Persistence of progesterone secretion after foetal death induced by vasopressin in rabbits

Synthetic lysine-vasopressin (2 IU/kg body weight) terminated pregnancy in the rabbit when administered im on day 20, but not when administered on days 8 through 11 of gestation. Rabbits treated with vasopressin on day 20 delivered necrotic foetuses at the expected time of parturition (13/19 animals, day 32), aborted (3/19), or resorbed their foetuses (3/19). Uterine bleeding was noted in 68% of rabbits 5 days after vasopressin treatment on day 20 of pregnancy. Plasma concentrations of progesterone in vasopressin and saline treated rabbits were identical throughout pregnancy. Placental engorgement by erythrocytes was associated with foetal death in rabbits 1 h after vasopressin treatment on day 28 of gestation. Although vasopressin administration during the last third of gestation is detrimental to foetal life in the rabbit, the continuing normal secretion of progesterone indicates that the placentas remain viable. Available evidence suggests that foetal death results from ischaemia caused by placental vascular congestion and stasis following vasopressin administration.