Hemorrhagic Hypotension

FOR IMMEDIATE RELEASEContact: Donna Krupa: 703.527.7357Cell: 703.967.2751 or [email protected]

HEMORRHAGIC HYPOTENSIONWhat triggers a secondary, "decompensatory" phase of hemorrhage?

October 11, 2001 - Bethesda, MD--Each month, the American Physiological Society (APS) spotlights recent research findings designed to improve human well being and understand human health. A summary of the peer-reviewed article noted below, which appears in a recent edition of The American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, has such a focus. The Journal is one of 14 peer-reviewed journals comprised of approximately 3,800 articles that are published by the Society each year.

HEMORRHAGIC HYPOTENSIONWhat triggers a secondary, "decompensatory" phase of hemorrhage?

Summary:During a progressive hemorrhage, the arterial pressure is initially maintained (within normal limits) by a compensatory increase in sympathetic activity. But if it is allowed to progress, a second, decompensatory phase develops in which the sympathetic activity abruptly decreases and blood pressure falls precipitously. Researchers Sinan Cavun and William R. Millington of the Albany College of Pharmacy tested the hypothesis that the ventrolateral midbrain periaqueductal gray region (vlPAG) plays an important role in triggering this second phase of hemorrhage.

Methodology:Neuronal activity in the vlPAG was inhibited with either lidocaine or cobalt chloride five minutes before hemorrhage was initiated in conscious, unrestrained rats.

Results: Bilateral injection of lidocaine into the caudal vlPAG delayed the onset and reduced the magnitude of the hypotension produced by hemorrhage significantly. In contrast, inactivation of the dorsolateral PAG with lidocaine was ineffective. Cobalt chloride, which inhibits synaptic transmission but not axonal conductance, also attenuated hemorrhagic hypotension significantly. Microinjection of lidocaine or cobalt chloride into the vlPAG of normotensive, non-hemorrhaged rats did not influence cardiovascular function.

Conclusion:The research data indicate that the vlPAG plays an important role in the response to hemorrhage.

Source: The American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, September 2001

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The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.

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Editor's Note: For the full text of the summaries cited above, or to set up an interview with a member of the research team, please contact Donna Krupa at 703.527.7357 (direct dial), 703.967.2751 (cell) or [email protected].