Summary
The biochemistry and functionality of platelets from two related subjects (mother
and son) with alpha-2-adrenoceptor-deficient platelets has been evaluated. Radioligand
binding experimentes with the specific alpha-2-adrenergic-receptor antagonist, 3H-yohimbine, showed a drastic reduction of alpha-2-adrenoceptors in platelets from
both subjects in comparison with the control values. Electron microscopy studies revealed
a normal morphology and a normal number of alpha granules and dense bodies. Levels
of adenine nucleotides; 5-hydroxytryptamine; B-thromboglobulin; platelet-factor-4
and thromboxane A2 production were within normal limits.
Platelet aggregation and 5-hydroxytryplamine production in response to adrenalin (at
concentrations up to 50 μM) were absent, whereas ADP, AA, PAF, collagen and thrombin-induced
aggregation, secretion, Ca++ flux and thromboxane A2 production were normal.
The inhibitory effect caused by different concentrations of prostacyclin on Ca++ flux, aggregation, secretion and thromboxane A2 production of platelet functionally lacking of alpha-2-adrenoceptor was not distinguishable
from control platelets and platelets preincubated with yohimbine.
Keywords
Alpha-2-adrenoceptors - Human platelets - Congenital deficiency