Manipulation of blood serotonin and platelets in the rat

Dietary administration of L-tryptophan to rats failed to increase blood platelets. Instead platelet counts were decreased after feeding either a tryptophan-deficient or tryptophan-enriched (10%) diet, but were unchanged in animals on a 1% tryptophan diet. Platelet median volumes were not affected by any of these dietary regimens. As expected these dietary manipulations altered both brain and blood serotonin levels in the direction expected for a substrate dependence of serotonin biosynthesis.