Metabolism of¹⁴C‐Histamine in Goats and Pigs Treated with Aminoguanidine

Abstract

Abstract The effect of aminoguanidine, an inhibitor of diamine oxidase (E.C. 1.4.3.6.) on the catabolism of 14 C‐histamine has been studied in goats, a species in which oxidative deamination dominates, and pigs, a species in which methylation is the most important route of inactivation. In aminoguanidine treated goats the total 14 C‐imidazoleacetic acid ( 14 C‐ImAA) in urine was reduced from about 70% to about 4% and in pigs from 18% to 2%. In goats the decrease in the formation of 14 C‐ImAA was partly compensated by an increased methylation though the fraction of 14 C‐histamine excreted unchanged was increased tenfold in the last‐mentioned species. In pigs the decrease in 14 C‐ImAA seemed to be fully compensated by increased methylation of histamine. The decrease in the excretion of non‐radioactive 1.4‐MeImAA in pigs and the change in the ratio: 14 C‐1.4‐MeImAA/ 14 C‐1.4‐MeHi in both pigs and goats during aminoguanidine treatment indicated that oxidation of 1.4‐MeHi to 1.4‐MeImAA is partly catalyzed by enzymes sensitive to aminoguanidine. The incomplete inhibition of the 14 C‐ImAA formation during aminoguanidine treatment indicates that enzymes other than diamine oxidase might participate in the oxidation of histamine to ImAA.