Histamine release induced by immobilization, gentle handling and decapitation from mast cells and its inhibition by nedocromil in rats

The effect of immobilization, gentle handling and decapitation on the level of plasma histamine in Wistar rats was investigated. Mast cell deficient ( Ws/Ws) rats were used to characterize the source of elevated histamine in p lasma by stress, and the effect of nedocromil, a mast cell stabilizer, on h istamine release was assessed in these models in vivo. The plasma histamine concentration of freely moving rats was 93.0 +/- 2.3 pmol/ml. Gentle handl ing produced a transient increase in plasma histamine level by 1.9-fold, wh ereas immobilization resulted in a longer-lasting elevation by 2.6-fold com pared to that in the freely moving rats. Decapitation increased the plasma histamine level by 10- to 16-fold compared with that in the freely moving r ats. No increase in plasma histamine was found in Ws/Ws rats exposed to str ess. Nedocromil inhibited the increase in plasma histamine level induced by stress in a dose-dependent manner. These findings suggest that stress indu ces histamine release from mast cells in Wistar rats and the extent of this histamine release increases with the severity of stress. Nedocromil proved to be a good pharmacological tool to inhibit stress-induced release of med iators from mast cells.