Bisphenol A may cause testosterone reduction by adversely affecting both testis and pituitary systems similar to estradiol

Bisphenol A (BPA) causes reproductive toxicities, but the mechanisms are still unclear. In the present study, we sought to clarify these mechanisms in comparison with those of 17beta-estradiol (E2). Prepubertal Wistar/ST male rats (4 weeks old) were subcutaneously administered BPA (0, 20, 100 and 200 mg/kg/day) or E2 (10 and 100 microg/kg/day) for 6 weeks. Both BPA and E2 treatments decreased plasma and testicular testosterone levels, and plasma luteinizing hormone (LH), but not E2 and follicle-stimulating hormone levels, though E2 treatment increased its plasma level. In relation to the decreased testosterone levels, BPA and E2 decreased expressions of steroidogenic enzymes and cholesterol carrier protein in Leydig cells. Thus, decreased testosterone levels in plasma might have resulted from decreased expressions of these enzymes and protein as well as from decreased plasma LH levels. Interestingly, the changes in steroidogenic enzymes and carrier protein were observed at lower levels of exposure to BPA or E2 than those inhibiting plasma LH levels. Microscopically, 200 mg/kg BPA and 100 microg/kg E2 significantly decreased Leydig cell numbers in the testis. In addition, BPA and E2 also decreased expression of estrogen receptor alpha-mRNA, which might be related to the decreased numbers of Leydig cells. Thus, BPA directly affects not only the Leydig cells but also the pituitary gland, but the former may be impaired at lower exposure concentrations than the latter.

Changes in plasma gonadotropins, inhibin and testosterone concentrations and testicular gonadotropin receptor mRNA expression during testicular active, regressive and recrudescent phase in the captive Japanese black bear (Ursus thibetanus japonicus)

Male Japanese black bears (Ursus thibetanus japonicus) have an explicit reproductive cycle. The objective of this study was to clarify the variation of plasma testosterone, FSH, inhibin, LH levels and testicular gonadotropin receptor mRNA expression of male bears associated with their testicular activity. Notably, this study investigated peripheral FSH concentration and localization of gonadotropin receptor mRNAs for the first time in male bears. Blood and testicular tissue samples were taken from captive, mature, male Japanese black bears during testicular active, regressive and recrudescent phases. Plasma hormone concentrations were measured by immunoassays, and gonadotropin receptor mRNA expression in the testis was investigated by in situ hybridization technique and also by real-time PCR. There were significant variations in plasma testosterone and inhibin concentrations. Changes in FSH concentration preceded these hormones with a similar tendency. Hormones started to increase during denning, and achieved the highest values at the end of the recrudescent phase for FSH and in the active phase for testosterone and inhibin. These changes in hormone concentrations were accompanied by testicular growth. In situ hybridization analysis revealed that FSH and LH receptor mRNA was possibly expressed in Sertoli cells and Leydig cells, respectively, as they are in other mammals. However, neither plasma LH concentration nor testicular gonadotropin receptor mRNA expression level varied significantly among the sampling months. These results suggest that FSH, inhibin and testosterone have roles in testicular activity in male bears. This study provides important endocrine information for comprehending seasonal reproductivity in male Japanese black bears.

Maternal isobutyl-paraben exposure decreases the plasma corticosterone level in dams and sensitivity to estrogen in female offspring rats

Isobutyl-paraben (IBP), a widely used preservative in a variety of foods, shows high comparative binding affinity to estrogen receptors. Here, we examined the effects of maternal exposure of rats to IBP on plasma hormone concentrations and organ weights in dams, ratio of male pups, anogenital distance, organ weights and plasma hormone concentrations in offspring, puberty, estrous cycle and response of organ weight and plasma hormone concentrations to estrogen in adult female offspring, and reproductive and adrenal function in adult male offspring, all of which are under developmental estrogen regulation, to clarify the estrogenic effects of IBP during gestation and lactation on the endocrine systems of dams and offspring. While maternal exposure of IBP decreased the plasma corticosterone concentration and increased the uterus weight in dams and increased uterine sensitivity to estrogen in adult female offspring, the other indices examined were largely unaffected by the present treatment. Even though these results indicate little sign of endocrine disrupting effects for IBP, the existence of activity may be a matter of concern due to the possible impact on the health of future generations.

