Hypothermia on NO-Mediated Neurogenic Relaxation and on Hypoxic Inhibition in the Response of Canine Cerebral Arteries

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    • OKAMURA Tomio
    • Department of Pharmacology, Shiga University of Medical Science
    • TODA Noboru
    • Department of Pharmacology, Shiga University of Medical Science


Cerebral arteries are innervated by nitric oxide (NO)-mediated vasodilator nerves, and hypoxia has been shown to attenuate neurogenic vasorelaxation. The present study examines the effects of hypothermia on neurogenic vasorelaxation and on the hypoxia-induced inhibition of the neurogenic vasorelaxation response. In isolated canine cerebral arteries, relaxant responses to transmural electrical stimulation (5 Hz for 40 s), mediated via NO synthesized from L-arginine, were not influenced by lowering the bathing media temperature from 37°C to 30°C but were attenuated at 25°C. On the other hand, relaxations caused by nicotine and exogenous NO were not significantly attenuated but were prolonged by cooling to 25°C. The responses associated with nerve stimulation by electrical pulses or nicotine were depressed by hypoxia (from about 500 mmHg of partial O<SUB>2</SUB> pressure to about 45 mmHg) under normothermia. However, hypothermia at 25°C prevented the inhibition by hypoxia of the neurogenic relaxation. It is concluded that the hypothermia-induced inhibition in the response to electrical nerve stimulation is not associated with a decreased synthesis and release of NO in vasodilator nerves nor with a reduced ability of smooth muscle to relax in response to NO. Interference with the propagation of action potentials might be involved in the inhibition via a fall of temperature. The fact that the hypoxia-induced impairment of vasodilator nerve function was prevented by cooling may partially explain the efficacy of hypothermia in protecting against ischemic neuronal injury in the brain. (Hypertens Res 2001; 24: 47-53)


  • Hypertension Research

    Hypertension Research 24(1), 47-53, 2001-01-01

    The Japanese Society of Hypertension

References:  36


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