Observations on the histamine forming capacity of mouse tissues and of its potentiation after adrenaline.

1. The histamine forming capacity (h.f.c.) was determined in minced or homogenized skin, lung, skeletal muscle or stomach of mice weighing 18-20 g using radioactive (14)C histidine as substrate and determining the radioactive (14)C histamine formed by conversion to its dibenzenesulphonyl derivative.2. The optimal pH for the formation of histamine was 7.0-7.5 for lung and skin, 6.5-7.5 for skeletal muscle. For stomach a more acid pH was optimal and depended on substrate concentration.3. The formation of histamine increased with an increase of the substrate histidine.4. The formation of histamine was not affected by the presence in the incubation mixture of chlorpromazine, pyridoxal-5-phosphate, non-radioactive histamine or benzene. The addition of aminoguanidine slightly increased the formation in skin, lung and skeletal muscle but not in stomach. The formation was unchanged when incubation was in an atmosphere of nitrogen instead of air.5. H.f.c. for stomach of normally fed mice varied 170-fold. For stomachs of mice unfed for 16 hr, h.f.c. was much lower and it varied only sevenfold.6. Injection of adrenaline into mice increased h.f.c. of the skin, lung and skeletal muscle. With skin tissue a linear log. dose log. response relation was demonstrated. The injection of adrenaline caused however either no or only a slight increase in the h.f.c. of stomach tissue.7. The effect of adrenaline on h.f.c. in skin, lung and skeletal muscle was not abolished by alpha- or beta-adrenergic blocking agents either injected separately or together before the injection of adrenaline.