REGULATION OF RAT-LIVER TYPE-1 IODOTHYRONINE DEIODINASE MESSENGER-RNALEVELS BY TESTOSTERONE

To investigate the underlying mechanisms of sex-related differences in liver type 1 iodothyronine deiodinase (ID1), we studied the sex-relat ed differences and roles of sex steroids in liver ID1 mRNA levels in t he rat. In both euthyroid and thyroidectomized rats, liver ID1 activit y and ID1 mRNA levels in female rats were less than those in male rats . A positive correlation was observed between liver ID1 activity and I D1 mRNA levels. Liver ID1 activity and ID1 mRNA levels in male rats de creased after orchiectomy, and were increased to control levels by tes tosterone administration. Ovariectomy or beta-estradiol administration did not alter liver ID1 activity or ID1 mRNA levels in female rats. I D1 mRNA levels in cultured rat hepatocytes were significantly increase d by testosterone, but not by beta-estradiol. These results suggest th at the sex-related differences in liver ID1 activity are attributable to differences in ID1 mRNA levels, and that testosterone plays an impo rtant role in the sex-related differences in liver ID1 mRNA levels.