The effect of acute intradermal administration of ascorbate on heat loss responses in older adults with uncomplicated controlled hypertension

Abstract

Nitric oxide synthase (NOS) contributes to the heat loss responses of cutaneous vasodilatation and sweating during exercise. However, the contribution of NOS may be attenuated in individuals with uncomplicated, controlled hypertension due to elevated oxidative stress, which can reduce NO bioavailability. We evaluated the hypothesis that the acute local intradermal administration of the antioxidant ascorbate would enhance cutaneous vasodilatation and sweating via NOS-dependent mechanisms during an exercise-heat stress in adults with hypertension. Habitually active adults who were normotensive (n = 14, 7 females, 62 ± 4 years) or had uncomplicated, controlled hypertension (n = 13, 6 females, 62 ± 5 years) performed 30 min of moderate-intensity (50% of their pre-determined peak oxygen uptake) semi-recumbent cycling in the heat (35 • C, 20% relative humidity). Cutaneous vascular conductance (CVC) and sweat rate were assessed at four forearm skin sites continuously perfused with (1) lactated Ringer solution (Control), (2) 10 mM antioxidant ascorbate, (3) 10 mM N G -nitro-Larginine methyl ester (L-NAME), a non-selective NOS inhibitor, or (4) a combination of ascorbate and L-NAME. Relative to Control, no effect of ascorbate was observed on CVC or sweating in either group (P = 0.619). However, L-NAME reduced CVC relative to Control in both groups (P ≤ 0.038). No effect of any treatment on sweating was observed (P ≥ 0.306). Thus, acute local administration of ascorbate to forearm skin does not enhance the activation of heat loss responses of cutaneous vasodilatation and sweating in older adults, and those with hypertension during an exercise-heat stress.

The effect of taurine supplementation on physiological and thermoregulatory responses in humans during rest and exercise in hot environmental conditions

“…These effects could be directly extended to sudomotor function, based on the reported relationships between systemic markers of lipid peroxidation and sweat production (Hoeldtke et al, 2011). However, further research is needed to explore this possibility, owing to the failure of local anti-oxidant infusion to acutely alter the local sweating response during exercise-heat stress (Fujii et al, 2022), which questions the likelihood that anti-oxidants play a major role in thermoregulatory sweating. Indeed, a greater sweating response was not observed for the majority of these supplements.…”