Metabolism of doubly labelled ethynylestradiol-3-cyclopentyl ether in women

The metabolic fate of orally administered 17α-ethynylestradiol-3-cyclopentyl ether (EECPE) labelled with 3H in the steroid nucleus and with 14C in the cyclo-pentyl group has been studied in women in two independent laboratories. Radioactivity was excreted over a period of up to 127 days, and unchanged EECPE was recovered from fat at 2 and 3 days after ingestion. Substantial quantities of ethynylestradiol were identified in the processed urine by recrystallization with carrier. Three other urinary metabolites were detected; the least polar contained 3H and 14C but was not EECPE. This metabolite is probably present in the urine over the entire excretion period. The most polar metabolite contained only 3H and was quantitatively prominent in urines from the first few days collections but disappeared from the excretion pattern with time. A metabolite of intermediate polarity increased in relative amount during the collection period.