Volume 104, Issue 12 p. 1801-1807

RESEARCH PAPER

Free Access

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

Naoto Fujii

Corresponding Author

fujii.naoto.gb@u.tsukuba.ac.jp

orcid.org/0000-0001-9696-8291

Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Ontario, Canada

Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan

Correspondence

Naoto Fujii, Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki 305‐8574, Japan.

Email: fujii.naoto.gb@u.tsukuba.ac.jp

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Gregory W. McGarr

Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Ontario, Canada

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Ronald J. Sigal

Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Ontario, Canada

Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada

Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada

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Pierre Boulay

Faculty of Physical Activity Sciences, University of Sherbrooke, Sherbrooke, Quebec, Canada

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Takeshi Nishiyasu

orcid.org/0000-0002-6040-7756

Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan

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Glen P. Kenny

orcid.org/0000-0001-8683-6973

Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Ontario, Canada

Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada

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Naoto Fujii

Corresponding Author

fujii.naoto.gb@u.tsukuba.ac.jp

orcid.org/0000-0001-9696-8291

Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Ontario, Canada

Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan

Correspondence

Naoto Fujii, Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki 305‐8574, Japan.

Email: fujii.naoto.gb@u.tsukuba.ac.jp

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Gregory W. McGarr

Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Ontario, Canada

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Ronald J. Sigal

Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Ontario, Canada

Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada

Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada

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Pierre Boulay

Faculty of Physical Activity Sciences, University of Sherbrooke, Sherbrooke, Quebec, Canada

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Takeshi Nishiyasu

orcid.org/0000-0002-6040-7756

Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan

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Glen P. Kenny

orcid.org/0000-0001-8683-6973

Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, Ontario, Canada

Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada

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First published: 10 October 2019

https://doi.org/10.1113/EP088144

Citations: 2

Funding information:

This study was supported by the Canadian Institutes of Health Research (399434). G.P.K. is Director of the Human and Environmental Physiology Unit and is supported by a University of Ottawa Research Chair Award. G.W.M. is supported by the Human and Environmental Physiology Research Unit. N.F. was supported by the Human and Environmental Physiology Research Unit.

Present address:

N. Fujii: University of Tsukuba, Faculty of Health and Sport Sciences, Tsukuba City, Japan.

Edited by: Jeremy Ward

Abstract

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.

1 INTRODUCTION

Older adults are at greater risk of cardiovascular disease (North & Sinclair, 2012). Alterations in cutaneous vascular function can precede overt cardiovascular disease (Ijzerman et al., 2003; Kraemer‐Aguiar, Laflor, & Bouskela, 2008). Consequently, assessment of the cutaneous vascular response can provide valuable insights into the mechanisms underlying age‐related alterations in vascular regulation that may advance clinically relevant information to define age‐related decrements in cardiovascular health.

The endothelial muscarinic receptor agonist acetylcholine, or its analogue methacholine, induces cutaneous vasodilatation (Fujii, Halili, Singh, Meade, & Kenny, 2015a; Gagnon, Crandall, & Kenny, 2013; Inoue et al., 2014; Kimura, Low, Keller, Davis, & Crandall, 2007; Patik, Christmas, Hurr, & Brothers, 2016; Tucker, Six, Moyen, Satterfield, & Ganio, 2017). This muscarinic cutaneous vasodilatation is mediated in part through nitric oxide synthase‐related mechanisms (Fujii et al., 2014; Kellogg, Zhao, Coey, & Green, 2005; Medow, Glover, & Stewart, 2008) and is commonly employed to assess cutaneous endothelium‐dependent vasodilatation. However, mixed results have been reported on the age‐related effects of muscarinic cutaneous vasodilatation, with some studies observing no age‐related alterations (Fujii et al., 2018; Holowatz, Thompson, Minson, & Kenney, 2005; Smith, Alexander, & Kenney, 2013), while others have reported an attenuated response in older adults (Bruning et al., 2012; Stapleton et al., 2014). Importantly, all of the above studies assessed responses in older men or a combined group of older women and men. Consequently, it remains unclear how ageing specifically modulates muscarinic cutaneous vasodilatation in women. We recently reported that prostacyclin‐induced cutaneous vasodilatation was similar between young and older men (Fujii, Notley, Minson, & Kenny, 2016b), whereas this vasodilatation was greater in older relative to young women (Fujii, McNeely, Nishiyasu, & Kenny, 2017c). These findings provide evidence that differences exist in the age‐related alterations in the regulation of cutaneous vasodilatation between men and women and that ageing may augment cutaneous vascular responsiveness to receptor agonists in women. However, it remains to be determined if this response holds true for methacholine‐induced cutaneous vasodilatation in women.

