ISCHEMIC PRECONDITIONING, CARDIOPLEGIA OR BOTH - DIFFERING APPROACHESTO MYOCARDIAL AND VASCULAR PROTECTION

We compared the anti-ischemic efficacy of cardioplegia and ischemic pr econditioning and whether their effects are additive for both myocyte and vascular protection. Isolated blood-perfused rat hearts were subje cted to zero now global ischemia (37 degrees C) for 30 min and reperfu sion for 40 min. Left ventricular developed pressure (LVDP) was assess ed with an intraventricular balloon. Coronary now and vascular reactiv ity (percentage change in coronary vascular resistance, CVR) to 5-hydr oxytryptamine (5HT; 0.0215 mmol/l) and sodium nitroprusside (SNP; 0.01 60 mmol/l) were measured, Study 1: ''dose'' effect of preconditioning in four groups (n = 6/group): (i) controls (unprotected ischemia) and (ii, iii and iv) 1, 2, or 3 cycles of preconditioning (3 min ischemia + 3 min reperfusion) prior to ischemia, LVDP recovery in controls was 31 +/- 9%; preconditioning by 1, 2 or 3 cycles afforded significant (P <0.05) improvements (58 +/- 6%, 54 +/- 3% and 54 +/- 5%, respectively) . Overall, the pre-ischemic change of CVR to SNP was -28 +/- 1%. The p ost-ischemic response in controls was -4 +/- 7% (P<0.05); with 1, 2, o r 3 cycles of preconditioning the values were -23 +/- 4%, -24 +/- 5%, and -26 +/- 3% respectively (P<0.05 v controls). With 5HT the overall pre-ischemic change in CVR was -18 +/- 2%: after ischemia a vasoconstr ictor response was seen in all groups. Study 2: the effect of precondi tioning added to cardioplegia, with four groups subjected to 35 min is chemia (n = 8/group): (i) controls, (ii) one cycle of preconditioning (3 min ischemia + 3 min reperfusion), (iii) cardioplegia with St Thoma s' solution immediately prior to ischemia, and (iv) preconditioning fo llowed by cardioplegia prior to ischemia. The recoveries of LVDP were 26 +/- 6%, 44 +/- 2%, 53 +/- 3% and 54 +/- 4%, respectively (P<0.05 al l interventions v controls). Post-ischemic CVR increased greatly in co ntrols (+167 +/- 60% of its pre-ischemic value) but was little changed in groups (ii), (iii), and (iv) (+11 +/- 7%, +27 +/- 10% and -2 +/- 6 % respectively; P<0.05 v controls). The post-ischemic change in CVR to SNP was protected by all interventions (-21 +/- 1%, -21 +/- 1%, and - 22 +/- 1% v -14 +/- 2% in controls; P<0.05). Again, the post-ischemic response to 5HT was vasoconstriction in all groups. In conclusion, pre conditioning and cardioplegia alone afford similar and substantial pro tection of post-ischemic contractile and vascular functions. In genera l, the combination of the two techniques afforded no significant addit ional protection. (C) 1996 Academic Press Limited