Non-mast cell histamine levels in rat tissues after histidine loading.

The i.p. administration of L-histidine in doses of 500 and 1000 mg/kg, caused prolonged high levels of histidine but did not influence the levels of histamine in the non-mast cell tissues such as the stomach, lungs and liver in the rat. After polymyxin B or 48/80 treatments as well as in anaphylaxis, the levels of histamine in the lungs and liver were greatly reduced but histidine administration failed to alter noticeably the concentrations of histamine in these organs. Similarly, the low contents of histamine in the stomach of 48/50-treated or polymyxin B-treated rats remained unchanged in the presence of excess histidine. Histidine loadings however produced a marked increase in histidine decarboxylase activity of the glandular stomach and a simultaneous elevation in the serum histamine concentrations. Results suggest that the increased level of serum histamine is the consequence of the increased activity of histidine decarboxylase in the tissues and a rapid elimination of the newly formed histamine into the blood. This led us to consider that the flux rather than the formation of histamine might be regulatory for the actual concentration of the non-mast cell histamine, especially in stomach tissue.