compared thymuses of male and female wild-type (WT) and ERalpha knockout (alphaERKO) mice from birth to adulthood. Although thymic size was similar in both male and female WT and alphaERKO mice at birth (d 0), by postnatal d 5 and at all subsequent ages, both male and female alphaERKO mice had significant (30-55%) reductions in thymic weight. Morphometric analysis revealed a reduction in thymic medullary areas in adult alphaERKO mice compared with age-matched WT controls that paralleled thymic involution. There were changes in relative percentages of CD4+ and CD4+CD8+ T-cells, and large decreases (70-80%) in overall absolute numbers of CD4+ and CD4+CD8+ T-cells. Serum corticosterone and testosterone levels were not different in either neonatal or adult male WT or alphaERKO mice, and serum levels of 17beta-estradiol (E2) were similar in neonatal WT and alphaERKO males, indicating that increases in these thymolytic hormones are not responsible for the decreased thymic weight in alphaERKO males. Additionally, delayed-type hypersensitivity was significantly increased in male alphaERKO mice compared with WT mice. In summary, ERalpha deficiency does not inhibit initial differentiation or fetal thymic development, but the absence of ERalpha results in marked decreases in thymic size in both sexes during the postnatal period. These results are the first direct demonstration that the E2/ERalpha signaling system is necessary for maintenance of normal postnatal function of the female thymus gland. The similar results obtained in males demonstrate a role for the E2/ERalpha signaling system in the male thymus and emphasize that estrogens play a more critical role in the male than previously realized.

Myocardial ischemia-reperfusion injury in estrogen receptor-alpha knockout and wild-type mice

We investigated the function of estrogen receptor-alpha in global myocardial ischemia and reperfusion injury in male estrogen receptor-alpha knockout (ERKO) and wild-type mice. Mouse hearts were subjected to 45 min of global ischemia followed by 180 min of reperfusion. The hearts were excised, cannulated, and maintained in a chilled (4 degrees C) cardioplegia solution until warm (37 degrees C) oxygenated Krebs-Henseleit bicarbonate buffer was perfused through the coronary arteries. ERKO hearts started beating later and had a higher incidence of ventricular fibrillation and/or tachycardia than control hearts. Coronary flow rate was significantly lower in ERKO hearts during the 90- and 120-min periods of reperfusion. Ca(2+) accumulation was significantly greater following 30, 90, 120, 150, and 180 min of reperfusion in ERKO hearts. Nitrite production was significantly less in ERKO hearts following 90, 120, and 150 min of reperfusion. Myocardial reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide was significantly lower in experimental ERKO hearts. Marked interstitial edema and contraction bands were seen in hematoxylin-eosin-stained sections of ischemia-reperfused ERKO hearts but not in control tissues. Hematoxylin-basic fuchsin-picric acid-stained sections from experimental ERKO hearts had fewer viable myocytes compared with controls. Transmission electron microscopy revealed swollen and fragmented mitochondria with amorphous and granular bodies, loss of matrix, and rupture of cristae in experimental ERKO hearts. This is the first demonstration that estrogen receptor-alpha plays a cardioprotective role in ischemia-reperfusion injury in males.

Paracrine regulation of epithelial progesterone receptor by estradiol in the mouse female reproductive tract

Regulation of progesterone receptor (PR) by estradiol-17beta (E(2)) in mouse uterine and vaginal epithelia was studied. In ovariectomized mice, PR expression was low in both vaginal stroma and epithelium, but high in uterine epithelium. E(2) induced PR in vaginal epithelium and stroma, but down-regulated PR in uterine epithelium. Analysis of estrogen receptor alpha (ERalpha) knockout (ERKO) mice showed that ERalpha is essential for E(2)-induced PR expression in both vaginal epithelium and stroma, and for E(2)-induced down-regulation, but not constitutive expression of PR in uterine epithelium. Regulation of PR by E(2) was studied in vaginal and uterine tissue recombinants made with epithelium and stroma from wild-type and ERKO mice. In the vaginal tissue recombinants, PR was induced by E(2) only in wild-type epithelium and/or stroma. Hence, in vagina, E(2) induces PR directly via ERalpha within the tissue. Conversely, E(2) down-regulated epithelial PR only in uterine tissue recombinants constructed with wild-type stroma. Therefore, down-regulation of uterine epithelial PR by E(2) requires stromal, but not epithelial, ERalpha. In vitro, isolated uterine epithelial cells retained a high PR level with or without E(2), which is consistent with an indirect regulation of uterine epithelial PR in vivo. Thus, E(2) down-regulates PR in uterine epithelium through paracrine mechanisms mediated by stromal ERalpha.

Paracrine regulation of epithelial progesterone receptor and lactoferrin by progesterone in the mouse uterus

The objective of this study was to determine whether uterine stromal and/or epithelial progesterone receptor (PR) is required for the antagonism by progesterone (P(4)) of estradiol-17beta (E(2)) action on expression of PR and lactoferrin in uterine epithelium. Uterine tissue recombinants were prepared with epithelium (E) and stroma (S) from wild-type (wt) and PR knockout (PRKO) mice: wt-S+wt-E and PRKO-S+wt-E. P(4) action on epithelial PR expression was studied in wt-S+wt-E and PRKO-S+wt-E tissue recombinants. E(2) down-regulated epithelial PR in both types of tissue recombinants, but P(4) blocked E(2)-induced down-regulation of epithelial PR only in wt-S+wt-E tissue recombinants. Thus, P(4) requires stromal PR to inhibit E(2)-induced down-regulation of epithelial PR. Epithelial PR is not sufficient in itself. The inhibitory effect of P(4) on lactoferrin expression was studied in 4 types of tissue recombinants (wt-S+wt-E, PRKO-S+wt-E, wt-S+PRKO-E, and PRKO-S+PRKO-E). E(2) induced lactoferrin in all 4 types of tissue recombinants. P(4) blocked E(2)-induced lactoferrin expression only in wt-S+wt-E tissue recombinants. In wt-S+PRKO-E tissue recombinants, P(4) inhibited lactoferrin expression only partially. P(4) failed to block E(2)-induced lactoferrin expression in PRKO-S+wt-E and PRKO-S+PRKO-E tissue recombinants. Thus, both epithelial and stromal PR are essential for full P(4) inhibition of E(2)-induced lactoferrin expression.

