Role of histamine in pathophysiology of heat stress in rats.

Role of histamine in pathophysiology of heat stress (HS) was examined using a pharmacological approach. Subjection of young animals (6-7 wks old) to HS at 38 degrees C for 4 in a B.O.D. incubator resulted in a profound increase in blood-brain barrier (BBB) permeability to Evans blue albumin (EBA) and 131I-sodium by 375% and 478% from the control values respectively. At this time period, the brain water content showed a 3.6% increase from the control. Pretreatment with histamine H2 receptor antagonist cimetidine significantly reduced the extravasation of both the tracers and thwarted the increase of brain water content as compared to the untreated group. On the other hand, pretreatment with histamine H1 antagonist mepyramine failed to reduce these parameters. On the contrary, there was a significantly higher permeation of the tracers in brain along with a greater accumulation of brain water content as compared to the untreated group. These results point out a beneficial effect of histamine H2 receptor antagonists in the pathophysiology of HS.