Alterations in ovarian follicular progesterone secretion by elevated exposures to the drinking water disinfection by-product dibromoacetic acid: examination of the potential site(s) of impact along the steroidogenic pathway.
Previous data from our laboratory indicated that the drinking water disinfection by-product, dibromoacetic acid (DBA), when applied in vitro to rat preovulatory follicles at a concentration consistent with blood levels found to disrupt estrous cyclicity, was able to block the stimulated secretion of progesterone. The present experiments focused on establishing a dose-response for such an effect and identifying the point(s)of impact of this compound along the steroidogenic pathway that underlie this suppression. Immature Sprague-Dawley rats were primed with PMSG on day 26 and killed 48 h later. Preovulatory follicles were removed and paired in culture with or without DBA (2-50 microg/ml) to reassess progesterone secretion under hCG-stimulated or baseline conditions. In addition, media supplemented with pregnenolone or 22(R)-hydroxycholesterol (22R-HC) were used to determine the effects of 50 microg/ml DBA on the initial steps leading to progesterone synthesis. Samples taken over the course of 24 h reaffirmed a significant DBA-associated suppression in baseline and stimulated progesterone release, while estradiol secretion was unaffected. This effect was mirrored by a reduction in follicular progesterone content in these DBA groups. The addition of pregnenolone eliminated this decrease, with the DBA-exposed follicles exhibiting a linear increase in progesterone release over the sampling period. The follicular progesterone content at 24 h showed that DBA treatment under pregnenolone supplementation caused marked elevations under both the hCG stimulated and non-stimulated conditions, something not reflected in the release data. Substitution of 22R-HC for pregnenolone eliminated the effect on baseline progesterone release, although the attenuation in stimulated secretion was still present. This suggests both an effect of DBA exposure on mitochondrial cholesterol transport by steroidogenic acute regulatory protein (StAR) and a possible impact on the receptor or postreceptor events triggered by hCG.[1]References
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