Activation of sensory nerves participates in stress-induced histamine release from mast cells in rats

To elucidate the mechanism by which stress induces rapid histamine release from mast cells, Wistar rats, pretreated as neonates with capsaicin, were s ubjected to immobilization stress for 2 h, and histamine release was measur ed in paws of anesthetized rats by using in vivo microdialysis after activa tion of sensory nerves by electrical or chemical stimulation. Immobilizatio n stress studies indicated that in control rats stress induced a 2.7-fold i ncrease in the level of plasma histamine compared to that in freely moving rats. Whereas pretreatment with capsaicin significantly decreased stress-in duced elevation of plasma histamine. Microdialysis studies showed that elec trical stimulation of the sciatic nerve resulted in a 4-fold increase of hi stamine release in rat paws. However, this increase was significantly inhib ited in rats pretreated with capsaicin. Furthermore, injection of capsaicin into rat paw significantly increased histamine release in a dose-dependent manner. These results suggest that activation of sensory nerves participat es in stress-induced histamine release from mast cells. (C) 1999 Elsevier S cience Ireland Ltd. All rights reserved.