1. α2-Adrenoceptors on platelet membranes and β2-adrenoceptors on lymphocytes were studied in 24 patients with primary Raynaud's phenomenon and in 24 age- and sex-matched control subjects. In two subgroups, a standardized mental arithmetic test and a finger-cooling test were performed.
2. Baseline blood pressure, heart rate and forearm blood flow did not differ between the two groups.
3. Baseline skin microcirculation (laser Doppler flux) was decreased in primary Raynaud's phenomenon (19 ± 15 arbitrary units) compared with control subjects (33 ± 14 arbitrary units) (P <0.01).
4. Baseline plasma noradrenaline concentration (2.0011.44 versus 1.16 ± 0.36 nmol/l) and α2-adrenoceptor density (301 ± 119 versus 210 ± 82 fmol/mg) were increased in patients with primary Raynaud's phenomenon in comparison with the control subjects. The α2-adrenoceptor density/β2-adrenoceptor density ratio in patients with primary Raynaud's phenomenon was, with a value of 0.37 ± 0.04, higher than in the control subjects, where a value of 0.25 ± 0.02 was measured (P <0.001). Plasma adrenaline concentration, β2-adrenoceptor density and the antagonist affinity to both receptor subtypes did not differ between both groups under baseline conditions.
5. Whereas during the finger-cooling test no differences were seen in the responses of the parameters measured, the mental arithmetic test induced an increase in laser Doppler flux in patients with primary Raynaud's phenomenon and a decrease in the control group. The increase of plasma noradrenaline concentration during the mental arithmetic test was only statistically significant in the control group.
6. The results are discussed in relation to the two common theories concerning the aetiology of primary Raynaud's phenomenon: a local vascular defect and a primary sympathetic hyperfunction.