Postulated human sperm count decline may involve historic elimination of juvenile iodine deficiency: a new hypothesis with experimental evidence in the rat

Human sperm count studies, historic dietary iodination, and an animal model where neonatal goitrogen administration causes unprecedented testis enlargement, together suggest an hypothesis relevant to the postulated fall in human sperm counts. We present the hypothesis with a supporting study extending the model to include iodine deficiency. In a one-generation rat reproduction study, dams were fed an iodine sufficient (control, 200 ppb I) or deficient (low iodine diet [LID], <20 ppb I) diet from prebreeding through weaning, when male offspring were divided into three groups: 1) controls from iodine sufficient dams, 2) neonatal LID (NLID) from the LID dams, fed control diet postweaning, and 3) chronic LID (CLID) from LID dams, fed a moderate LID (40 ppb I) postweaning. F1 males were euthanized on postnatal day (PND) 133+/-1. Each of the three diet groups comprised two subgroups in which testicular parameters were evaluated: 1) daily sperm production (DSP), sperm motility, morphology, and histopathology, and 2) Sertoli cell and round spermatid morphometry. In the first subgroup, NLID and CLID testes weights were 8.5% and 14.0% heavier than their unusually heavy controls (3.921 g; historical control mean approximately 3.5 g), with proportional DSP increases. Sperm motility, morphology, and testis histopathology were unaffected. In the morphometry subgroup, respective increases in NLID and CLID rats included testes weights (+28.6% and +20.3%), Sertoli cells (+24.8% and +23.9%), and round spermatids (+20.4% and +15.8%). The results indicate that neonatal iodine deficiency can significantly increase spermatogenic function in rats, and support our hypothesis concerning human sperm counts.

Ah receptor and ARNT protein and mRNA concentrations in rat prostate: effects of stage of development and 2,3,7, 8-tetrachlorodibenzo-p-dioxin treatment

Effects of stage of development and 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on aryl hydrocarbon receptor (AhR) and AhR nuclear translocator (ARNT) protein concentrations in reproductive organs of male rats were determined. AhR protein levels in developing rat ventral and dorsolateral prostate decreased with age, declining approximately 70% between Postnatal Days (PND) 1 and 21. ARNT protein levels also decreased with age in dorsolateral, but not ventral prostate. The developmental decreases in prostatic AhR and ARNT protein were associated with decreases in AhR and ARNT mRNA. AhR and ARNT protein concentrations in fetal urogenital sinus on Gestation Days (GD) 16, 18, and 20 were similar to levels in ventral prostate on PND 7. TCDD exposure of adult male rats (0.2, 1, 5, or 25 micrograms/kg po, 24 h) decreased AhR but not ARNT protein in ventral and dorsolateral prostate, vas deferens, and epididymis. In utero and lactational TCDD exposure (1.0 micrograms/kg dam po, GD 15) did not alter ARNT levels but reduced prostatic AhR protein levels on PND 7 and delayed the developmental decrease in AhR protein in ventral and dorsolateral prostate. Finally, pretreatment of rat pups for 24 h with TCDD (5 micrograms/kg ip) down-regulated prostatic AhR protein on PND 7, but not on PND 1. Thus, prostatic AhR and ARNT protein and mRNA levels are regulated with age, whereas only AhR protein concentration is altered by TCDD exposure. Because in utero and lactational TCDD exposure only decreased prostatic AhR on PND 7, it is unlikely that down-regulation of AhR is the mechanism by which perinatal TCDD exposure impairs prostate development.

Tissue compartment-specific estrogen receptor-alpha participation in the mouse uterine epithelial secretory response

17Beta-estradiol (E2) acts through the estrogen receptor (ER) to regulate uterine epithelial cell growth, proliferation, differentiation, and secretory protein production. We have previously shown that E2-induced uterine epithelial proliferation is mediated indirectly by ER alpha-positive stroma; epithelial ER alpha is neither necessary nor sufficient for E2-induced uterine epithelial mitogenesis. In the present study, we addressed the question of whether production of uterine epithelial secretory proteins and their messenger RNAs (mRNAs) requires ER alpha in stroma, epithelium, or both by analyzing tissue recombinations composed of uterine tissue from adult ER alpha knockout (ko) and neonatal BALB/c (wt) mice. Stroma (S) and epithelium (E) were separated by trypsinization, and four types of uterine tissue recombinants were prepared: wt-S + wt-E, wt-S + ko-E, ko-S + wt-E, and ko-S + ko-E. These tissue recombinants were grown as subrenal capsule grafts in intact female nude mice for 4 weeks, at which time the hosts were ovariectomized. To assess the production of secretory proteins and their mRNAs, 1 week after ovariectomy the hosts were given three daily injections of oil or E2 (100 ng), and then 24 h later the grafts were recovered and used for either ER or lactoferrin (LF) immunohistochemistry. To assess steady state mRNA levels by Northern blotting, hosts received one injection of oil or E2 24 h before harvest. ER immunohistochemistry was used to monitor the completeness of tissue separation. In wt-S + wt-E tissue recombinants from E2-treated hosts, the epithelium stained intensely for LF (an abundant E2-dependent uterine secretory protein), whereas similar tissue recombinants from oil-treated hosts showed minimal immunostaining. Conversely, LF immunostaining was minimal in wt-S + ko-E grafts from both oil- and E2-treated hosts. LF staining was also minimal in ko-S + ko-E and ko-S + wt-E tissue recombinants regardless of hormone treatment. For Northern analyses, the epithelial content of the tissue recombinants was monitored using the reference epithelial transcript, E-cadherin. While all tissue recombinant groups expressed E-cadherin mRNA, wt-S + wt-E tissue recombinants from E2-treated hosts produced a strong, single 2.6-kb band of LF mRNA. LF transcripts were minimal or absent in all other tissue recombinant types. Northern blotting results identical to those seen for LF were also observed for the uterine secretory protein complement component C3. Our data demonstrate that both stromal and epithelial ER alpha are required for the production of LF protein and of LF or C3 mRNAs in response to E2. Thus, in contrast to E2-induced epithelial mitogenesis, which requires only stromal ER alpha, both epithelial and stromal ER alpha are necessary for the production of E2-dependent epithelial secretory proteins.

Inhibin B levels in plasma of the male rat from birth to adulthood: effect of experimental manipulation of Sertoli cell number

Sertoli cells undergo important changes in their number and function at different ages in the rat and may be the primary source of circulating inhibin B. The aims of this study were 1) to establish the profile of inhibin B levels from birth to adulthood in normal rats and 2) to identify whether experimental manipulation of Sertoli cell numbers was able to alter this profile. Levels of inhibin B, measured by a specific two-site assay, increased fivefold in normal Wistar rats between day 3 and days 10-15, plateaued, and then declined in late puberty to reach adult levels which were approximately 60% of those observed on days 10-15. The increase in inhibin B levels in the neonatal period coincided with the period of Sertoli cell multiplication as indicated by incorporation of bromodeoxyuridine. Neonatal treatment of rats with a GnRH antagonist (GnRHa) reduced Sertoli cell number and adult testis weight by 48% and significantly reduced plasma levels of inhibin B at all ages through to adulthood. Induction of neonatal hypothyroidism in Sprague-Dawley rats by administration of propylthiouracil (PTU) up to day 25 of age increased final testis weight by 41% (indicative of increased Sertoli cell numbers) and resulted in elevation of plasma levels of inhibin B at all ages beyond 7 days of age. The degree of change in inhibin B levels in adult rats in the two experimental treatment groups was approximately proportional to the change in final testis weight. Plasma follicle-stimulating hormone (FSH) showed changes opposite to inhibin B, with levels being lowered in PTU-treated rats and elevated (beyond day 25) in GnRHa-treated animals. The present results suggest that final Sertoli cell number per testis exerts an important effect on the circulating level of inhibin B (and FSH) in the rat. These findings are compared to the emerging data for the human male.

