Exercise prevents age-related decline in nitric-oxide-mediated vasodilator function in cutaneous microvessels

Abstract

Ageing is associated with impaired endothelium-derived nitric oxide (NO) function in human microvessels. We investigated the impact of cardiorespiratory fitness and exercise training on physiological and pharmacological NO-mediated microvascular responses in older subjects. NO-mediated vasodilatation was examined in young, older sedentary and older fit subjects who had two microdialysis fibres embedded into the skin on the ventral aspect of the forearm and laser Doppler probes placed over these sites. Both sites were then heated to 42 degrees C, with Ringer solution infused in one probe and N-nitro-L-arginine methyl ester (L-NAME) through the second. In another study, three doses of ACh were infused in the presence or absence of L-NAME in similar subjects. The older sedentary subjects then undertook exercise training, with repeat studies at 12 and 24 weeks. The NO component of the heat-induced rise in cutaneous vascular conductance (CVC) was diminished in the older sedentary subjects after 30 min of prolonged heating at 42 degrees C (26.9 +/- 3.9%CVC(max)), compared to older fit (46.2 +/- 7.0%CVC(max), P < 0.05) and young subjects (41.2 +/- 5.2%CVC(max), P < 0.05), whereas exercise training in the older sedentary group enhanced NO-vasodilator function in response to incremental heating (P < 0.05). Similarly, the NO contribution to ACh responses was impaired in the older sedentary versus older fit subjects (low dose 3.2 +/- 1.3 versus 6.6 +/- 1.3%CVC(max); mid dose 11.4 +/- 2.4 versus 21.6 +/- 4.5%CVC(max); high dose 35.2 +/- 6.0 versus 52.6 +/- 7.9%CVC(max), P < 0.05) and training reversed this (12 weeks: 13.7 +/- 3.6, 28.9 +/- 5.3, 56.1 +/- 3.9%CVC(max), P < 0.05). These findings indicate that maintaining a high level of fitness, or undertaking exercise training, prevents age-related decline in indices of physiological and pharmacological microvascular NO-mediated vasodilator function. Since higher levels of NO confer anti-atherogenic benefit, this study has potential implications for the prevention of microvascular dysfunction in humans.

Figure 1. Exercise protocols and representative data

A, experimental protocol indicating the time lines associated with Ringer solution and l-NAME infusion at the microdialysis membrane sites and periods of incremental local heating and prolonged local heating at 42°C. The upper panel presents simultaneously derived data from an individual at the heating sites perfused with Ringer solution (upper trace) and l-NAME (lower trace). B, experimental protocol indicating the time lines associated with incremental doses of acetylcholine (ACh) in the absence or presence of l-NAME infusion at the microdialysis membrane sites. The upper panel presents simultaneously derived data from an individual at the site perfused with ACh alone (upper trace) and ACh in the presence of l-NAME (lower trace).

Figure 2. Time course of response to heating in the presence and absence of nitric oxide blockade

Cutaneous vascular conductance, normalized to intraindividual maximal flow responses (%CVC_max), in the Ringer solution (continuous lines) and l-NAME (dashed lines) infusion sites in young (upper panel ▴), older sedentary (middle panel ♦) and older fit subjects (lower panel ▪) in response to incremental heating to 42°C (0–90 min) and prolonged local heating at 42°C (90–120 min). At both the Ringer solution and l-NAME sites, data did not differ prior to local heating, but rose steadily and significantly in all groups at the end of the incremental and prolonged phases (P < 0.001, all groups). Significant differences existed between the Ringer solution and l-NAME sites for all groups by 2-way ANOVA (P < 0.001).

Figure 3. Comparison of responses at baseline, peak and prolonged heating

A, NO contribution data at baseline, peak heating (42°C) and prolonged heating (30 min at 42°C) for each of the three subjects groups. Contribution of NO to SkBF responses in young, older sedentary and older fit subjects was calculated for each subject at each data point by subtracting l-NAME %CVC data from Ringer solution %CVC data at the same time point and skin temperature. A significant difference (2-way ANOVA) was evident between the OF and OS groups (P < 0.05) and the OS and Y groups (P < 0.005), whereas no difference existed between the OF and Y groups. B, the data from panel A presented as the change in NO contribution between the attainment of peak heating (90 min) and following 30 min prolonged heating at 42°C. The NO contribution to %CVC at 42°C declined significantly in the OS group (P < 0.001), but not in either the OF or the Y groups and significant differences existed between the groups (OS versus OF, P < 0.05; OS versus Y, P < 0.01; OF versus Y, NS).

Figure 4. Dose–response curves to acetylcholine in the absence and presence of nitric oxide blockade

Cutaneous vascular conductance, normalized to intraindividual maximal flow responses (%CVC_max), in the acetylcholine infusion site (upper panel; continuous lines) and simultaneously infused site which received simultaneous and identical ACh doses in the presence of l-NAME (middle panel; dashed lines). Older sedentary (♦), older fit (▪) and young subjects (▴) are represented in each panel. ACh infusion increased %CVC responses significantly more in the OF and Y (P < 0.05) than in the OS group. The lower composite panel reflects the contribution of NO to skin blood flow responses, calculated for each subject at each data point by subtracting l-NAME %CVC data from Ringer solution %CVC data at the same time-point. The NO contribution to ACh was greater in both the OF and Y (P < 0.05) than the OS group.

Figure 5. Effects of exercise training on heating responses: Impact of nitric oxide blockade

The impact of 12 (◊ dashed lines) and 24 weeks (◊ continuous line) of exercise training in older sedentary subjects, compared to data collected at entry to the study (♦ continuous line), on the NO contribution to %CVC responses (lower panel), calculated for each subject at each data point by subtracting l-NAME %CVC data (middle panel) from Ringer solution %CVC data (upper panel) at the same time points and skin temperatures. Whilst training did not modify %CVC at the Ringer solution site, the impact of l-NAME and the contribution of NO to %CVC responses were significantly greater after training (P < 0.05) at both 12 and 24 weeks. This abolished the initial difference that existed between the old sedentary and older fit subjects (see Fig. 2).

Figure 6. Effects of exercise training on acetylcholine responses: impact of nitric oxide blockade

The impact of 12 (◊ dashed lines) and 24 weeks (◊ continuous line) of exercise training in older sedentary subjects, compared to data collected at entry to the study (♦ continuous line), on the NO contribution to %CVC responses (lower panel), calculated for each subject at each data point by subtracting l-NAME %CVC data (middle panel) from Ringer solution %CVC data (upper panel) at equivalent doses of ACh. Training significantly increased %CVC in response to ACh at both 12 and 24 weeks (P < 0.05, 2-way ANOVA baseline versus 12 versus 24 weeks) and the contribution of NO to the ACh response was significantly greater after training (P < 0.05). This abolished the initial difference that existed between the old sedentary and older fit subjects (see Fig. 4).