Evidence for potentiation in sympathetic neurovascular transduction following exercise in normotensive adults.

Abstract

Vascular conductance increases following a single bout of dynamic exercise, whereas sympathetic nerve traffic commonly appears unchanged. Discordance between vascular and sympathetic responses may reflect modulation in vasoconstrictor responsiveness. The primary study objective was to evaluate sympathetic neurovascular transduction following cycling exercise. The secondary objective was to explore mechanisms contributing to altered sympathetic neurovascular transduction by manipulating limb vascular conductance using local heating of the foot. We hypothesized that sympathetic neurovascular transduction would decrease following cycling exercise but would be unchanged by lower limb heating. Sixteen adults (22 ± 3 yr; 43 ± 8 mL·kg^-1·min^-1; 8 females) underwent measurements of heart rate (electrocardiography), mean arterial pressure (photoplethysmography), muscle sympathetic nerve activity (MSNA; microneurography), and femoral vascular conductance (FVC; duplex ultrasound) across three interventions: cycling exercise [60 min, 60% peak oxygen consumption (V̇O_2peak), n = 16], time control (60 min, n = 16), and lower limb heating (foot submersion into 40°C water, n = 9). MSNA-FVC transduction was quantified using signal averaging. Compared with control, exercise did not alter MSNA (P = 0.72) but increased FVC (P < 0.01) and MSNA-FVC transduction (-8.6 ± 4.5 vs. -15.1 ± 5.7 mL/min/100 mmHg; P < 0.01). Compared with exercise, heating did not alter MSNA (P = 0.71) and tended to increases FVC (P = 0.09). However, increases in MSNA-FVC transduction following exercise tended to persist when compared with heating (-8.7 ± 8.0 vs. -15.1 ± 5.9 mL/min/100 mmHg; P = 0.06). Contrary to our hypothesis, these findings provide evidence for potentiated sympathetic neurovascular transduction following acute cycling exercise in healthy adults. The observed increase in neurovascular transduction appears independent of resting vasomotor tone.NEW & NOTEWORTHY Following cycling exercise, leg vascular conductance increases, whereas sympathetic nerve traffic is unchanged in young healthy adults. Discordant vascular and sympathetic responses may reflect modulation in vasoconstrictor responsiveness. The current study demonstrated that signal-averaged sympathetic neurovascular transduction was increased by ∼75% following a single bout of cycling exercise. Secondary experiments using local heating suggest that potentiation in sympathetic neurovascular transduction after exercise may occur independent of changes in resting vascular conductance.