A new antagonist of the 5-hydroxytryptamine receptor of blood platelets.

The newly synthesized 1-desoxyfructo-alpha,beta-dehydro-4, 5-dioxotryptamine (M4) inhibited the 5-hydroxytryptamine (5-HT)-induced shape-change reaction of human and rabbit platelets and to a lesser extent the adenosine-3',5'-diphosphate-induced shape-change reaction of rabbit platelets. The 5-HT-antagonism was shown to be of the competitive type in human platelets. In the latter M4 also counteracted the 5-HT-uptake, but was virtually ineffective in releasing 5-HT. Another new derivative of desoxyfructo-5-HT (M5) was a 5-HT-agonist. It is concluded that M4 represents a new class of antagonists of 5-HT-receptors in platelets.