Nicotine induces cutaneous vasodilatation in young men or a combined group of young men and women (Fujii et al., 2017a,b; Izumi & Karita, 1992) via a cholinergic axon reflex wherein cholinergic nerves antidromically release acetylcholine, thereby activating endothelial muscarinic receptors. Thus, nicotine‐induced cutaneous vasodilatation can be used to assess peripheral nerve (i.e. axon) function (Schlereth, Brosda, & Birklein, 2005). However, a high dose of nicotine can cause cutaneous vasodilatation independently of muscarinic receptor activation (Fujii et al., 2017a). Also, in contrast to methacholine‐induced cutaneous vasodilatation, nitric oxide synthase does not play a role in mediating nicotine‐induced cutaneous vasodilatation; instead, K⁺ channels are largely involved (Fujii et al., 2017a). Consequently, nicotine‐induced cutaneous vasodilatation may be used to evaluate K⁺ channel function. We recently reported that ageing had no effect on nicotine‐induced cutaneous vasodilatation in men (Fujii et al., 2017c). However, given our observation of an age‐related augmentation of prostacyclin‐induced cutaneous vasodilatation in women noted above (Fujii et al., 2017c), ageing may also augment nicotinic cutaneous vasodilatation in women. Further studies are required to evaluate this possible mechanism.

Adenosine triphosphate (ATP) can cause a powerful cutaneous vasodilatory response in young adults (Fujii et al., 2015a,b; Wingo, Brothers, Del Coso, & Crandall, 2010) presumably via activation of purinergic receptors located on vascular endothelial cells. This ATP‐induced cutaneous vasodilatation is partly through nitric oxide synthase‐related mechanisms and may be used to assess endothelial vascular function. We recently reported that ageing attenuated ATP‐induced cutaneous vasodilatation with no influence on methacholine‐mediated cutaneous vasodilatation in men (Fujii et al., 2018). Thus ATP‐induced cutaneous vasodilatation may more precisely reflect age‐related alterations in endothelium‐dependent microvascular function compared with methacholine‐induced cutaneous vasodilatation. However, it is unclear if in fact ageing modulates ATP‐mediated cutaneous vasodilatation in women. It may be that ageing augments ATP‐mediated cutaneous vasodilatation in women as with prostacyclin‐induced cutaneous vasodilatation (Fujii et al., 2017c).

In the present study we evaluated the hypothesis that ageing augments muscarinic, nicotinic and ATP‐mediated cutaneous vasodilatation in women.

2 METHODS

2.1 Ethics approval

This study was approved by the University of Ottawa Health Sciences and Science Research Ethics Board (H01‐14‐01) and conformed to the standards outlined in the Declaration of Helsinki with the exception that registration in a database was not done in the present study. All volunteers provided their signed informed consent form before their participation.

2.2 Participants

Twenty‐two young (n = 11) and older (n = 11) women were enrolled in the present study. The physical characteristics of the participants are shown in Table 1. Participants had no history of specific medical conditions (i.e. cystic fibrosis transmembrane conductance regulator mutations, skin disorders, hypertension, heart disease, diabetes or autonomic disorders) and were not taking any prescription medications. They were also never‐smokers or had not smoked in the past 15 years. Young women participated in the experimental session during the early follicular phase (within 6 days of beginning menstruation) (n = 9), or during the placebo phase if on oral contraception (n = 2) to minimize the influence of sex hormones on local heat loss responses associated with the menstrual cycle (Kuwahara, Inoue, Abe, Sato, & Kondo, 2005). All older women were postmenopausal except for three who were premenopausal (aged 49–53 years), and none of them were on hormone replacement therapy. During the preliminary session, height and body mass were assessed by an eye‐level physician stadiometer (model 2391, Detecto Scale Company, Webb City, MO, USA) and a digital weight scale platform (model IND560, Mettler Toledo Inc., Schwerzenbach, Switzerland), respectively. Resting arterial blood pressure was obtained in the upright seated position by manual auscultation using a mercury column sphygmomanometer (Baumanometer Standby model, WA Baum, Copiague, NY, USA).

