Oestrogen and progesterone change the binding characteristics of alpha-adrenergic and serotonin receptors on rabbit platelets.

The binding characteristics of the alpha-adrenergic and serotonin receptors on intact rabbit platelets were identified using [3H]-dihydroergocryptine and [3H]-5-hydroxytryptamine respectively. In untreated female rabbits a single slpha-adrenoceptor and two serotonin receptors were identified with ligand affinities similar to those in human platelets. The effects of oestrogen and/or progesterone on the alpha-adrenergic and serotonin receptors of rabbit platelets were studied. Oestrogen alone increased the capacity of serotonin receptors but reduced that of the alpha-adrenoceptor. Oestrogen plus progesterone reduced the capacity of both receptors and reduced the affinity of the alpha-adrenoceptor. The possible mechanisms of the steroid-induced changes and the implications of these with regard to the effects of the oral contraceptive pill are discussed.