Mechanisms of nicotine-induced cutaneous vasodilation and sweating in young adults: roles for KCa, KATP, and KV channels, nitric oxide, and prostanoids

Cycling matters: Sex hormone regulation of vascular potassium channels

Sex hormones and the reproductive cycle (estrus in rodents and menstrual in humans) have a known impact on arterial function. In spite of this, sex hormones and the estrus/menstrual cycle are often neglected experimental factors in vascular basic preclinical scientific research. Recent research by our own laboratory indicates that cyclical changes in serum concentrations of sex -hormones across the rat estrus cycle, primary estradiol, have significant consequences for the subcellular trafficking and function of KV. Vascular potassium channels, including KV, are essential components of vascular reactivity. Our study represents a small part of a growing field of literature aimed at determining the role of sex hormones in regulating arterial ion channel function. This review covers key findings describing the current understanding of sex hormone regulation of vascular potassium channels, with a focus on KV channels. Further, we highlight areas of research where the estrus cycle should be considered in future studies to determine the consequences of physiological oscillations in concentrations of sex hormones on vascular potassium channel function.

Modulation of preeclampsia by the cholinergic anti-inflammatory pathway: Therapeutic perspectives

The cholinergic anti-inflammatory pathway (CAP) is vital for the orchestration of the immune and inflammatory responses under normal and challenged conditions. Over the past two decades, peripheral and central circuits of CAP have been shown to be critically involved in dampening the inflammatory reaction in a wide array of inflammatory disorders. Additionally, emerging evidence supports a key role for CAP in the regulation of the female reproductive system during gestation as well as in the advent of serious pregnancy-related inflammatory insults such as preeclampsia (PE). Within this framework, the modulatory action of CAP encompasses the perinatal maternal and fetal adverse consequences that surface due to antenatal PE programming. Albeit, a considerable gap still exists in our knowledge of the precise cellular and molecular underpinnings of PE/CAP interaction, which hampered global efforts in safeguarding effective preventive or therapeutic measures against PE complications. Here, we summarize reports in the literature regarding the roles of peripheral and reflex cholinergic neuroinflammatory pathways of nicotinic acetylcholine receptors (nAChRs) in reprogramming PE complications in mothers and their progenies. The possible contributions of α7-nAChRs, cholinesterases, immune cells, adhesion molecules, angiogenesis, and endothelial dysfunction to the interaction have also been reviewed.

Ageing augments β-adrenergic cutaneous vasodilatation differently in men and women, with no effect on β-adrenergic sweating

NEW FINDINGS

What is the central question of this study? β-Adrenergic receptor activation modulates cutaneous vasodilatation and sweating in young adults. In this study, we assessed whether age-related differences in β-adrenergic regulation of these responses exist and whether they differ between men and women. What is the main finding and its importance? We showed that ageing augmented β-adrenergic cutaneous vasodilatation, although the pattern of response differed between men and women. Ageing had no effect on β-adrenergic sweating in men or women. Our findings advance our understanding of age-related changes in the regulation of cutaneous vasodilatation and sweating and provide new directions for research on the significance of enhanced β-adrenergic cutaneous vasodilatation in older adults.

ABSTRACT

β-Adrenergic receptor agonists, such as isoprenaline, can induce cutaneous vasodilatation and sweating in young adults. Given that cutaneous vasodilatation and sweating responses to whole-body heating and to pharmacological agonists, such as acetylcholine, ATP and nicotine, can differ in older adults, we assessed whether ageing also modulates β-adrenergic cutaneous vasodilatation and sweating and whether responses differ between men and women. In the context of the latter, prior reports showed that the effects of ageing on cutaneous vasodilatation (evoked with ATP and nicotine) and sweating (stimulated by acetylcholine) were sex dependent. Thus, in the present study, we assessed the role of β-adrenergic receptor activation on forearm cutaneous vasodilatation and sweating in 11 young men (24 ± 4 years of age), 11 young women (23 ± 5 years of age), 11 older men (61 ± 8 years of age) and 11 older women (60 ± 8 years of age). Initially, a high dose (100 µm) of isoprenaline was administered via intradermal microdialysis for 5 min to induce maximal β-adrenergic sweating. Approximately 60 min after the washout period, three incremental doses of isoprenaline were administered (1, 10 and 100 µm, each for 25 min) to assess dose-dependent cutaneous vasodilatation. Isoprenaline-mediated cutaneous vasodilatation was greater in both older men and older women relative to their young counterparts. Augmented cutaneous vasodilatory responses were observed at 1 and 10 µm in women and at 100 µm in men. Isoprenaline-mediated sweating was unaffected by ageing, regardless of sex. We show that ageing augments β-adrenergic cutaneous vasodilatation differently in men and women, without influencing β-adrenergic sweating.

