Abstract

PIP: The effect of ENT, a synthetic gestagen, on corpus luteum function in 62 normal and 31 insufficient cycles was studied by radioimmunassay o f plasma levels of progesteorne, immunoreactive estrogens, and gonadotro pins. Doses as high as 100 mg/day immediately after ovulation blocked synthesis of progesterone in normal cycles totally within 4-5 days. Estrogens seemed to be elevated. Smaller daily doses had the same effect, but less pronounced. The effect became weaker with every day after ovulation that therapy was begun. However, a start of therapy on Day 5 after ovulation showed some suppression. 3 tablets daily of a commercial preparation designed for corpus luteum phase defects (100 mcg EE2 and 2 mg ENT per tablet) showed slight suppression of progesterone levels if therapy began close to ovulation but administration during an insufficient luteal phase produced nothing but the expected menstrual delay. This indicates ENT suppresses corpus luteum function by blocking progesterone synthesis exclusively. Plasma levels of estrogens and gonadotropins remained unaltered. The blocking effect depends upon daily dose and age of corpus luteum at start of therapy. Substitution therapy of corpus luteum phase defects in patients with infertility problems should not be used any longer and should never begin earlier than 3 days after ovulation if used at all. Stimulation therapy during follicular phase with clomifene or gonadotropins gives better results.