Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on serum inhibin concentrations and inhibin immunostaining during follicular development in female Sprague-Dawley rats

The androgenic anabolic steroid tetrahydrogestrinone produces dioxin-like effects via the aryl hydrocarbon receptor

For a long time, athletes have used androgenic anabolic steroids (AASs) in an inappropriate and veiled manner with the aim of improving exercise performance or for cosmetic purposes. Abuse of AASs triggers adverse effects such as hepatocarcinogenesis, heart attacks, and aggressive behavior. However, AAS-induced toxicity is not completely understood at the molecular level. In the present study, we showed, by performing a dioxin response element (DRE)-luciferase reporter gene assay, that tetrahydrogestrinone (THG), a popular and potent androgen receptor agonist, has dioxin-like effects. In addition, we showed that THG increased cytochrome P-450 1A1 (CYP1A1) mRNA and protein levels, and enzyme activity. The gene encoding CYP1A1 is involved in phase 1 xenobiotic metabolism and a target gene of the aryl hydrocarbon receptor (AhR). Using the AhR antagonist CH-223191, we also examined whether the effects of THG on DRE activation depended on AhR. Our results suggest that synthetic anabolic steroids may have dioxin-like side effects that can disturb endocrine systems and may cause other side effects including cancer through AhR.

Changes of cyclic AMP levels and phosphodiesterase activities in the rat ovary

Cyclic AMP (cAMP) is a second messenger that plays a critical role in follicular recruitment, development and luteinization in the mammalian ovary. The cellular level of cAMP is largely dependent on the activity of phosphodiesterase (PDE), which degrades cAMP into 5'-AMP. The present study was conducted to investigate the level of cAMP and the activity of cAMP-PDE in postnatal rats; immature rats during gonadotropin-primed follicular development, ovulation and luteinization; adult rats during normal estrous cycling; and aged rats that spontaneously developed persistent estrous (PE) by radioimmunoassay (RIA). All four rat models were confirmed by histological examination of one ovary and assayed using the other ovary by RIA. In the postnatal rats, the ovarian cAMP level was high on day 10 after birth, while ovarian cAMP-PDE activity was highest at 21 days of age. In the immature female rats, both the ovarian cAMP level and cAMP-PDE activity increased remarkably after treatment with equine chorionic gonadotropin (eCG), increased continuously 24 h after injection of human chorionic gonadotropin (hCG) for induction of ovulation and luteinization, and then declined significantly. In the adult rats during the normal estrous cycle, the ovarian cAMP levels were low on the day of estrus, and there were no significant changes in ovarian cAMP-PDE activity throughout the estrous cycle. In the PE rats, the ovarian cAMP levels were similar to those of the adult rats on the day of estrus but were lower than those on the other days of the estrous cycle; ovarian cAMP-PDE activity was lower than that in the adult rats on any day of the estrous cycle. Together, these findings indicate that the ovarian cAMP level and cAMP-PDE activity were regulated in a stage-dependent manner during ovarian follicular development, atresia and luteinization and providing evidences that cAMP and cAMP-specific PDEs are involved in these physiological processes.

H. TCDD increases inhibin A production by human luteinized granulosa cells in vitro

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic of the halogenated dioxins and one of the most poisonous substances known to man. The major toxic effects of TCDD on reproduction are decreased fertility and diminished ability to maintain a pregnancy. Granulosa cells obtained from hormonally stimulated women participating in an in-vitro fertilization program were cultured with 3.1 femtomolar, 3.1 picomolar and 3.1 nanomolar TCDD. While inhibin B production was not altered, inhibin A production increased significantly after 4 hours of exposure to both nanomolar and micromolar TCDD concentrations. By 8 hours of exposure to these concentrations of dioxin, human luteinizing granulosa cells exhibited a pronounced increase in inhibin A, nearly quadrupling secretion from unexposed control cells. TCDD continued to increase inhibin A secretion at the picomolar concentration at 24 and 36 hours. It is conceivable that TCDD may act at the ovary to augment inhibin A secretion, thereby reducing FSH-stimulable estrogen secretion by granulosa cells.

