Endogenous and exogenous regulation of human alpha- and beta-adrenergic receptors

Regulation of human beta 2-adrenergic receptors in lymphocytes (determined by (+/-)-125iodocyanopindolol (ICYP) binding) and alpha 2-adrenergic receptors in platelets (determined by 3H-yohimbine binding) was studied. While beta 2-adrenergic receptor number did not change with age, a significant negative correlation between the number of alpha 2-adrenergic receptors and age was found; plasma catecholamines, on the contrary, were elevated in the elderly. In healthy women during normal menstrual cycle the number of alpha 2-adrenergic receptors decreased with increasing plasma estradiol levels. Incubation of lymphocyte membranes with isoprenaline (100 microM) and of platelet membranes with clonidine (1-100 microM) led to a reduction of the number of beta 2- and alpha 2-receptors, respectively, without changes in the KD-values. Treatment of hypertensive patients with clonidine (3x150 micrograms/die) for 7 days reduced the number of alpha 2-adrenergic receptors in platelets. In platelet membranes from such treated patients inhibition of 3H-yohimbine binding by clonidine and adrenaline was not affected by 10(-4)M GTP. It is concluded, that human alpha- and beta-adrenergic receptors undergo regulatory mechanisms similar to those recently described for adrenergic receptors in a variety of animal models.