Dynamics of Postischemia: Enzymes in Brain Capillaries

The isolated brain microvessels have been described as the morphological and functional correlate of the blood-brain barrier (9) and represent a separate and comparatively unique metabolic compartment (3, 5, 6). Previous investigations on the metabolism of brain capillaries have indicated that the brain microvasculature is more resistant to ischemia than the brain parenchyma (18). However, the metabolism of the microvessels does change during recirculation regardless of the intensity of the ischemic insult (5). Just as in the brain parenchyma, the pathophysiological events related to ischemia are evident in brain microvessels even after the blood circulation has been re-established (12). The severity of an ischemic insult is manifested primarily in the postischemic period (15). Recirculation appears to trigger its own set of events, including alterations in metabolite levels as well as in enzyme activities (5, 7, 19, 24). For example, some derangements in the levels of certain neurotransmitters of the brain were exhibited even after 7 days of recirculation following 15 minutes of bilateral ischemia in gerbils (2). In contrast, the enzymatic changes seem to be more pronounced in earlier stages of postischemia.