Dilatation of the uterine cervix.

Dilatation of the cervix at parturition necessitates changes in the physical characteristics of cervical collagen and glycosaminoglycans which are probably hormone-dependent. The infusion of prostaglandin F2alpha (PGF2alpha) into the arterial blood supply to uterus and cervix of sheep pregnant for about 125 days resulted in cervical dilatation after 24 hours but this response was inconsistent; one factor affecting the response appeared to be the progesterone status, low circulating progesterone being associated with dilatation. Preliminary experiments in goats in which pregnancy is terminated by removal of the corpora lutea at day 125, subject to modification by the administration of progesterone, indomethacin or PGF2alpha, support the view that PGF2alpha evokes softening and dilatation of the cervix but that this is blocked by progesterone.