(1) Endotoxins of Shigella flexneri 2b and 2a induced the appearance of a certain amount of HT (5-hydroxytryptamine) in the plasma of rabbits after an intravenous administration of 1-5mg. This was confirmed and estimated using the chromatographic technique and the concentration of HT was estimated as 0.004 to 0.01μg per 1cc of 3 specimens of all 5 plasmas tested 1-2 hours after the admisnistration. In the plasma of all 5 normal rabbits was found no detectable HT.
(2) 5 of 9 test specimens of heparinized plasmas and 3 of 10 test specimens of serum sampled after the administration of 100μg-5mg per kg of Shigella flexneri 2a and 2b to be endotoxin were found definitely to cause platelet-agglutination, whereas all of 12 test specimens of normal plasma and all of 19 test specimens of normal serum showed no effect on platelets.
(3) The appearance of HT in the plasma after the administration of bacterial endotoxin discovered by the present investigation was con sidered to be due to the release of HT from platelets clumped by endotoxin.
The relationship of the release of HT from the platelets, especially from the platelets thrombi on the wall of capillaries, to the ultimate local vasoconstriction, increased permeability, and damage of blood vessel as well as of the adjoining organ, resulting finally in circulatory shock, was newly proposed.