Table 1. Participant characteristics

Characteristic	Young women (n = 11)	Older women (n = 11)
Age (years)	23 ± 5	60 ± 8All values are expressed as means ± standard deviation. ^Significant difference between young and older women (P ≤ 0.05).
Height (m)	1.64 ± 0.07	1.65 ± 0.07
Body mass (kg)	62.4 ± 9.4	67.8 ± 11.7
Body mass index (kg/m²)	23.2 ± 1.9	25.0 ± 4.0
Blood pressure (mmHg)
Systolic	110 ± 10	116 ± 10
Diastolic	75 ± 5	76 ± 5
Mean arterial pressure	87 ± 6	89 ± 6

All values are expressed as means ± standard deviation. ^*Significant difference between young and older women (P ≤ 0.05).

2.3 Experimental session

Prior to the experimental session, all participants avoided consuming over‐the‐counter medications including non‐steroidal anti‐inflammatory drugs, vitamins and minerals for >48 h, alcohol and caffeine for >24 h, strenuous physical activity for >12 h, and food for >2 h.

The experimental protocol was the same as our previous work assessing responses in young and older men (Fujii et al., 2018). Briefly, a 25‐gauge needle was inserted into the un‐anaesthetized dermal layer of the skin of the left dorsal forearm while participants rested on a semi‐recumbent bed in an experimental room (∼24°C). A microdialysis fibre (30 kDa cutoff, 10 mm membrane) (MD2000, Bioanalytical Systems, West Lafayette, IN, USA) was then passed through the lumen of the needle after which the needle was withdrawn. In total, three fibres were implanted into the forearm skin. Each fibre was connected to a liquid switcher (model 110, CMA Microdialysis AB, Kista, Sweden).

Approximately 10 min after the placement of microdialysis fibres, all skin sites were perfused with lactated Ringer solution (Control, Baxter, Deerfield, IL, USA) for ≥80 min to ensure that the trauma associated with fibre insertion had subsided. Perfusion at each of the skin sites was maintained at a rate of 4.0 μl min⁻¹ regulated by a micro‐infusion pump (model 4004, CMA Microdialysis, Solna, Sweden). Thereafter, a 10 min baseline measurement was initiated, after which pharmacological agents were administered at the three intradermal forearm skin sites: (1) methacholine (Sigma‐Aldrich, St Louis, MO, USA; muscarinic receptor agonist, 5 doses: 0.0125, 0.25, 5, 100, 2000 mm), (2) nicotine (MP Biomedicals, Santa Ana, CA; nicotinic receptor agonist, 5 doses: 1.2, 3.6, 11, 33, 100 mm), or (3) ATP (Cayman Chemical, Ann Arbor, MI, USA; purinergic receptor agonist, 5 doses: 0.03, 0.3, 3, 30, 300 mm). All drugs administered in this study were dissolved in lactated Ringer solution. Methacholine, nicotine, and ATP were all administered in a dose‐dependent fashion for 25 min per dose at a fixed rate of 4.0 μl min⁻¹. After the completion of all agonist administration, all skin sites were perfused with 50 mm sodium nitroprusside (Sigma‐Aldrich), a nitric oxide donor, for 20–30 min at a rate of 6.0 μl min⁻¹ to obtain maximum cutaneous blood flow.

2.3.1 Measurements

An integrated laser‐Doppler flowmetry probe (model 413, Perimed, Stockholm, Sweden) was employed to assess cutaneous red blood cell flux, an index of cutaneous blood flow expressed in perfusion units, at a rate of 32 Hz. Each laser‐Doppler probe was connected to the recording system (PeriFlux System 5000, Perimed). Manual auscultation was performed using a mercury column sphygmomanometer (Baumanometer Standby model) to obtain blood pressures every 10–15 min. Cutaneous vascular conductance was assessed as cutaneous red blood cell flux/mean arterial pressure (diastolic arterial pressure plus one‐third the difference between systolic and diastolic pressures). Cutaneous vascular conductance was presented as %max to minimize the effect of site‐to‐site heterogeneity on the level of cutaneous blood flow (Minson, 2010).

