DEPENDENCE OF MYOCARDIAL BLOOD-FLOW AND METABOLISM ON CARDIAC INNERVATION

Summary: Left ventricular blood flow was measured in dogs with radioactive microspheres at a fixed heart rate for each dog, achieved by right atrial pacing. Blood samples were taken from an artery and from the coronary sinus, into which a catheter had been introduced under fluoroscopic control. These were analysed for oxygen content, lactate, glucose, and free fatty acids. The coronary A-V differences for these variables were used together with the flow to calculate left ventricular oxygen consumption and left ventricular uptake of the three substances. Each dog was then subjected to cardiac denervation and after three weeks, to allow for endogenous catecholamines to be depleted, a second measurement of the left ventricular blood flow was made using microspheres with a different radioactive label, together with second measurements of coronary A-V differences for oxygen content, lactate, glucose, and free fatty acids. These measurements were made with the same heart rate, arterial pressure, and anaesthetic as in the first study in each dog. Left ventricular oxygen consumptions in the innervated control study were 109.6 ± 15.9 (1 SD) mm3 O2 · min-1·g-1, and after denervation were 141.8 ± 35.7 mm3 O2 ·min-1·g-l respectively. This increase in left ventricular oxygen consumption was accompanied by concomitant increases in lactate consumption from 277.4 ± 156.7 nmol·min-1·g-1 to 917 ± 213.3 nmol·min-1·g-1 respectively, but no consistent changes in glucose and free fatty acid uptake. External left ventricular work per cm3 of oxygen consumed fell from 4.38 ± 0.63 to 2.77 ± 0.92 J (P <0.05) and for each μmol of lactate consumed fell from 2.004 ± 0.949 to 0.433 ± 0.151 J (0.05>P>0.025). This implies that tonic release of noradrenaline from nerve terminals controls the conversion of substrate and oxygen into mechanical energy.