Gender does not influence sympathetic neural reactivity to stress in healthy humans

Abstract

Previous data support the idea of heightened sympathetically mediated cardiovascular reactivity in males. However, definitive conclusions cannot be made because of inconsistent reports, possibly stemming from imprecise measurement of sympathetic activity and/or failure to equate the stress stimuli between genders. The present study tested the hypothesis that males exhibit heightened sympathetic reactivity that is associated with heightened cardiovascular and plasma catecholamine responses. In 37 healthy adults (20 males, 17 females: age = 20-42 yr), direct recordings of skeletal muscle sympathetic nerve activity (MSNA), plasma catecholamines, heart rate, blood pressure, and perceived stress were measured before and during three laboratory stressors (isometric handgrip, cold pressor, and mental arithmetic). MSNA, catecholamine, and cardiovascular reactivity (defined as change from rest) were not consistently different between genders. For the isometric handgrip, when expressed as absolute unit changes, males had larger MSNA responses (P < 0.01), which were partially explained by greater contraction force; they did not differ in terms of percent change from baseline or in perceived stress. The responses to the cold pressor and mental arithmetic tasks were similar between genders. These findings indicate that stress-evoked vasoconstrictor neural excitation and the associated increases in blood pressure are not consistently influenced by gender.

Women Have Lower Tonic Autonomic Support of Arterial Blood Pressure and Less Effective Baroreflex Buffering Than Men

“…10 Indeed, the gender-related difference in BRB in the present study was almost as great as the difference recently found between healthy adults and patients with long-standing essential hypertension. 10,16 Thus, consistent with previous reports of gender-related differences in other ANS-cardiovascular functions, [1][2][3][4]8,[23][24][25] the present findings indicate that subject gender is a major source of interindividual variability in tonic ANS support of BP and BRB of BP in healthy adult humans.…”

“…1,5,6 The ANS provides tonic support for resting BP, and we recently established that basal sympathetic nervous system activity is a key physiological determinant of the amount of tonic BP support provided by the ANS. 7 Because premenopausal women tend to have lower resting sympathetic activity than men, [2][3][4]8 we hypothesized that women have lower tonic ANS support of BP than men.…”

Relation of leptin and insulin to adiposity-associated elevations in sympathetic activity with age in humans

“…Based on this correlation, these investigators concluded that circulating levels of Leptin and elevated sympathetic activity with age MB Monroe et al leptin may be the physiological mechanism explaining the previously observed relation between MSNA and adiposity in younger adults. 16,18,24 The present ®nd-ings extend those of Snitker and colleagues in at least two ways. First, we have shown that the relation between plasma leptin concentrations and MSNA is maintained in middle-aged and older adult males.…”

“…23 Multiunit recordings of MSNA were obtained from the right peroneal nerve at the ®bular head using the microneurographic method previously described by our laboratory. 1,24 The neural activity was ampli®ed, ®ltered (bandwidth 700 ± 2000 Hz), full-wave recti®ed, and integrated (time constant 100 ms) to obtain a mean voltage neurogram determined to be acceptable according to criteria previously described. 1,25 After stable baseline activity was established, recordings of MSNA were obtained over a subsequent 20 min period.…”

“…The reliability of these measurements has been established previously by our laboratory. 24 The average of the values obtained from the three blood samples was used to determine fasting plasma concentrations of leptin, insulin and glucose.…”