The relaxant property of local prostaglandin E2 on the non-pregnant uterus — A cyclic triphasic response

The response of the non-pregnant human uterus to intravenous(i.v.) injections and intra-uterine instillation of various doses of prostaglandin E₂ (PGE₂) was evaluated at the different phases of the menstrual cycle in 13 fertile regularly menstruating woemn who were neither lactating nor using any hormonal therapy. Uterine contractility was recorded by the microballoon technique in at least three sessions(proliferative, mid-cycle and secretory) in a single cycle with endometrial biopsy performed immediately following the last session to ascertain that the particular cycle was an ovulatory one. Single i.v. injections of PGE₂ had a consistent stimulatory effect on the contractility throughout the cycle with a tendency towards a decreased uterine response at mid-cycle and luteal phase as compared to the proliferative part of the cycle. Intra-uterine instilation of the compound induced a peculiar and interesting type of response. In the proliferative and secretory phases of the cycle the response was one of stimulation ; being more pronounced in the former period. However, around ovulation time, the local administration induced an evident uterine relaxation in most cases without any instance of stimulation. The possible implication of this triphasic response behaviour of the non-pregnant uterus within certain physiological events and pathological conditions is discussed.