The effects of pregnancy and drugs on the biochemical and mechanical properties of the rat uterine cervix

Abstract

Collagenolytic activity was measured as the solubilisation of hydroxyproline containing peptides from rat cervical homogenates at 37°C and neutral pH. Latent collagenolytic enzymes were activated by treatment with trypsin followed by soyabean trypsin inhibitor. A variety of enzymes contribute to the solubilisation of hydroxyproline: the enzyme action was, therefore, ~collagenolytic~ rather than solely due to specific collagenase. 

The biomechanical behaviour of rat cervix during late pregnancy was investigated in vitro by application of a constant load (30g) at 37°C. The dynamic stretch of the cervix following loading had 3 components. Sequentially they were instantaneous deformation, short-term viscoelastic behaviour and creep. 

At parturition on day 22 but prior to the onset of labour, both the instantaneous deformation and short-term viscoelastic properties of the cervix were increased compared with the properties on day 19. The was associated with enhanced collagenolysis demonstrated both as increased collagenolytic activity and as loss of collagen from the tissue. 

Prostaglandin F2α and indomethacin given on day 18 and on days 17 and 18 of pregnancy respectively, induced similar, although much less extensive, increases in the short-term viscoelastic properties compared to those which occur spontaneously at term. However, collagenolytic activity was unaffected. This suggested a relationship between collagenolytic activity and the extent of cervical softening. 

Indomethacin plus arachidonic acid (2.5mg/kg) also increased the viscoelastic properties of rat cervix but was without effect on collagenolytic activity, although the collagen content and concentration of the cervix were reduced. Conversely, indomethacin plus a lower dose of arachidonic acid induced a similar loss of collagen from the cervix and increased collagenolytic activity, but was without effect on the biomechanical properties of the tissue. 

It was concluded that drugs induce changes in the mechanical properties of rat cervix by biochemical processes not involving solubilisation of hydroxyproline.

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