BIPHASIC ELEVATION OF PLASMA HISTAMINE-INDUCED BY WATER IMMERSION STRESS, AND THEIR SOURCES IN RATS

The effect of water immersion stress on the plasma concentration of hi stamine, in Wistar and mast cell-deficient (Ws/Ws) rats, was investiga ted. The histamine content of the plasma, skin and gastric mucosa, as well as the level of activity of histidine decarboxylase in the gastri c mucosa, were determined by high performance liquid chromatography (H PLC)-fluorometry. In Wistar rats exposed to water immersion stress for a total of 6 h, an initial, acute, four-fold, transient increase in t he plasma histamine level, followed by a sustained, though lower, elev ation of the plasma histamine level, was observed. The initial acute i ncrease in plasma histamine level was also seen in gastrectomized Wist ar rats exposed to water immersion stress, but not in Ws/Ws rats expos ed to stress. The sustained elevation of the plasma histamine level wa s observed in the Ws/Ws rats. However, in both the gastrectomized Wist ar rats and gastrectomized Ws/Ws rats, the sustained elevation in plas ma histamine level was not observed. The histamine content of the skin of Wistar rats after 15 min or more exposure to water immersion stres s, was 20% lower than that of control rats. The mucosal histamine cont ent of both Wistar rats and Ws/Ws rats, was 20% lower, whereas histidi ne decarboxylase activity in the gastric mucosa was enhanced by two-fo ld, during exposure to stress for 4 h. These findings indicate that wa ter immersion stress causes a biphasic increase in plasma histamine co ncentration in Wistar rats; the initial acute increase in plasma hista mine level originates from mast cells, and the second, sustained incre ase is attributed to enterochromaffin-like cells. (C) 1998 Elsevier Sc ience B.V. All rights reserved.