Effect of acidosis on the mechanism(s) of insulin-induced vasorelaxation in normal Wistar-Kyoto (WKY) rat aorta

The effect of acidosis on insulin-induced relaxation was studied in thoracic aortic rings (from Wistar-Kyoto (WKY) rats) with (+ ED) or without (− ED) endothelium. The rings were mounted in normal (pH 7.4) or acidotic (pH 7.2) Krebs solution for isometric tension recording. Phenylephrine (PE, 3.0 µM)-contracted tissues were exposed to insulin in the presence or absence of various inhibitors. Insulin exerted similar concentration-dependent relaxation of + ED tissues in normal and acidotic pH. Endothelium denudation, significantly (p < 0.05) reduced insulin effect in normal, but not acidotic pH. Under normal pH, treatment with L-NAME or methylene blue significantly (p < 0.05) reduced insulin responses in the + ED (but not the − ED) tissues. The insulin effect was also significantly (p < 0.05) inhibited by tetraethylammonium (TEA; BKCa blocker), 4-Aminopyridine (4-AP; KV channel blocker), combined treatments (L-NAME + 4-AP + TEA, in + ED tissues) or (4-AP + TEA, in − ED tissues). In either + ED or − ED tissues, indomethacin (cyclo-oxygenase inhibitor), glibenclamide (KATP channel blocker), barium chloride (Kir channel blocker) or Ouabain (a Na+/K+-ATPase inhibitor) had no effect. Except for methylene blue (effect on + ED tissues), none of the drug treatments inhibited insulin vasodilator effect in acidosis (+ ED or − ED tissues). These data indicate that insulin exerts an endothelium-dependent and -independent vasodilatation in rat aorta which in normal pH is mediated via BKCa and Kv channels, including the EDNO-cGMP cascade. Acidosis abolishes the endothelium-dependent relaxation mechanism unraveling a novel mechanism that is as efficacious and is cGMP-, but not EDNO-, BKCa- or Kv-mediated.