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THE ENDOCRINE PROFILE OF INTACT FEMALE RATS ON THE DAY OF PROESTRUS FOLLOWING EXPOSURE TO ATRAZINE
Citation:
Cooper, R L., A R. Buckalew, S C. Laws, AND T E. Stoker. THE ENDOCRINE PROFILE OF INTACT FEMALE RATS ON THE DAY OF PROESTRUS FOLLOWING EXPOSURE TO ATRAZINE. Presented at Society of Toxicology, New Orleans, LA, March 6-10, 2005.
Description:
The Endocrine Profile of Intact Female Rats on the Day of Proestrus Following Exposure to Atrazine.
RL Cooper, A Buckalew, SC Laws and TE Stoker
Endocrinology Branch, RTD, NHEERL, ORD, U.S. EPA, RTP, NC, 27711.
The chlorotriazine herbicide, atrazine, has been shown to disrupt the neuroendocrine control of reproductive function in both the male and female rat. We reported that atrazine caused a dose-dependent suppression of the estrogen-induced surge of luteinizing hormone (LH) in the ovariectomized female rat. We also found that this herbicide caused an increase in serum estrone and estradiol in the intact male. The purpose of the present study was to determine whether or not the pituitary and gonadal hormones are affected within the same dose range. Therefore, we examined the effect of atrazine on hormone concentrations in the intact proestrous female rat. LE rats with regular 4-day estrous cycles were gavaged daily for 3 days (diestrus I to proestrus) with 0, 6.25, 12.5, 25 and 75 mg/kg of atrazine. On the day of vaginal proestrus (final day of dosing) females were killed at 1200, 1400, 1600, 1800 and 2000 h. At each time point the brain, pituitary, and blood were collected and processed for subsequent assays. Serum prolactin (PRL), LH, progesterone, corticosterone, estradiol, estrone and androstenedione were measured by radioimmunoassay. The peak concentration of LH was suppressed at all doses of atrazine as compared to the controls. Progesterone and androstenedione were increased at 1600 and 1800 h in the 75 mg/kg group. There were no significant differences in estrone, estradiol or corticosterone, although there was an apparent trend for increased levels as the atrazine dose increased. The results of these experiments demonstrate that atrazine suppresses LH at doses as low as 6.25 mg/kg. However, changes in serum steroid hormones were not observed until doses of 75 mg/kg were administered. Further studies are needed to determine the NOEL for the suppression of LH by atrazine and to better evaluate the apparent alterations in steroids. (This abstract does not necessarily reflect EPA policy.)