Relation of plasma norepinephrine and sympathetic traffic during hypotension in humans

Abstract

We compared changes in antecubital venous plasma levels of norepinephrine (NE) and peroneal nerve muscle sympathetic activity (MSA) during and after nitroprusside (NP)-induced hypotension in nine healthy volunteers. During NP, MSA increased at 98.7%/min, peaked at 4 min at 399 +/- 77% (SE) of base line, and then decreased, so that at the end of the infusion MSA was 298 +/- 39% of base line. NE increased at 9.2%/min and peaked at 14.5 min at 231 +/- 31% of base line just before the end of the infusion. Percent increases of MSA and NE near the end of NP were not significantly different. The time-to-peak NE lagged the time-to-peak MSA by nearly 10 min. These results suggest that during increases of sympathetic outflow diffusion and washout of NE from neuroeffector junctions result in delayed increases in NE in the venous drainage; percent changes in MSA and NE during prolonged stable mild hypotension are similar. The findings provide conditional support for the use of changes in NE to indicate changes in sympathetic traffic.

Effect of the α2C-adrenoreceptor deletion322–325 variant on sympathetic activity and cardiovascular measures in healthy subjects

“…Nonetheless, venous norepinephrine concentrations have been used widely as an indirect marker of global sympathetic tone. They are correlated with more specific markers of sympathetic activity such as muscle sympathetic nerve activity (MSNA) at rest [43] and increase similarly after a reduction in blood pressure [44,45], have strong heritability [4], and in longitudinal studies predict cardiovascular morbidity in both healthy subjects [46] and patients with hypertension [47] or congestive heart failure [48,49]. Additionally, we studied subjects at rest, thus minimizing the confounding effect of changes in forearm norepinephrine release and of large differences in catecholamine clearance secondary to altered blood flow.…”

Immediate but not long-term intranasal administration of insulin raises blood pressure in human beings

“…The MSNA was continuously measured by microneurography of the peroneal nerve as described elsewhere [43]. This method allows direct recordings of summed potentials of sympathetic neurons to the vascular bed of the skeletal muscle [44,45] and correlates with plasma norepinephrine concentrations and norepinephrine spillover [46]. Sympathetic bursts were identified by inspection of the mean voltage neurogram and quantified as bursts per minute.…”

Catecholamine response to exercise in individuals with different levels of paraplegia

“…During the course of a progressive maximal exercise test, peripheral catecholamines increase exponentially with increasing work-load (7). The measurement of blood norepinephrine (Nor) can be used to estimate SNS activity (8), since it reflects its release at the nerve terminals (2,9). On the other hand, the activity of the adrenal glands can be evaluated by the measurement of blood epinephrine (Epi) (6).…”