EFFECT OF HYPOXIA AND REOXYGENATION ON THE ACTIVITY OF TRANSGLUTAMINASE IN BRAIN OF NEWBORN PIGLETS

The transglutaminase activity in five regions of the brain of newborn piglets was measured and the effects of hypoxia and posthypoxic period on this activity evaluated. Enzyme activity was measured in homogenat es from cortex, hippocampus, striatum, thalamus and midbrain. The cont rol activities were 7.2, 6.2, 6.0, 5.7 and 4.6 pmol/mg protein/min, re spectively. The activities at the end of an 18 min period of hypoxia i nduced by an FiO2, of 9% were not significantly different from control activities. By 3 h after the hypoxic episode, however, the transgluta minase activites were significantly above control levels in all five r egions of the brain. Measurements of the kinetic constants of tranglut aminase indicated that increases in enzyme activity were associated wi th an increase in Vmax with no significant change in the apparent affi nity of the enzyme for the substrate, putrescine. The increased activi ty of transglutaminase during the posthypoxic period, with no changes immediately after hypoxia, suggest that the increases could be due to increased enzyme synthesis rather then activation of existing enzyme. The rise in transglutaminase activity subsequent to a hypoxic episode may contribute significantly to the long-term disturbances in cellular metabolism in the immature brain induced by hypoxic episodes.