The physiological role of relaxin in the pregnant rat. III. The influence of relaxin on cervical extensibility.

Cervices from day 18 (D18) intact pregnant rats show significantly greater extensibility and ability to accommodate to extension than cervices from D9 pregnant rats. On D22, cervices from intact pregnant rats show even greater extensibility and accommodation to stretch. Cervices from ovariectomized pregnant rats treated with estrogen (E) and progesterone (P; group OPE) show markedly reduced extensibility and ability to accommodate to stretch compared with intact pregnant cervical tissue (group C) on both D18 and D22. Extensibility of group OPE cervices resembles that of cervices from D9 intact pregnant rats. Cervices from ovariectomized pregnant rats treated with E, porcine relaxin (R), and P (group OPER) or porcine R and P (group OPR) exhibit similar extensibility and ability to accommodate to stretch as cervices from intact pregnant rats on both D18 and D22. The importance of R for cervical softening during pregnancy and its interaction with E near term and during parturition are discussed.