Sympathetic nervous system activity was assessed in experimental and control subjects who were exposed to graded orthostatic and isometric stress during monthly hospital visits. After the first session, the experimental subjects practiced a technique that elicited the relaxation response. Their concentrations of plasma norepinephrine during subsequent graded stresses were significantly higher. No such changes were noted in the control group. These results were then replicated in the control group in a crossover experiment. The groups did not differ in their heart rate and blood pressure responses. These observations are consistent with reduced norepinephrine end-organ responsivity after regular elicitation of the relaxation response.
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