α₂-Adrenergic receptor levels in obstructive and spastic Raynaud's syndrome

The present study examines the hypothesis that alterations in the activity of α₂-adrenergic receptors (A₂R) may underlie the clinical vasospasm seen in patients with Raynaud's syndrome. Platelets were isolated from 13 normal subjects, from 50 patients with vasospastic Raynaud's syndrome, and from 20 patients with obstructive Raynaud's syndrome and A₂R levels measured. Binding capacity as determined in femtomoles per milligram of protein (fmol/mg of protein) and affinity were measured by Scatchard plot analysis. In a separate experiment normal human platelets were incubated with either buffer, normal serum, or serum from patients with spastic Raynaud's syndrome and A₂R levels were measured. A₂R levels in normal subjects averaged 112 ± 18 fmol/mg; in the patients with spastic Raynaud's syndrome, 191 ± 14 fmol/mg, p < 0.01; and in the patients with obstructive Raynaud's syndrome, 164 ± 31 fmol/mg, p > 0.05 (ns). Of the patients with spastic Raynaud's syndrome, 26% had values that were less than the mean value of the normal subjects (69 ± 7 fmol/mg, p < 0.05). The A₂R levels decreased after incubation with serum from patients who had spastic Raynaud's syndrome by 17.4 ± 3.1 fmol/mg (p < 0.05). These results indicate that most patients with vasospastic Raynaud's syndrome have increased platelet A₂R levels, which may constitute a primary pathophysiologic abnormality underlying this condition. The presence of subnormal A₂R levels in a portion of the patients and the finding of a decrease in measurable A₂R levels after incubation in serum from patients with spastic Raynaud's syndrome suggests the possibility of receptor modulation as a mechanism for increased cellular receptor synthesis.