Sex-differences in cholinergic, nicotinic, and β-adrenergic cutaneous vasodilation: Roles of nitric oxide synthase, cyclooxygenase, and K+ channels

Previous studies indicate that sex-related differences exist in the regulation of cutaneous vasodilation, however, the mechanisms remain unresolved. We assessed if sex-differences in young adults exist for cholinergic, nicotinic, and β-adrenergic cutaneous vasodilation with a focus on nitric oxide synthase (NOS), cyclooxygenase (COX), and K⁺ channel mechanisms. In twelve young men and thirteen young women, four intradermal forearm skin sites were perfused with the following: 1) lactated Ringer's solution (control), 2) 10 mM N^ω-nitro-l-arginine, a non-selective NOS inhibitor, 3) 10 mM ketorolac, a non-selective COX inhibitor, or 4) 50 mM BaCl₂, a nonspecific K⁺ channel blocker. At all four sites, cutaneous vasodilation was induced by 1) 10 mM nicotine, a nicotinic receptor agonist, 2) 100 μM isoproterenol, a nonselective β-adrenergic receptor agonist, and 3) 2 mM and 2000 mM acetylcholine, an acetylcholine receptor agonist. Nicotine and isoproterenol were administered for 3 min, whereas each acetylcholine dose was administered for 25 min. Regardless of treatment site, cutaneous vasodilation in response to nicotine and a high dose of acetylcholine (2000 mM) were lower in women than men. By contrast, isoproterenol induced cutaneous vasodilation was greater in women vs. men. Irrespective of sex, NOS inhibition or K⁺ channel blockade attenuated isoproterenol-mediated cutaneous vasodilation, whereas K⁺ channel blockade decreased nicotine-induced cutaneous vasodilation. Taken together, our findings indicate that while the mechanisms underlying cutaneous vasodilation are comparable between young men and women, sex-related differences in the magnitude of cutaneous vasodilation do exist and this response differs as a function of the receptor agonist.

NO-mediated activation of KATP channels contributes to cutaneous thermal hyperemia in young adults

Local skin heating to 42°C causes cutaneous thermal hyperemia largely via nitric oxide (NO) synthase (NOS)-related mechanisms. We assessed the hypothesis that ATP-sensitive K⁺ (K_ATP) channels interact with NOS to mediate cutaneous thermal hyperemia. In 13 young adults (6 women, 7 men), cutaneous vascular conductance (CVC) was measured at four intradermal microdialysis sites that were continuously perfused with 1) lactated Ringer solution (control), 2) 5 mM glibenclamide (K_ATP channel blocker), 3) 20 mM N^G-nitro-l-arginine methyl ester (NOS inhibitor), or 4) a combination of K_ATP channel blocker and NOS inhibitor. Local skin heating to 42°C was administered at all four treatment sites to elicit cutaneous thermal hyperemia. Thirty minutes after the local heating, 1.25 mM pinacidil (K_ATP channel opener) and subsequently 25 mM sodium nitroprusside (NO donor) were administered to three of the four sites (each 25-30 min). The local heating-induced prolonged elevation in CVC was attenuated by glibenclamide (19%), but the transient initial peak was not. However, glibenclamide had no effect on the prolonged elevation in CVC in the presence of NOS inhibition. Pinacidil caused an elevation in CVC, but this response was abolished at the glibenclamide-treated skin site, demonstrating its effectiveness as a K_ATP channel blocker. The pinacidil-induced increase in CVC was unaffected by NOS inhibition, whereas the increase in CVC elicited by sodium nitroprusside was partly (15%) inhibited by glibenclamide. In summary, we showed an interactive effect of K_ATP channels and NOS for the plateau of cutaneous thermal hyperemia. This interplay may reflect a vascular smooth muscle cell K_ATP channel activation by NO.

