Impaired microvascular response to cholinergic stimuli in primary Sjogren's syndrome

Objective-Signs of a parasympathetic dysfunction have been revealed in prim ary Sjogren's syndrome (SS). Its role in the pathogenesis and the clinical picture of the disease is not clear. To investigate the responsiveness of S S patients to a cholinergic agonist, a model was used involving examination of the cutaneous microcirculation. The microvascular response to the admin istration of carbachol was measured, a muscarinic cholinergic agonist. Methods-Twenty two SS patients and 12 controls were examined. Carbachol and 0.9% saline solution were administered intracutaneously into the forearm s kin at two distinct places. Skin blood flow (SBF) in the injected areas was measured continuously before and for 10 minutes after the injections by me ans of a laser Doppler perfusion monitor. The increase in SBF in response t o carbachol (dSBF), reflecting vasodilatation, was calculated by a formula including the baseline and the maximum SBF values after the injections of c arbachol and saline solution. Results-The vasodilatation was significantly lower in SS patients than in t he controls (mean dSBF: 2.1 (range: 1.0-4.5) versus 3.3 (range: 1.7-7.6), p = 0.02). With non-responder patients defined as those in whom a smaller re sponse was observed than in any of the controls, 11 of the 22 SS patients p roved to be non-responders to carbachol. Comparisons of demographic, clinic al and laboratory characteristics and HLA class II genotypes between respon der and non-responder SS patients did not show any significant differences. Conclusions-A diminished or absent response to carbachol indicates a cholin ergic dysfunction in SS patients. A disturbance in the neurotransmission at a receptorial or postreceptorial level is hypothesised. Unresponsiveness t o cholinergic stimuli may contribute to exocrine insufficiency.