Interindividual variability in renal and muscle sympathetic responses to mental stress: contributions to blood pressure regulation.

Abstract

Laboratory-based mental stress induces consistent increases in arterial blood pressure, while sympathetic nerve activity (MSNA) responses are highly variable. Given the ability of sympathetic nervous system to be regulated in an organ-dependent manner, we hypothesized that inter-individual variability in renal sympathetic vasoconstriction interacts with MSNA to control blood pressure during mental stress. Herein, renal artery blood velocity (Doppler ultrasound; n=33, 19M/14F), MSNA (microneurography; n=25, 17M/8F), and beat-to-beat mean arterial pressure (MAP; finger photoplethysmography) were measured at rest and during mental stress (arithmetic task) in young, healthy adults. Renal vascular resistance (RVR) was calculated as an index of sympathetically mediated renal vasoconstriction. Participants were classified as negative, non-responders, or positive responders if RVR or MSNA was below, within, or above the baseline variability, respectively. The proportions of negative (24% vs. 36%), non-responders (18% vs. 16%), and positive (58% vs. 48%) responders were significantly different between RVR and MSNA-responder types, respectively (P=0.02). Within the participants in whom both MSNA and RVR were obtained (n=25), only 13 (52%) displayed concordant response patterns (3 negative, 1 non-responder, and 9 positive-responders). Participants were further classified based on the combination of RVR and MSNA responsiveness as typically negative, mixed, or typically positive responders. Within this sub-analysis, MAP reactivity was lower in typically negative compared to mixed and typically positive responders (2±3 mmHg vs. 6±3 mmHg vs. 7±3 mmHg, respectively; P=0.02). These findings suggest that the interindividual variability in renal and muscle vasoconstrictor responses contribute to blood pressure regulation during mental stress in young, healthy adults.