Effects of methoxychlor (MXC) in male largemouth bass

Male largemouth bass were injected with 25 mg/kg MXC and sacrificed after 48 hours; liver dissected and used for total RNA extraction Keywords: Methoxychlor injection; single injection and time point The organochlorine pesticide methoxychlor (MXC) (1,1,1-trichloro-2,2-bis(p-methoxyphenyl)ethane) has been used increasingly as an insecticide since the banning of DDT, the primary advantage being that MXC is rapidly metabolized and does not show high levels of bioaccumulation in non-target organisms. However, studies have shown that MXC can be metabolized into additional metabolites, such as mono-demethylated 2-(p-hydroxyphenyl)-2-(p-methoxyphenyl)-1,1,1-trichloroethane (OH-MXC) and bis-demethylated 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), both of which are estrogenic in mammals. In addition, there is increased potential for disruptions to normal hepatic physiology (Schlenk et al., 1998; Stuchal et al., 2006). The objectives of the present study were to study the hepatic genomic response in male largemouth bass to an i.p. injection of MXC. We performed a microarray analysis on 25 mg/kg MXC 48 hour injection because there was a significant induction of ERα and ERβb mRNA in the liver which was comparable to a 48 hour 1 mg/kg injection of E2 (previous work done by Blum et al., 2008; Aquat Toxicol. 86(4), 459-469). We chose the liver because of the significant role this tissue plays in detoxification of contaminants and due to the high capacity to produce vitellogenin in response to estrogenic chemicals. We were also interested in comparing the genomic response of MXC to estradiol alone to identify putative candidate genes and pathways that may be specific to MXC and not due to direct estrogenic effects mediated via E2 receptors. Largemouth bass injected with single i.p. with 25 mg/kg methoxychlor; sacrificed 48 days later,liver tissue studied. 4 individual liver samples (control and treatment)