Correlation of heterogeneous blood flow and fatty acid uptake in the normal dog heart

Summary Blood flow heterogeneity in normal myocardium may be caused by heterogeneous metabolic demand. We studied, from 80 tissue samples of the left ventricle (LV) of eight anesthetised, open-chest dogs (with prior -blockade (metoprolol) in four dogs), the radioactivity of²⁰¹Thalliumchloride (²⁰¹Tl), an indicator of blood flow, and of the fatty acid¹³¹-Iodine-heptadecanoic acid (¹³¹I-HDA), an indicator of metabolic demand, 3 min after intravenous injection. Global LV uptake (in percent of injected dose ×10^–2, per g tissue; mean ±SD) was 4.94±0.71 for²⁰¹Tl and 4.48±0.58 for¹³¹I-HDA in the dogs without -blockade, and 2.08±0.26 and 1.69±0.20, respectively, in dogs with -blockade (p<0.05). Beta-blockade thus decreased the fraction of cardiac output delivered to the LV, concurrently with a decreased heart rate and arterial blood pressure (p<0.05) and, thus, global metabolic demand and fatty acid uptake. Regional radioactivities per gram were normalized for mean LV radioactivities and heterogeneity was expressed as the coefficient of variation (CV). For pooled data (n=320) in dogs without -blockade, regional²⁰¹Tl and¹³¹I-HDA radioactivities varied from a factor of 0.1 to 1.6 and 0.3 to 1.8 of mean radioactivities, with a CV of 22.9 and 19.4%, respectively, and correlated (r=0.77, p<0.005). For pooled data (n=320) in dogs with -blockade, regional²⁰¹Tl and¹³¹I-HDA radioactivities varied from a factor of 0.2 to 1.5 and 0.2 to 1.6 of mean radioactivity and CV was 23.6% and 24.8%, respectively: r=0.92 (p<0.005). The endo/epi ratio for both radioactivities exceeded unity in each dog. In normal myocardium, blood flow and fatty acid uptake are thus heterogeneous, both transmurally and circumferentially, and matched, concomitantly with coupling of global blood flow to global metabolic demand and fatty acid uptake. This supports the idea that heterogeneous myocardial O₂ supply reflects heterogeneous metabolic demand.