Vascular Response to Hypoxic Preconditioning in the Immature Brain

Abstract

We hypothesized that hypoxic preconditioning (PC) modifies the microvasculature in the immature brain and thereby affects the cerebral blood flow (CBF) during a subsequent hypoxic-ischemic (HI) insult. On postnatal day 6 rats were exposed to hypoxia (361C, 8.0% O 2 ) or normoxia for 3 h. Unilateral HI (unilateral carotid ligation and 8% hypoxia) was induced 24 h later. Cortical CBF was measured with the 14 C-iodoantipyrine technique (at the end of HI) or with laser Doppler flowmetry (Perimed PF5001) before and during HI. At 0, 2, 8, and 24 h cerebral cortex was sampled and analyzed with gene arrays (Affymetrix 230 2.0). L-nitroarginine or vehicle was administrated before hypoxic PC or 30 mins before HI followed by CBF measurement (laser Doppler) during subsequent HI. Twenty-four hours after PC animals were perfusion-fixed and brains immunolabeled for von Willebrand factor and vascular density was determined by stereological quantification. The decrease in CBF during HI was attenuated significantly in PC versus control animals (P < 0.01), as detected by both techniques. Several vascular genes (Angpt2, Adm, Apln, Vegf, Flt1, Kdr, Pdgfra, Agtrap, Adora2a, Ednra, serpine1, caveolin, Id1, Prrx1, Ero1l, Acvrl1, Egfl7, Nudt6, Angptl4, Anxa2, and NOS3) were upregulated and a few (Csrp2, Adora2b) were downregulated after PC. A significant increase in vascular density (P < 0.05) was seen after PC. Nitric oxide synthase inhibition did not affect CBF during HI after PC. In conclusion, hypoxic PC upregulates vascular genes, increases vascular density and attenuates the decrease of CBF during a subsequent HI, which could contribute to tolerance.

Prostaglandin D2Protects Neonatal Mouse Brain from Hypoxic Ischemic Injury

“…Because DP 1 was exclusively expressed on endothelial cells at 1 h after the start of reoxygenation, it is reasonable that PGD 2 exerted its action on endothelial cells, possibly by modulating the CBF. The standard method for quantification of blood flow is the [ 14 C]-iodoantipyrine method, but we chose to use the laser-Doppler flowmeter, which has been widely accepted in recent years (Aden et al, 2003;Ten et al, 2005;Gustavsson et al, 2007), because we had to assess the temporal change in blood flow in real time. HL-KO and DP 1 -KO mice showed a steep reduction in CBF during hypoxia and that CBF recovery post hypoxia was not achieved in the HL-KO mice (Fig.…”

A Central Role of Connexin 43 in Hypoxic Preconditioning

“…Essentially any injury paradigm, including hypoxia, spreading depression, inflammation, epilepsy, hypothermia and hyperthermia, and metabolic inhibition, will induce preconditioning if applied below the threshold for irreversible cell damage (Kirino, 2002;Dirnagl et al, 2003;Lo et al, 2003). The signaling pathways involved in injury tolerance have been extensively studied, and a key role of adenosine, a potent neuroprotective and cardioprotective agent, has been identified, but other pathways, including erythropoietin, inflammatory cytokines, ceramide, nitric oxide, vascular endothelial growth factor, and protein SUMOylation (for small ubiquitinrelated modifier), have also been implicated (Zimmermann et al, 2001;Kariko et al, 2004;Gustavsson et al, 2007;Lee et al, 2007).…”

3-Nitropropionic Acid-Induced Ischemia Tolerance in the Rat Brain is Mediated by Reduced Metabolic Activity and Cerebral Blood Flow

“…[35][36][37] Dawson et al used autoradiography to show that 15 minutes after the onset of MCAO, CBF was unchanged in animals subjected to lipopolysaccharide preconditioning; however, 4 and 24 hours later, microvascular perfusion as assessed by an intravascular fluorescent tracer technique was preserved at higher levels in preconditioned animals compared with controls. 38 Gustavsson et al observed an attenuation of the CBF decrease during a hypoxic/ischemic injury 24 hours after hypoxic preconditioning, along with an increase in microvascular density, 9 albeit in a neonatal model where angiogenesis is likely to remain more plastic compared with the adult brain. In our model, no increase in vascularization was observed in ischemia-tolerant brains, however, the lower ECP and reduced COX expression pattern suggested a significant decrease in mitochondrial phosphorylation capacity at the rate necessary to meet the cellular energy demand subsequent to NPA administration.…”

“…Although vascular adaptations in response to preconditioning could help to facilitate substrate delivery during subsequent ischemia, the potential role of blood vessel remodeling in ischemia tolerance remains open. 5,9 Our goal was to characterize mechanisms of preconditioning and to predict histologic and behavioral outcomes after stroke by defining a magnetic resonance imaging (MRI) signature of the ischemia-tolerant brain. We utilized a pharmacological preconditioning paradigm with the oxidative chain inhibitor 3-nitropropionic acid (NPA), which temporarily induces ischemia tolerance through inhibition of succinate dehydrogenase and a burst of reactive oxygen species.…”