Ten-day endurance training attenuates the hyperosmotic suppression of cutaneous vasodilation during exercise but not sweating

Abstract

It is well known that hyperosmolality suppresses thermoregulatory responses and that plasma osmolality (P(osmol)) increases with exercise intensity. We examined whether the decreased esophageal temperature thresholds for cutaneous vasodilation (TH(FVC)) and sweating (TH(SR)) after 10-day endurance training (ET) are caused by either attenuated increase in P(osmol) at a given exercise intensity or blunted sensitivity of hyperosmotic suppression. Nine young male volunteers exercised on a cycle ergometer at 60% peak oxygen consumption rate (V(O2 peak)) for 1 h/day for 10 days at 30 degrees C. Before and after ET, thermoregulatory responses were measured during 20-min exercise at pretraining 70% V(O2 peak) in the same environment as during ET under isoosmotic or hyperosmotic conditions. Hyperosmolality by approximately 10 mosmol/kgH2O was attained by acute hypertonic saline infusion. After ET, V(O2 peak) and blood volume (BV) both increased by approximately 4% (P < 0.05), followed by a decrease in TH(FVC) (P < 0.05) but not by that in TH(SR). Although there was no significant decrease in P(osmol) at the thresholds after ET, the sensitivity of increase in TH(FVC) at a given increase in P(osmol) [deltaTH(FVC)/deltaP(osmol), degrees C x (mosmol/kgH2O)(-1)], determined by hypertonic infusion, was reduced to 0.021 +/- 0.005 from 0.039 +/- 0.004 before ET (P < 0.05). The individual reductions in deltaTH(FVC)/deltaP(osmol) after ET were highly correlated with their increases in BV around TH(FVC) (r = -0.89, P < 0.005). In contrast, there was no alteration in the sensitivity of the hyperosmotic suppression of sweating after ET. Thus the downward shift of TH(FVC) after ET was partially explained by the blunted sensitivity to hyperosmolality, which occurred in proportion to the increase in BV.

Body Temperature Regulation During Exercise and Hyperthermia in Diabetics

“…It also improves the responses of SkBF and sweat rate to increased core body temperature during exercise [11,16,17]. Indeed, an increase in cardiac stroke volume and also the sensitivity of increase in SkBF to increased T es during exercise in a warm condition (T a , 30°C) was closely correlated to a PV expansion by a 10-day endurance training (60% VO 2max for 1 h/day at 30°C) [28]. Additionally, Goto et al [43] reported the influences of protein and carbohydrate (CHO) supplementation just after exercise (Pro-CHO; 0.36 g protein/kg and 3.6 kcal) during the 5-day training period (70% VO 2max for 30 min/day) in a warm environment (T a , 30°C) on PV and thermoregulatory responses.…”

“…The increased SkBF and sweating responses are characterized by the early start of cutaneous vasodilation and sweating responses to increased T es [28,29] and the increased sensitivity to increase SkBF and sweat rate in response to an increased T es compared with before exercise training [28,29]. It is suggested that the mechanisms of the increase in thermoregulatory responses with exercise training are similar to those following acclimations to repeated heat exposures, including adaptations of the thermoregulatory center and thermoregulatory effectors [1,12] as well as an increase in VO 2max [30] and PV [28,31,32].…”

Heat Illness during Working and Preventive Considerations from Body Fluid Homeostasis

“…5). Since the reduction in each subject was significantly correlated with the increase in PV after training, they suggested that the stretch of baroreceptors due to PV expansion 57,58) was involved in the reduction. However, they also suggested that there was no causal relationship between the reduction in osmotic suppression of cutaneous vasodilation and plasma expansion but they were caused by different mechanisms associated with heat acclimation.…”

“…The increased SkBF and sweating responses are characterized by the low T es threshold for cutaneous vasodilation and sweating 57,58) and their enhanced sensitivity to increased T es 57,59) . The magnitude of adaptation depends on the intensity, duration, and frequency of heat exposures, but the most effective maneuver to acquire the adaptation should include 'exercise in the heat' 56) .…”

“…These results suggest that the hyperosmotic suppression of sweating and cutaneous vasodilation was attenuated after heat acclimation with reduced [Na + ] sweat . To examine the hypothesis that the hyperosmotic suppression of cutaneous vasodilation was blunted after endurance training, Ichinose et al 58) measured SkBF and local SR responses to 20-min cycle ergometer exercise at 70% VO 2max in a warm environment of 30°C of T a and 50% r.h. in isoosmotic and hyperosmotic conditions, and compared the results before and after training. They suggested that the upward shift of T es threshold for cutaneous vasodilation at a given increase in P osmol was reduced after training whereas that for sweating remained unchanged (Fig.…”