In vitro analysis of muscular contractile ability and passive biomechanical properties of uterine cervical samples from nonpregnant women.

We assessed the maximal muscular contractile ability, the passive biomechanical properties, and the hydroxyproline concentration in uterine cervical tissue samples from 28 nonpregnant women. Circular cervical tissue strips were mounted in organ baths and isometric tension was recorded. The mean (+/- SEM) maximal mechanical responses induced at the length of optimal mechanical performance by K+ (124 mmol/L) equaled 0.16 +/- 0.05 mN/mm2 in the distal cervix and 0.84 +/- 0.47 mN/mm2 in the proximal cervix, as compared with 4.85 +/- 1.0 mN/mm2 in tissues from the isthmus and 6.50 +/- 1.4 mN/mm2 in the fundus. The passive biomechanical properties were analyzed by a materials-testing machine. No significant differences were found between tissues from the distal and proximal cervix or between circular and longitudinal preparations. Tensile strength equaled 1.5-1.7 N/mm2, ie, 10(4)-fold the maximal muscular contractile ability. The extensibility was 0.63-0.76 and the stress-relaxation was 41-48%. The hydroxyproline concentration was 22.5 micrograms/mg wet weight in the distal cervix and 21.6 micrograms/mg in the proximal cervix, as compared with 16.6 micrograms/mg in the isthmus and 12.6 micrograms/mg in the fundus. A method for analysis of the biomechanical properties of the human cervix was designed, and from the measurements obtained it may be concluded that the passive biomechanical strength of the cervix markedly exceeds the active muscular contractile ability. This may be explained by a high collagen concentration and a low content of smooth muscle in the cervical tissue.