Stability of glutathione peroxidase in swine plasma samples under various storage conditions.

The stability of plasma glutathione peroxidase under different temperatures (4 degrees C vs. -15 degrees C), various durations of storage (0, 1, 2, 3, 7, 14, 28 and 56 d), and storage under inert gas (nitrogen (N2)) vs air is described. The glutathione peroxidase activity of swine plasma decreased consistently with storage at either 4 degrees C or -15 degrees C 1-56 d after collection, and differed (P less than or equal to 0.01) from the initial values. Storage under N2 at -15 degrees C slowed the rate of enzyme activity decrease but did not maintain the initial activity. For absolute measurements, it is suggested that swine plasma glutathione peroxidase activity be measured immediately after separation from the blood cells or be assayed within 24 h in plasma samples stored at -15 degrees C with air space displaced by N2. If relative treatment differences in enzyme activity are satisfactory, then assays can be conducted after controlled periods of storage.