Thyroid hormone and follicle-stimulating hormone regulate Müllerian-inhibiting substance messenger ribonucleic acid expression in cultured neonatal rat Sertoli cells

Thyroid hormone is a major regulator of Sertoli cell development, and the present study sought to determine the role of T3 in Müllerian-inhibiting substance (MIS) messenger RNA (mRNA) expression. MIS, a Sertoli cell secretory protein that induces Müllerian duct regression and also may be critical for germ and Leydig cell development, is maximal perinatally, then decreases as Sertoli cells mature. The fall in MIS mRNA expression is delayed by hypothyroidism in vivo, indicating that T3 could regulate MIS mRNA. However, understanding of the hormonal regulation of MIS has been limited due partly to the lack of a primary Sertoli cell culture system in which sustained expression of MIS or its mRNA can be obtained. We have developed a Sertoli cell culture system for examining hormonal regulation of MIS mRNA. We then tested the effects of T3 and/or FSH treatment on MIS mRNA levels in this new system. Initial studies indicated that MIS mRNA production by 5-day-old rat Sertoli cells was minimal in vitro. Therefore, Sertoli cells from 2-day-old rats were cultured for 2 or 4 days. After 2 days in vitro, steady state MIS mRNA levels were decreased to 36% of the levels seen in freshly isolated Sertoli cells from 2-day-old rats. However, by day 4 of culture, steady state MIS mRNA production had recovered to 67% of that seen in freshly isolated 2-day-old Sertoli cells, which closely paralleled the decrease seen in MIS production in vivo from days 2-6. MIS mRNA levels were decreased 53%, 64%, and 86% in cultures treated with 0.01, 0.1, and 1.0 nM T3 (P < 0.05), respectively. This decrease in Sertoli cell MIS mRNA did not reflect a nonspecific effect on cell viability and/or activity, as shown by a dose-responsive increase in inhibin-alpha mRNA in these same cultures. FSH (2.5-100 ng/ml) also produced a dose-responsive decrease in MIS mRNA levels, and FSH and T3 together had an additive inhibitory effect on MIS mRNA levels, indicating that these hormones may act through distinct mechanisms. In summary, this is the first primary culture system in which sustained MIS mRNA production can be demonstrated, and it should prove useful for understanding the regulation of MIS in developing Sertoli cells. In addition, T3 and FSH are major regulators of the postnatal decrease in MIS production by the rat Sertoli cell, and these hormones may act through separate pathways.

Role of stromal and epithelial estrogen receptors in vaginal epithelial proliferation, stratification, and cornification

Estradiol 17-beta (E2) induces epithelial proliferation, stratification, and cornification in vaginal epithelium. Our aim was to determine the respective roles of epithelial and stromal estrogen receptor-alpha (ER alpha) in these E2-induced events. Vaginal epithelium (E) and stroma (S) from adult ER alpha knockout (ko) and wild-type (wt) neonatal Balb/c mice were enzymatically separated and used to produce four types of tissue recombinants in which epithelium, stroma, or both lack functional ER alpha. Tissue recombinants were grafted into female nude mice, which were subsequently ovariectomized and treated with oil or E2. In response to E2 treatment, grafts prepared with wt-S (wt-S + wt-E and wt-S + ko-E) showed similar large increases in epithelial labeling index, indicating that E2 stimulated epithelial proliferation despite a lack of epithelial ER alpha in wt-S + ko-E tissue recombinants. Conversely, in tissue recombinants prepared with ko-S (ko-S + wt-E and ko-S + ko-E), epithelial labeling index remained at baseline levels after E2 or oil treatment, even though epithelial ER alpha were detected in ko-S + wt-E grafts. Epithelial cornification was present in wt-S + wt-E grafts from E2-treated hosts, whereas epithelium in all other tissue recombinants failed to cornify. Grafts composed of wt-S + wt-E from E2-treated hosts had highly stratified epithelium, whereas epithelial thickness was reduced almost 60% in wt-S + ko-E tissue recombinants grown in E2-treated hosts and was atrophic in all other tissue recombinants. In addition, cytokeratin 10, a marker of epithelial differentiation, was strongly expressed in wt-S + wt-E tissue recombinants grown in E2-treated hosts but was markedly reduced or absent in all other tissue recombinants. These results indicate that E2-induced vaginal epithelial proliferation is mediated indirectly through stromal ER alpha, consistent with our recent findings in uterus. Conversely, both epithelial and stromal ER alpha are required for E2-induced cornification and normal epithelial stratification. These are the first known functions attributed to epithelial ER alpha in vivo and the first time any epithelial response to E2 has been shown to involve both stromal and epithelial ER alpha.

Thyroid hormone effects on androgen receptor messenger RNA expression in rat Sertoli and peritubular cells

Postnatal Sertoli cell maturation is characterized by a pronounced rise in androgen receptor (AR) expression, which increases several fold between birth and adulthood. Since both 3,3',5-triiodothyronine (T3) and FSH regulate Sertoli cell proliferation and differentiation, we have determined the effects of T3 and FSH on AR mRNA expression in cultured Sertoli cells from 5-day-old rats. These cultures contain 5-9% peritubular cells, which also express AR mRNA. To insure that the observed T3 responses did not result from peritubular cells, we examined T3 effects on AR mRNA expression in cultured 20-day-old Sertoli cells (which contain minimal peritubular contamination) and peritubular cells, and measured thyroid hormone receptor (TR) mRNA expression in both of these cell types. Sertoli cells from 5- and 20-day-old rat testes were grown in serum-free medium alone (controls) or with ovine FSH (100 ng/ml) and/or T3 (100 nM) for 4 days. Peritubular cells purified from 20-day-old rat testes were grown in serum-containing medium for 8 days. These cells were split 1:4, and grown an additional 8 days, the last 4 days in serum-free medium with or without T3. TR and AR mRNA levels in all cultures were determined by Northern blotting. AR mRNA levels in 5- and 20-day-old cultured Sertoli cells were significantly (P < 0.05) increased by both T3 and FSH alone. Furthermore, AR mRNA levels in Sertoli cells treated with T3 and FSH were greater than with either alone. TR mRNA expression was detected in cultured peritubular cells, but TR mRNA levels in these cells were only approximately 30% of that seen in 20-day-old cultured Sertoli cells. In contrast to Sertoli cells, T3 did not affect peritubular AR mRNA expression. These results indicate that T3 is an important regulator of the postnatal Sertoli cell AR mRNA increase. The additive effects of maximally stimulatory doses of FSH and T3 suggest these hormones work through different mechanisms to increase AR mRNA. TR mRNA expression in peritubular cells indicates these cells may be direct T3 targets, though the function of T3 in these cells is unknown.

