• S Bani Hashemi, J Braun, W M Bernhardt, W Rascher, J Dötsch, and R Trollmann.
• Department of Pediatrics, Friedrich-Alexander-University of Erlangen-Nuremberg, Loschgestrasse 15, Erlangen, Germany.
• Eur. J. Appl. Physiol. 2008 Sep 1; 104 (1): 95-102.

AbstractHypoxia-inducible transcription factor-1 (HIF-1) is the most important component of cellular and molecular adaptive responses to hypoxia. We aimed to analyze effects of systemic hypoxia and CO exposure on the oxygen-regulated alpha-subunit of HIF-1 and HIF-1-dependent vasoactive target genes in rat brain. Brains of adult Sprague-Dawley rats were investigated after incubation for 3 and 12 h under normoxia, hypoxia (8% O(2)) and CO 0.1% (n = 10 per group). Upon 3 h of exposure, hypoxia and CO-induced accumulation of HIF-1alpha protein in brain homogenates assessed by Western blot analysis. In contrast to hypoxia HIF-1alpha signals decreased markedly during 12 h-exposure to CO. By immunohistochemistry, intensive HIF-1alpha-positive staining was found in neurons of the cortex and hippocampus. Cerebral expression of vasoactive target genes adrenomedullin (ADM) and vascular endothelial growth factor (VEGF) showed up-regulation during both hypoxia and CO exposure indicating functional activation of HIF-1. Hypoxia increased ADM (P < 0.05) and VEGF mRNA levels within 3 h (P < 0.01) which persisted up to 12 h of exposure (ADM, P < 0.05; VEGF, P < 0.001). Similarly, CO inhalation led to early up-regulation of VEGF (3 h: P < 0.05; 12 h: P < 0.01), but a more delayed increase of ADM mRNA levels (3 h: n.s., 12 h: P < 0.01). We suggest that CO-induced oxygen deprivation is a potent stimulus to cerebral HIF-1-regulated hypoxic stress responses even though its effects are more transient than exposure to hypoxia.

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