Thrombocytic and Thrombopenic Factors in Normal Human Serum

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Abstract
Two substances were obtained by fractionation of normal human serum. One fraction increased thrombocytes in the blood of rabbits. Multiple injections sustained thrombocytosis. The second factor decreased thrombocytes in a repetitive pattern. Multiple injections sustained thrombopenia. Both substances were thermolabile at 90[degree]C for 1 minute and thermostabile at 60[degree]c for 30 minutes. Passive transfer showed their disappearance from circulation in 24 hours with stimulation of intrinsic thrombopoietic factors on the 5th day. It is postulated that control of normal mechanism of thrombopoiesis includes at least 3 factors. One stimulates megakaryocyte proliferation, another increases thrombocyte production in megakaryocytes. The third, a thrombopenic factor, controls the number of thrombocytes for physiological requirements.