Endogenous and Exogenous Regulation of Human α- and β-Adrenergic Receptors |
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Abstract: | AbstractRegulation of human β2-adrenergic receptors in lymphocytes (determined by (±)-125 iodocyanopindolol (ICYP) binding) and α2-adrenergic receptors in platelets (determined by 3H-yohimbine binding) was studied. While α2-adrenergic receptor number did not change with age, a significant negative correlation between the number of α2-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 α2-adrenergic receptors decreased with increasing plasma estradiol levels.Incubation of lymphocyte membranes with isoprenaline (100 μM) and of platelet membranes with clonidine (1-100 μM) led to a reduction of the number of β2- and α2-receptors, respectively, without changes in the KD-values. Treatment of hypertensive patients with clonidine (3x150 μg/die) for 7 days reduced the number of α2-adrenergic receptors in platelets. In platelet membranes from such treated patients inhibition of 3H-yohimbine binding by clonidine and adrenaline was not affected by 10-4MGTP. It is concluded, that human α- and β-adrenergic receptors undergo regulatory mechanisms similar to those recently described for adrenergic receptors in a variety of animal models. |
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