SUZUKI, M., YOSHIDA, K., SAKURADA, T., KITAOKA, H., KAISE, K., KAISE, N., FUKAZAWA, H., NOMURA, T., ITAGAKI, Y., YAMAMOTO, M., SAITO, S. and YOSHINAGA, K.
Monodeiodination of Thyroxine in the Maternal and Fetal Dog Kidneys and Placenta. Tohoku J. exp. Med. 1984,
142 (3), 313-320 - We studied the monodeiodinating activities of the dog placenta and the pregnant dog kidney and compared them with those of the non-pregnant dog kidney and fetal kidney. Each tissue was homogenized in 50mM Tris/HCl buffer, pH 7.5. The homogenate (1mg protein) was incubated with 1μg of T
4 at 37°C in the air for 15min or 60min in the presence of 5mM DTT. The T
3 and reverse T
3 generated in the reaction mixture were extracted into cold ethanol and then measured by RIA. Sulfhydryl group content in each tissue was determined. The characteristics of monodeiodinating activity of the dog placenta were in good concordance with those of the rat and human placentas. Net reverse T
3 production in the dog placenta was 1.4-13.2 (6.1±5.3, mean±S.D.) ng/mg protein/μg T
4/60min but net T
3 production was negligible. Although it seemed that the T
3 production/reverse T
3 production ratio in the pregnant dog kidney was lower than that in the non-pregnant dog kidney, there was no statistical significance. It is conceivable that the characteristics of deiodination in the placenta are tissue specific, independent of the changes in internal conditions induced by pregnancy. In the fetal dog kidney homogenate, T
3 and reverse T
3 were metabolized only minimally and productions of T
3 and reverse T
3 were also very low. An increase in DTT concentration up to 100mM had no effect on the production rates of these triiodothyronines. Total and non-protein SH group contents in the fetal dog kdney homogenate were about the half of those in the maternal tissue. These results indicate that the very low activity of monodeiodination in the dog fetal tissue is not due to the decreased concentration of SH group, but probably due to the qualitative or quantitative difference in the enzyme.
View full abstract