KCa and KV channels modulate the venoarteriolar reflex in non-glabrous human skin with no roles of KATP channels, NOS, and COX

The venoarteriolar reflex is a local mechanism that induces vasoconstriction during venous congestion in various tissues, including skin. This response is thought to play a critical role in minimizing capillary damage or edema resulting from overperfusion, though factors that modulate this response remain largely unknown. Here, we hypothesized that nitric oxide synthase (NOS), cyclooxygenase (COX), and Ca²⁺-activated, ATP-sensitive, and voltage-gated K⁺ channels (K_Ca, K_ATP, and K_V channels, respectively) modulate the venoarteriolar reflex in human skin. Cutaneous blood flow (laser-Doppler flowmetry) was monitored during a 3-min pre-occlusion baseline and following a 3-min venous occlusion of 45 mmHg, the latter maneuver was used to induce the venoarteriolar reflex. The venoarteriolar reflex was assessed at the following forearm skin sites: Experiment 1 (n = 11): 1) lactated Ringer solution (Control), 2) 10 mM N^ω-nitro-_L-arginine (NOS inhibitor), 3) 10 mM ketorolac (COX inhibitor), and 4) combined NOS + COX inhibition; Experiment 2 (n = 15): 1) lactated Ringer solution (Control), 2) 50 mM tetraethylammonium (K_Ca channel blocker), 3) 5 mM glybenclamide (K_ATP channel blocker), and 4) 10 mM 4-aminopyridine (K_V channel blocker). Separate and combined NOS and COX inhibition as well as K_ATP channel blocker had no effect on venoarteriolar reflex. Conversely, venoarteriolar reflex was attenuated by K_Ca channel blockade (36-38%) and augmented by K_V channel blockade (38-55%). We showed that K_Ca and K_V channels modulate the venoarteriolar reflex with minimum roles of NOS, COX, and K_ATP channels in human non-glabrous forearm skin in vivo. Thus, cutaneous venoarteriolar reflex changes could reflect altered K⁺ channel function.

Ageing augments nicotinic and adenosine triphosphate-induced, but not muscarinic, cutaneous vasodilatation in women

NEW FINDINGS

What is the central question of this study? Does ageing augment muscarinic, nicotinic and/or ATP-mediated cutaneous vasodilatation in women? What is the main finding and its importance? Ageing augments nicotinic and ATP-induced, but not muscarinic, cutaneous vasodilatation in women. This will stimulate future studies assessing the pathophysiological significance of the augmented microvascular responsiveness in older women compared to their young counterparts.

ABSTRACT

We previously reported that ageing attenuates adenosine triphosphate (ATP)-induced, but not muscarinic and nicotinic, cutaneous vasodilatation in men, and that ageing may augment cutaneous vascular responses in women. In the present study, we evaluated the hypothesis that ageing augments muscarinic, nicotinic and/or ATP-mediated cutaneous vasodilatation in healthy women. In 11 young (23 ± 5 years) and 11 older (60 ± 8 years) women, cutaneous vascular conductance was evaluated at three forearm skin sites that were perfused with (1) methacholine (muscarinic receptor agonist, 5 doses: 0.0125, 0.25, 5, 100, 2000 mm), (2) nicotine (nicotinic receptor agonist, 5 doses: 1.2, 3.6, 11, 33, 100 mm), or (3) ATP (purinergic receptor agonist, 5 doses: 0.03, 0.3, 3, 30, 300 mm). Each agonist was administered for 25 min per dose. Methacholine-induced increases in cutaneous vascular conductance were not different between groups at all doses (all P > 0.05). However, a nicotine-induced elevation in cutaneous vascular conductance at the lowest concentration (1.2 mm) was greater in older vs. young women (43 ± 15 vs. 26 ± 10%max, P = 0.04). ATP-induced increases in cutaneous vascular conductance at moderate and high doses (3 and 30 mm) were also greater in older relative to young women (3 mm, 44 ± 11 vs. 28 ± 10%max, P = 0.02; 30 mm, 83 ± 14 vs. 64 ± 17%max, P = 0.05). Therefore, ageing augments nicotinic and ATP-induced, but not muscarinic, cutaneous vasodilatation in women.

Separate and combined effects of KCa and KATP channel blockade with NOS inhibition on cutaneous vasodilation and sweating in older men during heat stress

