The effect of low doses of prostaglandin F2α infused into the aorta of unrestrained pregnant rats: Observations on induction of parturition and effect on plasma progesterone concentration

An intra-aortic infusion of 4.67 μg PGF2α/h for 11.5 h starting on Day 18 of gestation initiated parturition in rats within 40-41 h. There was no difference in latency in two groups in which the post-operative recovery period was approximately 5 h and 30 h respectively. Control animals infused with saline delivered live litters after 106 h. PGF2α-induced parturition was associated with a more rapid fall in the plasma progesterone concentration than in the saline infused control animals. Uterine activity was monitored by radiotelemetry. In Control saline infused animals changes occurring around the time of delivery were similar to those reported using intra-uterine balloons. The prostaglandin infused animals exhibited a similar sequence of changes. Maximal sensitivity of the uterus to stimulation by PGF2α was observed 25-35 h prior to delivery, and in the post-partum period.