Effects of low molecular weight fibrin degradation products 6A and 6D on rabbit aorta strips

Two small molecular weight fibrin degradation product, the pentapeptide 6A and the undecapeptide 6D, produced relaxations of norepinephrine-contracted rabbit aorta strips. The relaxations were slow-developing and were elicited by both peptides at supramicromolar concentrations; the amplitude of relaxations were small for 6D. The relaxations induced by 6A were not dependent on the presence of endothelium and were not modified by a mixture of indomethacin, pyrilamine, and cimetidine. The amplitude of the relaxations produced by 6A and 6D increased as a function of incubation time in vitro. In another experimental system, peptides 6A and 6D failed to increase 6-keto-PGF1 alpha release from cultured human umbilical endothelial cells. Histamine and bradykinin were both active in this system.