2.3.2 Data analysis

For all measurement sites, the averaged cutaneous vascular conductance over the final 5 min of the 10 min baseline period was defined as the baseline value. The maximum cutaneous vascular conductance was determined as the average values over a minimum 2 min period during sodium nitroprusside infusion. Cutaneous vascular conductance values during the administration of methacholine, nicotine and ATP were obtained by averaging values over the last 5 min of the 25 min infusion period at each dose. The methacholine, nicotine and ATP concentrations required to elicit 50% of maximal cutaneous vasodilatation (EC₅₀, in mm) were evaluated as conducted in our previous work (Fujii et al., 2018). EC₅₀ values were not identified in two older women given the data did not fit the logistic curve model.

2.3.3 Statistical analysis

Statistical analyses were conducted using SPSS Statistics v. 25 (IBM Corp., Armonk, NY, USA). Based on cutaneous vascular conductance response (Fujii et al., 2014) obtained in our previous work with 80% power and a significance level of 0.05, a minimum sample size of nine was determined. Cutaneous vascular conductance (%max) and mean arterial pressure were analysed with a two‐way mixed‐model analysis of variance with the factors of age (Young and Older) and stage (baseline and each dose of pharmacological agent employed). When detecting a significant interaction, or a main effect, multiple comparisons were carried out using a modified version of the Bonferroni correction (the Holm–Bonferroni method). In addition, Student's t test was employed where applicable. The level of significance for all analyses was set at P ≤ 0.05. All values are reported with a mean ± 95% confidence interval (1.96 × standard error of the mean).

3 RESULTS

3.1 Cutaneous vascular conductance

All doses of methacholine and nicotine increased cutaneous vascular conductance from baseline for both groups (all P ≤ 0.05, Figure 1a,b). Also, cutaneous vascular conductance was elevated from baseline by all doses of ATP in older women, whereas it was elevated only by the administration of ≥3 mm ATP in young women (all P ≤ 0.05, Figure 1c). Cutaneous vascular conductance during methacholine administration did not differ between groups for all doses (all P > 0.05, Figure 1a). By contrast, cutaneous vascular conductance during 1.2 mm nicotine administration was greater in older relative to young women (P = 0.04, Figure 1b). Cutaneous vascular conductance during ATP administration was also greater in older vs. young women at 3 mm (P = 0.02) and 30 mm (P = 0.05) (Figure 1c). The EC₅₀ of cutaneous vasodilatation was similar between young and older women for methacholine (7.5 ± 12.6 vs. 1.5 ± 2.0 mm, P = 0.36), nicotine (9.9 ± 8.4 vs. 3.3 ± 2.7 mm, P = 0.19) and ATP (13.5 ± 8.2 vs. 9.3 ± 7.0 mm, P = 0.45) (Figure 2). There were no between‐group differences in absolute maximum cutaneous vascular conductance (all P > 0.05), whereas absolute baseline cutaneous vascular conductance was lower in older compared to young women (all P < 0.05) (Table 2).

**Figure 1**
Open in figure viewer PowerPoint

Cutaneous vascular response to methacholine (a), nicotine (b), and ATP (c) in young (open circles, n = 11) and older women (filled squares, n = 11). Data are presented as mean ± 95% confidence interval. ^*Significant difference between young and older women (P ≤ 0.05)

**Figure 2**
Open in figure viewer PowerPoint

Methacholine (a), nicotine (b), and ATP (c) concentrations required to induce half of the maximal cutaneous vasodilator response (EC₅₀). The total number of participants was 11 each for both young (open bar) and older women (filled bar). However, only 9 older women were used for the nicotine data (EC₅₀ was not identified for 2 older participants since the data did not fit the logistic curve model). Data are presented as mean ± 95% confidence interval

Table 2. Absolute baseline and maximal cutaneous vascular conductance at the three skin sites

	Cutaneous vascular conductance (perfusion units mmHg⁻¹)
	Baseline		Maximum
Site	Young women	Older women	Young women	Older women
Methacholine site	0.21 ± 0.04	0.15 ± 0.04Values are expressed as means ± 95% confidence interval. Data are presented in separate groups of young women (n = 11) and older women (n = 11). ^Significant difference between young and older women (P ≤ 0.05).	1.85 ± 0.25	2.21 ± 0.50
Nicotine site	0.22 ± 0.05	0.14 ± 0.03Values are expressed as means ± 95% confidence interval. Data are presented in separate groups of young women (n = 11) and older women (n = 11). ^Significant difference between young and older women (P ≤ 0.05).	1.55 ± 0.32	1.63 ± 0.34
ATP site	0.21 ± 0.05	0.14 ± 0.03Values are expressed as means ± 95% confidence interval. Data are presented in separate groups of young women (n = 11) and older women (n = 11). ^Significant difference between young and older women (P ≤ 0.05).	1.45 ± 0.25	2.04 ± 0.61

Values are expressed as means ± 95% confidence interval. Data are presented in separate groups of young women (n = 11) and older women (n = 11). ^*Significant difference between young and older women (P ≤ 0.05).

