Effects of prostaglandins F-2 alpha and E-2 on cervical extensibility in the late pregnant rat.

The extensibility of the cervix of rats was measured in vitro on Day 19 of pregnancy and was doubled after 2 s.c. injections of PGF-2 alpha (1 mg/kg) or PGE-2 (5 mg/kg) on Day 18. Progesterone (10 mg/kg) given on Day 18 had no effect alone or on the effect of PGE-2 but abolished the action of PGF-2 alpha. PGE-2, but not PGF-2 alpha, increased extensibility when given on Day 18 to rats which had been bilaterally ovariectomized on Day 16 and given oestradiol benzoate plus progesterone twice daily. High concentrations of PGF-2 alpha or PGE-2 had no effect on the extensibility of Day-18 pregnant rat cervix in vitro. It is suggested that PGF-2 alpha acts via the ovaries to decrease progesterone secretion and perhaps release relaxin, but PGE-2 would appear to have another site of action.