Isometric handgrip exercise-induced muscarinic vasodilation in the human skin microvasculature

The existence of an active vasodilator system in the human skin microvasculature is well documented, but its physiological role and the underlying mechanisms are not completely understood. Cutaneous blood flow increases during isometric handgrip exercise. To examine whether this response is mediated by active vasodilation, isometric handgrip exercise testing was performed in nine healthy subjects. Local iontophoresis of atropine was applied to the forearm skin. Skin blood flow (SBF) monitoring by means of laser Doppler flowmetry was combined with continuous noninvasive blood pressure monitoring. SBF monitoring was performed at a site pretreated with atropine and an adjacent control area. Mean arterial pressure (MAP) was recorded noninvasively. Cutaneous vascular resistance (CVR) was calculated as MAP/SBF for the atropine treated and the control areas. Changes in CVR were expressed as percent deviation from the baseline (dCVR). Isometric handgrip exercise resulted in a marked reduction in CVR at the control site (dCVR: -66 +/- 4%). In contrast, the CVR was not significantly altered at the atropinetreated site (2.4 +/- 7%). It is concluded that isometric exercise induces an atropine-sensitive vasodilation which is mediated by muscarinic receptors in the human skin.