Stroke was modeled in male rats (n = 140) by electrocoagulation of the middle cerebral artery branch (MCAO). The nonselective K+ATP-channel blocker glibenclamide and K+ATP-channel opener diazoxide were used. IP and PhP were performed one day before MCAO: IP - by alternately clamping of the right and left common carotid arteries, and PhP – by intraventricular administration of the diazoxide solution. The concentrations of NO and its metabolites (NO3- and NO2-) were assessed at 5, 9, 24, 72 hours after MCAO.
IP reduced the lesion area by 37% (p<0.05). A similar effect was observed with the diazoxide PhP. Pretreatment with glibenclamide abolished the effect of IP, indicating a key role of the K+ATP-channels in
neuroprotective effect of preconditioning. On the third day the NO levels in brain tissue of rats pretreated with glibenclamide were increased by 65% (p = 0.0005), that may be due to activation of the inducible NO-synthase of microglial cells in response to K+ATP-channel blockade. However earlier, at the 24-hour timepoint blockade of K+ATP-channels led to decrease in NO3- and NO2- serum levels (p < 0.03). A possible explanation for this is the inclusion of NO in free-radical reactions within the microglial activation zone, preventing its oxidation to the final products.
It is assumed that during the delayed phase of preconditioning, mitochondria pass into the low-energy state, reducing the oxygen consumption and facilitating its diffusion from the capillaries to distant cells. K+ATP-channel activation by diazoxide reduced the NO content in cerebral cortex after 9 and 72 hours following MCAO (p=0.037 and p=0.002, respectively). We refer this result to the reduced NO-synthase activity in preconditioned mitochondria.