Control of mucus hydration as a Donnan equilibrium process.

Abstract

The physical properties of the mucus secreted by the uterine cervix of primates and other animals undergo periodic changes which are important in the regulation of fertility. During the luteal phase of the sexual cycle, cervical mucus is thick, rubbery and impenetrable by spermatozoa; by the time of ovulation, it is a watery gel easily penetrated by spermatozoa. Although these changes in the rheological properties of mucus have been attributed to variations in the covalent cross-linking between long chains of glycoproteins, the main macromolecular constituent of cervical mucus1,2, recent studies3,4 suggest that the macromolecular matrix of cervical mucus is probably not covalently cross-linked. Rather it is an entangled random network of long mucins3, in which case the observed changes in the physical properties of mucus would be explained by varying degrees of hydration, the mechanism of which is not understood5. We now describe experiments which show that the hydration of cervical mucus may be controlled by a Donnan equilibrium process.