The Influence of Intra-arterial Administration of Histamine upon the Circulating Leukocytes of Man

1. The leukocyte content of femoral arterial and venous blood was determined simultaneously following the administration of 0.1 to 0.3 mg. of histamine (as base) directly into the femoral artery in 5 patients at rates varying from 1.1 to 6.7 µg. per second.

2. A marked and prompt decrease in leukocyte number was found in the blood from the femoral vein of the same leg after the histamine infusion started; this preceded the changes in the blood from the femoral artery.

3. The discrepancy between the venous and arterial counts indicates the withdrawal of leukocytes within the circulation of the lower extremity which is generally related to the rate and amount of histamine administered.

4. In 6 patients, histamine (0.15 to 0.4 mg.) was administered directly into the aorta at levels from T₃ to L₂. In five of nine instances, blood from the pulmonary artery or inferior vena cava initially showed a prompt fall in leukocyte number, which exceeded the leukopenia observed in blood sampled from the aorta. In two instances, the leukocyte counts from the aorta exhibited no significant change.

5. The venous leukopenia following the administration of histamine into the aorta probably occurs as a result of sequestration of leukocytes in the peripheral capillaries which accompanies the arterial leukopenia due to a similar effect in the pulmonary circulation.