Age-dependent decrease of alpha 2-adrenergic receptor number in human platelets.

In 36 healthy subjects of various ages (14-76 years) the number of alpha 2-adrenergic receptors in platelets - as determined by [3H]yohimbine binding - and plasma catecholamine levels were measured. A highly significant negative correlation (r = -0.666, P less than 0.001) between the number of alpha 2-adrenergic receptors and age was found; on the contrary, plasma catecholamine concentrations increased with increasing age. Thus, reduced responses in the elderly to adrenergic stimuli may be due to reduced number of adrenergic receptors.