Muscle sympathetic activity and norepinephrine release during mental challenge in humans

Abstract

Muscle sympathetic nerve activity (MSA; peroneal nerve) and arterial and femoral venous plasma norepinephrine (NE) were studied in 10 volunteers at rest, during a relaxation procedure (RELAX), and during two mental challenges, a word identification test (WIT) and a color word test (CWT). [3H]NE infusions were used to assess NE spillover to and clearance from plasma. Net NE overflow from the leg was calculated. RELAX reduced MSA and femoral venous NE concentrations. CWT increased blood pressure, cardiac output (thermodilution), and calf flow and reduced systemic vascular resistance. Responses to WIT were less marked. CWT increased MSA by 25%, femoral venous NE concentrations by 25%, and NE overflow from the leg by 26% at 3 min. Fractional epinephrine and [3H]NE extractions were flow related and decreased during CWT. The arterial contribution to femoral venous NE (about half) increased by 10% during CWT. Arterial NE levels and spillover increased, but NE clearance was unchanged. Femoral venous NE concentrations and NE spillover (not based on flow measurements) and regional NE overflow correlated with MSA. Thus NE concentrations in plasma reflect spillover rather than clearance at rest and during mental challenge. Biochemical and neurophysiological indexes of sympathetic activity correlate when assessed in the same region. Mental stress increases sympathetic activity in leg muscle.

Neuroendocrine Dysregulation in Irritable Bowel Syndrome Patients: A Pilot Study

“…Throughout the mental arithmetic stress test, the subjects were urged to work more quickly and more accurately. 18,19 The cold pressor test was performed by immersing the left hand of the subject in ice water up to the wrist for 2 minutes. 20 MSNA was analyzed by visual inspection by a single investigator (R.M.B.).…”

Sympathetic Nerve Activity in Response to Hypotensive Stress in the Postural Tachycardia Syndrome

“…23 We cannot exclude the possibility that primary central factors also play a role in the increased sympathetic activation in POTS patients; however, it is of interest that the increase in sympathetic outflow in response to mental stress (a condition characterized by a central increase in sympathetic outflow that is not provoked by hypotension) is associated with an increase in both burst number and burst amplitude. 24,25 In contrast to the enhanced sympathetic burst activity in response to baroreceptor unloading in POTS patients, sympathetic nerve activity in the supine resting condition was characterized by a lower burst incidence. The lower probability of burst generation during a cardiac cycle at rest in POTS patients may be attributable to the following, acting alone or in combination: (1) increased resting blood pressure, (2) shorter cardiac interval, (3) lower-extremity sympathetic denervation, and (4) impairment of the central sympathetic burst generator.…”

Sympathetic activity is influenced by task difficulty and stress perception during mental challenge in humans.

“…One possible mechanism underlying the skeletal muscle vasodilatation and consequent decrease (lack of increase) in systemic vascular resistance would be a reduction in sympathetic (vasoconstrictor) nerve activity to skeletal muscle (MSNA). Previous studies, however, have reported both increases and decreases in MSNA during mental tasks (Delius, Hagbarth, Hongell & Wallin, 1972;Wallin, Delius & Hagbarth, 1973;Wallin, 1981;Anderson, Wallin & Mark, 1987;Hjemdahl, Fagius, Freyschuss, Wallin, Daleskog, Bohlin & Perski, 1989;Matsukawa, Gotoh, Uneda, Miyajima, Shionoiri, Tochikubo & Ishii, 1991). Within these studies, individual variability in both the direction and magnitude of MSNA responses has been noted frequently.…”