Comparative metabolism of histamine in two Amphibia anura

The metabolism of histamine has been compared in Rana ridibunda and Discoglossus pictus, both Amphibia anura. An intralymphatic injection of 14C-histamine (5 microCi) was administered to the animals and the total radioactivity excreted in the urine was measured 24, 48, and 72 hours later. The metabolites excreted in the urine at 24 hours were analyzed by thin-layer chromatography and subsequent autoradiography. In both species approximately 60--70% of the injected dose was found in the urine by 72 hours. In Rana ridibunda two histamine metabolites were found: imidazoleacetic and methylimidazoleacetic acid. The present results suggest that the catabolism of histamine differs in the two species.