Impairment of neuronal nitric oxide synthase-dependent dilation of cerebral arterioles during chronic alcohol consumption.
BACKGROUND
Although chronic alcohol consumption impairs endothelial nitric oxide synthase-dependent reactivity of cerebral arterioles, the effect of alcohol consumption on vasodilation in response to activation of neuronal nitric oxide synthase (nNOS) has not been examined. Thus, our first goal was to determine whether chronic alcohol consumption impairs nNOS-dependent reactivity of pial arterioles. Our second goal was to examine potential mechanisms for impaired responses of pial arterioles during chronic alcohol consumption.


METHODS
Sprague Dawley rats were fed liquid diets with or without alcohol for 8 to 12 weeks. By using intravital microscopy, we measured the diameter of pial arterioles in response to nNOS-dependent agonists--NMDA and kainate (KA)--in the absence and presence of N(G)-monomethyl-L-arginine (L-NMMA) or 7-nitroindazole (7-NI). We also measured responses of pial arterioles to nitroglycerin. Next, using Western blot analysis, we measured protein levels of the NMDA receptor subunit, KA receptor subunit, and nNOS protein in cerebral microvessels, parietal cortex, cerebellum, and brainstem of non-alcohol-fed and alcohol-fed rats.


RESULTS
Topical application of NMDA (100 and 300 microM) and KA (100 and 300 microM) produced dose-related dilation of pial arterioles in non-alcohol-fed and alcohol-fed rats. However, the magnitude of vasodilation in response to NMDA and KA, but not nitroglycerin, was significantly less in alcohol-fed compared with non-alcohol-fed rats. Topical application of L-NMMA (10 microM) or 7-NI (10 microM) significantly inhibited dilation of pial arterioles in response to NMDA and KA in non-alcohol-fed rats. In alcohol-fed rats, only NMDA-induced vasodilation was inhibited by L-NMMA. In addition, we found that NMDA receptor subunit and KA receptor subunit protein levels increased in the parietal cortex and cerebellum of alcohol-fed compared with non-alcohol-fed rats. However, no significant difference in protein level of nNOS was observed between non-alcohol-fed and alcohol-fed rats.


CONCLUSIONS
Our findings suggest that chronic alcohol consumption impairs nNOS-dependent dilation of pial arterioles via a mechanism that appears to be unrelated to quantitative changes in NMDA receptors, KA receptors, or nNOS. Because the regulation of cerebral blood flow is influenced by neuronal activation, impaired reactivity of cerebral blood vessels to neuronal activation may contribute to the pathogenesis of cerebrovascular disorders observed during chronic alcohol consumption.
Sun
Hong
H
Department of Physiology and Biophysics, University of Nebraska Medical Center, Omaha 68198-4575, USA.
Patel
Kaushik P
KP
Mayhan
William G
WG
D000428:Alcohol Drinking / Q000378:metabolism*; D000818:Animals; D001160:Arterioles / Q000187:drug effects* / Q000201:enzymology; D000431:Ethanol / Q000494:pharmacology; D007608:Kainic Acid / Q000494:pharmacology; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D010841:Pia Mater / Q000098:blood supply* / Q000187:drug effects* / Q000201:enzymology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018092:Kainic Acid Receptors / Q000096:biosynthesis; D016194:Receptors, N-Methyl-D-Aspartate / Q000096:biosynthesis; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology
D000431:Ethanol; D007608:Kainic Acid; D016202:N-Methylaspartate; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate; C496322:Nos1 protein, rat