RESUMO
ATP-sensitive potassium (K(ATP)) channels and nitric oxide (NO) have been suggested to contribute in mediating active hyperemia in diaphragm. However, no data is available in the current literature concerning their comparative contributions to arteriolar dilation during muscle contraction. The aim of this study was therefore to examine, by video microscopy in rats, the effects of superfusing the muscle with Krebs solution alone (group C), or Krebs solution containing either glybenclamide (3mdeltaM, a blocker of K(ATP), group GLY), or Nwdelta-nitro-L-arginine (300 mdeltaM, a NO synthase inhibitor, group NNA), or mefenamic acid (50 mdeltaM, a prostaglandin synthesis inhibitor, group MA) on second and third order of diaphragm (A2 and A3 respectively) arteriolar dilation elicited by 3 min muscle stimulation (40 Hz, train duration: 300 milliseconds, 90 cycles per min). In group C, A2 diameters increased by 67.5 +/- 1.9% referring to baseline at the end of the stimulation. This increase was significantly reduced in groups GLY and NNA (16.7 +/- 2.5% and 47.3 +/- 2.2% respectively, p < 0.001 as compared to group C) and was more important in group GLY than in group NNA (p < 0.001). By contrast, no difference in post-contraction diameter was observed between groups C and MA. Similar results were observed in A3 vessels. These results indicate that K(ATP) are more important mediators of functional diaphragm arteriolar dilation in rat than NO, whereas prostaglandins are not involved in this phenomenon.
