Transmural bioenergetic responses of normal myocardium to high workstates
Zhang, J.; Duncker, D.J.; Xu, Y.; Zhang, Y.; Path, G.; Merkle, H.; Hendrich, K.; From, A.H.; Bache, R.J.; Uğurbil, K.
American Journal of Physiology 268(5 Pt 2): H1891-H1905
1995
ISSN/ISBN: 0002-9513 PMID: 7771539 Document Number: 447278
The response of myocardial high-energy and inorganic phosphates (HEP and P-i, respectively) and associated changes in myocardial blood flow, lactate uptake, and O-2 consumption (M ovrhdot VO-2) rates were examined in an open-chest canine model during progressively increasing workloads achieved by catecholamine infusion. HEP and P-i levels (measured with transmurally localized 31P-nuclear magnetic resonance spectroscopy) were unaffected by moderate increases in the level of energy expenditure but were significantly altered by high workloads, especially in the subepicardium. The M ovrhdot VO-2 and HEP data from three different protocols that utilized pharmacological augmentation of blood flow demonstrated that the maximal rate of myocardial energy production during inotropic stimulation was dictated by perfusion limitation. This limitation was more severe in the subepicardial layer at the high workloads despite equivalent or even higher increases in blood flow to this layer, reflecting a preferential enhancement of demand in the outer layer by catecholamines. In contrast, under basal conditions, existence of a marginal perfusion limitation was evident in the inner but not in the outer layer.