To evaluate the age- and sex-related changes in Type 1 iodothyronine deiodinase gene
expression in the liver and kidneys, we measured 5′-deiodinating activity and deiodinase
mRNA in developing rats. The activity in the liver increased after birth, and that
in neonates was approximately half that in adults. In contrast, the activity in neonatal
kidneys remained very low. The relative importance of activity in male kidneys compared
to the liver increased from the ages of 1 to 20 days. The male adult rat liver showed
a higher level of activity than the female liver. Deiodinase mRNA in the male liver
gradually increased from 1 to 20 days, in correlation with the activity. In kidneys,
deiodinase mRNA was low before day 20, and there was no significant sex difference
in all age groups. In orchiectomized male rats, the activity and mRNA in the liver
was similar to the low levels found in females; however, the levels in the kidneys
were not significantly different than those of normal males. These data suggest that
the age- and sex-related changes in iodothyronine deiodinase gene expression are regulated
mainly at the pretranslational level, and that the relative importance of kidneys
to liver in iodothyronine deiodinase increases from birth to age 20 days due to the
difference in the gene expression.
Key words
Sex - Testosterone - Development - Triiodothyronine - Gene
