Effects of flow and energy metabolism on injury and Rb(+) uptake in pig hearts: an (87)Rb and (31)P NMR study

In this work the roles of coronary flow (CF) and metabolism in Rb(+) (K(+) congener) uptake were studied. In isolated pig hearts the left anterior descending artery (LAD) was cannulated to maintain adequate perfusion of the LAD bed. Rb(+) loading was initiated and the LAD flow was either completely stopped (no flow (NF)) or reduced to 12% (low flow (LF)), or buffer was deoxygenated without change in flow (hypoxic flow (HYP)) for 2 h. CF through the LAD was then restored to normal, or perfusion was switched to oxygenated buffer. Serial (87)Rb MR images or localized (31)P spectra were acquired to compare the Rb(+) uptake and energetics in the left ventricular (LV) anterior (ischemic/hypoxic) and posterior (normal) walls. End-ischemic/hypoxic (87)Rb signal intensities in the anterior wall were higher and the fluxes were greater in the HYP and LF groups than in the NF group. Phosphocreatine and ATP decreased less significantly and recovered better in the HYP and LF groups. Upon reperfusion/reoxygenation, the HYP and LF groups showed higher (87)Rb signal intensities and smaller or no infarctions in the anterior wall compared to those in the NF group. Ischemia reduces Rb(+) uptake due to both flow limitations and metabolic inhibition of cellular transport. (87)Rb MRI has a potential for distinguishing necrotic and reversibly damaged tissue.