Alpha and Beta Adrenergic Receptor Activity in Circulating Blood Cells of Patients with Idiopathic Orthostatic Hypotension and Pheochromocytoma

Abstract

Alpha and beta adrenergic receptor binding has been studied in circulating blood cells of 22 normal subjects, 6 patients with chronic orthostatic hypotension, and 1 with pheochromocytoma. Binding of the radioligand /³H/ dihydroergocryptine to platelet membranes was used to assess alpha 2 receptors and /³H/ dihydroalprenolol binding to polymorphonuclear leukocyte membranes was utilized to examine beta receptors. The findings were correlated with the results of tests of adrenergic function.

The alpha 2 and beta receptor levels of most normal subjects varied within relatively narrow limits over several months. In patients with idiopathic orthostatic hypotension, marked increases in the number of both types of receptor sites were present. The changes were associated with significant reduction in plasma norepinephrine and exaggerated responses of blood pressure to infused norepinephrine. Chronic treatment of 4 of the patients with the alpha agonist, ergotamine bitartrate, produced significant increases in blood pressure, particularly in the upright position, and marked clinical improvement. Platelet alpha receptor number was reduced to either normal or subnormal levels by ergotamine therapy.

In a patient with pheochromocytoma, alpha and beta receptor number were both low but were restored to normal following surgical cure by adrenalectomy.

The results suggest that circulating levels of plasma catecholamines influence the regulation of both alpha and beta receptors in man and that study of these receptors in peripheral blood cells may provide useful predictive information concerning changes at tissue sites involved in circulatory regulation.