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The present study was designed to investigate the role of plasma catecholamines in the regulation of adrenoceptors in human hypertension. Thirty-three patients with newly detected essential hypertension were treated for 4 weeks with either nifedipine (2 x 20 mg/day), hydergine ( 2 x 2 mg/day), or both (20 and 2 mg/day, respectively, twice daily each), which lowered blood pressure equally well. Plasma noradrenaline increased during nifedipine, decreased during hydergine and was unaltered during the combination therapy. Lymphocyte β2-adrenoceptor density decreased by similar amounts, independent of whether blood pressure was normalized by treatment with nifedipine or hydergine. Platelet α2 -adrenoceptor density, however, decreased during nifedipine, slightly increased during hydergine and was unchanged during the combination treatment. We conclude that lymphocyte β2-adrenoceptors of hypertensive patients are not regulated primarily by plasma catecholamines but rather by a distinct factor associated with the extent of blood pressure elevation. The density of platelet α2 -adrenoceptors, however, appears to be dynamically regulated by catecholamines.