Effect of Histamine Loading on the Metabolism of 14C‐Histarnine, Administered Intravenously or Orally, in Domestic Animals (Goat and Pig)

Abstract Isotope dilution technique has been used to examine the effect of histamine loading on the metabolism of orally and parenterally administered 14 C‐histamine. 3% and 45% of the radio‐activity was recovered in the urine of goats and pigs, respectively, when only 14 C‐histamine was given orally. In goats the radioactivity was mostly present as unidentified metabolites. In goats, oral loading with 0.9–1.2 g histamine increased the fraction excreted as ImAA on an average from about 5% to 34% whereas the amount of unidentified metabolites was reduced. Independent of the dose given about 30% of orally administered radioactivity was excreted as 14 CO 2 . In pigs a moderate increase in 14 ‐imidazoleacetic acid was observed after oral histamine loading. In contrast to i.v. administered histamine, orally administered histamine was partly excreted as 14 C‐conjugated histamine in the pig. In pigs and goats neither oral nor i.v. histamine loading seemed to have any effect on the fraction excreted in urine as 14 C‐histamine. The only significant effect on histamine catabolism of i.v. loading of histamine was a reduction of the fraction excreted as 14 C‐1.4‐MeHi. However, such loading of histamine in pigs seems to liberate histamine and/or histamine metabolites, since the increments in urinary histamine and histamine metaboiites exceeded the administered dose.