Immunoneutralization of inhibin in cycling rats increases follicle-stimulating hormone secretion, stimulates the ovary and attenuates progesterone receptor-dependent preovulatory luteinizing hormone secretion

Passive immunization against inhibin with an anti-inhibin serum (AIS) during the diestrous phase in cycling rats increased follicle-stimulating hormone secretion, stimulated the ovaries and reduced the magnitude of the luteinizing hormone (LH) surge in the afternoon of proestrus. The involvement of gonadotrope progesterone receptor (PR) expression/action in the inhibitory effects of the follicle-stimulating hormone-dependent putative ovarian factor gonadotropin surge-attenuating factor on preovulatory LH secretion was studied in the absence of circulating free inhibin. Proestrous pituitaries from rats injected with AIS or a non-immune serum (NIS) were studied for determination of PR-AB and PR-B mRNAs by RT-PCR and PR-B and PR-A isoform proteins by Western blot. In addition, pituitaries from AIS- and NIS-injected rats were incubated and studied for PR-dependent LH secretion parameters: LH-releasing hormone (LHRH)-stimulated LH secretion, progesterone-potentiated LHRH-stimulated LH secretion and LHRH self-priming. Also, the effects of the antiprogestagen RU486 on these LH secretion parameters were evaluated and compared with those of AIS. Finally, gonadotrope PR phosphorylation was evaluated by immunohistochemistry. Results showed that the hyperstimulated ovaries of AIS-injected rats produce a factor, different from inhibin, that blocked LHRH self-priming and P-potentiation of LHRH-stimulated LH secretion. These effects were not due to decreased pituitary PR mRNAs, PR protein expression or PR protein B/A ratio. The inhibitory effect of AIS on PR-dependent LH secretion seemed to be due to gonadotrope PR dephosphorylation. Taken together, the findings indicated that the putative gonadotropin surge-attenuating factor affected LH surge through an inhibition of PR phosphorylation/action but not PR expression.

Effects of inhaled nanoparticle-rich diesel exhaust on regulation of testicular function in adult male rats

We investigated the effects of nanoparticle-rich diesel exhaust (NR-DE) on reproductive function. Eight-week-old male F344 rats were divided into 12 experimental groups and exposed to either whole NR-DE at low (15.37 microg/m(3), 2.27 x 10(5) particles/cm(3)), middle (36.35 microg/m(3), 5.11 x 10(5) particles/cm(3)), or high (168.84 microg/m(3), 1.36 x 10(6) particles/cm(3)) concentrations or clean air for 4, 8, or 12 weeks (5 hours/day, 5 days/week). NR-DE exposure for 4 or 8 weeks did not affect body weight; however, body weight was significantly decreased in rats exposed to low- or high- concentration NR-DE for 12 weeks compared to the control group. Relative weights of testes, epididymides, seminal vesicles, and prostate had increased non-significantly in all NR-DE-exposed rats at 4, 8, and 12 weeks. Adrenal gland relative weights were significantly increased at 4 weeks in rats exposed to low-concentration NR-DE. Plasma luteinizing hormone and follicle stimulating hormone concentrations did not change significantly. Plasma testosterone concentrations were significantly increased after exposure to low- or middle-concentration NR-DE for 4 or 8 weeks compared to controls. Plasma immunoreactive (ir-) inhibin concentrations were significantly increased after exposure to high-concentration NR-DE for 4 weeks or middle- or high-concentration NR-DE for 12 weeks compared to controls. Testicular testosterone concentrations were significantly increased at 4, 8, and 12 weeks after exposure to low-concentration NR-DE compared to controls. In contrast, with exposure to low- or high-concentration NR-DE, testicular ir-inhibin concentrations were significantly greater than in controls, but only at 4 weeks. These results suggest that NR-DE inhalation disrupts the endocrine activity of the male reproductive system.

