Spermatogenesis in aged rats after prenatal 3,3',4,4',5-pentachlorobiphenyl exposure.

We previously reported that prenatal exposure to 3,3',4,4',5-pentachlorobiphenyl (PCB126) had dose-related adverse effects on the spermatogenesis of 7(pubescent)- and 17(adult)-week-old rats, but the effects in middle and old age have been unclear. In this study, the spermatogenesis of male Sprague-Dawley rats whose dams had been injected (i.g.) with 25 pg, 2.5 ng, 250 ng, or 7.5 microg of PCB126/kg or the vehicle on days 13-19 post-conception was investigated at 52 and 90 weeks of age. At 52 weeks, the 7.5 microg group showed a significant decrease of preleptotene spermatocytes in stages VII-VIII seminiferous tubules, round spermatids increased at stages VI-VII and elongated spermatids decreased at stage VIII, while the spermatogenesis of the other PCB-treated groups were similar to that of the vehicle group. At 90 weeks, the 7.5 microg group showed a significant decrease of spermatogenic cells at many stages, and the 250 ng group showed a significant decrease of preleptotene spermatocytes at stages VII-VIII, and round spermatids increased at stages VI-VII, elongated spermatids decreased at stage VIII, and the spermatogenesis of the 2.5 ng and 25 pg groups were similar to those of the vehicle group. The present study showed that prenatal PCB126 exposure had dose-related adverse effects on spermatogenesis in aging rats and may have accelerated spermatogenic senescence. Because the serum testosterone levels of the PCB126 groups and the vehicle group were similar, a direct endocrine cause for the observed effects was unlikely.

Localization of Ang-1, -2, Tie-2, and VEGF expression at endothelial-pericyte interdigitation in rat angiogenesis.

Endothelial cells and pericytes play critical role in angiogenesis, which is controlled, in part, by the angiopoietin (Ang)/Tie-2 system and vascular endothelial growth factor (VEGF). Here, we investigated Ang, Tie-2, and VEGF expression within endothelial cells and pericyte interdigitations (EPI), which consist of cytoplasmic projections of pericytes and corresponding endothelial indentations. After subcutaneous implantation of a thermoreversible gelation polymer disc in rats, the capillary density was low on day 5, increased to a peak on day 7, and then decreased on days 10-20. A small number of EPI were observed on day 5, then increased sharply to a peak on day 10, but had decreased on day 20. Light and electron microscopy immunohistochemical and RNA in situ hybridization analyses revealed that Tie-2 localized at endothelial cells, and Ang-2 localized at endothelial cells and pericytes, while Ang-1 and VEGF localized at pericytes, and Ang-1 was most intensely observed at EPI of pericytes. Conventional quantitative RT-PCR and Western blot analyses revealed that the level of Ang-1 was low on days 5-7, then increased on days 10-20, while the level of VEGF was high on days 5-10, but had decreased on day 20. The level of Ang-2 remained high and Tie-2 remained at the level of the control on days 5-20. The present study showed that the angiogenic phase might be initiated by increases in Ang-2 and VEGF, while the microvessel maturation phase might be initiated by a relative increase in Ang-1 and a decrease in VEGF. Moreover, EPI might serve as a pathway for the Ang-1/Tie-2 system, with VEGF promoting pericyte recruitment for microvascular integrity.

Prenatal 3,3',4,4',5-pentachlorobiphenyl exposure modulates induction of rat hepatic CYP 1A1, 1B1, and AhR by 7,12-dimethylbenz[a]anthracene.

We previously reported the finding that prenatal exposure to a relatively low dose of PCB126 increases the rate of DMBA-induced rat mammary carcinoma, while a high dose decreased it. One of the most important factors determining the sensitivity to mammary carcinogenesis is the metabolic stage at administration of the carcinogenic agent. DMBA is a procarcinogen that recruits the host metabolism to yield its ultimate carcinogenic form, and CYP1A1 and CYP1B1 (CYP1) conduct this metabolism. We investigated the hepatic expression of CYP1 and AhR following oral administration of DMBA (100 mg/kg b.w.) (i.g.) to 50-day-old female Sprague-Dawley rats whose dams had been treated (i.g.) with 2.5 ng, 250 ng, 7.5 microg of PCB126/kg or the vehicle on days 13 to 19 post-conception. Real-time quantitative RT-PCR analysis revealed that the prenatal exposure to a relatively low dose of PCB126 (the 250 ng group) prolonged the higher expression of CYP1A1, CYP1B1, and AhR mRNA, while prenatal exposure to a high dose of PCB126 (the 7.5 microg group) prolonged the higher expression of CYP1A1 and AhR mRNA. Western blotting and immunohistochemical analyses were consistent with mRNAs changes. Because DMBA oxidation produces a highly mutagenic metabolite and is finally catalyzed by CYP1B1, a relatively low PCB126 dose might produce the biological character to potentially increase the risk of DMBA-induced mammary carcinoma.

CYP1 and AhR expression in 7,12-dimethylbenz[a]anthracene-induced mammary carcinoma of rats prenatally exposed to 3,3',4,4',5-pentachlorobiphenyl.

We previously reported the finding that prenatal exposure to a relatively low dose of 3,3',4,4',5-pentachlorobiphenyl (PCB126) acted as an enhancing agent for 17-beta-estradiol (E2)-dependent 7,12-dimethylbenz[a]anthracene (DMBA)-induced rat mammary carcinoma, while a high dose decreased it. E2 is a known risk factor for mammary carcinoma, and CYP1A1 and 1B1 (CYP1) are the major enzymes catalyzing 2- and 4-hydroxylation of E2, respectively. We investigated the induction of CYP1 and aryl hydrocarbon receptor (AhR) in DMBA-induced mammary carcinoma using female Sprague-Dawley rats whose dams had been treated (i.g.) with 2.5 ng, 250 ng, 7.5 microg of PCB126/kg or the vehicle on days 13-19 post-conception. Immunohistochemical analysis revealed that the mammary carcinoma of the 250 ng group showed a significantly higher number of nuclei expressing estrogen receptor alpha (ER) and proliferating cell nuclear antigen (PCNA) compared to those of the other groups. Quantitative real-time RT-PCR analysis revealed that the 7.5 microg group showed a significantly higher level of CYP1A1 mRNA, and that the 250 ng group showed significantly higher levels of CYP1B1 mRNA. The level of AhR mRNA was significantly higher in both the 7.5 microg and 250 ng groups. Western blotting analysis was consistent with mRNA changes. It has been revealed that CYP1B1 catalyzes a step in the formation of 4-hydroxylated E2 metabolites, which show quite high mammary carcinogenicity. This study indicates that the enhancement of DMBA-induced mammary carcinogenicity in a relatively low PCB126 dose group might partially involve the higher expression of CYP1B1 and AhR in these carcinomas.