Previous exercise attenuates muscle sympathetic activity and increases blood flow during acute euglycemic hyperinsulinemia

Abstract

. Previous exercise attenuates muscle sympathetic activity and increases blood flow during acute euglycemic hyperinsulinemia. J Appl Physiol 98: 866 -871, 2005. First published November 12, 2004 doi:10.1152/japplphysiol.00251.2004.-Insulin infusion causes muscle vasodilation, despite the increase in sympathetic nerve activity. In contrast, a single bout of exercise decreases sympathetic activity and increases muscle blood flow during the postexercise period. We tested the hypothesis that muscle sympathetic activity would be lower and muscle vasodilation would be higher during hyperinsulinemia performed after a single bout of dynamic exercise. Twenty-one healthy young men randomly underwent two hyperinsulinemic euglycemic clamps performed after 45 min of seated rest (control) or bicycle exercise (50% of peak oxygen uptake). Muscle sympathetic nerve activity (MSNA, microneurography), forearm blood flow (FBF, plethysmography), blood pressure (BP, oscillometric method), and heart rate (HR, ECG) were measured at baseline (90 min after exercise or seated rest) and during hyperinsulinemic euglycemic clamps. Baseline glucose and insulin concentrations were similar in the exercise and control sessions. Insulin sensitivity was unchanged by previous exercise. During the clamp, insulin levels increased similarly in both sessions. As expected, insulin infusion increased MSNA, FBF, BP, and HR in both sessions (23 Ϯ 1 vs. 36 Ϯ 2 bursts/min, 1.8 Ϯ 0.1 vs. 2.2 Ϯ 0.2 ml ⅐ min Ϫ1 ⅐ 100 ml Ϫ1 , 89 Ϯ 2 vs. 92 Ϯ 2 mmHg, and 58 Ϯ 1 vs. 62 Ϯ 1 beats/min, respectively, P Ͻ 0.05). BP and HR were similar between sessions. However, MSNA was significantly lower (27 Ϯ 2 vs. 31 Ϯ 2 bursts/min), and FBF was significantly higher (2.2 Ϯ 0.2 vs. 1.8 Ϯ 0.1 ml ⅐ min Ϫ1 ⅐ 100 ml Ϫ1 , P Ͻ 0.05) in the exercise session compared with the control session. In conclusion, in healthy men, a prolonged bout of dynamic exercise decreases MSNA and increases FBF. These effects persist during acute hyperinsulinemia performed after exercise.

Low-dose estrogen therapy does not change postexercise hypotension, sympathetic nerve activity reduction, and vasodilation in healthy postmenopausal women

“…The reduction in peripheral vascular resistance after a single session of aerobic exercise has been previously reported in various populations (3,13,16,21), including postmenopausal women (29). Many mechanisms have been proposed to explain this vasodilator response.…”

“…This phenomenon is known as postexercise hypotension and is considered clinically relevant (53). The results of various studies have suggested that a reduction in muscle sympathetic nerve activity (MSNA) is one of the mechanisms involved in postexercise hypotension in healthy individuals (3,16,23,40), since it leads to a decrease in peripheral resistance. Other studies, however, have demonstrated no such sympatholysis after exercise (26 -28).…”

Neural mechanismsand post-exercise hypotension: The importance of experimental studies

“…In table 1 are presented post-exercise autonomic responses assessed by different methods. Overall, there were reductions of muscle sympathetic nerve activity after aerobic exercise 10,11,52 , reduction of cardiac autonomic balance 14,53 , and increase of baroreflex sensitivity and heart rate variability 54 . Contrarily, other studies reported increased cardiac and vasomotor sympathetic modulation, decreased parasympathetic modulation and/or attenuation of baroreflex sensitivity 12,13,15,55 however, those studies used resistance exercise 13,15,55 or maximal aerobic exercise 12 .…”

“…It is known that neural mechanisms are associated with PEH, such as reduction of sympathetic nervous activity, increase of vagal modulation, and improved baroreflex sensitivity 10,11,26,46 . In table 1 are presented post-exercise autonomic responses assessed by different methods.…”

“…Post-exercise hypotension [PEH] is a prolonged decrease in arterial blood pressure after a single bout of exercise 7 . The autonomic mechanisms attributed to PEH are welldocumented, such as reduced peripheral sympathetic activity 10,11 , modifications in the cardiac autonomic activity 12,13 and adjustments in the baroreflex sensitivity 14,15 . On the other hand, the central neural mechanisms have only recently been discovered and investigated.…”