Cutaneous blood flow and local sweating after systemic atropine administration

Localized cutaneous vasodilation (flush) is seen following systemic atropine administration. To verify calculated enhanced dry heat loss with actual changes in cutaneous blood flow, four men were studied in both control and atropine (0.025 mg·kg⁻¹;im) experiments (T _a=30°C,T _dp=7°C) during moderate exercise (55%\(\dot V\)O₂ peak). Esophageal temperature (T _es) and arm sweating (\(\dot m_s \)) by local dewpoint were measured continously. Skin (forearm) blood flow (FBF) was measured twice each minute by venous occlusion plethysmography. Injection of atropine (2 mg) caused an increased sensitivity (+85%,p<0.01) in FBF toT _es with no change in the vasodilator threshold. An elevatedT _es onset (0.3°C,p<0.05) for sweating occurred with no change in the sensitivity of\(\dot m_s \) toT _es (−27%,p<0.20). No elevation in either forearm or\(\bar T_{sk} \) occurred before the onset of vasodilation, however, both mean skin (\(\bar T_{sk} \)) and local arm temperatures were higher in the atropine experiments after 15 min of exercise. Systemic atropine resulted in higher cutaneous vasodilation at the same core temperature with the local skin temperature following passively. The effect of systemic atropine in stimulation of increased cutaneous vasodilation is suggested to result by a combination of central and local responses which may be mediated through the release of vasoactive sustances.