Transmural distribution of left ventricular glucose uptake in spontaneously hypertensive rats during rest and exercise

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Abstract
The transmural distribution of glucose uptake was studied in the left ventricle of 6‐month‐old male Wistar–Kyoto (WKY) and spontaneously hypertensive rats (SHR) during rest and swimming (20 min) using the 2‐deoxyglucose method. The baseline mean arterial pressure was 128 ± 8 (n= 8) in the WKY and 188 ± 22 mmHg (n= 8) in the SHR (P < 0.001). This pressure remained constant in the resting groups, whereas the product of mean arterial pressure and heart rate was initially 45×103± 3 times 103 and 63×103± 4×103 mmHg beats min‐1 in the swimming WKY and SHR and increased by 34–48×103 mmHg beats min‐1 during the swimming period. Total glucose uptake was 3.9 ± 1.2 μ mol min‐1 g‐1 protein in the resting WKY rats and 1.4 ± 0.4, μ mol min‐1 g‐1 protein (P < 0.001) in the swimming ones, the corresponding values for the resting and swimming SHR being 4.8 ± 1.4 μ mol min‐1 g‐1 protein and 3.2 ± 1.2 μmol min‐1 g‐1 protein (P < 0.01). Glucose uptake was 30% greater in the subendocardium (ENDO) of the resting WKY than in the subepicardium (EPI) (P < 0.01), but this gradient disappeared during swimming. Glucose uptake in the resting SHR was greatest in the middle layer of the ventricular wall, with no difference between ENDO and EPI, whereas during swimming the glucose uptake was distributed evenly across the left ventricular wall.The blood lactate/pyruvate ratio increased only transitorily during the first minutes in the swimming SHR, while their plasma free fatty acid concentration was 1.2–1.3 mm initially and decreased by 32% (P < 0.01). The data show that both hypertension and acute exercise alter the transmural distribution of glucose uptake. Swimming caused a decrease in total left ventricular glucose uptake in both the WKY and SHR, which cannot be explained solely by an altered supply of competitive myocardial fuels.