A physiologically based approach to the study of bisphenol A and other estrogenic chemicals on the size of reproductive organs, daily sperm production, and behavior

Two chemicals previously shown to have estrogenic activity, bisphenol A and octylphenol, were examined for their effects on accessory reproductive organs and daily sperm production in male offspring of mice fed these chemicals during pregnancy. These chemicals are used in the manufacture of plastics and other products, and have been detected in food and water consumed by animals and people. From gestation day 11-17 female mice were fed an average concentration (dissolved in oil) of bisphenol A or octylphenol of 2 ng/g body weight (2 ppb) and 20 ng/g (20 ppb). The 2 ppb dose of bisphenol A is lower than the amount reported to be swallowed during the first hour after application of a plastic dental sealant (up to 931 micrograms; 13.3 ppb in a 70 kg adult). We found that the 2 ng/g dose of bisphenol A permanently increased the size of the preputial glands, but reduced the size of the epididymides; these organs develop from different embryonic tissues. At 20 ng/g, bisphenol A significantly decreased efficiency of sperm production (daily sperm production per g testis) by 20% relative to control males. The only significant effect of octylphenol was a reduction in daily sperm production and efficiency of sperm production at the 2 ng/g dose. A new approach to studying physiologically relevant doses of environmental endocrine disruptors is discussed, particularly with regard to the development of the reproductive organs, the brain, and behavior.

Estrogen receptor (alpha and beta) expression in the excurrent ducts of the adult male rat reproductive tract

The understanding of estrogen's function in the male reproductive tract is limited, and estrogen receptor (ER) localization in the reproductive tract of the adult male rat has not been described. In the present study, ERalpha was localized by immunohistochemistry using ER21 antibody, which recognizes only ERalpha. Strongest immunoreactivity was seen in epithelia of ductuli efferentes and the initial segment of the epididymis. Nuclei of both ciliated and nonciliated cells were positive. The epithelium of the rete testis, and caput, corpus, and cauda epididymides stained less intensely for ERalpha. The vas deferens epithelium was ERalpha-negative. Stromal tissue in the excurrent ducts was also ERalpha-positive. Using 3H-estradiol autoradiography, specific binding of estradiol was seen in nuclei of ductuli efferentes. Estrogen receptor alpha mRNA expression was greatly enhanced in ductuli efferentes compared to other regions of the male tract and was 3.5x greater than in the uterus. For comparison, the presence of ERalpha was determined using reverse transcription-polymerase chain reaction (RT-PCR) amplification. Estrogen receptor beta mRNA was expressed throughout the male tract and in the prostate. These results indicate that all organs in the male excurrent ductal system of the rat express ERalpha and are potential targets of estrogen. However, the ductuli efferentes are the site of the most intense ERalpha expression. The role of ERbeta remains to be determined, but its expression appears ubiguitous in the male tract.

Elucidation of a role for stromal steroid hormone receptors in mammary gland growth and development using tissue recombinants

The use of tissue recombinants in conjunction with steroid receptor deficient mice is described as a tool to dissect the complex paracrine pathways of sex-hormone-regulated epithelial growth and ductal morphogenesis in the mammary gland and other hormone target organs. The basic methodology involves the construction of the four possible tissue recombinants composed of epithelium (E) and stroma (S) from wild-type (wt) and knock-out (KO) mice: wt-S + wt-S, wt-S + KO-E, KO-S + KO-E, and KO-S + wt-E. All tissue recombinants are grown as subrenal capsule grafts in nude mice. Following appropriate hormonal challenge epithelial growth can be studied in the four types of tissue recombinants. Such studies using estrogen receptor, androgen receptor and progesterone receptor knockout mice demonstrate that epithelial steroid receptors are neither necessary nor sufficient for hormonal regulation of epithelial proliferation. Instead, hormonal regulation of epithelial proliferation is a paracrine event mediated by hormone-receptor-positive stromal cells.

Neonatal hypothyroidism permanently alters follicle-stimulating hormone and luteinizing hormone production in the male rat

Transient neonatal hypothyroidism, induced with the goitrogen 6-n-propyl-2-thiouracil (PTU), results in dramatic increases in both testis size and sperm production in the adult rat. The observed increases in testis size and function occur in the presence of normal circulating testosterone levels. However, circulating gonadotropin levels are chronically reduced by 30-50% at all times in treated males. To better understand the permanent reduction in serum gonadotropin levels following transient neonatal hypothyroidism, we conducted a series of experiments to evaluate pituitary and hypothalamic function in the adult male PTU-treated rat. PTU treatment led to a significant reduction in GnRH-stimulated LH production. Castration resulted in 3.9- to 8.5-fold increases in circulating gonadotropin levels in both treated and control males; however, the absolute increases were significantly reduced in treated males. In contrast to circulating levels, pituitary gonadotropin contents did not increase in treated males after castration. PTU treatment did not lead to a reduction in the density of either luteotropes or folliculotropes, and both cell types increased in size and density after castration. The relative concentrations of both gonadotropin beta-subunit messenger RNAs increased more slowly in treated males than in controls after castration. Thus, although treated rats have the intrinsic ability to produce normal circulating levels of LH and FSH, gonadal feedback and an overall reduction in gonadotrope synthetic ability combine to produce the chronically reduced circulating levels of these hormones.

Stromal estrogen receptors mediate mitogenic effects of estradiol on uterine epithelium

Estradiol-17beta (E2) acts through the estrogen receptor (ER) to regulate uterine growth and functional differentiation. To determine whether E2 elicits epithelial mitogenesis through epithelial ER versus indirectly via ER-positive stromal cells, uteri from adult ER-deficient ER knockout (ko) mice and neonatal ER-positive wild-type (wt) BALB/c mice were used to produce the following tissue recombinants containing ER in epithelium (E) and/or stroma (S), or lacking ER altogether: wt-S + wt-E, wt-S + ko-E, ko-S + ko-E, and ko-S + wt-E. Tissue recombinants were grown for 4 weeks as subrenal capsule grafts in intact female nude mice, then the hosts were treated with either E2 or oil a week after ovariectomy. Epithelial labeling index and ER expression were determined by [3H]thymidine autoradiography and immunohistochemistry, respectively. In tissue recombinants containing wt-S (wt-S + wt-E, wt-S + ko-E), E2 induced a similar large increase in epithelial labeling index compared with oil-treated controls in both types of tissue recombinants despite the absence of epithelial ER in wt-S + ko-E tissue recombinants. This proliferative effect was blocked by an ER antagonist, indicating it was mediated through ER. In contrast, in tissue recombinants prepared with ko-S (ko-S + ko-E and ko-S + wt-E), epithelial labeling index was low and not stimulated by E2 despite epithelial ER expression in ko-S + wt-E grafts. In conclusion, these data demonstrate that epithelial ER is neither necessary nor sufficient for E2-induced uterine epithelial proliferation. Instead, E2 induction of epithelial proliferation appears to be a paracrine event mediated by ER-positive stroma. These data in the uterus and similar studies in the prostate suggest that epithelial mitogenesis in both estrogen and androgen target organs are stromally mediated events.

