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Effect of Actinomycin D on Corpus Luteum Regression in Ewes¹

University of Wisconsin, Madison 53706

Abstract

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 17ß-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.

¹ Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, by the Ford Foundation Grant No. 63-505, Public Health Service Training Grant No. T01 HD000 104-05 from the National Institute of Child Health and Human Development, and by the Program Project in Genetics Grant No. GM 15422 from the National Institutes of Health. This paper is No. 1463 from the Laboratory of Genetics and No. 628 from the Department of Meat and Animal Science.