Observations on the Release of Histaminase After 48/80 and Polymyxin B in Sensitized and Unsensitized Rats. ∗

Summary

Neither sensitized nor unsensitized rats consistently released significant amounts of histaminase into the bloodstream after intravenous administration of 48/80 or polymyxin B. Only 30% of unsensitized rats given 48/80 or polymyxin B by the intraperitoneal route showed release into the blood of histamine-destroying activity, and this in small amount. It is concluded that either (1) the intraperitoneal route allows a higher concentration of drug to reach the gut and hence release histaminase or (2) 48/80 and polymyxin B do not consistently release histaminase, in contrast to the effect of anaphylactic shock in rats.