DILATION OF THE UTERINE CERVIX OF THE RAT AND ACCOMPANYING CHANGES DURING THE ESTROUS CYCLE, PREGNANCY AND FOLLOWING TREATMENT WITH ESTRADIOL, PROGESTERONE AND RELAXIN1

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Abstract
An in vitro method was employed to measure the dilatability and tensile strength of the uterine cervix of the rat during the estrous cycle, gestation and the puerperium. Dilatability, percent water and cervical weight increased throughout gestation to a maximum at parturition. Tensile strength and percent collagen (as measured by hydroxyproline) of the cervix decreased throughout gestation. Within 48 hours post-partum, all measurements tended to return to values seen in the nonpregnant rat. The maximum dilatability, observed at parturition, was found to be due in part to stretching induced by the fetus traversing the birth canal. Relaxin caused similar changes in dilatability, tensile strengh, percent water and collagen in pregnant ovariectomized rats treated with the ovarian steroids. Measurements obtained in non-pregnant, ovariectomized rats treated with estrogen, progesterone and relaxin yielded comparable results but the magnitude of the cervical dilatability was not as great as that observed in the intact, pregnant animal.