Abstract
Studies on the distribution of ^67^Ga in pregnant rabbits showed a marked concentration of the isotope in uterine tissue and flushings of 5βday pregnant rabbits 24 hours after isotope injection. The isotope no longer localized throughout the uterine tissues and flushings on injection of 7β to 8βday pregnant rabbits but was specifically associated with the blastocysts and sites of implantation. As the gestation time progressed ^67^Ga increasingly concentrated in placental and mammary tissue while the concentration in serum and thymus tissue decreased. The marked concentration in placental tissue was readily discernible on totalβbody scans of pregnant rabbits.
Column chromatography of uterine washings and placental extracts from pregnant rabbits and thymus extracts from estrous rabbits showed most of the isotope associated with moieties β©Ύ 200,000 MW whereas the isotope in βmilkβ and extracts of mammary tissue was bound to components of 25,000β35,000 MW. Extracts of thymus from pregnant rats showed a marked, selective loss of ^67^Ga binding in two peaks of approximately 50,000 and 120,000 MW compared to the chromatographic profile of extracts from normal rat thymus.