Effect of Actinomycin D on Corpus Luteum Regression in Ewes

Four experiments using a total of 49 ewes were conducted to investigate the ability of actinomycin D to prevent corpus luteum (CL) regession at the end of an estrous cycle and in response to exogenous estradiol. In experiment I intrauterine administration of 500 µg of actinomycin D on day 11 of the estrous cycle prevented CL regression (P < .01) as indicated by the mean weight of CL 9 days after treatment. In experiment II intrauterine administration of actinomycin D on day 11 prevented CL regression (P < .01) even when 750 µg of 17β-estradiol were injected intramuscularly on days 11 and 12. Treatment of ewes with estradiol in experiment II reduced (P < .01) the weight of follicular fluid at day 18 and delayed ovulation. Ewes with one CL on each ovary were treated unilaterally with actinomycin D in experiments III and IV. Unilateral maintenance of CL was observed when the uterine horns were ligated and severed to prevent transport of actinomycin D from the treated to the control horn. The results of these experiments indicate that intrauterine administration of actinomycin D can delay CL regression at the end of an estrous cycle and prevent the luteolytic effects of exogenous estradiol.