Influences of gender on sympathetic nerve responses to static exercise

Abstract

We compared reflex responses to static handgrip at 30% maximal voluntary contraction (MVC) in 26 untrained men (mean age 35 +/- 3 yr) and 23 untrained women (mean age 39 +/- 4 yr). Women demonstrated attenuated increases in blood pressure and muscle sympathetic nerve activity (MSNA; by microneurography) compared with men. This difference was also observed during a period of posthandgrip circulatory arrest. 31P-nuclear magnetic resonance (NMR) spectroscopy studies demonstrated attenuations in the production of diprotonated phosphate and the development of cellular acidosis in women compared with men. Subjects also performed ischemic handgrip to fatigue. During this paradigm, MSNA responses were similar in the two groups, suggesting that freely perfused conditions are necessary for the full expression of the gender effect. Finally, we examined MSNA responses to adductor pollicus exercise in 7 men (26 +/- 1 yr) and 6 women (25 +/- 2 yr). MVC values and times to fatigue were similar in the two groups (MVC: men, 4.3 +/- 0.4 kg; women, 4.0 +/- 0.3 kg; not significant. Time to fatigue: men, 209 +/- 16 s; women, 287 +/- 50 s; not significant). At periods of end exercise and postexercise circulatory arrest, MSNA responses were attenuated in the women compared with the men. We conclude that, during nonischemic static exercise, sympathetic neural outflow is less in women compared with men. This response is due to an attenuated metaboreflex in women. Finally, on the basis of the adductor pollicus experiments, this effect appears independent of muscle mass, workload, and the level of training.

Estrogen attenuates the cardiovascular and ventilatory responses to central command in cats

“…Our finding that administration of 17␤-estradiol had no effect on the pressor response to static contraction might appear at first glance to conflict with the finding by Ettinger et al (11), who reported that premenopausal women displayed smaller pressor and muscle sympathetic nerve activity responses to static handgrip than did men of similar age. Ettinger et al attributed this difference to an attenuated muscle metaboreflex in women.…”

“…Second, and possibly most important, we used cats, whereas Ettinger et al used humans. The importance of this difference, in addition to the obvious difference pertaining to species, is that in cats the metabolic by-products of triceps surae contraction have been measured by microdialysis (23), whereas in humans the by-products for static handgrip have been measured by NMR (11). The time course and the specific metabolites measured by the two techniques were different.…”

“…The time course and the specific metabolites measured by the two techniques were different. Consequently, any comparison between the two studies (11,23) would be difficult. A difference between humans and cats in these metabolites might be critical if estrogen exerts its effects on the responsiveness of metaboreceptors to contraction.…”

“…The exercise pressor reflex arises from the stimulation of group III and IV muscle afferents. This reflex is believed to be evoked by mechanical and metabolic factors in muscles while they are contracting (4,18,24).The cardiovascular responses to exercise have been reported to be less in premenopausal women than in postmenopausal women or men (11,12). The difference has been attributed to estrogen, a hormone that is well known to decrease vascular resistance (28).…”

“…The cardiovascular responses to exercise have been reported to be less in premenopausal women than in postmenopausal women or men (11,12). The difference has been attributed to estrogen, a hormone that is well known to decrease vascular resistance (28).…”