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How cocaine elevates blood pressure. (Cardiovascular System).

Researchers at The University of Texas Southwestern Medical Center at Dallas have identified the underlying mechanism by which cocaine triggers hypertensive crisis, the most-severe form of high blood pressure and one of the most-common cocaine-related, cardiovascular emergencies in the U.S. The findings may lead to the development of new treatment strategies for cocaine-induced blood pressure elevation and related complications, including stroke and acute myocardial infarction.

"The underlying mechanism of the blood-pressure-raising effect of cocaine use in humans has not been well studied," notes Wanpen Vongpatanasin, senior author of the study and assistant professor of internal medicine. "Most of us believe that cocaine increases blood pressure mainly by preventing clearance or reuptake of noradrenaline from blood vessels into the nerve endings, and the excess levels of noradrenaline cause blood vessels to constrict. However, we found that this mechanism plays a very small role in humans. Instead, cocaine increases blood pressure by stimulation of the heart to cause rapid heartbeat and increased cardiac output. This elevation in blood pressure, if severe or persistent, can lead to damage of multiple vital organs such as the heart, brain, and kidney."

Approximately 25,000,000 Americans have tried cocaine, and the drug is the most-frequent cause of narcotics-related deaths reported by medical examiners. Cocain is the most-commonly used illicit substance among people seeking care in hospital emergency departments or drug treatment centers.

"The textbook explanation of cocaine-related elevated blood pressure is based on evidence from previous studies in rats and mice," explains Meryem Tuncel, lead author of the study and a postdoctoral fellow in hypertension. "However, anesthesia used to sedate these animals interferes with the effects of cocaine on the central nervous system, and it is very difficult to show that even a large dose of cocaine can increase blood pressure in animals. Therefore, we suspected that the results would be different in humans? he indicates.

The investigators administered a small, medically approved dose of cocaine nose drops to 15 healthy cocaine-naive study participants. To measure the drug's effect on blood vessels directly without influencing the brain or heart, they administered two different doses of cocaine into the artery of the forearm and measured blood pressure, forearm blood flow, and forearm venous noradrenaline concentration in the same study participants on two different days. Microelectrodes, which are similar to acupuncture needles, were used to record sympathetic nerve activity during administration of the cocaine nose drops.

The researchers discovered that, when cocaine is injected directly into the artery in the upper arm, it causes blood vessels to constrict, as shown in previous animal studies. "However, when cocaine is given through the nose, it causes dilation, rather than constriction, of the blood vessels," points out Vongpatanasin. "Blood pressure is determined by two factors--vascular tone and cardiac output. If intranasal cocaine increases blood pressure and the blood vessels dilate instead of constrict, the cardiac output must increase. Now that we know the mechanisms involved in how cocaine elevates blood pressure, I think we should refocus our strategy to use medications that will affect sympathetic stimulation of the heart, rather than medications that have effects only on blood vessels."
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Title Annotation:medical research
Publication:USA Today (Magazine)
Geographic Code:1USA
Date:Feb 1, 2003
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