Pentaerythritol trinitrate and glyceryl trinitrate on intramyocardial oxygenation and perfusion in the dog. Krogh analysis of transmural metabolism

1. The effect of intravenous pentaerythritol trinitrate and glyceryl trinitrate on left ventricular subepicardial (epi) and subendocardial (endo) Po₂ and perfusion were compared in anaesthetized open‐chest mongrel dogs. Tissue Po₂ was determined simultaneously at a depth of 3 mm (epicardial) and 9 mm (endocardial) with small platinum electrodes by polarography. In a separate series of dogs tissue perfusion of those regions was measured by hydrogen (H₂) clearance using similar electrodes. 2. Both nitrates increased endocardial Po₂ while epicardial Po₂ was not altered. Perfusion was determined at the point of the maximal rise in endocardial Po₂ (4–7 min after injection of either nitrate). At that period average coronary artery inflow and epicardial perfusion were decreased but endocardial perfusion was not significantly altered. 3. Using the data on Po₂, hydrogen clearance and intercapillary distance, the effect of the nitrates on transmural metabolism (oxygen consumption) was estimated by Krogh analysis. Basal endocardial metabolism was 20–30% higher than epicardial metabolism. The nitrates reduced metabolism in each region. The absolute decrease in oxygen consumption was greater in the endocardium. 4. The results show that both pentaerythritol trinitrate and glyceryl trinitrate improve endocardial oxygenation by producing a more favourable balance between perfusion and oxygen requirements in that region.