The effect of progesterone on recorded parturition and on oxytocmn sensitivity in the sheep

Intra-uterine pressure changes were recorded at the end of pregnancy and during parturition in eight ewes by means ofendo-radiosondes implanted in one uterine horn some weeks previously. Recordings were made at frequent intervals so that the progress of parturition could be carefully monitored. When the early stages of parturition were established, a single injection of 80 mg. progesterone in oil was made in six ewes. As a result, parturition was delayed and the intra-uterine pressure waves declined or were abolished. Delivery of the lambs occurred up to 7 days later. In two ewes the injection was given somewhat later during parturition and, in these animals, the depressant effect of progesterone was much less. The increased intra-uterine pressure waves which followed digital examination of the cervical canal were abolished for more than 20 hr. in all eight ewes. Deter-mination of threshold doses of oxytocin showed wide variations and revealed no more than a general trend of increasing myometrial sensitivity with approaching parturition, a trend which was temporarily reversed in five ewes by the injection of progesterone. The eight ewes delivered 13 viable lambs and one dead lamb