Modulation of testosterone and 17β-estradiol metabolism by amitraz in rats

Autor: Chen-Ping Chou, 周正平
Rok vydání: 2008
Druh dokumentu: 學位論文 ; thesis
Popis: 96
The present study has investigated the ability of amitraz (N’-(2,4-dimethylphenyl)-N-[[2,4-dimethylphenyl]imino]methyl)-N-methanimidamide), a formamidine insecticide widely used to control eriophyid mites on pears and mange in animals, to modulate testosterone and 17β-estradiol (E2) metabolism and to alter the circulating levels of the hormones in rats. Endocrine-disrupting chemicals (EDCs) are exogenous agents that interfere with the production, release, transport, metabolism, binding, action, or elimination of the natural hormones in the body responsible for the maintenance of homeostasis and the regulation of developmental processes. The main hypothesis of this study was that amitraz is an EDC which has the ability to modulate testosterone and E2 metabolism and to alter the circulating levels of the hormones in rats. To test the hypothesis, the present study established analytical methods to detect and identify testosterone metabolites in rat serum and microsomes using high performance liquid chromatography-ultraviolet detector and tandem mass spectrometry and to detect E2 and metabolites using gas chromatography equipped with electron capture detector and mass spectrometry. To determine the effects of amitraz on liver cytochrome P450 content and erythromycin N-demethylase activity, amitraz was administered intraperitoneally at 25 and 50 mg/kg once daily for 5 and 7 days to male and female rats or to ovariectomized (OVX) female rats treated with 0.5 mg/kg E2. The results showed that in male rats, 50 mg/kg amitraz increased respective 39% and 68% of P450 and erythromycin N-demethylase activities. In female rats, 50 mg/kg of amitraz resulted in 51% and 81% increases of P450 content and erythromycin N-demethylase activity. In OVX female rats, cotreatment with E2 and 50 mg/kg of amitraz produced 178% and 71% increases of the aforementioned monooxygenase content or activity. The effects of amitraz on liver phase Ⅱ enzymes including uridine diphosphate-glucuronosyltransferase (UGT),glutathione S-transferase (GST), N-acetyltransferase (NAT), catechol O-methyltransferase (COMT), and sulfotransferase (SULT) activities were also studied. The results showed that in male rats, 25 mg/kg amitraz resulted in respective 39 and 46% increases of UGT and SULT activities. Amitraz at 50 mg/kg produced 0.8-, 1.0-, 2.0-, and 1.13-fold increases of UGT, GST, NAT and SULT enzymes activities, respectively. In female rats, 25 mg/kg amitraz produced 0.8- and 0.73-fold decreases of GST and SULT activities and 72% and 57% increases of NAT and UGT activities, respectively. Amitraz at 50 mg/kg produced 113%, 40%, and 86% increases of UGT, GST, and NAT activities, but decreased SULT by a 0.3-fold, respectively. The results of immunoblot analysis indicated that SULT 1E2 and 2A1 protein showed sex differences in their responses to amitraz treatment. Amitraz showed no effects on COMT activities of male and female rats. The results of testosterone metabolism studies of the liver of male and female rats showed that amitraz at the dose of 50 mg/kg produced respective 2.0-, 1.4-, and 2.8-fold increases of the ability of liver microsomes to metabolize testosterone to 6β-, 16α-, and 2β- hydroxylated products in male rats and 1.5-, 2.9-, and 3.0-fold increases in female rats. The insecticide resulted in an 8.6-fold increase of 16β-OH-testosterone formation in female rats and 2.6- and 1.7-fold increases of androstenedione formation in males and females, respectively. Amitraz increased testosterone 6β-hydroxylation by a 1.5-fold and had no effects on other metabolites formation in OVX and E2-treated female rats. The results of E2 metabolism on the liver of male and female rats showed that amitraz produced respective 1.7- and 3.6-fold increases of the capacity of liver microsomes to metabolize E2 to 2-OH-E2 and estrone in male rats and 1.9- and 3.1-fold increases in females. The formamidine did not have effects on E2 metabolism in OVX and E2-treated female rats. In male rat serum, amitraz increased testosterone and 2β-OH-testosterone concentrations by 12- and 20-fold, respectively. In OVX and E2-treated female rat serum, the insecticide produced a 6.7-fold decrease of E2 concentration and an increase of 2-OH-E2 concentration. The present findings show that amitraz induces testosterone and E2 metabolism in the liver and decreases the hormone concentrations in the serum of rats. These findings also demonstrate that amitraz is an endocrine disruptor.
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