Activation of myocardial constitutive nitric oxide synthase during coronary artery surgery

Objective: The role of nitric oxide (NO) in myocardial ischemia/reperfusion is controversial. While some studies have shown cardioprotective effects o f NO, others suggested that increased myocardial NO release secondary to is chemia may contribute to reperfusion injury. However, the impact of cardiop legia-induced myocardial ischemia/reperfusion on the activity of the NO-pro ducing enzyme constitutive NO-synthase (cNOS or NOS-III) has not been inves tigated. Methods: Twenty elective CABG patients were randomized to receive myocardial protection using either intermittent cold blood cardioplegia wit h 'hot-shot' (CBC; n = 10) or continuous warm blood enriched with the ultra fast-acting P-blocker esmolol (WBE; n = 10). We collected transmural LV bio psies prior to cardiopulmonary bypass (CPB), at the end of the cross-clamp period, and at the end of CPB. Specimen were subjected to immunocytochemica l staining against myocardial NOS-III and cGMP using polyclonal antibodies. NOS-In activity was determined using TV-densitometry (gray units) and cGMP content using a semiquantitative score. Global myocardial metabolism was a ssessed by arterio-coronary sinus lactate concentration difference (a-csD(L AC)). For LV function determination we measured the fractional area of cont raction (FAC) using TEE. Results: In CBC hearts a-csD(LAC) was significantl y decreased following cross-clamp removal as compared to pre-CPB indicating global ischemia during cross-clamp. In contrast, a-csD(LAC) was unchanged in WEE hearts indicating absence of relevant ischemia in this group. In CBC hearts NOS-III activity did not change from pre-CPB (35.6 +/- 11.1 U) to t he end of the cross-clamp period (38.0 +/- 8.1 U; P = 0.2), but increased s ignificantly to 48.5 +/- 12.1 U at the end of CPB following initial warm bl ood reperfusion (P = 0.026). In WEE hearts NOS-LII activity remained unchan ged throughout (29.2 +/- 10.8, 35.1 +/- 11.8, and 32.2 +/- 14.7 U, respecti vely; P > 0.3). At the end of CPB, nine CBC hearts, but only one WBE heart showed increased cGMP content (P = 0.002). Compared to pre-CPB, FAC in the CBC group was 109 +/- 25% following weaning off CPB (P = 0.26), but was sli ghtly decreased to 87 +/- 22% at 4 h post-CPB (P = 0.03). In the WEE group FAC remained unchanged compared to pre-CPB throughout (103 +/- 21 and 96 +/ - 37%, respectively; P > 0.5). Conclusions: Our data show that global myoca rdial ischemia and reperfusion induced by CBC is associated with myocardial NOS-III activation and increased cGMP content suggesting increased NO rele ase. In contrast, avoidance of ischemia by use of WEE prevented NOS-III and c-GMP increase. As LV function was decreased at 4 h post-CPB in the CBC gr oup, these data suggest that increased NO release secondary to NOS-III acti vation may have contributed to ischemia-reperfusion injury as has been show n experimentally. (C) 2000 Elsevier Science B.V. All rights reserved.