A C-13 NMR double-labeling method to quantitate local myocardial O-2 consumption using frozen tissue samples

Measurement of local myocardial O-2 consumption (V) over dot o(2)) has been problematic but is needed to investigate the heterogeneity of aerobic meta bolism. The goal of the present investigation was to develop a method to me asure local (V) over dot o(2) using small frozen myocardial samples, suitab le for determining (V) over dot o(2) profiles. In 26 isolated rabbit hearts , 1.5 mmol/l [2-C-13]acetate was infused for 4 min, followed by 1.5 min of [1,2-C-13]acetate. The left ventricular (LV) free wall was then quickly fro zen. High-resolution C-13-NMR spectra were measured from extracts taken fro m 2- to 3-mm thick transmural layer samples. The multiplet intensities of g lutamate were analyzed with a computer model allowing simultaneous estimati on of the absolute flux through the tricarboxylic acid cycle and the fracti onal contribution of acetate to acetyl CoA formation from which local (V) o ver dot o(2) was calculated. The C-13-derived (V) over dot o(2), in the LV free wall was linearly related to "gold standard" (V over dot o(2) from cor onary venous O-2 electrode measurements in the same region (r = 0.932, n = 22, P < 0.0001, slope 1.05) for control and lowered metabolic rates. The ra tio of subendocardial to subepicardial (V) over dot o(2) was 1.52 +/- 0.19 (SE, significantly >1, P < 0.025). Local myocardial (V) over dot o(2) can n ow be quantitated with this new C-13 method to determine profiles of aerobi c energy metabolism.