Atropine-induced cutaneous vasodilation decreases esophageal temperature during exercise

Four healthy adult males volunteered for this study, which followed informed-consent procedures administered by our local Human Use Committee. Esophageal (Tes) and mean skin (Tsk, eight site) temperatures, forearm sweating rate (ms), metabolism (M), heart rate (HR), and forearm blood flow (FBF) were measured at rest and during forearm blood flow (FBF) were measured at rest and during exercise [55% oxygen consumption (Vo2) peak] during control experiments and after 2 mg im atropine (ATR). Experiments were randomized and separated by at least 72 h. ATR increased heart rate at rest by 15 beats/min and during exercise by 24 beats/min. ATR decreased whole body sweating by 57%. All eight local skin temperatures were higher in ATR than in control. Tsk was 32.6 degrees C in ATR and 31.0 degrees C in control (P less than 0.01). During exercise, ATR increased vasodilation of the forearm compared with control. The slope of FBF to Tes increased over 300% in ATR experiments compared with control (P less than 0.05). The higher sensible heat flux from this vasodilation decreased Tes during exercise, which further decreased sweating. Skin blood flow remained elevated as Tes decreased, suggesting that local vasodilatory factors promoted atropine-induced cutaneous vasodilation.