Do plasma norepinephrine levels reflect behavioral stress?

The interpretation of plasma norepinephrine (NE) levels is not straightforward because such levels represent a complex of synaptic discharge, metabolism, uptake, and regional blood flow. Some investigators have argued that peripheral NE levels bear little semblance to sympathetic nervous system activity affecting the cardiovascular system. This study examines this question in further detail. Eleven men (average age = 29) were studied. Plasma NE levels were obtained through continuous blood withdrawal from an antecubital vein, and simultaneous blood pressures were also monitored. Each subject was studied during four 4-min intervals of rest and during four 4-min intervals of a psychiatric stress interview. The interview was a friendly, intense discussion about upsetting situations the subject faced. The interview was a powerful and consistent tool for evoking physiologic responses. It led to an 83% increase in NE levels across all time intervals (p less than 0.001). During these same intervals, systolic pressure increased by 16 mm (p less than 0.0003) and diastolic by 13 mm (p less than 0.0001); furthermore, systolic and diastolic pressures were correlated with peripheral NE levels. This implies that the increased peripheral NE level was not merely a local phenomenon but reflected a signal affecting the entire vascular system.