A comparison of the characteristics of parturition induced by prostaglandin F2α, infused intra aortically, with those following ovariectomy in the rat

Prostaglandin F2α (PGF2α) was infused intra aortically at different rates into rats for 11.5 hr from day 18 of gestation. At doses in excess of 5 μg/hr premature delivery invariably occurred 40 to 41 hr later. At lower doses an all or none effect was observed, some animals delivering prematurely and others continuing to term. Parturition could not be induced earlier than 40 hr after the start of the treatment even by a continuous infusion of PGF2α, suggesting that the luteolytic role of PGF2α is more important than its oxytocic action in this case. The rate of fall in plasma progesterone was greater in the rats delivering prematurely than in those delivering at term, although the final concentrations of between 15 and 30 ng/ml at delivery were the same. Labour appeared more normal in the animals receiving PGF2α than in those which had been bilaterally ovariectomized. The possible significance of this in relation to an effect of PGF2α on oestrogen secretion is discussed.