Changes in cervical function at parturition.

In sheep and goats changes in the wall of the uterine cervix associated with parturition were studied in relation to the preparturient sequence of endocrine events. Evidence was obtained of separation of collagen fibrils, possibly due to changes in the electrostatic binding of the fibrils by glycosaminoglycans. The mechanical properties of the cervix were investigated quantitatively on isolated tissues by radial loading to destruction, and by progressive extension on a tensometer; the extension experiments revealed that at parturition (but not before) the cervical wall acts mechanically as if composed of two different tissues, one of which, the collagen layer, changes profoundly at parturition to facilitate dilatation. Resistance to dilatation (compliance) was investigated in vivo using indwelling intracervical balloons which could be inflated with water at standard speed. This permitted serial observations in the same animal during the progress of parturition induced with foetal dexamethasone (sheep) or maternal cloprostenol (goats). Compliance increased progressively in all 13 parturient animals, but not in untreated controls, and this increase occurred coincidentally with the expected fall in progesterone and rise in oestrogen concentrations: it occurred before the preparturient rise in PGF. Meclofenamic acid administration to cloprostenol treated goats successfully delayed the PGF surge and delayed parturition but did not delay the increase in compliance which reached maximum within the 36 hours of treatment with the PG synthetase inhibitor.