Neonatal hypothyroidism alters the pattern of prostatic growth and differentiation, as well as plasminogen activator and metalloprotease expression, in the rat

The purpose of this study was to examine whether changes in growth, ductal histology, and expression of plasminogen activator (PA) and matrix metalloproteases are associated with the increased prostatic weight and DNA content seen in adult rats that were treated neonatally with the goitrogen 6-propyl-2-thiouracil (PTU). Ventral prostatic weights were initially reduced in PTU-treated rats but were increased 40% over those of controls by Day 180; this increase in prostatic weight was also accompanied by increases in the number of prostatic ductal tips. In controls, prostatic PA and gelatinase A activities decreased after completion of morphogenesis at 21-28 days of age. In contrast to controls, PA and gelatinase A activities were maintained through puberty (42 days) in PTU-treated rats but declined by 90 days. The elevated PA activity in both prostatic lobes at 42 days of age in PTU-treated rats was inhibited by amiloride, indicating that it is the urokinase form of PA. These data show that the increased prostatic weight and DNA content in adult rats following neonatal PTU treatment results from a delayed but extended period of growth and the formation of new ductal elements. There is a temporal overexpression of urokinase and gelatinase A associated with the increased ductal branching, indicating as well an extended period of morphogenesis that results in their eventual increased adult size. The prostatic enlargement in PTU-treated rats may serve as a useful model to study regulation of both normal and abnormal prostatic growth and morphogenesis.

Increased proliferation of Leydig cells induced by neonatal hypothyroidism in the rat

Treatment of male rat pups with the reversible goitrogen 6-n-propyl-2-thiouracil (PTU), administered by adding 0.1% PTU to the mother's drinking water from birth through weaning, increases adult testis size, number of Sertoli cells, and daily sperm production. Adult Leydig cell numbers are also increased by 70%, despite permanent suppression of serum luteinizing hormone (LH). The present study was designed to test whether this effect results from an increase in proliferation of Leydig cells or the mesenchymal precursors. The labeling indices (LI) of six interstitial cell types were measured by tritiated thymidine autoradiography. With the exception of Leydig cells, LI declined after birth for all interstitial cell types in both control and PTU-treated rats, but mesenchymal cell proliferation was not significantly different in control and treated rats. In contrast, the LI of Leydig cells from PTU-treated rats rose by day 10, remained elevated through day 45 (highest on day 35 at 3.6-fold higher than control, P < 0.05), and declined to control values by day 50. The LI of Leydig cells in control rats was unchanged during the experiment. Proliferating Leydig cells were immature, as shown by their cytoplasmic lipid droplets. Adult Leydig cells, which lack lipid droplets, did not proliferate. Mesenchymal and immature Leydig cells contained thyroid hormone receptor mRNA; levels in adult Leydig cells were reduced but detectable. In conclusion, proliferation of Leydig cells, rather than increased proliferation of their mesenchymal precursors, is the principal mechanism responsible for the increase in Leydig cell number after neonatal hypothyroidism. Increased Leydig cell proliferation could result from direct effects of hypothyroidism on these cells. Alternatively, the increased Sertoli cell population that results from PTU treatment could also stimulate increased Leydig cell proliferation, or both of these mechanisms could contribute to the Leydig cell increase.

Neonatal polychlorinated biphenyl treatment increases adult testis size and sperm production in the rat

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants which decrease serum thyroxine (T4) concentrations. We have previously demonstrated that neonatal hypothyroidism in the rat increases Sertoli cell numbers, adult testis weight, and daily sperm production (DSP). The aim of this study was to determine if neonatal PCB treatment increases adult testis weight and DSP. Treated rats received either Aroclor 1242 or 1254 (0.4-3.2 mg/day), from birth to Day 25 by daily injection; some treated litters also received T4 replacement. Controls received vehicle alone. Tritiated thymidine autoradiography was used to assess Sertoli cell proliferation in 15-day control and Aroclor-treated rats. Serum T4 was measured at 25, 45, and 135 days of age, and serum testosterone, testis weight, DSP, and testicular histology were examined at 135 days. Both Aroclor 1242 and 1254 suppressed serum T4 concentrations; Aroclor 1254 was more potent and long lasting. Testis weight was increased 22 and 13% in rats that received the 1.6 and 3.2 mg/day Aroclor 1242 doses, respectively, while the 0.4 mg/day dose did not produce significant increases. Aroclor 1254 produced significant increases in testis weight of 13 and 23% at the 0.4 and 1.6 mg/day doses, respectively. The 1.6 mg/day Aroclor 1242 and the 0.4 and 1.6 mg/day Aroclor 1254 doses increased DSP by 27, 11, and 42%, respectively; other treatments did not produce significant increases. At 15 days of age, Sertoli cell proliferation was greater in treated rats than in controls. T4 replacement decreased or eliminated the increased testis weight and DSP seen in Aroclor-treated rats. The highest dose of Aroclor 1242 and both doses of Aroclor 1254 decreased adult body weight, while other treatments did not. These results indicate that neonatal PCB treatment increases adult testis weight and DSP in rats. PCBs produce this effect primarily by inducing hypothyroidism, which leads to increased Sertoli cell proliferation, testis weight, and DSP. Thus PCBs, despite inhibitory effects on adult reproductive organs, can paradoxically stimulate increases in adult testis weight and DSP when administered neonatally. These data emphasize the pleiotropic nature of PCB effects and the susceptibility of the developing reproductive system to environmental factors.

Neonatal hypothyroidism causes delayed Sertoli cell maturation in rats treated with propylthiouracil: evidence that the Sertoli cell controls testis growth

BACKGROUND

The testes of rats treated neonatally with propylthiouracil (PTU) grow to almost twice their normal size. The cause of testicular enlargement has been suggested to be the result of delayed maturation of Sertoli cells, allowing Sertoli cell division to occur beyond the 15th postnatal day, the commonly recognized cutoff date for Sertoli cell divisions. It has been shown that an increased population of Sertoli cells in postnatal development supports increased numbers of germ cells in adult animals. After examining developing rats treated neonatally with PTU, we hypothesized that an approximate 10-day delay in maturation was occurring and proceeded to test this hypothesis experimentally. Thus the purpose of this report was to determine if a 10-day delay in maturation could explain the increased numbers of Sertoli cells and increased testis size in PTU-treated animals.

METHODS

Both control animals and animals treated neonatally with PTU N = 5/group were sacrificed at 15 and 25 days of age and prepared for electron microscopy.

RESULTS

Micrographs show and morphometric ultrastructural analysis of numerous parameters demonstrated at the 95% probability level that Sertoli cells from 25-day-old PTU animals are not different in size and most constituents (volume and surface area) from 15-day-old control animals and are less mature than 25-day-old control animals. Mitosis of Sertoli cells was observed in PTU-treated animals in 25-day-old animals but not in age-matched controls. The number of Sertoli cells in 25-day-old PTU-treated animals is significantly increased over age-matched controls. Micrographs show the presence of immature Sertoli cell nuclei in 25-day-old animals receiving PTU as well as increased germ cell degeneration in this group. Sertoli cell tight junction formation is also delayed in PTU-treated animals as compared with controls.

