The effects of oestradiol benzoate, progesterone, relaxin and ovariectomy on cervical extensibility in the late pregnant rat.

Cervical extensibility increased from Day 16 to term in the pregnant rat. Following ovariectomy on Day 16 of pregnancy the cervix became as inextensible by Day 20 as that of non-pregnant animals. Fetal growth was maintained in rats ovariectomized on Day 16 if given oestradiol benzoate plus progesterone but cervical extensibility only increased to a small extent. Relaxin given to these animals further increased cervical extensibility, suggesting a role for this hormone.