Preliminary study of modification of serum albumin through paracellular pathway of rat submandibular gland.

One of structural characteristics in human serum albumin is a single reactive free sulfhydryl group in position 34. In extracellular fluid such as serum and interstitial fluid, albumin is a mixture of oxidized forms and reduced form having free sulfhydryl group (1). The oxidized form of albumin is induced by oxidization of free sulfhydryl group due to several oxidants such as cystine, oxidized glutathione and hydrogen peroxide. It has been reported that the sulfhydryl group in albumin is highly oxidized in aging, exercise and renal dysfunctions, having attracted clinical application as an extracellular marker of oxidative stress (2-4). However, the oxidization mechanism including the site within organ still remains to be explained. The isolated rat salivary gland (5) allows us to sample venous effluent from the organ, interstitial fluid and saliva, thus useful for understanding the site of oxidization through capillary, across vascular wall or through paracellular route. In this study, to clarify the oxidization mechanism of albumin in the living system, we isolated a rat submandibular gland and perfused it vascularly with the perfusate containing commercial human albumin. Then, the collected samples were analyzed by a specially designed system of high-performance liquid chromatography (HPLC) which could separate albumin into reduced and oxidized forms (2, 3).