CONCLUSIONS

Together, the data show that delayed maturation of Sertoli cells occurs in treated animals that corresponds to a minimum of 10 developmental days. In the immature state, Sertoli cells continue to divide. Data presented herein and published data related to PTU treatment indicate that delayed maturation of the Sertoli cell results in delayed maturation and proliferation of other testicular cell types. From this and from published data, the hypothesis is presented that the Sertoli cell is responsible for the overall control of testis development.

Triiodothyronine inhibits proliferation and stimulates differentiation of cultured neonatal Sertoli cells: possible mechanism for increased adult testis weight and sperm production induced by neonatal goitrogen treatment

Transient neonatal hypothyroidism in the rat causes prolonged Sertoli cell proliferation, delayed Sertoli cell maturation, and increased adult Sertoli cell number, testis weight, and sperm production. Conversely, neonatal hyperthyroidism decreases Sertoli cell proliferation and ultimate testis size. This suggests that thyroid hormones might normally directly inhibit Sertoli cell proliferation while promoting maturation. However, these Sertoli cell effects could be due to secondary hormonal or metabolic effects of hypo- or hyperthyroidism. In this study, we directly tested thyroid hormone effects on Sertoli cell proliferation and differentiation in vitro. Sertoli cells from 5-day-old rat testes were grown in serum-free medium alone (controls) or with additional triiodothyronine (T3; 1-200 nM) and/or FSH (1 microgram/ml). After 4 days, cultures were used to obtain RNA for Northern hybridization or for thymidine autoradiography. Labeling index (LI) for control cultures and cultures receiving 100 nM T3 alone was 5.2 +/- 0.5% and 5.0 +/- 0.4%, respectively. The LI of FSH-treated cultures increased to 8.4 +/- 0.8% (p < 0.01 vs. control). Cultures treated with FSH and 1, 10, 100, or 200 nM T3 had LIs of 8.0 +/- 0.9%, 6.1 +/- 0.4%, 5.3 +/- 0.6%, and 4.8 +/- 0.6%, respectively; the last three values were less than for cells receiving FSH alone (p < 0.01) or FSH + 1 nM T3 (p < 0.05). Northern hybridization indicated that mRNA levels for clusterin and inhibin-beta B, Sertoli cell secretory proteins whose production normally increases during postnatal differentiation in vivo, were significantly increased by T3 or FSH alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental expression of testis messenger ribonucleic acids in the rat following propylthiouracil-induced neonatal hypothyroidism

Propylthiouracil- (PTU) induced transient neonatal hypothyroidism increases adult rat testis weight 80-100%; this effect involves prolongation of Sertoli cell proliferation. To gain insight into developmental effects of PTU on the testis, we used Northern analysis to examine chronological expression of Sertoli cell mRNA in postnatal rat testes from rats that were untreated (controls) or were given PTU from birth to Day 25. Treated rats showed prolonged early expression of genes associated with dividing Sertoli cells such as MIS (Müllerian inhibiting substance) and c-erbA alpha (thyroid hormone receptor). Expression of several other Sertoli cell mRNAs (androgen-binding protein [ABP], clusterin, and inhibin-beta B) was delayed, as was that of hemiferrin, a spermatid-specific mRNA. Temporal expression patterns for other mRNAs (sulfated glycoprotein [SGP]-1, transferrin, and inhibin-alpha) were similar in control and treated animals. Additionally, thyroid hormone replacement in PTU-treated animals decreased MIS and c-erbA alpha mRNA expression to control levels. The altered developmental pattern of expression of a number of major Sertoli cell genes reflects a prolonged mitogenesis and delayed maturation of Sertoli cells in neonatally hypothyroid animals. Furthermore, our results suggest that thyroid hormone may directly potentiate molecular events associated with cessation of Sertoli cell proliferation and maturation during early testis development.

Toxicokinetic and Toxicodynamic Influences on Endocrine Disruption by Polychlorinated Biphenyls

Polychlorinated biphenyl (PCB) mixtures and individual chlorobiphenyl (CB) congeners have various endocrine-disrupting effects, but ultimate responses may be altered by concurrent effects on enzyme levels and enzyme activities. The toxicodynamics of estrogenic PCBs and metabolites have been studied in vitro, but nonlinear dose-response relationships in vivo suggest that tests must integrate toxicokinetic parameters to explain whole-animal responses. To determine if any such interactions occurred, relatively large doses were subdivided into different treatment regimens for immature female Sprague-Dawley rats. Aroclor 1242 was uterotropic when 120 mg/kg (total) was administered (intraperitoneally) in two, three or five doses. CB 47 (2,2',4,4'-tetraCB) and CB 153 (2,2',4,4',5,5'-hexaCB) increased absolute uterine weights at 30 mg/kg on days 20 and 21. Results at 25 days in rats that received zero, two, three or five doses between days 20 and 24 were much more variable due to changes in tissue responsiveness and/or toxicokinetic interactions. In rats receiving treatment for 5 days, pentoxyresorufin O-dealkylase (PROD) activity was inversely related to CB serum residues; in rats receiving CB 153 for 2 days, PROD activity was directly related to serum residues. It was not clear whether PROD activity was the cause of or a reflection of lower serum residues; however, nonplanar CBs are better substrates for PROD than are planar CBs, and the longer-term dosing may enhance metabolism and excretion, changing the biological effects observed.

Neonatal goitrogen treatment increases adult testis size and sperm production in the mouse

Male rats made hypothyroid during neonatal life show unprecedented increases in adult testis size and daily sperm production (DSP). To determine if this effect was unique to the rat or could also be demonstrated in other species, we examined the effects of neonatal treatment with the reversible goitrogen 6-propyl-2-thiouracil (PTU) on adult testis size and function in the mouse. Male Swiss-Webster mice were untreated (control) or given PTU by adding 0.1% (w/v) to their mother's water from birth to day 25 postpartum. All pups were then weaned and given no further treatment. Sertoli cell proliferation was examined using tritiated thymidine autoradiography in some control and treated mice at 0, 5, 10, 15, 20, and 25 days, while the remainder were killed at 90 days to determine a variety of reproductive parameters. Neonatal PTU treatment decreased growth; body weight of treated mice at 4 weeks of age was 57% less than controls. Treated mice grew rapidly following cessation of PTU treatment, although their weights never equalled controls, remaining 17% smaller at 90 days of age. At 90 days of age, testis weight and DSP were increased by approximately 30% and 50%, respectively, in PTU-treated mice compared to controls. Despite the increased testis weight and function, serum testosterone concentrations were not different in control and treated mice. Testicular and epididymal histology in treated mice was similar to controls, while epididymal sperm in treated mice were motile and morphologically normal. Sertoli cell proliferation was altered in treated mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Leydig cells increase their numbers but decline in steroidogenic function in the adult rat after neonatal hypothyroidism

Administration of the goitrogen, 6-propyl-2-thiouracil (PTU), to suckling rat pups from birth through day 24 postpartum as a 0.1% solution in the mother's drinking water increases adult testis size and sperm production by about 80% and 140%, respectively, without affecting peripheral testosterone levels. The objectives of this study were to determine whether adult Leydig cell numbers were altered in PTU-treated rats and whether the steroidogenic function of these cells was normal. The number of Leydig cells per testis at 180 days increased by 69% in PTU-treated compared to control rats, whereas the average Leydig cell volume declined by about 20%. Steroidogenic function assessed in isolated adult Leydig cells decreased after neonatal PTU treatment. LH-stimulated testosterone production was reduced by 55% in Leydig cells from treated rats, commensurate with a 50% decline in the number of hCG-binding sites in these cells. The difference in steroidogenic potential was even more striking after incubations with saturating concentrations of steroid substrate, 22(R)-hydroxycholesterol; Leydig cells from treated males produced 73% less testosterone than controls. Therefore, this decrease in testosterone production may be partially due to a reduction in the numbers of LH receptors, but also reflects the impaired steroidogenic potential of these cells. These results clearly show that the dramatic increase in adult Leydig cell number after neonatal PTU treatment is counterbalanced by a permanent decline in Leydig cell steroidogenic function, producing no net change in peripheral testosterone levels.

