Effects of topical methylene blue on cyclic GMP level, blood flow, and O2 consumption in focal cerebral ischaemia.
We hypothesized that a decrease in cyclic GMP, a second messenger in the glutamate-nitric oxide pathway, would reduce oxygen consumption and improve O2 balance in the ischaemic cerebral cortex. To test this hypothesis, a study was performed in unilateral middle cerebral artery occluded rats which were assigned to either a control or methylene blue (10(-3) M) group. Regional cerebral blood flow was determined using 14C-iodoantipyrine and regional arterial and venous O2 saturations were determined by microspectrophotometry (n = 6). Cyclic GMP level was measured by radioimmunoassay (n = 8). Guanylate cyclase and cyclic GMP-phosphodiesterase activities were determined in an additional set of control rats (n = 10). The cyclic GMP levels were not different between the ischaemic and contralateral areas in the control group. Compared to the cyclic GMP in the control ischaemic cortex, topical methylene blue significantly decreased the cyclic GMP level by 56% in the ischaemic cortex of the methylene blue group. Ischaemia did not alter the activities of guanylate cyclase but mildly decreased cyclic GMP-phosphodiesterase. The regional cerebral blood flow and O2 consumption in the control group were 50% and 32% lower than those in corresponding contralateral cortex. Topical methylene blue did not alter regional cerebral blood flow and O2 consumption in the ischaemic cortex. Our data showed that cyclic GMP is not a major controller on O2 supply or O2 consumption in the ischaemic brain.
Wei
H M
HM
Department of Anesthesia, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854-5635.
Tse
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J
Chi
O Z
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Weiss
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D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism; D000287:Administration, Topical; D000704:Analysis of Variance; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001921:Brain / Q000098:blood supply* / Q000187:drug effects / Q000378:metabolism*; D002245:Carbon Dioxide / Q000097:blood; D002540:Cerebral Cortex / Q000378:metabolism; D002560:Cerebrovascular Circulation / Q000187:drug effects; D006152:Cyclic GMP / Q000378:metabolism*; D006162:Guanylate Cyclase / Q000378:metabolism; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006454:Hemoglobins / Q000378:metabolism; D002546:Ischemic Attack, Transient / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D008751:Methylene Blue / Q000008:administration & dosage / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000187:drug effects*; D010313:Partial Pressure; D011149:Pons / Q000378:metabolism; D051381:Rats; D012039:Regional Blood Flow / Q000187:drug effects
D006454:Hemoglobins; D002245:Carbon Dioxide; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D008751:Methylene Blue