The Effect of Lanthanides and Actinides on Blood Coagulation. I. Evidence for and Properties of a New Serum Thromboplastic Factor*

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Abstract
Thorium in the form of its oxide (thorotrast) in vivo or as the chloride (in vitro) produces a marked clotting defect characterized by poor thromboplastin generation. In plasma Factor V becomes progressively inactivated. The serum also becomes rapidly and progressively unable to support thromboplastin generation. The serum defect, also induced by the related elements neodymium, lanthanum, cerium, neodymium and uranium, involves an entity distinct from any hitherto known clotting factor or intermediate. The factor (thorium vulnerable factor, TVF) is absorbable by BaSO4, elutable by citrate, precipitated at 50 - 60% (NH4)2SO4, is relatively labile, and has been separated from other coagulation factors by physicochemical means. It can be markedly activated by trypsin. The thorium-induced defect can be completely reversed by oxalate or citrate but not by EDTA. An assay procedure for measuring the serum factor, and its variation in health and disease is described in an accompanying communication.