Adult testicular enlargement induced by neonatal hypothyroidism is accompanied by increased Sertoli and germ cell numbers

Our previous studies have shown that transient neonatal hypothyroidism, induced by treatment with the reversible goitrogen 6-propyl-2-thiouracil (PTU), increases testicular size and daily sperm production in the adult rat by up to 82% and 136%, respectively. The objective of the present study was to examine morphological and functional changes in adult seminiferous tubules associated with PTU-induced increases in testicular size and sperm production. Sprague-Dawley rats were treated with PTU from birth to day 25 or left untreated; for morphometry, all testes were fixed by vascular perfusion at 90 days of age. Although testicular weight was increased 62% in treated rats, gross pathological changes were not evident in these organs, and spermatogenesis appeared morphologically normal. The percent area of testis occupied by seminiferous tubules was equal in control and treated testes, but mean seminiferous tubule diameter and length were increased in the PTU-treated testis. The adult number of Sertoli cells in treated testes was increased by 157%, and the numbers of leptotene spermatocytes and round spermatids were increased 84% and 93%, respectively. These results demonstrate that increases in Sertoli cell numbers result in increased sperm production and support the idea that Sertoli cells are the major regulators of the magnitude of sperm production. Although the round spermatid to Sertoli cell ratio was reduced by nearly 30%, the number of round spermatids per g testis was increased by 14%. This increased efficiency of sperm production was accomplished by an increased density of Sertoli cells along the basement membrane and an increased height of the seminiferous epithelium. Despite the large increase in Sertoli cell numbers in treated rats, Northern blot analysis using Sertoli cell-specific cDNA probes for transferrin and androgen-binding protein indicated that relative steady state levels of mRNAs per Sertoli cell for these two secretory proteins were similar in control and treated rats at 90 days of age.

Estrogenic and antiestrogenic actions of PCBs in the female rat: in vitro and in vivo studies

A series of studies were performed to examine the effects of various PCB congeners [3,4,3',4'-TCB (PCB77), 2,5,2',5'-TCB (PCB52), 4' OH-2,4,6-TCB (OHPCB)] and a complex PCB mixture (Aroclor 1242; A1242) on the weights and patterns of cell proliferation of immature rat uteri in vivo and the effects of A1242 on gonadotropin release by dispersed anterior pituitary cells in vitro. Immature (20-day) rats were treated ip with corn oil (vehicle), PCBs, or 17 beta-estradiol (E2) once or daily for two consecutive days. Except for PCB77, all PCBs and E2 produced significant increases in uterine weights (P < 0.01) and increases in uterine 3H-thymidine labeling. PCB77 attenuated (P < 0.01) the increase in uterine weight due to either A1242 or E2 treatment. Cultured anterior pituitary cells exposed to varying concentrations of A1242 (0.1 to 50 ppm) exhibited enhanced gonadotropin responses to gonadotropin-releasing hormone (GnRH) similar to that of E2. These results demonstrate that PCBs can produce either estrogenic or antiestrogenic effects.

Increased testis growth and sperm production in adult rats following transient neonatal goitrogen treatment: optimization of the propylthiouracil dose and effects of methimazole

Treatment of male rat pups with the reversible goitrogen 6-propyl-2-thiouracil (PTU), administered by adding 0.1% PTU to the mother's drinking water from birth to day 25, increases their testis size and daily sperm production (DSP) at 160 days of age by up to 80% and 140%, respectively. The purpose of this study was to examine the effectiveness of various concentrations of PTU and determine the PTU dose that would maximize testis growth while minimizing side effects such as decreased maternal water consumption and decreased pup growth. Whether this effect was specific to PTU was determined by evaluating the effects of another commonly used goitrogen, methimazole (MMI), in increasing adult testis size and sperm production. Dams were given PTU (0.1-0.0004% w/v) or 0.025% MMI (w/v) in their water from birth to day 25 post partum, then given no further treatment. Thyroxine concentrations were measured in all groups of pups at 25, 35 and 45 days, and testis weight and DSP were determined at 90 days of age. At 25 days of age, thyroxine concentrations were maximally decreased by PTU treatments of 0.0015% or greater; less severe decreases were produced by 0.0004% PTU or 0.025% MMI. Thyroxine concentrations increased in all treated groups at day 35 compared with day 25, and returned to normal by day 45. At 90 days of age, testis weight was increased by about 40% in rats whose mothers had been treated with doses of 0.006% PTU or greater, whereas testis weights in groups given 0.0015 and 0.0004% PTU or 0.025% MMI were increased 31, 15 and 18%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental hormonal profiles accompanying the neonatal hypothyroidism-induced increase in adult testicular size and sperm production in the rat

Neonatal treatment with the reversible goitrogen 6-N-propyl-2-thiouracil (PTU) results in a near doubling of testicular size and a 25% increase in the efficiency of spermatogenesis, without affecting circulating testosterone (T) levels in adult rats. The objectives of the present study were to examine the effects of neonatal PTU treatment on the pattern of testicular growth and circulating levels of anterior pituitary (FSH, LH, PRL, GH, and TSH), gonadal [immunoreactive inhibin-alpha (irI alpha) and T], and thyroid (T3 and T4) hormones over the first 100 days of life. Treatment of rats with PTU from birth to 24 days of age significantly reduced testicular weights between 10 and 60 days of age. However, the duration of testicular growth was extended in treated males, resulting in a 68% increase at 100 days of age. Serum gonadotropin levels in treated males were reduced throughout the experimental period, typically remaining between 50-70% of control levels. The characteristic robust prepubertal FSH peak was absent in PTU-treated males. Initially high until 20 days of age, irI alpha levels characteristically declined to adult levels (200-300 pg/ml) in control males. In treated males, irI alpha levels were reduced during the period of hypothyroidism, increased between 30 and 60 days, and then declined, but remained significantly higher (1.7- to 2-fold greater) than those observed in control males. Serum T levels were similar in treated and control males. Control males demonstrated increased T levels beginning at 45 days of age, earlier than observed in treated males; however, similar peak T levels were observed in all males. PTU treatment significantly suppressed serum GH and PRL and led to a 14-fold increase in circulating TSH during the period of treatment. However, unlike the gonadotropins, these hormones returned to control levels after PTU treatment, suggesting that the reduced levels of FSH and LH observed are not due to a generalized reduction in pituitary function. Serum T4 and T3 levels returned to control levels within 15 days after the removal of PTU. These results demonstrate that the neonatal PTU treatment-induced increases in adult testicular size and sperm production were not due to increased levels of FSH at any point in development. On the contrary, the observed increases occur in spite of chronically reduced FSH levels.

