Regression of Corpora Lutea and Interruption of Pregnancy in Rabbits Following Treatment with Rabbit Serum to Ovine LH1

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Abstract
Antibodies againstovine luteinizing hormone (LH) were prepared in male rabbits. The antiserum was injected iv daily into pregnant rabbits at various stages between 16 hr following mating and day 18 of pregnancy. Doses of 0.25 ml or more of the antiserum given between days 3 and 18 of pregnancy induced regression of corporta lutea and complete resorption of embryos, whereas antiserum administered initially between 16 hr. following mating and day 3 did not significantly affect weight of corpora lutea or the percentage of normally cleaved ova. Four mg of progesterone sc daily between days 11 and 18 of pregnancy in either ovariectomized or intact-antiserum treated rabbits maintained normal survival and growth of embryos. Progesterone alone had no effect on weight of corpora lutea in intact pregnant rabbits or on survival of embryos, nor did it influence the luteolytic effect of the antiserum in antiserum-progesterone treated animals. Two [mu]g of estradiol-17 [beta] in beeswax-sesame oil injected every 12 hr between days 11 and 18 prevented the antiserum-induced luteal regession and maintained survival of embryos, although their growth was retarded. Higher levels of estrogen interrupted pregnancy. However, the weight of corpora lutea was normal when 20 [mu]g estradiol was administered daily with 0.25 ml antiserum. The results indicate that antiovine LH suppresses the secretion of endogenous estrogen, thereby prompting regression of corpora lutea, with a consequent shortage of progestin and interruption of pregnancy.