Functional significance of the platelet alpha2-adrenoceptor: studies in patients with myeloproliferative disorders.

Platelet alpha-adrenoceptor status was examined in 35 patients with myeloproliferative disorders (MPD) and 35 normal controls by means of radioligand binding studies with 3H-yohimbine (3H-YOH) and in vitro platelet function tests. A group of 'adrenaline insensitive' MPD patients identified in the functional studies were found to be identical to normal controls and other MPD patients with respect to their alpha 2-adrenoceptor status as assessed by the binding studies. Possible explanations for the dissociation between radioligand binding studies and functional responses in the platelet are discussed.