Synovial Fluid Mucin

Abstract

Synovial mucin is a complex of protein and carbohydrate components. It is still unsettled whether connective tissue mucins found in different situations in the body are all similar or whether there are a great variety of mucins differing one from another in the character of their protein groups or even also in the hyaluronic acids they contain. These complexes of protein (mucin) are united to a polysaccharide which possesses acidic characteristics. The mucins appear to act as cementing substances of extra-cellular ground substance in the connective tissue. Most tissues of mesenchymal origin appear to produce the uronic acid type of mucin, collectively termed hyaluronate or hyaluronic acid mucin. These are found in synovial fluid, umbilical cord, lungs, malignant tumors of the pleura, aqueous and vitreous humors, connective tissue generally, and skin connective tissue. It is also produced in abnormal quantities in myxedema and in osteochondromatoses. Solns. of hyaluronic acid form mucin when soluble protein is added and then dilute acetic acid. The mucin separates as a tough, ropy mass leaving any excess of protein in soln. The polysaccharide is responsible for the high viscosity of mucins. Removal of mucin by acetic acid precipitation reduces the viscosity of sy-novial fluid to approx. that of water. The property of viscosity itself depends upon the concn. of the soln., the presence of inorganic salts, the pH, and the temp. Mucin is a normal product of connective tissue, where no doubt it subserves several functions. It appears to be an intercellular cement, to regulate ionic distribution and osmotic equilibria, and to impart resiliency to the subcut. matrix. Its abundance appears to be affected to some extent by hormonal influences, and it is an intriguing possibility that the loss of resilience and the relative dehydration of the subcut. tissues which occur in old age are associated with a decrease in mucin content.