Metabolism of ¹⁴C‐Histamine in Domestic Animals

Abstract

Abstract The metabolism of 14 C‐histamine injected i.v. in 3 ruminant species (goat, sheep, and cow) has been studied previously. In the present study isotope dilution‐ and paper chromatographic techniques were used to examine urinary 14 C‐metabolites of i.v. injected 14 C‐histamine in the horse and the pig. The urine excreted the first 24 hrs after injection accounted for 64–76 % and 81–91 % of the radioactivity injected in horses and pigs, respectively. Less than 2 % of the injected radioactivity could be accounted for in the feces excreted the first week after injection. Known metabolites in the first 24 hr urine on an average accounted for about 94 % and 103 % of the urinary radioactivity in horses and pigs, respectively. Methylation of his‐tamine to 1.4‐methylhistamine and further oxidation to 1.4‐methylimidazoleacetic acid was quantitatively the most important pathway for histamine degradation, accounting on an average for about 63 % and 76 % of the radioactivity in horse and pig urine, respectively. The horse and the pig seemed to metabolize histamine in quite a similar way which again was quite different from that previously found in the ruminants in which oxidative deamination of histamine to imidazoleacetic acid was the only pathway of quantitative importance. As in ruminants histaminol seemed to be a metabolite of i.v. injected histamine accounting for about 2 % of the urinary radioactivity. The specific radioactivity of histamine was about tenfold larger than for 1.4‐methylmidazoleacetic acid, in horses and pigs.