The Protective Effect of Late Preconditioning Against Myocardial Stunning in Conscious Rabbits Is Mediated by Nitric Oxide Synthase

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Abstract
Seventy-four conscious rabbits undergoing a sequence of six 4-minute coronary occlusion/4-minute reperfusion cycles for 3 consecutive days (days 1, 2, and 3) were assigned to nine groups. In group I (controls, n=8), the recovery of systolic wall thickening (WTh) after the sixth reperfusion was markedly improved on days 2 and 3 compared with day 1, indicating late preconditioning (PC) against myocardial stunning; the total deficit of WTh after the sixth reperfusion was reduced by 56% on day 2 and 50% on day 3 compared with day 1 (P<.01). Administration on day 2 of the nonselective NO synthase (NOS) inhibitor Nω-nitro-l-arginine (L-NA) (group II, n=8) or of the selective inducible NOS inhibitors aminoguanidine (AG) (group IV, n=8) and S-methylisothiourea sulfate (SMT) (group VI, n=6) completely abrogated late PC against stunning on day 2. On day 3, the expected PC effect became manifest in all groups. Administration of L-NA, AG, or SMT on day 1 (groups III [n=7], V [n=6], and VII [n=5], respectivel...

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