Transient middle cerebral artery occlusion influence on systemic oxygen homeostasis and erythropoiesis in Wistar rats

Systemic hypoxia is a common complication in stroke patients and may exacerbate ischemic brain damage. Expression of the hypoxia-inducible cytokine erythropoietin (Epo) is upregulated in the brain in both stroke patients and in animal stroke models and exerts local neuroprotective effects in the ischemic brain. Epo is also well known to stimulate red blood cell (RBC) production. The purpose of the present study was to evaluate whether poststroke systemic hypoxia is present in the rat model and whether it is associated with increased peripheral Epo and RBC production.

Wistar rats underwent 1-hour transient middle cerebral artery occlusion (MCAO) under mechanical ventilation, followed by reperfusion without further ventilation. Groups of MCAO and sham-operated animals were evaluated at extended times after reperfusion for assessment of arterial blood gases, plasma Epo, and complete blood count.

Arterial oxygen saturation was significantly lower in the infarct group between 6 and 24 hours after reperfusion (P=0.0005), and plasma Epo levels were increased 6 hours after reperfusion (P<0.05). RBC counts and hematocrit were transiently increased 2 to 7 days after reperfusion in animals with MCAO compared with sham. Maximal increases were seen at day 7 (22% and 16% increases of RBC count and hematocrit, respectively; P<0.001). In contrast, the white blood cell counts in animals with MCAO decreased by >30% in the same time period.

Plasma Epo levels, RBC counts, and hematocrit are all increased in response to systemic hypoxia after cerebral ischemia in rats.