Plasma Thrombopoietic Activity in Humans With Normal and Abnormal Platelet Counts

Abstract

Although much experimental evidence suggests the presence of a humoral stimulator of thrombopoiesis, relatively few human studies have been done to determine the presence of such a stimulator in disorders of thrombopoiesis. Human plasma fractions from patients with normal and abnormal platelet counts were tested for thrombopoietic stimulatory or inhibitory activity in a mouse bioassay system by measuring the incorporation of 75Se-methionine into platelets of mice injected with plasma fractions. Twenty-two patients with normal platelet counts had no evidence of stimulatory activity in plasma, except for one postoperative patient. Fifty-three percent of 17 patients with thrombocytosis had increased stimulatory activity, and 33% of patients with thrombocytopenia had such activity in plasma. Inhibitory activity in plasma was found in 4 patients with normal platelet counts, 7 with thrombocytopenia, and none with thrombocytosis. A hypothesis based on the presence of both stimulatory and inhibitory factors in plasma is advanced to explain the humoral control mechanisms in normal patients and in patients with abnormal platelet counts of diverse etiology.