Variations in circulating catecholamines fail to alter human platelet alpha-2-adrenergic receptor number or affinity for [3H]yohimbine or [3H]dihydroergocryptine.

Abstract

Abstract. A series of studies were performed to determine the relationship between physiologic levels of circulating plasma norepinephrine and epinephrine and human platelet alpha-2 binding site number and the affinity (KD) of these sites for antagonist radioligands. In one study, alpha-2-adrenergic binding site number and affinity were compared using both were significantly changed in six normal subjects when plasma norepinephrine levels increased during oral administration of prazosin for 1 wk. Thus, in a crosssectional analysis and after a change in plasma catecholamine concentrations, there was no relationship in normal subjects between platelet alpha-2 binding site number or affinity of these sites for antagonist radioligands and the circulating catecholamine levels to which the platelets were exposed. 74, September 198474, September , 106374, September -1072 In a group (n = 7) of patients who lack epinephrineinduced platelet aggregation due to abnormal thrombopoiesis, binding site number was decreased (304±36 vs. 572±29 sites/platelet, P < 0.001) and KD tended to be greater (8.69±2.44 vs. 5.40±0.31 nM, P = NS) than in normal subjects (n = 46), despite having similar plasma catecholamine levels. There was no difference in binding site number (491 + 116 sites/platelet) and KD (5.61±0.84 nM) in patients (n = 5) with autonomic insufficiency and low levels of upright plasma norepinephrine when compared with the normal subjects. Two patients were examined before and after the removal of a pheochromocytoma. Their binding site number and KD were normal before the operation and essentially unchanged after the tumor removal and fall of plasma catecholamines.Thus, this study demonstrates that within the physiologic and pathophysiologic range of plasma catecholamines (in men), there is no relationship between the circulating catecholamine concentration and either platelet alpha-2 adrenergic binding site number or the affinity of these sites for antagonist radioligands.

&alpha;-Adrenoceptor Responses of an Isolated Human Artery and Blood Pressure

“…Per haps this finding is to be expected given the narrow range o f values encountered in the present study. Similar find ing have been reported by others [44], and as indicated above, the literature on this point has become confusing.…”

Platelet alpha-2-receptor binding and adenylate cyclase activity in panic disorder

“…However, several studies indicate that circulating levels of plasma catecholamines do not have important regulatory effects on platelet alpha-2-receptor density (Snavely et al 1982;Pfeifer et al 1984;Egan et al 1985).…”

Decreased High Affinity State in Plateletα2-Adrenoceptors from Diabetic Patients with Orthostatic Hypotension

“…The present results agree with some data from Abrahm et al (14) who found that mean basal plasma norepinephrine levels were not different in the four groups studied (diabetic patients with autonomic neuropathy and orthostatic hypotension (group 1) or without orthostatic hypotension (group 2), diabetic patients without autonomic neuropathy (group 3) and normal subjects (group 4). Moreover, these authors, as did Pfeifer et al (13), indicated that there was no relationship between orthostasis and norepinephrine. In contrast, Hilsted et al (6) did find such a relationship.…”

“…In diabetes mellitus, conflicting results were obtained since either no change (13) or a decrease (14) in total platelet « 2 -adrenoceptor number were reported.…”