ALTERED PLATELET ALPHA(2)-ADRENOCEPTORS IN PATIENTS WITH ISCHEMIC-HEART-DISEASE

We evaluated the characteristics of platelet alpha(2)-adrenoceptors in 12 patients with effort angina pectoris, 11 patients with variant ang ina pectoris and 11 normal control subjects. alpha(2)-Adrenoceptors we re quantified using a radioligand binding assay with radiolabelled rau wolscine, an alpha(2)-selective antagonist. In addition, plasma norepi nephrine concentrations were measured by high performance liquid chrom atography. The mean value of the maximal number of binding sites (B-ma x) in patients with effort angina (205.1+/-11.3 fmol/mg protein) was s ignificantly lower than that in control subjects (293.0+/-10.2 fmol/mg protein). B-max did not differ between patients with variant angina ( 322.9+/-45.4 fmol/mg protein) and control subjects. There was no signi ficant difference in the dissociation constant (K-d) among the 3 group s. The plasma norepinephrine concentration tended to be higher in pati ents with effort angina or variant angina than in normal controls, but this difference was not statistically significant. In addition, studi es in another group of young volunteers (n=20) revealed a negative cor relation (r=-0.50, p<0.05) between the B-max of H-3-rauwolscine bindin g to platelets and the percent change in the plasma norepinephrine con centration when subjects moved from the supine to the standing positio n. This suggests a functional correlation between platelet alpha(2)-ad renoceptors and those located at presynaptic sites. If platelet a 2-ad renoceptors correlate with presynaptic alpha(2)-adrenoceptors, the cur rent findings of decreased alpha(2)-adrenoceptor density in platelets from patients with effort angina could represent attenuated negative f eedback of norepinephrine by presynaptic alpha(2)-adrenoceptors.