Effect of actinomycin D on uterine prostaglandin production and oestrous cycle length in guinea-pigs

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Abstract
Intrauterine, but not systemic, administration of actinomycin D, a protein synthesis inhibitor, on day 10 increased estrous cycle length in guinea-pigs. Peripheral plasma progesterone levels remained elevated during these lengthened cycles presumably because luteal life-span was extended. Prostaglandin (PG) F2.alpha. production in vitro, on day 15, by the uterus of guinea-pigs which received intrauterine actinomycin D was much lower than control values. This decrease in PG production was not due to lack of precursor, increased metabolism, redirection of synthesis towards PGE2 or a direct inhibition by actinomycin D of the conversion of arachidonic acid to PG. The effects of actionomycin D treatment were not reversed by estradiol. Actinomycin D evidently prevents the increase in uterine PG synthetase levels that normally takes place after day 11, thereby reducing uterine PGF2.alpha. synthesis and output in vivo, and resulting in luteal maintenance and longer estrous cycles.