Effects of methoxychlor (M) or its active metabolite, 2, 2-bis (p-hydroxyphenyl)-1, 1, 1-trichloroethane (HPTE), on testosterone (T) formation by cultured adult rat Leydig cells (LC).
M is a pesticide developed as a replacement for dichlorodiphenyltrichloroethane (DDT). Its active metabolite is reported to be HPTE. Both M and HPTE have been shown to exhibit weak estrogenic or antiandrogenic activities in various in vivo or in vitro testing protocols. In the present studies, we examined the direct effects of M or HPTE on T biosynthesis by cultured LC from young adult rats. Increasing concentrations of M or HPTE (1-1000 nM) caused a progressive decline in both basal and 10 mIU/ml human chorionic gonadotropin (hCG)- or 1 mM 8-Br-cAMP-stimulated T following exposure for 4 or 24 h, beginning at 100 or 500 nM, although the declines with HPTE generally were greater. To localize the site(s) of action of HPTE, LC were exposed to HPTE (1-1000 nM) alone for 24 h, then fresh media containing steroid precursors of T were added to follow the ability of exposed cells to convert these substrates to T over 4 h. The conversion of 0.01 mM pregnenolone, progesterone, or androstenedione to T was unaffected by prior exposure to HPTE; however, there was a progressive decline in the conversion of 0.01 mM 22(R)-hydroxycholesterol to T, suggesting that among the enzymes involved in the conversion of cholesterol to T, P450 cholesterol side-cleavage activity is inhibited by HPTE. The concomitant inclusion of the pure estrogen antagonist, ICI 182, 780, did not alter the inhibitive effects of HPTE, suggesting that the actions of HPTE are not mediated by binding to estrogen receptor alpha or beta. Also of interest, the addition of the native estrogen, 17beta-estradiol, or the antiandrogens, cyproterone acetate (1-1000 nM) or hydroxyflutamide (1-1000 nM), had no effect on basal or hCG-stimulated T following exposure for 24 h, suggesting that the actions of HPTE are not due to its estrogenic or antiandrogenic properties.
The Toxicologist. Society of Toxicology 41st Annual Meeting and ToxExpo, March 17-21, 2002, Nashville, Tennessee