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Folic acid supplementation increases cutaneous vasodilator sensitivity to sympathetic nerve activity in older adults
Journal article   Open access   Peer reviewed

Folic acid supplementation increases cutaneous vasodilator sensitivity to sympathetic nerve activity in older adults

Anna E. Stanhewicz, Jody L. Greaney, Lacy M. Alexander and W. Larry Kenney
American journal of physiology. Regulatory, integrative and comparative physiology, Vol.312(5), pp.R681-R688
05/01/2017
DOI: 10.1152/ajpregu.00493.2016
PMID: 28228418
url
https://doi.org/10.1152/ajpregu.00493.2016View
Published (Version of record) Open Access

Abstract

During heat stress, blunted increases in skin sympathetic nervous system activity (SSNA) and reductions in end-organ vascular responsiveness contribute to the age-related reduction in reflex cutaneous vasodilation. In older adults, folic acid supplementation improves the cutaneous vascular conductance (CVC) response to passive heating; however, the influence of folic acid supplementation on SSNA: CVC transduction is unknown. Fourteen older adults (66 +/- 1 yr, 8 male/6 female) ingested folic acid (5 mg/day) or placebo for 6 wk in a randomized, double-blind, crossover design. In protocol 1, esophageal temperature (T-es) was increased by 1.0 degrees C (water-perfused suit) while SSNA (peroneal microneurography) and red cell flux in the innervated dermatome (laser Doppler flowmetry; dorsum of the foot) were continuously measured. In protocol 2, two intradermal microdialysis fibers were placed in the skin of the lateral calf for graded infusions of acetylcholine (ACh; 10(-10) to 10(-1) M) with and without nitric oxide synthase (NOS) blockade (20 mM nitro-L-arginine methyl ester). Folic acid improved reflex vasodilation (46 +/- 4% vs. 31 +/- 3% CVCmax for placebo; P < 0.001) without affecting the increase in SSNA (Delta 506 +/- 104% vs. Delta 415 +/- 73% for placebo; NS). Folic acid increased the slope of the SSNA-to-CVC relation (0.08 +/- 0.02 vs. 0.05 +/- 0.01 for placebo; P < 0.05) and extended the response range. Folic acid augmented ACh-induced vasodilation (83 +/- 3% vs. 66 +/- 4% CVCmax for placebo; P = 0.002); however, there was no difference between treatments at the NOS-inhibited site (53 +/- 4% vs. 52 +/- 4% CVCmax for placebo; NS). These data demonstrate that folic acid supplementation enhances reflex vasodilation by increasing the sensitivity of skin arterioles to central sympathetic nerve outflow during hyperthermia in aged human subjects.
 Life Sciences & Biomedicine Physiology Science & Technology

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