MELATONIN PREVENTS ISCHEMIA-REPERFUSION INJURY IN HAMSTER-CHEEK POUCHMICROCIRCULATION

Objective: We used the hamster cheek pouch microcirculation to investi gate the effects of melatonin (ME) on ischemia reperfusion (I-R) injur y by in vivo microscopy, ME is a hormone produced by the pineal gland and is the most powerful and effective hydroxyl radical scavenger dete cted to date in vitro. The second aim was to determine the scavenger e ffect of ME in cheek pouch microcirculation when topically applying an oxygen-derived free radical generating system, Methods: Ischemia was induced by clamping the cheek pouch for 30 min followed by 30 min of r eperfusion. We quantified the increase in permeability, the perfused c apillary length and leukocyte adhesion by computerized methods. Microc irculation was also exposed to a hypoxanthine-xanthine oxidase (H-X) s ystem. Results: In control hamsters I-R was associated with increased permeability, increased number of leukocytes sticking to venules, and decreased perfused capillary length, Treatment with ME completely inhi bited microvascular edema formation and reduced the number of leukocyt es sticking to venules after reperfusion. Moreover, ME prevented the m arked decrease in perfused capillary length, preserving microvascular perfusion, ME topically applied reduced significantly the permeability increase due to H-X exposure, Conclusions: The beneficial effect of M E may be related to its antioxidant properties, These protect the endo thelial barrier integrity as well as preserve microvascular blood perf usion by dysfunctions after I-R.