Protective effect of quercetin on the reproductive toxicity of 4-nitrophenol in diesel exhaust particles on male embryonic chickens

The 4-nitrophenol (PNP) in diesel exhaust particles (DEP) has been identified as a vasodilator and is a known degradation product of the insecticide parathion. In this study, the protective effect of quercetin, a potent oxygen free radical scavenger and metal chelator, against the oxidative damage of PNP on cultured testicular cells was studied in male embryonic chickens. Testicular cells from Day 18 embryos were cultured in serum-free McCoy's 5A medium and challenged with quercetin (1.0 microg/ml) alone or in combinations with PNP (10(-7)-10(-5) M) for 48 h. The oxidative damage was estimated by measuring cell viability, content of malondialdehyde (MDA), activity of superoxide dismutase (SOD) and glutathione peroxidation (GSH-Px) activity. The results showed that exposure to PNP (10(-5) M) induced condensed nuclei, vacuolated cytoplasm and a decrease in testicular cell viability and spermatogonial cell number. Exposure to PNP induced lipid peroxidation by elevation of the content of MDA. Exposure to PNP also decreased GSH-Px activity and SOD activity. However, simultaneous supplementation with quercetin restored these parameters to the same levels as the control. Consequently, PNP induced oxidative stress in spermatogonial cells, and dietary quercetin may attenuate the reproductive toxicity of PNP to restore the intracellular antioxidant system in the testicular cells of embryonic chickens.

Formation of primordial follicles and immunolocalization of PTEN, PKB and FOXO3A proteins in the ovaries of fetal and neonatal pigs

The assembly of primordial follicles and subsequent development and transition of the primordial follicle to the primary follicle are critical processes in ovarian biology. In order to examine follicle formation and development in fetal and neonatal pigs, ovarian samples were obtained from a famous local breed of Chinese pigs, Erhualian pigs, ranging in age from 50 days postcoitum to 1 day postpartum in our current study. Morphological changes in the ovaries of the fetal and neonatal pigs indicated that egg nests were the earliest recognizable gamete cells. The proportion of egg nests decreased from 98.4 to 25.6% and the proportion of single follicles increased from 1.6 to 74.4% between 70 and 90 days postcoitum. The proportions of primordial follicles increased between 70 and 90 days postcoitum but decreased from 90 days postcoitum to 1 day postpartum. Our results suggested that the key stage of primordial follicle formation was between 70 and 90 days postcoitum and that the major stage of transition from primordial follicles into primary follicles was between 90 days postcoitum and 1 day postpartum. Experiments were also conducted to examine the localization of PTEN, PKB and FOXO3A proteins in the porcine ovaries by immunohistochemistry and immunoblotting. The results indicated that PTEN, PKB and FOXO3A were localized in the germ cells of egg nests, cytoplasm of oocytes and granulosa cells of follicles ranging from the primordial to secondary stages and that the staining intensity was weak in granulosa cells but strong in oocytes. The different staining patterns of PTEN, FOXO3A and PKB suggested that these proteins were expressed in a stage- and cell-specific manner during ovarian follicle formation and development in the fetal and neonatal pig.

Nanoparticle-rich diesel exhaust may disrupt testosterone biosynthesis and metabolism via growth hormone

We previously reported that exposure to low (22.5+/-0.2 nm in diameter, 15.4+/-1.0 microg/m(3) in mass weight, 2.27x10(5)/cm(3) in mean number concentration), and medium (26.1+/-0.5 nm, 36.4+/-1.2 microg/m(3), 5.11x10(5)/cm(3)) concentrations of nanoparticle-rich diesel exhaust (NR-DE) for 1 and 2 months (5 h/day, 5 days/week) significantly increased plasma testosterone in male Fischer 344 rats, whereas exposure to a high concentration (27.1+/-0.5 nm, 168.8+/-2.7 microg/m(3), 1.36x10(6)/cm(3)) did not. The present study attempts to clarify the mechanism of this elevation. Low and medium exposures to NR-DE for 1 and 2 months significantly increased steroidogenic acute regulatory protein (StAR)- and cytochrome P450 side-chain cleavage (P450scc)-mRNA and their protein expressions in the testis of rats, in which the elevation pattern was very similar to that of plasma testosterone levels. Interestingly, both exposure levels for 1 month significantly increased growth hormone (GH) receptor expression in the testis, and low exposure also increased testicular insulin-like growth factor I-mRNA levels and hepatic microsomal cytochrome P450 2C11-mRNA and their protein levels in rats. These two factors are thought to be related to growth hormone secretion. Disruption of testosterone biosynthesis by NR-DE exposure may be a mode of action for reproductive toxicity, which may, in part, be regulated by increasing StAR and P450scc expressions via GH signalling.

