Reversal of glibenclamide-induced coronary vasoconstriction by enhanced perfusion pulsatility: possible role for nitric oxide.
OBJECTIVE
ATP-sensitive potassium channels (K+ATP) prominently contribute to basal coronary tone; however, flow reserve during exercise remains unchanged despite channel blockade with glibenclamide (GLI). We hypothesized that increasing perfusion pulsatility, as accompanies exercise, offsets vasoconstriction from K+ATP-channel blockade, and that this effect is blunted by nitric oxide synthase (NOS) inhibition.


METHODS
In 31 anaesthetized dogs the left anterior descending artery was blood-perfused by computer-controlled servo-pump, with real-time arterial perfusion pulse pressure (PP) varied from 40 and 100 mm Hg at a constant mean pressure and cardiac workload.


RESULTS
At control PP (40 mm Hg), GLI (50 micrograms/min/kg, i.c.) lowered mean regional coronary flow from 37 +/- 5 to 25 +/- 4 ml/min (P < 0.001). However, this was not observed at 100 mm Hg PP (41 +/- 2 vs. 45 +/- 4). NOS inhibition by NG-monomethyl-L-arginine (L-NMMA) did not alter basal flow at 40 mm Hg PP, but modestly lowered flow (-5%, P < 0.001) at higher PP (100 mm Hg), reducing PP-flow augmentation by -36%, and acetylcholine (ACh) induced flow elevation by -39%. Co-infusion of L-NMMA with GLI resulted in net vasoconstriction at both PP levels (-60% and -40% at 40 and 100 mm Hg PP, respectively). Unlike GLI, vasoconstriction by vasopressin (-43 +/- 3% flow reduction at 40 mm Hg PP) or quinacrine (-23 +/- 7%) was not offset at higher pulsatility (-44 +/- 4 and -23 +/- 6%, respectively). Neither of the latter agents inhibited ACh- or PP-induced flow responses, nor did they modify the effect of L-NMMA on these responses.


CONCLUSIONS
Increased coronary flow pulsatility offsets vasoconstriction from K+ATP blockade by likely enhancing NO release. This mechanism may assist exercise-mediated dilation in settings where K+ATP opening is partially compromised.
Pagliaro
P
P
Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, MD 21287, USA.
Paolocci
N
N
Isoda
T
T
Saavedra
W F
WF
Sunagawa
G
G
Kass
D A
DA
D000109:Acetylcholine / Q000494:pharmacology; D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D003326:Coronary Circulation / Q000187:drug effects / Q000502:physiology; D003331:Coronary Vessels / Q000187:drug effects* / Q000502:physiology; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D026902:Potassium Channel Blockers; D011673:Pulsatile Flow; D011796:Quinacrine / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D019323:omega-N-Methylarginine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D026902:Potassium Channel Blockers; D014662:Vasoconstrictor Agents; D001127:Arginine Vasopressin; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D011796:Quinacrine; D000241:Adenosine; D000109:Acetylcholine; D005905:Glyburide