The uptake of radioactivity by the uterus of the rabbit following the sytemic administration of (3H) estradiol-17beta and (3H) estrone and the identification and subcellular localization of radiometabolites in the uterus

In an effort to determine the relevance of the uterine oxido-reduction of estrogens to their action in the rabbit uterus, the uterine uptake of radioactivity administered subcutaneously as ³h] estradiol-17β or ³H]estrone and the subcellular distribution of radio-metabolites in the uterine tissue were studied. The animals were killed 20 min, 1, 3 and 9 hr after the administration of 0.1 μg tritiated steroid and the relative proportions of radioactive estradiol-17β and estrone in plasma and in ‘cytosol’, ‘mitochondrial/microsomal’ and ‘nuclear’ fractions of the uterine homogenates were studied. Despite the presence of a high proportion of estrone in chloroform extract of plasma, very little was found in the fractions from uterine tissue irrespective of the steroid administered. Highest levels of uterine estrone were found in the ‘mitochondrial/microsomal’ preparation. There was no apparent difference in the pattern of uptake of radioactivity administered as ³H] estradiol-17β or ³H] estrone. The presence of high levels of 17β-hydroxysteroid dehydrogenase activity in the rabbit uterus may be responsible for the apparent difference between these results and those of similar experiments using the rat.