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 microM)-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; BK(Ca) blocker), 4-Aminopyridine (4-AP; K(V) 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 (K(ATP) channel blocker), barium chloride (K(ir) 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 BK(Ca) and K(v) 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-, BK(Ca)- or K(v)-mediated.
Department of Pharmacology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
Gopal
G
Subramaniam
Francis I
FI
Achike
Mohd Rais
MR
Mustafa
D015761:4-Aminopyridine / Q000494:pharmacology; D000138:Acidosis / Q000378:metabolism*; D000818:Animals; D001011:Aorta / Q000187:drug effects*; D017609:Barium Compounds / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D005905:Glyburide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007213:Indomethacin / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D008751:Methylene Blue / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D011921:Rats, Inbred WKY; D019789:Tetraethylammonium / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects*
D017609:Barium Compounds; D002712:Chlorides; D007004:Hypoglycemic Agents; D007328:Insulin; D026902:Potassium Channel Blockers; C024986:barium chloride; D010656:Phenylephrine; D010042:Ouabain; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D005905:Glyburide; D008751:Methylene Blue; D019331:NG-Nitroarginine Methyl Ester; D007213:Indomethacin