Desensitization of platelet α₂-adrenoceptors after short term infusions of adrenoceptor agonist in man

1. The effect of intravenous infusion of catecholamines and related drugs on human platelet α₂-adrenoceptor number and function was investgated.

2. Short (60–120 min) infusions of catecholamines with α₂ agonist activity in vivo produced attenuation of the platelet responses to adrenaline in vitro. This desensitization was specific for the adrenaline induced aggregatory response.

3. The maximum number of [³H]yohimbine binding sites on platelets was not altered by adrenaline infusion.

4. The ability of adrenaline to reduce platelet cyclic AMP levels was significantly reduced after the infusions.

5. Acute infusions of α₂-adrenoceptor agonists may alter the coupling of the platelet α₂-adrenoceptor to adenylate cyclase.