Distribution of norethisterone and ethinylestradiol in the gravid rat and in the feto-placental unit of rhesus monkeys following intragastric administration of norethisterone acetate in combination with ethinylestradiol. II. Autoradiography.

The tissue distribution of 14C- and 3H-radioactivity was studied in pregnant rats and in fetuses of rhesus monkeys after intragastric administration of a combination of 14C-norethisterone acetate (14C-NET-Ac; 1 mg/kg rat, 2 mg/kg rhesus monkey) and of 3H-ethinyl-estradiol (3H-EE2; 2 micrograms/kg rat, 10 micrograms/kg rhesus monkey), respective commercial formulation: Ostro-Primolut, by means of autoradiographic methodology. The results of these present investigations confirm quantitative studies of a low, transitory passage of 14C-NET-Ac and 3H-EE2 into the fetuses. Within the fetuses the highest concentrations of 14C-radioactivity were found in the liver, in the vertebra, in heart and brain. No 3H-radioactivity could be observed within the fetuses. The autoradiographic studies do not indicate any specific enrichment of NET-Ac or EE2 and their metabolites in fetal organs and tissues.