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Simazine (SIM) Effects on Serum Testosterone and Testicular Function in the Juvenile Wistar Rat
Citation:
KAYDOS, E., J. M. FERRELL, R. L. COOPER, AND T. E. STOKER. Simazine (SIM) Effects on Serum Testosterone and Testicular Function in the Juvenile Wistar Rat. Presented at Triangle Consortium for Reproductive Biology, Chapel Hill, NC, January 27, 2007.
Impact/Purpose:
To determine the effect of simazine on the hypothalamic-pituitary regulation of LH secretion during the pubertal period.
Description:
Chlorotriazine herbicides, such as SIM, are used extensively in the U.S. each year and both the parent compound and the metabolites are detected in ground water in areas of major usage. Previously we found that SIM exposure from postnatal day 23 to 53 increased serum testosterone (T) on postnatal day (PND) 53 in the rat. We hypothesized that SIM was either advancing the hypothalamic-pituitary-gonadal (HPG) activation of puberty by targeting the hypothalamic regulation of pituitary luteinizing hormone (LH) release or inducing the secretion of testosterone by altering testes function. The present study examines the effects of SIM on testes function more closely. We measured intra-testicular T concentrations and ex-vivo T production following a 20 day exposure to 0, 3.125, 6.25, 25 and 100 mg/kg of SIM by gavage (PND 23 to 43). Specifically, we measured interstitial fluid (IF) and seminiferous tubule fluid (SNF) in one testis of each rat and determined T content. There were no significant differences in testis weight or IF and SNF volume or T content. The other testis was incubated in supplemented Med 199 based upon the sliced testes assay and baseline and challenged collections (100 mIU/ml hCG) were obtained at seven 30 minute intervals. In the initial baseline collection, the concentration of T in the media was increased at simazine doses of 25 mg/kg or higher. All other incubation media T concentrations were not different from controls in the baseline or hCG stimulated collections. Lactate dehydrogenase activity from the last collection indicated no cytotoxicity. In conclusion, SIM did not alter testicular function and suggests that the previously observed effects of SIM on serum T concentrations are not due to any direct effects on the testes, but may be due to increased LH stimulation. Further studies are ongoing to determine the effect of simazine on the hypothalamic-pituitary regulation of LH secretion during the pubertal period.