The presence of hyperglycemia prior to stroke or cardiac arrest can increase neuronal damage caused by brain ischemia. Acute hyperglycemia shows this effect in animal models of stroke. However, chronic hyperglycemia and chronic hyperglycemia with additional acute elevation of blood glucose are more common premorbid states for stroke patients. The effect of chronic hyperglycemia on regional cerebral blood flow (rCBF) is unclear but blood flow changes may play a role in this ischemic cell damage. We measured rCBF in awake restrained rats that had chronic hyperglycemia induced by treatment with streptozotocin. This was compared to that measured in rats made acutely hypergh/cemic by injecting glucose into the peritoneal space. rCBF was measured in 17 brain regions using [ u C]iodoantipyrine. During chronic hyperglycemia, when plasma glucose was 29 ^.m/ml, rCBF was decreased and a regional distribution of this effect was noted; 9 hindbrain regions showed a mean flow decrease of 14% while forebraln regions demonstrated less flow reduction. Acute elevation of plasma glucose during normoglycemia or superimposed on chronic hyperglycemia produced flow reductions of 7% for each 10 /xm/mJ increment in plasma glucose up to 60 /xm/ml. Both chronic and acute hyperglycemia are associated with decreased rCBF and the mechanism for this effect does not appear to adapt to chronic hyperglycemia. (Stroke 1987; 18:52-58) C LINICAL studies suggest that hyperglycemia is a risk factor for stroke 1 and that it increases brain injury during stroke or cardiac arrest.2 "4In animal models of stroke, acute hyperglycemia before ischemia increases mortality 3 and the number of neurons that die. 6 "* After transient ischemia, hyperglycemia increases and prolongs postischemic hyperemia 89 and enhances the heterogeneity of reperfusion.
10However, in normal animals an acute elevation of plasma glucose is associated with decreased regional cerebral blood flow (rCBF). 10 " This effect could limit compensatory blood flow mechanisms during an ischemic event.In clinical situations hyperglycemia, whether iatrogenic or the result of stroke itself, 12 is seldom as acute or as severe as that induced in animal models of stroke. Also, diabetics are frequently exposed to acute increases in blood glucose superimposed on a background of chronic hyperglycemia. Little is known about the effect of chronic hyperglycemia on rCBF. For these reasons we measured rCBF in awake restrained rats that had a moderate chronic hyperglycemia produced by treatment with streptozotocin. We found that chronic hyperglycemia was associated with decreased rCBF. Also, a specific regional distribution of this effect was noted with hindbrain regions manifesting CBF decreases during chronic hyperglycemia.
Materials and Methods The isotope 4-iodo|7V-methyl-14 C]antipyrine, 53 mCi/mmol, was obtained from Amersham, Arlington Heights, El. Streptozotocin, 2-deoxy-2-([methylnitrosoamino]carbonyl)-amino(-
The presence of hyperglycemia before brain ischemia increases stroke-related morbidity and mortality in experimental animals and humans. However, little is known of the effect of hyperglycemia on regional cerebral blood flow (rCBF). Acute hyperglycemia was induced in awake but restrained rats by intraperitoneal injection of 50% D-glucose. Regional flow was determined using [14C]iodoantipyrine and quantitative autoradiography. Elevation of plasma glucose from 11 to 39 mM was associated with a 24% reduction in rCBF when compared with controls that received normal saline. Intraperitoneal D-mannitol produced an elevation of plasma osmolality equivalent to that observed with glucose. However, rCBF was only reduced by 10%. Hyperglycemia appears to produce a global decrease in rCBF in awake rats that cannot be completely explained by the attendant increase in plasma osmolality. If a similar influence is present during brain ischemia, hyperglycemia could extend areas of critical flow limitation.
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