The biodistribution of Br-77-labeled estrone: visualization of tissues containing increased estrogen receptors

The biodistribution of a lipid-soluble brominated female sex hormone, Br-77-labeled estrone, has been determined in dogs and rabbits. Following i.v. or intragastric administration, Br-77-labeled estrone localized in the gallbladder bile within 20-25 min. Fifty-six percent of the injected activity was found in the bile at 90 min. Breast tissue was imaged by scintillation camera in three female dogs with postpartum breast enlargement at 24 hr following i.v. injection. Analysis of digitized images revealed 50% more counts per pixel in stimulated female breast tissue than was in surrounding tissue. Increased Br-77 activity in the breast was associated with the presence of increased concentrations of estrogen receptors.