4-Nitrophenol isolated from diesel exhaust particles disrupts regulation of reproductive hormones in immature male rats

In previous studies, we found that 4-nitrophenol (PNP) isolated from diesel exhaust particles exhibited both estrogenic and anti-androgenic activities. This compound is also a degradation product of the insecticide parathion. Here, we investigated the in vivo effect of PNP on reproductive function in immature male rats. Twenty-eight-day-old rats were injected subcutaneously with PNP (0.01, 0.1, 1, or 10 mg/kg) daily for 14 days. Plasma concentrations of luteinizing hormone (LH) were significantly lower in all PNP dosage groups than in the control group, and follicle-stimulating hormone (FSH) was significantly decreased in rats treated with 0.1, 1, or 10 mg/kg PNP. However, plasma concentrations of testosterone were significantly increased by 10 mg/kg PNP, and plasma concentrations of immunoreactive (ir)-inhibin were also significantly increased in the 0.1, 1, and 10 mg/kg PNP groups. Plasma concentrations of prolactin were significantly increased by 10 mg/kg PNP, and plasma concentrations of corticosterone were significantly increased in all treatment groups. These findings clearly show that PNP influences the hypothalamic-pituitary-gonadal axis in immature male rats, with decreased secretion of LH and FSH and increased secretion of testosterone and inhibin. PNP, therefore, appears to disrupt endocrine activity in the immature male reproductive system.

Prolactin induces phosphorylation of the STAT5 in adrenal glands of Hatano rats during stress

AIMS

To investigate the signaling of prolactin (PRL) in the adrenal gland during stress in Hatano high- (HAA) and low-avoidance (LAA) rats.

MAIN METHODS

Adrenal glands of both strains were collected at 0, 15 and 30 min after stress. The protein levels of phosphorylated STAT5 and the mRNA levels of melanocortin receptor 2 (MC2R) and PRL receptor (PRLR) were analyzed. Furthermore, the effects of bromocriptine-induced hypoprolactinemia on adrenocortical responses to stress were investigated.

KEY FINDINGS

Adrenocorticotropic hormone (ACTH) concentrations in HAA were greater than LAA, while the difference in PRL concentrations were found only at 120 min after stress induction. No strain differences were observed in corticosterone or progesterone in response to stress. The stress-induced increase in MC2R mRNA expression was higher in HAA, but there was a lowered PRLR mRNA expression. STAT5 become highly phosphorylated in response to stress in both strains, but bromocriptine led to a reduction the STAT5 phosphorylation. Exposure to bromocriptine was associated with a reduction in plasma PRL in response to stress in both strains, while the ACTH levels were not altered. However, the decrease in corticosterone and progesterone in response to stress was observed only in bromocriptine-treated LAA rats.

SIGNIFICANCE

These data show that PRL plays an important role in the regulation of corticosterone and progesterone release in LAA but not in HAA during stress. These results suggest that PRL increase in response to stress, and it acts on the adrenal cortex and thereby plays an important physiologic role in protecting against acute stress.

Immunolocalization of steroidogenic enzymes in the fetal, neonatal and adult testis of the Shiba goat

The localizations of steroidogenic enzymes (P450scc, 3 beta HSD, P450c17 and P450arom) in testes of Shiba goats were investigated by immunohistochemistry. P450scc, 3 beta HSD, P450c17 and P450arom were detected in all Leydig cells of adults. P450scc and P450c17 were observed in most Leydig cells in the fetus (90 days) and neonate (15 days). 3 beta HSD and P450arom were found in some Leydig cells of the fetus with weak immunostaining but the numbers of immunopositive Leydig cells and intense immunostaining were increased in Leydig cells of the neonate. These results suggest that Shiba goat testes have the ability to synthesize progestin, androgen and estrogen in the fetus, neonate and adult, and synthesis of these steroid hormones showed an age-related rise.