4 DISCUSSION

We examined the influence of ageing on muscarinic, nicotinic and ATP‐mediated cutaneous vasodilatation in women. In keeping with our hypothesis, we showed that ageing augments nicotinic and ATP‐mediated cutaneous vasodilatation in women. However, in contrast to our hypothesis, we did not observe an ageing effect on muscarinic cutaneous vasodilatation in women.

4.1 Ageing effect on cutaneous vasodilatation

We demonstrated that methacholine‐induced cutaneous vasodilatation was similar between young and older women (Figure 1a) and this response is consistent with our recent observations in men (Fujii et al., 2018). Further, the lack of an ageing effect on acetylcholine‐induced cutaneous vasodilatation was also previously reported in a combined group of men and women (Holowatz et al., 2005; Smith et al., 2013). Taken together, these results suggest that ageing has no effect on muscarinic cutaneous vasodilatation in men or women.

Nicotine‐induced cutaneous vasodilatation was augmented in older women relative to young women at the lowest concentration of 1.2 mm (Figure 1b), indicating an age‐related augmentation of nicotine‐mediated cutaneous vasodilatation in women. In view of our prior observation of a similar nicotinic cutaneous vasodilatation in young and older men (Fujii et al., 2018), our findings suggest a disparate ageing effect of nicotinic cutaneous vasodilatation in men and women. Further, the divergent responses in young and older women parallel our prior work demonstrating prostacyclin‐induced cutaneous vasodilatation was greater in older relative to young women (Fujii et al., 2017c). Nicotine‐induced cutaneous vasodilatation is highly K⁺ channel‐dependent such that blockade of either the K_Ca, or the K_ATP, or the K_V channel can induce an attenuation of nicotinic cutaneous vasodilatation as assessed in a combined group of young men and women (Fujii et al., 2017a). It is plausible, therefore, that the augmented nicotinic cutaneous vasodilatation observed in older women may be the result of a greater K⁺ channel‐induced cutaneous vasodilatation. In support of this possibility, our previous work showed that the K_Ca channel component of prostacyclin‐induced cutaneous vasodilatation is elevated in older relative to young women (Fujii et al., 2017c). Further studies are required to confirm this potential mechanism.

As with nicotinic cutaneous vasodilatation, we demonstrated that ATP‐induced cutaneous vasodilatation at concentrations of 3 and 30 mm was augmented in older versus young women (Figure 1c), suggesting that ageing enhances cutaneous microvascular responsiveness to ATP in women. This is in marked contrast to our prior observations wherein we showed that ATP‐induced cutaneous vasodilatation was attenuated in older relative to young men (Fujii et al., 2018). Our findings therefore indicate that age‐related differences in ATP‐induced cutaneous vasodilatation exist between men and women.

The mechanism(s) underpinning the greater ATP‐induced cutaneous vasodilatation in older relative to young women remain(s) unclear. We previously reported that 30 mm ATP‐induced cutaneous vasodilatation is partly dependent upon by nitric oxide synthase‐ but not cyclooxygenase‐mediated mechanisms (Fujii et al., 2015b) as assessed in a combined group of young men and women. However, several studies have demonstrated that ageing reduces nitric oxide synthase‐dependent cutaneous vasodilatation in a combined group of older men and women (Fujii et al., 2016a; Stanhewicz, Alexander, & Kenney, 2015; Stanhewicz, Bruning, Smith, Kenney, & Holowatz, 2012). Furthermore, our previous work showed that ATP‐induced cutaneous vasodilatation at 3 mm occurred independently of nitric oxide synthase and cyclooxygenase in a combined group of young men and women (Fujii et al., 2015b). Thus, the augmented ATP‐induced cutaneous vasodilatation at 3 and 30 mm in the older women in the present study could be explained by a nitric oxide synthase‐ and cyclooxygenase‐independent mechanism (i.e. endothelium‐dependent hyperpolarization induced by activation of K_Ca channels) (Garland & Dora, 2017). Further, Lang, Krajek, and Smaller (2017) demonstrated in a combined group of young men and women that ATP can also induce cutaneous vasoconstriction. It is possible that this vasoconstrictor effect might be attenuated in older women, contributing to greater ATP‐induced cutaneous vasodilatation. Moreover, ATP is hydrolysed by ectoenzymes, reducing ATP bioavailability. The action of ectoenzymes may be blunted in older women relative to young women, thereby partly underlying the greater ATP‐induced cutaneous vasodilatation in older women. Additional studies are required to assess these different possibilities.

