Abstract
After preliminary administration of ergotoxine, pregnant rats were treated with prolactin to test whether ergotoxine-induced termination of early pregnancy was due to destruction of the capacity of the ovary to produce progesterone. Prolactin treatment maintained pregnancy in 82 of 217 ergotoxine-treated rats; when prolactin treatment was withheld, pregnancy terminated within 96 hours after ergotoxine administration in 198 of 200 rats. Observations are reported on the basis of normal and abnormal maintenance of pregnancy, litter size, gestation time and nature of vaginal smears.