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.

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