Effect of lack of noradrenaline on myocardial oxygen consumption in denervated dog hearts.

Surgical cardiac denervation was carried out in dogs under halothane anaesthesia. In a paired experimental design control biopsy specimens were obtained before surgical denervation. The dogs were allowed to recover and three weeks to elapse before the second biopsy specimen was taken. Both right and left ventricular specimens had higher in vitro oxygen consumption after denervation than before. Other specimens were immediately cooled in hexane at -60 degrees C and stored under liquid nitrogen until analysed. Succinate dehydrogenase and cytochrome oxidase activities were then measured histochemically in sequential 10 or 12 microns sections. There was no significant difference between the enzyme activities measured before or after cardiac denervation (succinate dehydrogenase 20.3(6.3) before, 19.4(4.02) pmol.H2.cm-2.s-1, after; cytochrome oxidase 223(73.4) before, 263(61.6) (measured as extinction coefficient) after). Thus the changes in oxygen consumption in the chronically denervated dog heart are not due to any lack of these mitochondrial enzymes.