Disappearance of (14,15-3H)d,1-norgestrel from plasma and its distribution in the reproductive tract of women.

After an iv injection of [14,15-3H]d,1-norgestrel into 7 women, its disappearance from the plasma and its distribution in the reproductive organs has been investigated. It was found that initially norgestrel disappeared rapidly from the plasma with a half-life of 38.8 min followed by a slower disappearance with a half-life of 45.18 h. The disappearance curve has been analysed on the basis of a biexponential curve representing a two compartmental model. The low metabolic clearance rate of 458.5 1/24 h indicated a more prolonged persistance of norgestrel in the body. Uptake of norgestrel and its metabolites was very high in the endometrium, myometrium, cervix. Fallopian tube, ovary and body fat. Compared to the myometrium, more norgestrel as such was concentrated in the endometrium at 30 min and 12 h after injection of [14,15-3H]d,1-norgestrel. The myometrium on the other hand contained higher amounts of norgestrel at 5 min. The significance and the possible role of localization of norgestrel at multiple sites in the reproductive tract and its contraceptive action are discussed.