ROLE OF SEROTONIN AND PROSTAGLANDINS IN BRAIN EDEMA INDUCED BY HEAT-STRESS - AN EXPERIMENTAL-STUDY IN THE YOUNG-RAT

The possibility that serotonin and prostaglandins participate in edema formation following heat stress (HS) was examined in young rats. Expo sure of conscious young animals (8-9 weeks old) to heat at 38-degrees- C in a biological oxygen demand (BOD) incubator (relative humidity 50- 55%; wind velocity 20-25 cm/s) for 4 h resulted in marked increase in the whole brain water content (about 3%) as compared to animals kept a t room temperature (21-degrees-C). A marked extravasation of Evans blu e and I-131-sodium occurred in the brain of heat exposed animals as co mpared to normal animals. Morphological examination using electron mic roscopy of selected brain regions of heat stressed animals showed prof ound cell changes. Thus perivascular edema, swollen neuronal and glial cells, membrane damage, vesiculation of myelin, axonal swelling and s ynaptic damage was frequent in this group of untreated animals. Pretre atment with ketanserin (a selective serotonin2 receptor antagonist) or indomethacin (an inhibitor of prostaglandin synthesis) markedly reduc ed edema formation after 4 h HS in young animals. These heat stressed animals had considerably less extravasation of protein tracers as comp ared to the untreated group. Cell changes and edema at the ultrastruct ural level were mainly absent. Our results suggest that serotonin and prostaglandins are involved in heat stress induced breakdown of the BB B permeability, edema formation, and cell damage.