AGE-RELATED-CHANGES IN ALBUMIN-EXCLUDED VOLUME FRACTION

The space available to large macromolecules, such as albumin and globu lin, is less than the total interstitial fluid volume due to the dense matrix formed by the interstitial ground substance. Changes in exclud ed volume are likely to indicate changes in the composition of the mat rix. Sprague-Dawley rats were anesthetized with sodium pentobarbital. Serum, mesenteric tissue, and peritoneal fluid samples were obtained. Albumin contents were determined by microrod electrophoresis. Serum an d mesenteric tissue chloride concentrations were measured by the coulo metric-amperometric method. Serum and mesenteric tissue sample chlorid e concentrations were not significantly different, suggesting that thi s loose connective tissue is composed almost entirely of extracellular matrix. Matrix hydration decreased with a regression slope of -0.014 (mu g tissue water/mu g tissue dry wt)/10 days. Serum and tissue album in concentrations decreased between 210 and 630 days of age. Mesenteri c loose connective tissue albumin-excluded volume fraction increased b y 80% over this age range. The increase could not be accounted for by dehydration alone, suggesting that the increase in excluded volume fra ction for albumin is also due to changes in tissue glycosaminoglycans or collagen. (C) 1995 Academic Press, Inc.