LOCAL MYOCARDIAL GLUCOSE-UPTAKE IS PROPORTIONAL TO, BUT NOT DEPENDENTON BLOOD-FLOW

In nonischaemic myocardium local deoxyglucose deposition is proportion al to local blood flow (y = 0.77x + 0.25 for normalized deoxyglucose d eposition and blood flow). The cause for this relationship was evaluat ed using a mathematical model of (deoxy)glucose metabolism to elucidat e whether differences in local deoxyglucose deposition are dependent o n local blood flow or whether they reflect differences of the local me tabolic rate. The axially distributed model consists of two blood-tiss ue exchange regions arranged concentrically representing the capillary and the extracapillary regions, the latter being a composite of the e ndothelial, interstitial and parenchymal cell regions. Exchange betwee n the two model regions is described by a permeability-surface area pr oduct, consumption in the extracapillary region is modelled by an intr aregional clearance term. Twenty blood-tissue exchange units are arran ged as parallel pathways to account for the effects of flow heterogene ity and in series with a single, nonexchanging, large vessel segment ( 0.1 ml/g). Regional volumes (capillary 0.07 ml/g. extracapillary 0.60 ml/g) and the permeability-surface area product (0.2 ml min(-1) g(-1)) are taken from pu blished sources, the local myocardial blood flow is that determined experimentally (between 0.1 and 2.5 ml min(-1) g(-1)) . The only free parameter in the model is the extracapillary clearance term (0.0275-0.102 ml min(-1) g(-1)) which was used to fit the measur ed tissue radioactivity concentration taking the measured arterial con centration of H-3-deoxyglucose into account. The results obtained indi cate that variations in local myocardial blood flow, and hence differe nces in deoxyglucose supply, can not explain quantitatively the differ ences in local deoxyglucose deposition. However, differences of the me tabolic rate (0.336 versus 0.120 mu mol min(-1) g(-1)) assumed to occu r in parallel to the flow differences (1.26 versus 0.42 ml min(-1) g(- 1)) can well explain the different mean deoxyglucose deposition in hig h and low flow areas. This result supports the view that blood flow he terogeneity in the heart is paralleled by a spatial heterogeneity of g lucose metabolism.