Platelets XVIII. Relationship of Platelets to Activity of 5-hydroxytryptamine Creatinine Sulfate.

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Abstract
1. 5-hydroxytryptamine cre-atinine sulfate (5-HT) administered intravenously causes significant elevation of the local venous pressure at doses as small as 0.3 γ/min. This effect is not affected by short-time incubation with fresh serum, platelet-rich and platelet-poor plasma. Incubation for 16 hours causes destruction of 5-HT activity. 2. Activity of 5-HT also disappears after incubation for 16 hours with suspensions of washed platelets. Some of the activity, however, can be recovered after total disruption of thrombocytes. Also a protein solution from human platelets exhibits significant venopres-sor activity, while intact platelets are inactive. 3. These findings suggest: (a) presence of natural 5-HT or of substances with veno-pressor effect in human platelets; (b) absorption of 5-HT by platelets upon incubation; (c) strong bondage between 5-HT and platelet constituents.