Interconversion of estrone and estradiol-17 beta in lung slices of the adult human.
The metabolism of tritium-labeled estrone and estradiol-17 beta in slices of lung tissue obtained from an adult human was studied; estrone was identified as the only metabolite of estradiol-17 beta and estradiol-17 beta as the exclusive product of estrone metabolism. Product formation remained linear as a function of time of incubation up to 3 h and of wet lung tissue mass up to 300 mg/ml. At equimolar substrate concentrations, the rates of estrone formation were at least 2-fold greater than those of estradiol-17 beta. The apparent KM of 17 beta-hydroxysteroid oxidoreductase for estrone was 11 microM and that for estradiol-17 beta was 10 microM. These results are suggestive that the human lung enzyme binds estrone and estradiol-17 beta with similar affinities; however, the oxidative pathway is favored as indicated by the greater Vmax attained in the formation of estrone. It is possible that, in vivo, the human lung constitutes a site for estradiol-17 beta inactivation to estrone as well as a site for the conversion of estrone to estradiol-17 beta. This last process may become particularly important in instances in which the ovaries have ceased to function and secrete estradiol-17 beta, e.g. the postmenopausal women.
D002294:Carcinoma, Squamous Cell / Q000601:surgery; D004958:Estradiol / Q000378:metabolism*; D004970:Estrone / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008168:Lung / Q000378:metabolism*; D008175:Lung Neoplasms / Q000601:surgery; D008297:Male; D008875:Middle Aged; D014316:Tritium
D014316:Tritium; D004970:Estrone; D004958:Estradiol