Androgenic activity of the Thai traditional male potency herb, Butea superba Roxb., in female rats

AIM OF THE STUDY

Butea superba Roxb. (Leguminosae) is a well-known Thai male potency herb with androgenic and anti-estrogenic activities. We evaluated whether oral administration of Butea superba has an androgenic or anti-estrogenic activity in female rats.

MATERIALS AND METHODS

Normal and ovariectomized adult female rats were each subdivided into five groups, DW, BS-10, BS-50, BS-250 and TP, and gavaged with 0, 10, 50 and 250 mg/kg BW/day of the crude of Butea superba and subcutaneously injected with 6 mg/kg BW/day of testosterone propionate (TP), respectively, during the treatment period.

RESULTS

In intact rats, only BS-250 increased the uterine thickness and the number of uterine glands, and could induce a prolonged diestrous phase. In ovariectomized rats, treatment with BS-50 as well as BS-250 increased the uterine thickness and the number of uterine glands. However, serum luteinizing hormone (LH) levels were also increased. TP reduced serum follicle stimulating hormone and LH levels with the appearance of anestrous cycle, and could significantly increase the relative uterine weight and thickness and the number of uterine glands in both intact and ovariectomized rats.

CONCLUSIONS

Orally administered Butea superba tubers have an androgenic effect on the reproductive organs of intact and ovariectomized rats, and exhibit anti-estrogenic activity on LH secretion in ovariectomized rats.

Effects of 3-methyl-4-nitrophenol on the reproductive toxicity in female Japanese quail (Coturnix japonica)

We previously showed that 3-methyl-4-nitrophenol (4-nitro-m-cresol, PNMC), a component of diesel exhaust particles and a degradation product of the insecticide fenitrothion, has reproductive toxicity in adult male and immature female Japanese quail (Coturnix japonica). Here we investigated effects of PNMC on the reproductive toxicity of mature female Japanese quail. The experiment consists of 3 periods of pretreatment, treatment, and post-treatment for 5 d each. The birds were reared, bred naturally for 1 week, and after 5 d of pretreatment, then injected intramuscularly with PNMC at doses 1, 10, or 100 mg/kg body weight daily for 5 d. Body weight, egg weight, and hatchability did not differ among the observation periods. However, at all doses of PNMC, the egg-laying rate showed a modest decrease during the treatment period, with recovery during the post-treatment period. Plasma concentrations of luteinizing hormone (LH) and estrodiol-17beta, were significantly decreased (p<0.05), and plasma concentrations of progesterone significantly increased (p<0.05) in birds treated with 10 and 100 mg/kg PNMC. These results suggest that PNMC have acute toxicity, and inhibited LH secretion, disturbing egg-laying in mature female quail. Our findings indicate that PNMC induces endocrine malfunction at the central level and subsequently disrupts reproductive processes in mature female quails.

Differences in adrenocortical secretory and gene expression responses to stimulation in vitro by ACTH or prolactin between high- and low-avoidance Hatano rats

