Thermoregulatory responses are decreased by carbohydrate ingestion through hyperosmotic suppression while the effects were attenuated by insulin in passively heated men

Abstract

Plasma hyperosmolality with thermal sweating or hypertonic saline infusion increases esophageal temperature (Tes) threshold for sweating and cutaneous vasodilation. We assessed whether plasma hyperosmolality with carbohydrate (CHO) ingestion increased Tes threshold. Furthermore, we assessed the effects of insulin secreted with CHO ingestion which was known to modify the sensitivity of thermo‐sensitive neurons on Tes threshold.MethodsSeven healthy young men performed three trials in a sitting position in an artificial climate chamber (28°C of Ta, 40% of RH). After 10 min baseline, subjects drank water (CNT; water 300 ml), glucose (GLU; water 300 ml + glucose 75 g), or fructose solution (FRU; water 300 ml + fructose 75 g). Twenty min later, they were heated passively (lower legs immersion in 42°C water) for 60 min. Plasma insulin concentration ([Ins]p), plasma osmolality (Posm), percent change in plasma volume (%ΔPV), Tes, sweat rate and cutaneous vascular conductance at forearm and chest were measured.ResultsPosm in GLU and FRU were equally higher than CNT, though there was no difference in %ΔPV among trials. [Ins]p was higher in GLU than CNT and FRU. Tes threshold for cutaneous vasodilation was higher in FRU than CNT and GLU, while similar in CNT and GLU.ConclusionThermoregulatory responses are decreased after CHO ingestion via hyperosmotic suppression, while the effects were attenuated by insulin.