Androgen receptor expression and 5 alpha-reductase activity along the proximal-distal axis of the rat prostatic duct

The rat prostate consists of a series of branched ducts that eminate from the urethra. Heterogeneity of rat prostatic growth, secretory activity, and cell turnover has been observed along the proximal-distal axis of the branched ductal network. In addition, there are regional differences in androgen sensitivity along the ducts, with the distal ductal tips being highly androgen dependent and the proximal regions being relatively androgen independent. To determine the underlying mechanisms that may regulate these regional differences in androgen responsiveness, androgen receptor (AR) levels and 5 alpha-reductase activity were examined along the proximal-distal axis of microdissected ventral prostatic ducts from 15-, 30-, and 100-day-old rats. As in the murine prostate, DNA synthetic activity was concentrated in the distal tip region of the 15- and 30-day ducts. Immunocytochemistry and autoradiography with [3H] dihydrotestosterone were used to examine AR expression and functional ability to bind ligand, respectively. The results revealed no discernable differences in AR levels or binding activity in any cell type along the ductal length in prepubertal, pubertal, or adult rats. In addition, 5 alpha-reductase activity was the same in the distal and proximal ductal regions. We conclude that regional heterogeneity in prostatic growth and function is not a result of differences in levels of AR and 5 alpha-reductase. Rather, other region-specific structural, intracellular, or paracrine factors may be responsible for the differences in androgen responsiveness along the prostatic duct.

Blind-ending tubules and branching patterns of the rat ductuli efferentes

The ductuli efferentes of Sprague-Dawley rats were studied by microdissection and microscopic evaluation to document the presence of blind-ending tubules (ductuli aberrantes) and to describe morphological and ultrastructural differences between normally open ductules and blind-ending tubules. The branching patterns of the ductuli efferentes varied considerably between animals. A majority of the animals studied had either six or seven ductuli connected to the rete testis, with some animals having as few as four or as many as eight. Pairs of ductules began merging in the conus vasculosa, ultimately forming a single terminal duct within the capsule of the initial segment epididymidis. In a majority of animals, the junctions were unequally matched and located at various positions within the conus. Blind-ending tubules, found in 60% of the animals, were surrounded by thick connective tissue, and had a smaller diameter (78.7 +/- 1.4 microns) than normal ductules in the conus vasculosa (119.5 +/- 2.1 microns) or the terminus (102.2 +/- 1.5 microns). The lumina of blind-ending tubules were contracted and did not contain sperm. Nonciliated cells in the epithelium of blind-ending tubules contained fewer PAS-positive granules and electron-dense bodies (lysosomes) than nonciliated cells in normal ductules. Consideration of these characteristics will prevent blind-ending tubules from being mistaken for pathological changes in efferent ductules.

Induction of increased testis growth and sperm production in adult rats by neonatal administration of the goitrogen propylthiouracil (PTU): the critical period

We have previously shown that treating rats with the reversible goitrogen 6-propyl-2-thiouracil (PTU) from birth to Day 25 increases testis size and sperm production in adulthood by up to 80% and 140%, respectively. The purpose of this study was to determine the critical period(s) during development when PTU treatment can increase adult testis size and sperm production. Rats were treated with PTU beginning on Days 0, 8, 16, or 24 for periods of 9, 17, or 25 days. To further define the critical period, additional rats were treated with PTU prenatally or on Days 4-24. PTU treatments of 9, 17, or 25 days beginning at birth increased testis weight 18%, 38%, and 69%, respectively, by 135 days of age, while daily sperm production (DSP) increased 35%, 65%, and 94%, respectively. Efficiency of sperm production (DSP/g testis) also increased by approximately 25% in these rats. There was an inverse relationship between testis and body weights: increasing lengths of PTU treatment increased testis weight but decreased body weight. PTU treatment starting on Day 8 or later did not increase testis weight or DSP regardless of duration. Treatment on Days 4-24 increased adult testis weight and DSP similarly to treatment from birth to Day 24, but prenatal PTU treatment was ineffective. Testosterone concentrations were not altered in treated rats, even those with increased testis weight. These results indicate that the later part of the first postnatal week (Days 4-8) is the crucial period during which PTU treatment must begin in order to increase adult testis size and sperm production.(ABSTRACT TRUNCATED AT 250 WORDS)

Discharge planning: whose responsibility is it?

A survey of twenty hospitals in southwestern Virginia revealed that a lack of a discharge planning process was the most frequently reported reason for failure in the discharge system. All health professionals who come in contact with clients during hospitalization are responsible for preparing them and their families for discharge--only then can true continuity of care occur.

Thyroid hormones and testis development: a model system for increasing testis growth and sperm production

In conclusion, the unique transient hypothyroidism system described here provides a noninvasive means by which testicular size and sperm production can be increased to unprecedented degrees. This system may be useful as a model for understanding the factors which regulate testicular growth and the eventual size that the testes attain, as well as the factors which normally establish and then maintain the amount of sperm produced by an animal.

Early hypothyroidism in rats causes increased adult testis and reproductive organ size but does not change testosterone levels

The role of thyroid hormones in the testis is unclear, although recent evidence indicates they may be important for testicular development. Here we describe a novel method for increasing adult testicular size in the rat by induction of transient hypothyroidism during neonatal life. Rats were treated with a reversible goitrogen, 6-propyl-2-thiouracil from birth to day 25 when treatment was stopped, allowing return to a euthyroid state. At days 90, 135, 160, and 180, wt and DNA content of the testis, epididymis, ventral prostate, seminal vesicle, and those of some nonreproductive organs were determined, as well as serum levels of testosterone (T) and thyroid hormones. Despite decreased body wts in 90-day and older 6-propyl-2-thiouracil-treated rats, testis wt was increased by 40% and 60% at 90 and 135 days, respectively; maximal increase (80%) occurred at 160 days. These wt increases were accompanied by proportional changes in DNA content. Significant enlargements were also seen in other reproductive organs, but they occurred after a time lag and were smaller in magnitude. Interestingly, serum T levels showed no increase at any age. Weight and DNA content of nonreproductive organs, like body wts, were less than controls at all ages but thyroid hormone levels were normal. Thus, transient hypothyroidism in neonatal rats is associated with lasting enlargements in the ultimate size of testis and other reproductive organs in the adult. These changes are not related to excess T levels. The results indicate early critical influences of thyroid hormones on growth and development of the reproductive system and suggest an experimental model for inducing lasting enlargements in testis and reproductive organs. The model may also be useful for studying regulation of reproductive growth and final size.