抄録
Dioxins (PCDD, PCDF, coplaner-PCB) are known as the highly toxic environmental chemicals on the growth and maintenance of many organs. On the other hand, thyroid hormone (TH) is important factor for normal brain development. Previous study has reported that TCDD induced an increase in the number of TSH-producing cell without changing TH (T3) level. Recently, we reported that PCB and its metabolites (hydroxylated-PCB: OH-PCB) suppressed TH receptor (TR)-mediated transcriptional activation. Thus, dioxins may also partly affect TH system to disrupt brain development and function. To investigate the effects of dioxins on TR, we performed transient cotransfection experiments. Interestingly, 2,3,7,8-TCDD and PCDFs did not affect on TR-mediated transcription. When we used coplanar-PCBs, (PCB77, PCB126) they suppressed TR-mediated transcription. However, these repressions were weaker than that of OH-PCBs. Furthermore, various effects were observed with OH-PCBs. These results suggest that toxicities of dioxins to TH systems are different among each compound and the effect of TR-mediated transcription of dioxins may not always be related to their toxicities. [Jpn J Physiol 55 Suppl:S209 (2005)]
