Ascorbate improves circulation in postural tachycardia syndrome

Abstract

Stewart JM, Ocon AJ, Medow MS. Ascorbate improves circulation in postural tachycardia syndrome. Am J Physiol Heart Circ Physiol 301: H1033-H1042, 2011. First published May 27, 2011 doi:10.1152/ajpheart.00018.2011.-Low flow postural tachycardia syndrome (LFP) is associated with vasoconstriction, reduced cardiac output, increased plasma angiotensin II, reduced bioavailable nitric oxide (NO), and oxidative stress. We tested whether ascorbate would improve cutaneous NO and reduce vasoconstriction when delivered systemically. We used local cutaneous heating to 42°C and laser Doppler flowmetry to assess NO-dependent conductance (%CVCmax) to sodium ascorbate and the systemic hemodynamic response to ascorbic acid in 11 LFP patients and in 8 control subjects (aged 23 Ϯ 2 yr). We perfused intradermal microdialysis catheters with sodium ascorbate (10 mM) or Ringer solution. Predrug heat response was reduced in LFP, particularly the NO-dependent plateau phase (56 Ϯ 6 vs. 88 Ϯ 7%CVCmax). Ascorbate increased baseline skin flow in LFP and control subjects and increased the LFP plateau response (82 Ϯ 6 vs. 92 Ϯ 6 control). Systemic infusion experiments used Finometer and ModelFlow to estimate relative cardiac index (CI) and forearm and calf venous occlusion plethysmography to estimate blood flows, peripheral arterial and venous resistances, and capacitance before and after infusing ascorbic acid. CI increased 40% after ascorbate as did peripheral flows. Peripheral resistances were increased (nearly double control) and decreased by nearly 50% after ascorbate. Calf capacitance and venous resistance were decreased compared with control but normalized with ascorbate. These data provide experimental support for the concept that oxidative stress and reduced NO possibly contribute to vasoconstriction and venoconstriction of LFP. free radicals; vasoconstriction POSTURAL TACHYCARDIA SYNDROME (POTS) accounts for most cases of chronic orthostatic intolerance (21,28,39,47,48). POTS is defined by excessive increase in upright heart rate and symptoms of orthostatic intolerance (39) improving with recumbence. Our laboratory (42) has described a subset of POTS designated "low flow POTS" (LFP) in which there is marked upright tachycardia and circulatory insufficiency even while supine including resting tachycardia, decreased cardiac output (CO), and decreased regional blood flows with peripheral and cutaneous vasoconstriction, findings often ascribed to a hyperadrenergic state (1, 6). A consistent observation has been increased plasma angiotensin II (ANG II; Refs. 40,43,45), which can act locally to decrease bioavailable nitric oxide (NO) by superoxide scavenging to create peroxynitrite (36). ANG II also acts through reactive oxygen species (ROS; Ref. 35) to increase central and peripheral sympathetic activity (9, 52). Both increased ANG II due to deficient ACE2 and decreased bioavailable NO have been demonstrated in LFP during prior experiments using intradermal microdialysis techniques. Experiments made extensive use of the local vasodilator...

To reheat, or to not reheat: that is the question: The efficacy of a local reheating protocol on mechanisms of cutaneous vasodilatation

“…Additionally, Cracowski et al (2007) following a similar heat-reheat protocol, raising skin temperature at a rate of 0.09°C·s − 1 , also noted no differences in the thermal hyperemia response to a local heating stimulus (Cracowski et al, 2007). Thus, it seems as though the rapid rate of heating employed in the studies by Ciplak et al and Frantz et al may explain the conflicting results compared to those of protocols 1 and 2 of the present study and those previously published by others (Cracowski et al, 2007;Medow et al, 2011;Shastry and Joyner, 2002;Stewart et al, 2007a;Stewart et al, 2009;Stewart et al, 2011;Stewart et al, 2008a).…”

“…In protocol 1, we examined the effect of a heat-reheat protocol on cutaneous vasodilatation at forearm and leg skin sites. Based on the work of Stewart and coworkers (Medow et al, 2011;Stewart et al, 2007a;Stewart et al, 2009;Stewart et al, 2011;Stewart et al, 2008a) we hypothesized that the vasodilator response to the second bout of heating would be the same as the first. In protocol 2, we examined the effect of NOS inhibition combined with the same (protocol 1) heat-reheating procedure.…”

Blunted cerebral blood flow velocity in response to a nitric oxide donor in postural tachycardia syndrome

“…*P Ͻ 0.05 compared with the control group. When present, systemic circulatory abnormalities are also found in the brain (34,55) and may account for impaired CBF autoregulation in the upright POTS patient (34). Impairment of cerebral autoregulation is associated with a reduction in neurovascular coupling (52) as well as cognition (33).…”

Retrodialysis: A Review of Experimental and Clinical Applications of Reverse Microdialysis in the Skin

“…Furthermore, mechanisms of acetylcholine (ACh)-induced vasodilatation remain to be fully understood and can certainly not be related to a single vasoactive mediator. Using retrodialysis, ACh-induced vasodilatation has been shown to involve release of both NO and prostaglandins [62,68,69] and, further, a study investigating splanchnic vasodilatation in normal-flow postural tachycardia syndrome showed that NO produced by endothelial NOS is released by ACh [70]. …”

“…Stewart et al [70] tested whether ascorbate would improve cutaneous NO and reduce vasoconstriction when delivered systemically using retrodialysis. Their data provided experimental support for the concept that oxidative stress and reduced NO contribute to vasoconstriction and venoconstriction in patients with low-flow postural tachycardia syndrome compared to healthy controls.…”