PARENT SESSION
REPRODUCTIVE TOXICOLOGY
Harborside C
7:30 AM-10:00 AM

(300) IN UTERO AND LACTATIONAL EXPOSURE OF RATS TO 2,3,7,8 TETRACHLORODIBENZO-p-DIOXIN DOES NOT REDUCE OVARIAN AROMATASE ENZYME.

Salisbury, Travis¹, Marcinkiewicz, Jennifer¹, ¹ Dept of Biological Sciences, Kent, OH

ABSTRACT- TCDD is a wide-spread environmental contaminant. In utero and lactational (IUL) exposure of rat pups to TCDD delays growth, causes reproductive tract abnormalities, disrupts estrous cycles and ovulation. Additionally, we demonstrated that IUL exposure of TCDD (2.5 g/kg) reduced serum estradiol levels and the number of large preovulatory follicles in immature rats 48 hours post PMSG stimulation. The objective of the present study was to investigate the effects of IUL exposure to TCDD on aromatase immunoactive mass and activity within rat granulosa cells. On day 15 of pregnancy, rats were treated with a single oral dose of TCDD (2.5 g/kg) or vehicle (acetone:corn oil, 19:1). On postnatal day 23, rats were injected with (PMSG) (10 IU in 0.1 ml PBS). Granulosa cells from large antral follicles were collected from 2-3 rats/experiment on days 23 (prior to PMSG) and 25 (48hrs after PMSG) and pooled for analysis. A tritiated water assay was used to measure aromatase activity by determining the rate at which tritiated androgen precursors are aromatized into estrogens following the addition of saturating amounts of the cofactor NADPH. Western blot was used to evaluate aromatase protein levels. Differences between groups were analyzed by ANOVA. Within granulosa cells aromatase activity increased 16-18 fold following PMSG treatment (48 hours) in control and TCDD-animals when compared to non-PMSG treated animals(day 23) (3 experiments run in triplicate). Accompanying increased enzyme activity, aromatase protein levels were also elevated following PMSG treatment (48 hours). There were no significant differences in aromatase activity or protein levels in TCDD-treated animals compared to controls at either time point. The results of this experiment demonstrate that on a per cell basis aromatase activity and protein levels are not compromised following IUL exposure to TCDD suggesting that the mechanism by which TCDD acts to reduce serum estradiol levels and the number of large antral follicles in response to PMSG treatment is not a consequence of reduced aromatase activity.

KEY WORDS: Ovary, Granulosa cells, Aromatase, Dioxin