Rats of the Hatano high-avoidance (HAA) and low-avoidance (LAA) strains have been genetically selected on the basis of their two-way active avoidance behavior, and have different endocrine responses to stress. The present study focused on the adrenal steroid hormone responses of the Hatano strains and identifies differences in regulation of the adrenal cortex in vitro of HAA and LAA rats. Although incubation with prolactin (PRL) and/or adrenocorticotrophic hormone (ACTH) resulted in a dose-dependent increase of corticosterone and progesterone release by adrenal cells from both HAA and LAA male rats, the responses were markedly increased for adrenal cells from LAA rats as compared with HAA rats. This finding suggested that adrenal glands of HAA rats are less sensitive to PRL and/or ACTH than adrenals from LAA rats. Several possible intra-adrenal regulators were investigated. The basal level of expression of steroidogenic acute regulatory protein (StAR) and the long form of the PRL receptor (PRLR-L) mRNAs was higher in adrenals of LAA rats. ACTH treatment of adrenal cells from HAA rats resulted in statistically significant increases in melanocortin receptor 2 (MC2R) mRNA expression, while neither ACTH nor PRL altered MC2R mRNA expression in adrenal cells of LAA rats. Conversely, the increase in PRLR-L mRNA expression induced by PRL was observed only in adrenal cells from LAA rats. Treatment of adrenal cells with PRL and/or ACTH increased the expression of StAR and CYP11A1 mRNAs for both Hatano strains. However, the induction of StAR mRNA expression was higher in LAA rats, but the CYP11A1 response was lower. These findings indicate that adrenal cells of the LAA strain have higher sensitivity to secretagogues than those of the HAA strain. These results suggest that PRL may also be important in stimulating secretion of adrenal steroid hormones.

Physiological roles of inhibin in regulation of FSH secretion and follicular development during early pregnancy in goats

The aim of the current study was to clarify the physiological role of inhibin in controlling FSH secretion and follicular development during the early pregnancy in goats. Eight goats investigated sonographically on Days 19-21 (Day 0=day of mating) for pregnancy were assigned into control (n=3) and treated (n=5) groups. The ovaries of all animals were daily scanned with ultrasound for follicles 2mm or more in diameter from 1 day before to 5 days after treatment. On Day 25 postbreeding; animals received either 10 ml, of normal goat serum or antiserum against [Tyr (30)]-inhibin alpha (1-30). Jugular blood samples were collected every 6 h starting 24 h before and until 120 h after treatment. The plasma concentration of FSH increased at 6 h and remained at significantly high levels until 120 h in treated vs. control group. The plasma concentrations of estradiol showed a marked increased at 66 h, with peak levels at 120 h after treatment of antiserum. The basal concentrations of LH and the pattern of plasma concentrations of progesterone were not significantly different between the two groups. The number of medium size (3.5-5.0 mm) follicles increased considerably from Day 2, whereas small (3.5 mm or less) and large (5 mm or more) follicles increased noticeably from Day 3, as compared with pre-treatment and controls. These results clearly indicated that inhibin is a key hormone in regulation of follicular development through regulation of endogenous FSH secretion during early pregnancy in goats.

Expression of nerve growth factor and its receptors trkA and p75 and inhibin alpha-subunit in the ovarian interstitial cells of lactating golden hamsters

Characteristic daily increases in the plasma levels of luteinizing hormone (LH) are present every afternoon during lactation in golden hamsters. The objective of this study was to investigate the effect of the diurnal rhythm of increases in LH on expression of nerve growth factor (NGF), its receptors trkA and p75 and inhibin alpha-subunit in the ovarian interstitial cells of lactating golden hamsters. Both lactating and non-lactating groups of postpartum golden hamsters were used in this study. The expression of NGF, its receptors trkA and p75 and inhibin alpha-subunit were determined by immunohistochemistry. Positive staining of NGF, trkA and p75 was found in the interstitial cells of the lactating group, and no immunoreactivity for NGF, trkA or p75 was observed in the ovarian interstitial cells of the non-lactating group. In addition, immunostaining of inhibin alpha-subunit was also observed in the interstitial cells of the lactating group but not in those of the non-lactating group. Immunostaining of the inhibin/activin beta(A)- and beta(B)-subunits was observed in the granulosa cells of antral follicles, but not in the interstitial cells of the lactating and non-lactating animals. These results suggest that the diurnal rhythm increases in LH can induce expression of NGF, trkA, p75 and inhibin alpha-subunit in the ovarian interstitial cells of lactating golden hamsters and that NGF, its receptors trkA and p75 and inhibin alpha-subunit may have the capacity for autocrine or paracrine modulation of interstitial cell differentiation in golden hamsters.

