Comparative effects of polymyxin B and compound 48/80 on histamine metabolism in rat muscle and gastric tissue.

Polymyxin B, administered in vivo, increased histidine decarboxylase (HDC) activity and histamine (HM) concentrations in muscle tissue homogenates and supernatants. When administered in vitro it increased HDC activity and HM concentrations in both muscle and gastric tissue. The stimulatory effect on muscle was similar to that obtained with compound 48/80, but 48/80, unlike polymyxin B, did not affect gastric tissue. In vitro additions of alpha-fluoromethylhistidine inhibited both in vivo and in vitro stimulatory effects of polymyxin B. The results of these studies show that the action of compound 48/80 and of polymyxin B are similar, and that both affect HM synthesis in a manner that requires further elucidation.