Retardation of protein synthesis in rat foetal liver on inhibiting rate of histamine formation.

1. The rate of protein synthesis, as gauged by the incorporation of [(14)C]leucine, has been determined in vitro in foetal and 5-day-old rat liver, tissues with respectively high and low histidine decarboxylase activity.2. Incorporation of [(14)C]leucine was considerably faster in foetal liver than in liver of the young.3. Following inhibition of histamine formation by alpha-methyl histidine, a specific inhibitor of histidine decarboxylase, the rate of incorporation of [(14)C]leucine was substantially diminished in foetal but not in liver of the young.4. The retarded incorporation of [(14)C]leucine consequent on inhibition of endogenous histamine formation could not be restored by extracellular histamine, i.e. by adding histamine to foetal liver tissue.5. On complete inhibition of protein synthesis by puromycin in foetal and 5-day-old rat liver the rate of histamine formation was not affected.6. The present observations support the view of endogenous histamine formation, ;nascent histamine', as an essential part of the metabolic machinery in some rapidly growing tissues.