The augmentation in nicotinic cutaneous vasodilatation in older women was not observed when higher doses of nicotine were administered (Figure 1b). Further, there were no between‐group differences in ATP‐induced cutaneous vasodilatation at the lower doses (0.03 and 0.3 mm) and highest dose (300 mm). Thus, we showed that the age‐related augmentation of both nicotinic and ATP‐induced vasodilatation is dose‐specific. Similarly, the age‐related attenuation in ATP‐induced cutaneous vasodilatation in men was only measured at 3 and 30 mm (Fujii et al., 2018). While we do not know the exact mechanisms underlying why an ageing‐related effect was not observed over a wide range of receptor agonists employed, our findings do highlight the fact that the dosage employed is a critical factor that must be considered to identify potential age‐related alterations in cutaneous vascular function in men and women.

4.2 Limitations

Although we detected between‐group differences in nicotinic and ATP‐induced cutaneous vasodilatation, these differences were not reflected by comparable differences in EC₅₀ (Figure 2). This could be attributed in part to high individual variability in EC₅₀. However, it must be noted that the between‐group differences in cutaneous vascular conductance during nicotine and ATP administrations were ∼16–19%max, which is consistent with a meaningful physiological difference that we used for the calculation of minimum sample size (see ‘Statistical analysis’ section). Thus we believe that the differences in cutaneous vascular conductance observed between groups are physiologically important.

4.3 Perspectives

The present study demonstrated that ageing augments nicotinic and ATP‐induced cutaneous vasodilatation without affecting muscarinic cutaneous vasodilatation in women. This is in contrast to our previous work in which we showed that ageing attenuates ATP‐induced cutaneous vasodilatation with no effect on nicotinic and muscarinic cutaneous vasodilatation in men (Fujii et al., 2018). Thus sex is an important factor that must be considered when assessing age‐related alterations in cutaneous microvascular function. Our observation of an augmented cutaneous vasodilatation in older women might be considered counter‐intuitive since ageing generally increases risk of cardiovascular diseases (North & Sinclair, 2012). We do not know if the augmented cutaneous microvascular function in older women relates to age‐related elevations in cardiovascular risk and if so by what mechanism. However, augmented vasodilatation might reflect an increased risk of overperfusion, which ultimately can cause capillary damage and/or oedema. Future work is warranted to elucidate the pathophysiological significance of the augmented microvascular responsiveness in older women.

5 CONCLUSION

We showed that ageing augments nicotinic and ATP‐induced, but not muscarinic cutaneous vasodilatation in women.

ACKNOWLEDGEMENTS

We greatly appreciate all of the volunteers’ taking time to participate in this study. We thank B. D. McNeely, Lyra Halili, Sarah Y. Zhang and Mercy O. Danquah for their help in conducting this study.

COMPETING INTERESTS

None.

AUTHOR CONTRIBUTIONS

All experiments took place at the Human and Environmental Physiology Research Unit located at the University of Ottawa. N.F. and G.P.K. conceived and designed experiments. N.F. contributed to data collection. N.F. performed data analysis. N.F., G.W.M., R.J.S., P.B., T.N., and G.P.K. interpreted the experimental results. N.F. drafted the manuscript. N.F., G.W.M., R.J.S., P.B., T.N., and G.P.K. edited and revised the manuscript. All authors have read and approved the final version of this manuscript and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All persons designated as authors qualify for authorship, and all those who qualify for authorship are listed.

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Citing Literature

Volume104, Issue12

1 December 2019

Pages 1801-1807

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