Effects of pantothenic acid supplementation on adrenal steroid secretion from male rats

The effects of pantothenic acid-supplementation on the adrenal secretion of corticosterone and progesterone in male rats were investigated using an in vitro cell culture system. Male rats at 21 d of age were given 0.03% pantothenic acid in their drinking water for 9 weeks. After 9 weeks of treatment, the animals were decapitated, and adrenal cells were cultured in the absence or presence of rat adrenocorticotropic hormone (ACTH; 10(-15) to 10(-10) M) and/or ovine prolactin (oPRL; 10(-9) to 10(-7) M) for 4 h. Adrenal cells in pantothenic acid-treated rats exhibited higher basal levels of corticosterone and progesterone than control rats. The response of ACTH and/or PRL on corticosterone and progesterone release was higher in the pantothenic acid-treated rats than in the control rats. In addition, PRL increased the stimulatory effect of ACTH-induced corticosterone secretion in both normal and pantothenic acid-treated rats. These results clearly demonstrated that pantothenic acid supplementation stimulates the ability of adrenal cells in male rats to secrete corticosterone and progesterone. Additionally, these results also showed that pantothenic acid supplementation induced adrenal hyperresponsiveness to ACTH stimulation, and PRL further stimulated adrenal sensitivity to ACTH.

Developmental exposure to pentachlorophenol affects the expression of thyroid hormone receptor beta1 and synapsin I in brain, resulting in thyroid function vulnerability in rats

Pentachlorophenol (PCP), a component of biocides and a contaminant in diverse tissue samples from humans from various geographic areas, disrupts regulatory effects of thyroid hormones. Here we examined the effects of developmental exposure of rats to PCP on various aspects of brain development, male reproductive function, and adrenal function, all of which are under thyroid hormones regulation. PCP was administered to dams and their offspring via drinking water (6.6 mg l(-1)) during gestation and lactation. Tissue samples were obtained from dams, 3-week-old weanling pups, and 12-week-old pups. Gene expressions of thyroid hormone receptor beta1 and synapsin I, factors that promote brain growth, was increased in the cerebral cortex of PCP-treated weanling females, whereas plasma concentrations of total thyroxine were decreased in dams and weanling pups, and plasma thyroid-stimulating hormone concentrations were higher in PCP-treated weanling males. PCP caused a decrease in plasma corticosterone concentrations in 12-week-old female rats, but not in male rats or weanling females. PCP-treated male pups had significantly increased testis weight at 12 week of age. No overt signs of toxicity were noted throughout this study. Our results show that PCP exposure during development causes thyroid function vulnerability, testicular hypertrophy in adults, and aberrations of brain gene expression.

Styrene trimer may increase thyroid hormone levels via down-regulation of the aryl hydrocarbon receptor (AhR) target gene UDP-glucuronosyltransferase

BACKGROUND

Styrene trimers (STs) are polystyrene-container-eluted materials that are sometimes detected in packaged foods. Although the possible endocrine-disrupting effects of STs, such as estrogenic activities, have been reported, their potential thyroid toxicity, such as that caused by the related endocrine disruptor 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has not been studied in detail.

OBJECTIVE

Using wild-type and aryl hydrocarbon receptor (Ahr)-null mice, we investigated whether 2,4,6-triphenyl-1-hexene (ST-1), an isomer of STs, influences thyroxin (T(4)) levels in the same manner as TCDD, which induces UDP-glucuronosyltransferase (UGT) via the AhR, resulting in a decrease in T(4) levels in the plasma of mice.

METHODS

Both wild-type and Ahr-null mice (five mice per group) were treated for 4 days by gavage with ST-1 (0, 32, or 64 micromol/kg).

RESULTS

High-dose (64 micromol/kg) ST-1 decreased the expression of AhR, cytochrome P450 (CYP) 1A1/2, UGT1A1/A6, and CYP2B10 mRNAs and the enzyme activity for CYP1A and UGT1A only in the wild-type mice. This dose decreased AhR DNA binding, but paradoxically increased AhR translocation to the nucleus. In contrast, a high dose of ST-1 increased T(4) levels in the plasma in wild-type mice but did not influence T(4) levels in AhR-null mice.

CONCLUSIONS

Although ST-1 treatment might cause an increase in AhR levels in the nucleus by inhibiting AhR export, this chemical down-regulated AhR mRNA, thus leading to down-regulation of AhR target genes and an increase in plasma T(4) levels.

