Effect of thyroid state on estradiol-17beta metabolism in the rabbit

It is well known that the metabolic clearance rate (MCR) of a hormone is influenced highly by the level of its specific binding protein. It was interesting, therefore, to study the metabolism of estradiol-17beta (E2) in an animal model such as the rabbit where there is a lack for a highly specific binding protein for the steroid. The kinetics of the hormone was studied in relation to the thyroid state, namely in rabbits receiving thyroxin or propylthiouracil. In the absence of any significant decrease of the level of the rabbit androgen binding protein (R-ABP), the accelerated MCRE2 and the elevated conversion ratio of estradiol to estrone (CR E2 leads to E1) observed in hyperthyroid rabbits were attributed to the important role of metabolizing enzymes in the liver and/or extrahepatic tissues. In hypothyroid rabbits, while the CR E2 leads to E1 decreased significantly the MCRE2 was not altered.