Potassium Channel Activators Protect the N-Methyl-D-Aspartate-Induced Cerebral Vascular Dilation After Combined Hypoxia and Ischemia in Piglets

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Abstract

Background and Purpose

Cerebral arteriolar dilation to N-methyl-D-aspartate (NMDA) is a neuronally mediated multistep process that is sensitive to cerebral hypoxia and ischemia (H/I). We tested the hypothesis that topical pretreatment with the selective potassium channel agonists NS1619 and aprikalim preserves the vascular response to NMDA after consecutive H/I.

Methods

Pial arteriolar diameters were measured in anesthetized piglets with the use of a closed cranial window and intravital microscopy. Arteriolar responses to NMDA (10 sup [horizontal bar]5, 5x10 sup [horizontal bar]5, and 10 sup -4 mol/L) were recorded before and 1 hour after 10 minutes of hypoxia (8.5% O2 in N2) plus 10 minutes of ischemia (H/I). Ischemia was induced by increasing intracranial pressure. Subgroups were topically pretreated with 10 sup [horizontal bar]5 mol/L NS1619, 10 sup [horizontal bar]6 mol/L aprikalim, 10 sup [horizontal bar]6 mol/L calcitonin gene-related peptide (CGRP), or 10 sup [horizontal bar]5 mol/L papaverine. We also examined the effects of H/I on vascular responses to kainate (10 sup [horizontal bar]4 mol/L) to assess specificity of neuronal injury.

Results

Arteriolar responses to NMDA were significantly attenuated after H/I. Baseline compared with post-H/I arteriolar diameters were 9 +/- 4% versus 3 +/- 2% at 10 sup [horizontal bar]5 mol/L, 22 +/- 4% versus 4 +/- 2% at 5x10 sup -5 mol/L, and 33 +/- 4% versus 7 +/- 2% at 10 sup [horizontal bar]4 mol/L (mean +/- SE; all P<.05, n=7). Pretreatment with NS1619 and aprikalim preserved the arteriolar responses to NMDA after H/I. For NS1619 (n=6), values were as follows: 9 +/- 2% versus 6 +/- 4% at 10 sup -5 mol/L, 19 +/- 6% versus 21 +/- 5% at 5x10 sup -5 mol/L, and 35 +/- 3% versus 31 +/- 5% at 10 sup [horizontal bar]4 mol/L. For aprikalim (n=7), values were as follows: 6 +/- 2% versus 8 +/- 2% at 10 sup [horizontal bar]5 mol/L, 22 +/- 6% versus 15 +/- 3% at 5x10 sup [horizontal bar]5 mol/L, and 41 +/- 5% versus 32 +/- 6% at 10 sup [horizontal bar]4 mol/L. In contrast, piglets pretreated with CGRP (n=6) or papaverine (n=5) showed no preservation of the vascular response to NMDA after H/I, although these compounds dilated the arterioles to an extent similar to that with NS1619/aprikalim. Kainate-induced arteriolar dilation (n=6) was largely preserved after H/I compared with preischemic responses.

Conclusions

(1) Vascular responses of cerebral arterioles to NMDA after H/I are preserved by pretreatment with NS1619 or aprikalim, indicating a neuroprotective effect. (2) CGRP and papaverine do not preserve the vascular response to NMDA despite causing vasodilation similar to that with NS1619 or aprikalim. This suggests that activation of potassium channels on neurons accounts for the protective effect of potassium channel agonists. (3) Preserved arteriolar dilation to kainate suggests largely intact functioning of neuronal nitric oxide synthase after H/I. (Stroke. 1998;29:837-843.)

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