On the mechanism of action of intra-amniotic hypertonic saline treatment in rabbits.

Abstract

Summary. A study was made into the effects of hypertonic saline upon the intra-uterine pressure in non-pregnant and pregnant rabbits. In non-pregnant rabbits intra-luminal administration of hypertonic saline caused an almost immediate transient increase in amplitude and frequency of uterine pressure cycles, a response which was abolished by prior treatment with progesterone. In pregnant rabbits, provided all placentae were damaged by the treatment, intra-amniotic administration of 20% NaCl resulted in abortion of all foetuses in 56 ± 7·3 hr SE. If one conceptus escaped damage pregnancy was not interrupted. Furthermore, treatment with 25 μg/day oestradiol propionate prevented abortion. Of the procedures carried out, only dislocation of the placentae also caused abortion, whereas pregnancy was not terminated by extra-amniotic administration of hypertonic saline, by cutting the umbilical cords (i.e. causing foetal death), nor by the intra-amniotic administration of normal (0·9%) saline. The abortion produced by both intra-amniotic hypertonic saline and dislocation of the placentae could be prevented by oestrogen administration, but not if ovariectomy were combined with placental dislocation. From these results, it is concluded that intra-amniotic hypertonic saline induced abortion in rabbits by interrupting the luteotrophic function of the placenta which resulted in loss of the luteal function essential for the defence of pregnancy.