Histidine and histamine metabolism in rat enterocytes.

To study the metabolic fate of L-histidine and histamine in rat isolated enterocytes, enterocytes were incubated in the presence of 0.1 mM L-[U-14C] histidine. At the rate of 11.1 +/- 2.7 pmol/10(6) cells/30 min, the amino acid was incorporated into cellular proteins. 80 microM cycloheximide, i.e. a protein synthesis inhibitor, inhibited this incorporation by 70 +/- 17%. L-histidine was used for cellular protein synthesis which depended on time and concentration. 0.1 mM L-[U-14C] histidine was little oxidized by intestinal cells, i.e. 0.12 +/- 0.06 pmol/10(6) cells/30 min, and was not converted into histamine. When 10 mM histamine was added to the incubation medium, it completely inhibited the incorporation of 0.1 mM [1,4-14C] putrescine into isolated enterocytes. In enterocyte homogenates, this corresponded to inhibition by histamine of putrescine incorporation as catalyzed by transglutaminase activity. Since histamine incorporation into TCA-precipitable material derived from enterocyte homogenates depended on time and concentration, we concluded that exogenous, but not de novo-formed histamine was able to compete with putrescine incorporation into enterocytes as catalyzed by transglutaminase activity.