OBJECTIVETo investigate the effect of endogenous histamine on ischemic preconditioning induced cerebral ischemic tolerance in rats.

METHODSWild-type (WT) mice and histidine decarboxylase knock-out (HDC-KO) mice were preconditioned by bilateral carotid artery occlusion (BCCAO) for 6, 10,or 14 min and reperfused for 48 h,then subjected to permanent BCCAO and the survival time of WT and HDC-KO mice subjected to permanent BCCAO was observed. Histamine levels in the hypothalamus, hippocampus, striatum and cortex at 0.5 h,5 h or 48 h after 10 min BCCAO were determined with high-performance liquid chromatography.

RESULTTen minutes ischemic preconditioning significantly prolonged the survival time of WT mice subjected to permanent BCCAO. However,in HDC-KO mice, the ischemic tolerance was not induced with 10 min preconditioning. The histamine levels at 0.5 h or 48 h increased after 10 min preconditioning, but not at 5 h.

CONCLUSIONEndogenous histamine in brain may be an essential mediator in ischemic preconditioning induced cerebral ischemic tolerance.