Tissue distribution of 14C-lynestrenol in pregnant rats

The tissue distribution of 4-14C-lynestrenol (17 alpha-ethynyl-oestr-4-en-17 beta-ol) following oral administration to pregnant rats was studied by whole body autoradiography and liquid scintillation counting. Pregnant females were sacrificed on days 10, 12, 14 and 19 of gestation, in each case 5 hours after oral administration of 43 microCi 4-14C-lynestrenol per animal. The isotopelabelled compound was distributed throughout most tissues, including the fetuses. The highest concentrations were found in the liver, while there was lower activity in the fatty tissues and the activity in the fetuses was comparable with that in the brain. The placental transfer was verified by the results of liquid scintillation counting. The concentration of labelled substance in the fetuses increased with the duration of pregnancy.