Catecholamine Binding Protein: Binding of Tritium to a Specific Protein Fraction of Human Plasma following in vitro Incubation with Tritiated Noradrenaline

Abstract

MANY investigators have shown that catecholamines are unusually stable in whole blood^1,2. The persistence of catecholamines in blood has variously been attributed to non-specific absorption by erythrocytes³, platelets⁴, phospholipids⁵ and albumin (Cohen-Fraction V)⁶. Bovine adrenal glands perfused with acetylcholine containing Locke's solution have been shown to release catecholamines and a specific protein into the perfusate⁷, and recent work utilizing tritiated noradrenaline has demonstrated that intravenously administered catecholamines are removed from the circulation in at least two stages: an initial rapid phase causing disappearance of 60–70 per cent of a given dose within 2 min and a slow phase lasting several hours⁸. These data suggest that under physiological conditions circulating catecholamines may bind to formed blood elements and thereby become temporarily unavailable for biotransformation. The present investigation was undertaken to determine whether circulating catecholamines were bound to a specific protein component of plasma (catecholamine binding protein) in a manner analogous to corticosteroid binding globulin⁹ or thyroxine binding globulin¹⁰.