Dose-dependent effects of a glucocorticoid on prolactin production

Glucocorticoids are known to stimulate growth hormone (GH) production but to suppress prolactin (PRL) production. However, previous data were obtained with rather high doses of corticosterone. In this study we examined the effects of various doses (10 (-12) -10 (-7) M) of corticosterone on GH and PRL production in a rat pituitary somatomammotropic cell line, MtT/SM cells, and found that GH mRNA expression was facilitated by high doses (10 (-7) and 10 (-8) M). In contrast, a biphasic effect of corticosterone on PRL mRNA expression and secretion was observed, i.e., high doses (10 (-7) and 10 (-8) M) suppressed and low doses (10 (-12) -10 (-10) M) facilitated them. In an immunofluorescent staining study, the number of PRL immunopositive cells increased with low doses of corticosterone while it decreased with high doses of it, which corresponded to PRL mRNA expression and hormone secretion, respectively. These effects of corticosterone on PRL production were abolished by a glucocorticoid receptor (GR) antagonist, mifepristone. In addition, co-treatment with low doses of corticosterone (10 (-12) -10 (-10) M) and 17beta-estradiol (E(2), 10 nM) additively increased the number of PRL immunopositive cells. Moreover, a 24 h BrdU incorporation experiment suggested that the increase in the number of PRL immunopositive cells treated with low dose corticosterone was caused by novel synthesis of PRL while, on the other hand, that of those treated with E(2) resulted from PRL cell proliferation. Thus, we concluded that corticosterone biphasically regulates PRL production and the sensitivity of E(2) to different degrees.

Reproduction and Development of the Released Przewalski's Horses (Equus przewalskii) in Xinjiang, China

In China, the first Przewalski’s horse (Equus przewalskii) group was released in Kalamaili Ungulate Protected Area in Xinjiang, in August 2001. The objective of this study was to investigate reproduction and development of released Przewalski’s horses in Xinjiang, China from 2002 to 2006. Twenty-four descendants were naturally born, average reproduction rate was 38.7%, and average survival rate of foals was 69.1% in this interim. Frequent alternation of the leading stallion and infertility in female horses due to environmental factors were main causes for the low reproduction rate. The infant mortality rate of released Przewalski’s horses was 25.0%, and 83.3% of death in infants was due to the leading stallion infanticide. The released Przewalski’s horses exhibited seasonal breeding, 70.8% of infants were born in May and June. The fertility rates were 8.3% in April and 37.5% in May, which were lower compared to those of the captive Przewalski’s horse groups (18.3% and 44.3%, respectively). Furthermore, the fertility rate in June was 33.3% and higher than the captive groups (18.3%). These findings showed that the breeding peak of the released Przewalski’s horse groups was later than the captive groups, and suggested that the altered survival environment and food supplies were the main reasons contributing to the delayed breeding peak.

Placental activin A is required for follicular development during the second half of pregnancy in the golden hamster (Mesocricetus auratus)

Numerous antral follicles develop during the second half of pregnancy in the golden hamster even though LH and FSH are maintained at basal levels. To investigate the possible hormone actions of activin A associated with follicular development, pregnant golden hamsters were placentectomized on day 6 of pregnancy and animals were sacrificed at day 8, 10, 12, or 14 of pregnancy. There was a drastic decrease in the plasma concentrations of activin A from day 10 of pregnancy in the operated group compared to the controls. Positive immunohistochemical staining of inhibin/activin subunits betaA and betaB in the syncytiotrophoblast of the placenta revealed the source of activin A, AB, or B. The number of healthy follicles did not change until day 12 between the operated and the control groups, but decreased in numbers in the operated groups thereafter. The decreased concentrations of inhibin A, B, and estradiol-17beta in the operated groups at day 10 and 12 correlated well with the number of mature follicles in response to hCG treatment. In conclusion, we revealed that activin A secreted from the placenta induces folliculogenesis to maintain the high levels of estradiol-17beta needed to induce uterine dilatation for fetus growth and impending parturition.