Abstract 11874: Sympathetic Control of Reflex Cutaneous Vasoconstriction in Human Hypertension

Abstract

Introduction: Cardiovascular-related morbidity and mortality during environmental cold exposures increase disproportionally in hypertensive (HTN) adults. Although alterations in central control of sympathetic outflow and peripheral regulation of vascular function are evident in hypertension and contribute to increased cardiovascular risk, no studies have examined sympathetic control of reflex cutaneous vasoconstriction during cold stress in humans with hypertension. We hypothesized that 1) whole-body cold stress would elicit exaggerated increases in skin sympathetic nervous system activity (SSNA) and greater reductions in skin blood flow in HTN [n=10; 56±3 yrs; resting blood pressure (BP) 145±7/84±3 mmHg] compared to normotensive adults (NTN; n=12, 55±3 yrs; resting BP 126±4/79±3 mmHg) and 2) cutaneous adrenergic sensitivity would be increased in HTN adults. Methods: In Protocol 1, reflex vasoconstriction was induced by gradual whole-body cooling (to a mean skin temperature of 30.5°C) using a water-perfused suit. SSNA (peroneal microneurography) and red cell flux (laser Doppler flowmetry; dorsum of foot) were measured continuously. SSNA was expressed as a percent change from baseline. In Protocol 2, an intradermal microdialysis fiber was placed in the skin of the lateral calf to measure red cell flux in response to graded intradermal infusions of norepinephrine (NE; 10 -12 to 10 -2 M). In each study, cutaneous vascular conductance (CVC=flux/mean arterial pressure) was expressed as a change from baseline. Results: During cooling, HTN exhibited greater increases in SSNA compared to NTN adults (Δ = 194±26% HTN vs. 51±12% NTN; P<0.01) but cutaneous vasoconstriction was not different between groups (ΔCVC base = -0.03±0.003 ητν vs. -0.02±0.01 flux units mmHg -1 NTN; P=0.97). The slope of the relation between ΔSSNA and ΔCVC base during cold stress was blunted in HTN adults (P<0.01). There was no group difference in cutaneous adrenergic responsiveness to exogenous NE (dose-response logEC 50 ; -7.2±0.2 HTN vs. -7.5±0.4 NTN; P=0.75). Conclusion: Although cutaneous microvascular adrenergic responsiveness to NE is preserved, the sensitivity of the sympathetic reflex response to whole-body cold stress is diminished in human hypertension.