1. α2-Adrenoceptors on blood platelets have been widely used as a model for α-adrenoceptors in less accessible tissues.
2. The effect of oestrogen (200 μg/day intramuscularly) on α2-adrenoceptor number and function was studied in immature female rabbits. α2-Adrenoceptor number was measured in whole platelets, and membrane preparations of forebrain, hindbrain, spleen and kidney by radioligand binding. α2-Adrenoceptor function was examined by measuring platelet aggregation in vitro and circulatory responses to selective α2-adrenoceptor agonists in vivo.
3. Oestrogen treatment resulted in a significant decrease in platelet α2-adrenoceptor number and function. However, no changes were observed either in receptor number in other tissues or in responses to α2-agonists in vivo.
4. The results suggest that oestrogen modulation of rabbit platelet α2-adrenoreceptor number and function may be different from that of brain, kidney and spleen. Caution should be exercised in extrapolating results from platelets to α-adrenoceptors at other sites.