title: Folic acid supplementation increases cutaneous vasodilator sensitivity to sympathetic nerve activity in older adults.
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. Inprotocol 1, esophageal temperature (Tes) was increased by 1.0°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. Inprotocol 2, two intradermal microdialysis fibers were placed in the skin of the lateral calf for graded infusions of acetylcholine (ACh; 10-10to 10-1M) 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% CVCmaxfor placebo;P< 0.001) without affecting the increase in SSNA (Δ506 ± 104% vs. Δ415 ± 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% CVCmaxfor placebo;P= 0.002); however, there was no difference between treatments at the NOS-inhibited site (53 ± 4% vs. 52 ± 4% CVCmaxfor 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.
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania axs1056@psu.edu.
authors.forename: Anna E
authors.initials: AE
authors.lastname: Stanhewicz
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Jody L
authors.initials: JL
authors.lastname: Greaney
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Lacy M
authors.initials: LM
authors.lastname: Alexander
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania.
authors.forename: W Larry
authors.initials: WL
authors.lastname: Kenney
mesh_terms: D000284:Administration, Oral; D000368:Aged; D000375:Aging / Q000502:physiology; D001783:Blood Flow Velocity / Q000187:drug effects / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D018592:Cross-Over Studies; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage*; D018869:Heat-Shock Response / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008297:Male; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D012867:Skin / Q000098:blood supply* / Q000294:innervation; D012879:Skin Physiological Phenomena; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
chemical_list: D005492:Folic Acid
keywords: aging; folic acid; skin blood flow; sympathetic nervous system