[A basic study on cervical ripening--with special reference to the stretch modulus in the rat uterine cervix].

To study the physiological factors in cervical ripening, we analyzed static stress-strain diagrams of experiments done on cervical tissue from Wistar rats. The measured strips (N = 220) were stretched at a given increasing tension while the length and tension were continuously recorded. The data obtained were converted to a stress-strain relationship and the following results were obtained: 1. The average stretch moduli for nonpregnant, term and puerperal rats were 466.91 +/- 129.95 x 10(3) mgw/mm2, 9.80 +/- 1.26 x 10(3) mgw/mm2 and 29.76 +/- 5.78 x 10(3) mgw/mm2 (mean +/- S.E.) respectively. 2. The yield and break points were lowest in rats at labor. 3. Succeeding two or several repetitions of loading and unloading of cervical tissue samples revealed a reduction in their stiffness. 4. The cervical tissue samples were pulled after adding PGF2 alpha, PGE1, PGE2, DHA-S etc., and the results of these experiments indicate that some of these drugs had the effect of elongating the strain at the beginning of the linear portion and the effect of changing cervical contractions. 5. DHA-S or its metabolites except estradiol might have a direct effect on the dilatation of the rat cervix. 6. Microscopically detected edema in the term specimen suggested collagen dispersion.