Effects of Acute and Chronic Exposure to the Aryl Hydrocarbon Receptor Agonist 2,3,7,8-Tetrachlorodibenzo-p-Dioxin on the Transition to Reproductive Senescence in Female Sprague-Dawley Rats1

Activation of the aryl hydrocarbon receptor (AHR) can occur in polluted environments, either from smoking-related toxicants or from endogenous ligands. We tested whether acute or chronic exposure to the AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters the transition to reproductive senescence in female Sprague-Dawley rats. In experiment 1, rats (n = 6 per experimental group) received a single dose of 0 or 10 mug/kg of TCDD orally (p.o.) on Postnatal Day 29. Vaginal cytology was monitored for 1 wk each month until rats were killed at 1 yr of age. The single prepubertal exposure to TCDD hastened the transition to reproductive senescence in female rats and was associated with delayed puberty, abnormal cyclicity, and premature reproductive senescence. In a second experiment, rats were exposed to TCDD chronically through weekly dosing (0, 50, or 200 ng kg(-1) wk(-1) p.o., n = 7 each dose) beginning in utero. Lifelong exposure to these lower doses of TCDD induced a dose- and time-dependent loss of normal cyclicity and significantly hastened the onset of the transition to reproductive senescence (P < 0.05). This premature transition to reproductive senescence was associated with prolonged estrous cycles and, at the highest dose of TCDD, persistent estrus or diestrus. The number and size of ovarian follicles were not altered by TCDD. Diestrous concentrations of LH in rats exposed chronically to TCDD were similar to those in controls, whereas progesterone tended to be elevated at both doses of the dioxin (P < 0.08). Serum FSH was elevated in the group exposed to 50 ng/kg of TCDD (P < 0.02), whereas estradiol was decreased at both doses of dioxin (P < 0.01). Data thus far support endocrine disruption rather than depletion of follicular reserves as a primary mechanism of the premature transition to reproductive senescence following activation of the AHR pathway by TCDD in female rats.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) stimulates gonadotropin secretion in the immature female Sprague-Dawley rat through a pentobarbital- and estradiol-sensitive mechanism but does not alter gonadotropin-releasing hormone (GnRH) secretion by immortalized GnRH neurons in vitro

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces aberrant release of gonadotropins, FSH, and LH and blocks ovulation during induced ovarian follicular development in rats by an unknown mechanism. In the current study, TCDD (0, 8, or 32 microg/kg orally) was administered to immature female Sprague-Dawley rats, and synchronous follicular development was induced 24 h later with equine chorionic gonadotropin (eCG, 5 IU s.c.). Both doses of TCDD induced a significant premature increase in serum FSH and LH (P < 0.05) at 12 h post-eCG. This premature gonadotropin surge was facilitated by the administration of a long-acting estradiol (estradiol cypionate, 0.01, 0.1, and 0.5 mg/kg s.c.), whereas the progesterone and cortisol receptor antagonist RU486 (0, 1, and 10 mg/kg s.c.) potentiated the premature release of FSH and LH following TCDD as well. Pentobarbital (32 mg/kg i.p.) administered at 6 or 9 h, but not 0 h, post-eCG ablated the ability of TCDD to stimulate the release of FSH and LH in vivo. TCDD had no significant effect on GnRH accumulation in vitro from immortalized GnRH neuronal (GT1-7) cells and failed to alter the cell number. Transfection of these cells with a rat GnRH promoter-reporter construct revealed no significant acute effect of TCDD on GnRH promoter activity. Aryl hydrocarbon receptor mRNA was not detected in the GT1-7 cells by reverse transcription polymerase chain reaction. TCDD appears to stimulate premature gonadotropin release in the gonadotropin-primed immature rat by interacting with an estradiol- and pentobarbital-sensitive neural signal for GnRH release but not by acting upon the GnRH neuron directly.