The effect of prostaglandin on the electric activity of the pregnant uterus

Abstract

Of 30 unilaterally pregnant rats, each had been equipped with an extracellular multielectrode assembly and an extraovular microballoon, for the simultaneous recording of electric activity and intrauterine pressure (IUP). Sequential recording, between the 17th day of pregnancy and post partum, in the intact Controls, revealed gradual transitions from local, non-propagating, asynchronic, electric activity and irregular low level oscillations in IUP to propagating, synchronic, electric activity and regular high level IUP. This transition of uterine activity occurred when the progesterone (P) levels decreased from 108±9ng/ml to 24±4ng/ml. Ovariectomy, which provokes a precipitous rather than gradual P-withdrawal, induced and accelerated evolution of electric activity and IUP, culminating in abortion. In earlier studies this ovariectomy-induced evolution of uterine activity had been intercepted by preventing P-withdrawal through replacement therapy. Exposure of animals to extraovular Prostaglandin “Impact” (PGI) in previous experiments, also resulted in P-withdrawal (probably through interference with placental luteotrophic support) and accelerated evolution of uterine activity, culminating in abortion. This accelerated process had been intercepted by preventing P-withdrawal through substitution therapy. In the present studies PGI (50–100μg PG F2, extraovular) at days 17 of pregnancy provoked an unphysiological response, manifesting in sustained multipacemaker activity and high level resting pressure. However, subsequently the transition, from local, non-propagating, asynchronic, electric activity to propagating, synchronic, electric activity and the evolution of IUP accelerated. Pharmacological reactivity increased, the same and lesser PGIs provoked more physiological uterine responses and eventually the animals aborted. Apparently, the first PGI cannot provoke in the uterus physiological electric and mechanic responses, nor does it induce abortion. However, it converts the uterus, with the progress of time, into a spontaneously active and reactive organ, which upon physiological stimulation expells the uterine contents thorugh a process similar to that of normal delivery at term. Thus the PGI provides a therapeutic measure, when the termination of pregnancy is desired by non-surgical means.