Our objective in this study was to examine the separate and combined effects of potassium (K⁺) channels and nitric oxide synthase (NOS) on cutaneous vasodilation and sweating in older men during rest and exercise in the heat. In 13 habitually active men (61 ± 4 yr), cutaneous vascular conductance and local sweat rate were assessed at six dorsal forearm skin sites continuously perfused with either 1) lactated Ringer (control), 2) 10 mM N^G-nitro-l-arginine methyl ester (l-NAME, NOS inhibitor), 3) 50 mM tetraethylammonium (TEA; Ca²⁺-activated K⁺ channel blocker), 4) 5 mM glybenclamide (GLY; ATP-sensitive K⁺ channel blocker), 5) 50 mM TEA + 10 mM l-NAME, and 6) 5 mM GLY + 10 mM l-NAME via microdialysis. Participants rested in non-heat stress (25°C) and heat stress (35°C) conditions for ∼60 min each, followed by 50 min of moderate-intensity cycling (∼55% V̇o_2peak) and 30 min of recovery in the heat. During rest and exercise in the heat, l-NAME, TEA + l-NAME, and GLY + l-NAME attenuated CVC relative to control (all P ≤ 0.05), although l-NAME was not different from TEA + l-NAME or GLY + l-NAME (all P > 0.05). TEA attenuated CVC during rest, whereas GLY attenuated CVC during exercise (both P ≤ 0.05). Additionally, whereas neither l-NAME nor TEA altered sweating throughout the protocol (all P > 0.05), combined TEA + l-NAME attenuated sweating during exercise in the heat (P ≤ 0.05). We conclude that in habitually active older men blockade of K_Ca and K_ATP channels attenuates cutaneous vasodilation during rest and exercise in the heat, respectively, and these effects are NOS dependent. Furthermore, combined NOS inhibition and K_Ca channel blockade attenuates sweating during exercise in the heat.

Aging attenuates adenosine triphosphate-induced, but not muscarinic and nicotinic, cutaneous vasodilation in men

OBJECTIVE

We evaluated the hypothesis that aging attenuates muscarinic, nicotinic, and ATP-related cutaneous vasodilation.

METHODS

In 11 young (24 ± 4 years) and 11 older males (61 ± 8 years), CVC was assessed at 3 forearm skin sites that were infused with either: (i) methacholine (muscarinic receptor agonist, 5 doses: 0.0125, 0.25, 5, 100, 2000 mmol/L), (ii) nicotine (nicotinic receptor agonist, 5 doses: 1.2, 3.6, 11, 33, 100 mmol/L), or (iii) ATP (purinergic receptor agonist, 5 doses: 0.03, 0.3, 3, 30, 300 mmol/L). Each agonist was administered for 25 minutes per dose.

RESULTS

We showed that CVC at all doses of methacholine did not differ between groups. Similarly, no between-group differences in CVC were observed during nicotine administration at all doses administered. By contrast, while no differences in CVC were measured during the administration of ATP at low (0.03 and 0.3 mmol/L) or high (300 mmol/L) concentrations, CVC was reduced in the older relative to the young males at moderate concentrations of ATP (3 mmol/L: 23 ± 6 vs 40 ± 13%max, 30 mmol/L: 62 ± 11 vs 83 ± 8%max, both P ≤ .05).

CONCLUSIONS

We show that aging attenuates ATP-induced, but not muscarinic or nicotinic, cutaneous vasodilation in men.

Voltage-gated potassium channels and NOS contribute to a sustained cutaneous vasodilation elicited by local heating in an interactive manner in young adults

Local skin heating to 42°C causes rapid increases in cutaneous perfusion (initial peak), followed by a brief nadir and subsequent sustained elevation (plateau). Several studies have demonstrated that nitric oxide synthase (NOS) largely contributes to the plateau response during local heating. In this study, we tested the hypothesis that voltage-gated potassium (Kv) channels contribute to the plateau of the cutaneous vasodilation during local heating through NOS-dependent mechanisms. Eleven young males (25±4years) participated in this study wherein cutaneous vascular conductance (CVC) was measured at four intradermal microdialysis sites that were continuously perfused with either 1) lactated Ringer (Control), 2) 10mM 4-aminopyridine (Kv channel blocker), 3) 10mM Nω-Nitro-L-arginine (NOS inhibitor), or 4) a combination of 4-aminopyridine and Nω-Nitro-L-arginine. In comparison to the Control site, the inhibition of Kv channels alone attenuated the increase in CVC observed at the initial peak, nadir, and plateau phases measured during local heating; in contrast, the inhibition of NOS alone attenuated the increase in CVC at the nadir and plateau phases only (e.g., plateau response: Control site: 59±5%max, Kv channel blockade site: 49±8%max, NOS inhibition site: 35±11%max, combined inhibition site: 40±12%max). Further, no effect of Kv channel blockade on CVC was measured at any phase of the local heating response when the modulating influence of NOS was simultaneously removed. We show that Kv channels and NOS contribute to the local heating mediated sustained increase (i.e., plateau) in cutaneous vasodilation in an interactive manner. (243/250 words).