Response of the Pregnant Human Uterus to Low and High Doses of Prostaglandin E₁ and E₂

Uterine sensitivity to low doses of prostaglandin E 2 was compared at midpregnancy and at term. An analysis of the amniotic pressure recordings revealed that the uterus in midpregnancy responded by increased contractility to an infusion rate of the same order as that, commonly used for induction of labour at term. However, the absolute intensity of the contractions was significantly higher at term than at midpregnancy. Intravenous infusion of high doses of prostaglandin Et (maximum dose without consistent subjective side effects) at midpregnancy stimulated the uterus to frequent contractions (6–8 contractions per 10 min) of gradually increasing intensity, which reached an average value of 35 mmHg following 6 hours of infusion. The individual uterine response to prostaglandin varied considerably from one case to another. The “maximum tolerable infusion rate” which could be administered without major subjective side effects also varied within a wide range.