Histamine release inhibition in anti-inflammatory mechanism

Rats were depleted of skin histamine by more than 80 % by intraperitoneal injections of sinomenine with daily increasing doses for 6 days. In these rats, egg-white edema induced in the hind paws was inhibited by 68 % of control. The weight of the wall of granuloma pouch made by croton oil was also evidently smaller in the rat treated similarly with sinomenine than that of control. This suggests an important role of histamine participating in the inflammation. It has been observed that a variety of non-steroidal anti-inflammatory drugs inhibited both degranulation and histamine release induced by compound 48/80 of mast cells isolated from rat peritoneal fluid. The degranulation inhibiting actions of anti-inflammatory drugs were markedly decreased in the presence of glucose as in cases of dinitrophenol, dicumarol and warfarin which are known uncouplers of oxidative phosphorylation. Also, prevention of edema provoked by anti-rat serum is roughly correlated to a potency of degranulation inhibiting effect of anti-inflammatory agents. These observations suggest that there is a common mechanism between these two phenomena, and the prevention of mast cell degranulation by the anti-inflammatory agents is, at least, partially due to their uncoupling effects. A working hypothesis explaining the process of edema formation at the inflammatory site has. been made based on the data of the present experiment and other ob3ervations: a leakage of plasma into the tissue space from the gap between two adjacent endothelial cells which are contracted by released histamine may activate a kinin-forming system in the plasma, and kinin(s) may further aggravate a leakage. The mechanism of action of anti-inflammatory agents, which interfere with the histamine effect in inflammation, should be understood in twofold: one is prevention of histamine release from the tissue, mainly by inhibiting mast-cell degranulation, and the other is prevention of the contraction of endothial cells by their uncoupling activities.