Body Temperature Regulation During Exercise and Hyperthermia in Diabetics

Thermoregulatory function, that is, heat dissipative responses such as skin blood flow (SkBF) and sweating to an increased body temperature, is critical during physical work or exercise in warm and hot conditions and during hyperthermia. Thermoregulatory function is associated with individual somatotype, fitness level, normal aging, and physiological status and diseases. Individuals with type 2 diabetes have decreased thermoregulatory responses compared with healthy counterparts, characterized by decreased SkBF and sweating. The decreased SkBF and sweating would be associated with the reduction in nitric oxide bioavailability and endothelial functions in skin vasculatures, also with central mechanisms, and so on. Aerobic exercise training and/or acclimation to the heat improve heat dissipative responses in healthy subjects. The effects of exercise training in type 2 diabetics on glycemic control are well established while it remains unclear that high levels of aerobic fitness or exercise training in diabetics improve thermoregulatory function during heat stress

Effects of Gender and Hypovolemia on Sympathetic Neural Responses to Orthostatic Stress

We tested the hypothesis that women have blunted sympathetic neural responses to orthostatic stress compared with men, which may be elicited under hypovolemic conditions. Muscle sympathetic nerve activity (MSNA) and hemodynamics were measured in eight healthy young women and seven men in supine position and during 6 min of 60° head-up tilt (HUT) under normovolemic and hypovolemic conditions (randomly), with ∼4-wk interval. Acute hypovolemia was produced by diuretic (furosemide) administration ∼2 h before testing. Orthostatic tolerance was determined by progressive lower body negative pressure to presyncope. We found that furosemide produced an ∼13% reduction in plasma volume, causing a similar increase in supine MSNA in men and women (mean ± SD of 5 ± 7 vs. 6 ± 5 bursts/min; P = 0.895). MSNA increased during HUT and was greater in the hypovolemic than in the normovolemic condition (32 ± 6 bursts/min in normovolemia vs. 44 ± 15 bursts/min in hypovolemia in men, P = 0.055; 35 ± 9 vs. 45 ± 8 bursts/min in women, P \u3c 0.001); these responses were not different between the genders (gender effect: P = 0.832 and 0.814 in normovolemia and hypovolemia, respectively). Total peripheral resistance increased proportionately with increases in MSNA during HUT; these responses were similar between the genders. However, systolic blood pressure was lower, whereas diastolic blood pressure was similar in women compared with men during HUT, which was associated with a smaller stroke volume or stroke index. Orthostatic tolerance was lower in women, especially under hypovolemic conditions. These results indicate that men and women have comparable sympathetic neural responses during orthostatic stress under normovolemic and hypovolemic conditions. The lower orthostatic tolerance in women is predominantly because of a smaller stroke volume, presumably due to less cardiac filling during orthostasis, especially under hypovolemic conditions, which may overwhelm the vasomotor reserve available for vasoconstriction or precipitate neurally mediated sympathetic withdrawal and syncope

The Impact of Heat Acclimation on Gastrointestinal Function following Endurance Exercise in a Hot Environment

To determine the effects of heat acclimation on gastrointestinal (GI) damage and the gastric emptying (GE) rate following endurance exercise in a hot environment. Fifteen healthy men were divided into two groups: endurance training in hot (HOT, 35 °C, n = 8) or cool (COOL, 18 °C, n = 7) environment. All subjects completed 10 days of endurance training (eight sessions of 60 min continuous exercise at 50% of the maximal oxygen uptake (V·O2max). Subjects completed a heat stress exercise tests (HST, 60 min exercise at 60% V·O2max) to evaluate the plasma intestinal fatty acid-binding protein (I-FABP) level and the GE rate following endurance exercise in a hot environment (35 °C) before (pre-HST) and after (post-HST) the training period. We assessed the GE rate using the 13C-sodium acetate breath test. The core temperature during post-HST exercise decreased significantly in the HOT group compared to the pre-HST (p = 0.004) but not in the COOL group. Both the HOT and COOL groups showed exercise-induced plasma I-FABP elevations in the pre-HST (p = 0.002). Both groups had significantly attenuated exercise-induced I-FABP elevation in the post-HST. However, the reduction of exercise-induced I-FABP elevation was not different significantly between both groups. GE rate following HST did not change between pre- and post-HST in both groups, with no significant difference between two groups in the post-HST. Ten days of endurance training in a hot environment improved thermoregulation, whereas exercise-induced GI damage and delay of GE rate were not further attenuated compared with training in a cool environment