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

ABSTRACT

NEW FINDINGS: What is the central question of this study? Does acute intradermal administration of the antioxidant ascorbate augment local forearm cutaneous vasodilatation and sweating via nitric oxide synthase (NOS)-dependent mechanisms during exercise-heat stress in older adults with uncomplicated controlled hypertension? What is the main finding and its importance? Relative to the control site, ascorbate had no effect on forearm cutaneous vascular conductance (CVC) and sweat rate, although CVC was reduced with NOS inhibition in older adults with hypertension. Acute local administration of ascorbate to forearm skin does not modulate heat loss responses during exercise-heat stress in older adults with 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 NG -nitro-l-arginine 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.