Study adds to knowledge of what it takes to stan...( signals from the Central Nervous Syste...),Health

Microdialysis uses tiny probes to measure fluid composition in interstitial tissue - spaces outside of cells - and the changes in that fluid when exposed to certain factors. In this study, microdialysis was used to measure norepinephrine near the blood vessels in leg muscle both at rest and when the lower body is under pressure. The pressure applied to the lower body mimics the action of someone moving from a seated to standing position.

In addition to microdialysis to measure the chemical reactions to CNS signals, Sinoway also used microneurography to record the intensity of the "messages" sent by the CNS and directed to blood vessels. Blood samples also were taken to compare the norepinephrine levels.

Subjects were placed on a padded table with the left leg and pelvis placed in a lower body negative pressure (LBNP) chamber specifically designed and built for this study. The right leg was left outside of the chamber so that microdialysis and microneurography could be performed. An I.V. was inserted in the arm. Patients' heart rates were continuously monitored.

After baseline microdialysis measurements and blood samples were taken, the pressure was slowly increased in the chamber and additional readings and blood samples were recorded.

"One-legged LBNP led to a rise in muscle sympathetic nerve activity, the amount of norepinephrine in the blood plasma, and the norepinephrine in the interstitium, or tissue near the blood vessels," Sinoway said. "The important factor is that the rate of rise of norepinephrine in the blood plasma was much less than the rate of increase found in interstitial norepinephrine."

The reason: Blood samples give only the amount of norepinephrine that reaches the blood stream. Such samples don't take into
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Contact: Valerie Gliem
vgliem@psu.edu
717-531-8604
Penn State
7-Aug-2002