DEPRESSION OF THE PROGESTERONE LEVELS IN WOMEN TREATED WITH SYNTHETIC GESTAGENS AFTER OVULATION

Abstract

ABSTRACT Norethisterone1), norgestrel, chlormadinone acetate or medroxyprogesterone acetate was given orally from the third day after ovulation or later for various numbers of days to healthy young women. The day of ovulation was calculated from the urinary excretion of oestrogens and the plasma levels of progesterone. The daily plasma levels of progesterone and the length of the luteal phase was used to evaluate the effect of treatment during 32 cycles. All four tested gestagens produced a significant depression of the plasma levels of progesterone. The dose required varied with the gestagen used. The lowest total dose used to produce this decrease in the progesterone levels was for norethisterone 30 mg, for dl-norgestrel 12 mg, for chlormadinone acetate 300 mg and for medroxyprogesterone acetate 360 mg. Apart from the total dose the duration of treatment seemed to influence the result. As expected the onset of menstrual bleeding was delayed despite plasma levels of progesterone below 1 ng per ml when the treatment was prolonged. Chlormadinone acetate delayed menstrual bleeding more than medroxyprogesterone acetate, norethisterone or norgestrel. The depression of progesterone production is probably mediated through an inhibition of enzyme systems in the corpus luteum. No true luteolytic effect could be assigned to the compounds tested, as injections of human chorionic gonadotrophin caused an increase in the plasma levels of progesterone, indicating the capacity of the corpus luteum to produce progesterone despite the inhibition caused by the gestagens.