Enhanced cholinergic cutaneous vasodilation in Raynaud's phenomenon.

BACKGROUND Vasodilator function was determined in patients with Raynaud's phenomenon during intra-arterial infusions of the endothelium-dependent and -independent vasodilators, methacholine and sodium nitroprusside, respectively. Reactive hyperemia, induced by 5 minutes of arterial occlusion with exercise, was also measured. METHODS AND RESULTS Total blood flow was measured in the fingertip and forearm by venous occlusion plethysmography, and blood flow in the forearm skin was determined with laser Doppler flowmetry. Basal fingertip blood flow was not significantly different between control subjects and patients with Raynaud's phenomenon. Infusions of methacholine had no significant effect on fingertip blood flow in control subjects, whereas patients with Raynaud's phenomenon showed a significant increase in fingertip blood flow. Basal total forearm blood flow was significantly lower in patients with Raynaud's phenomenon than in control subjects. Infusions of methacholine and sodium nitroprusside produced dose-related increases in total forearm blood flow that were of similar magnitudes in the two groups, as were the reactive hyperemic responses. Laser Doppler measurements of forearm skin blood flow, however, showed a significantly greater vasodilator response to methacholine in patients with Raynaud's phenomenon than in control subjects. Infusions of sodium nitroprusside produced a relatively small vasodilator response in the skin of the forearm that was smaller than that to methacholine and not significantly different between the two groups. CONCLUSIONS In Raynaud's phenomenon, a greater vasodilator response to infusions of methacholine in the fingertip, where changes in blood flow mainly reflect those of skin, and in the skin of the forearm may reflect increased responsiveness of cutaneous blood vessels to stimulation of the endothelium. The mechanism involved is unclear but may result from a general abnormality of blood vessels in the skin, which is related to the pathophysiology of cutaneous vasospasm.