Do the cardiac nerves optimise efficiency?
The cardiac nerves were removed by surgical dissection in anaesthetised dogs. At least 3 weeks were then allowed to elapse to permit degeneration of post-ganglionic sympathetic nerve fibres and myocardial catecholamines. We then established that: 1) Myocardial oxygen consumption was increased for a given work output, indicating metabolic inefficiency; 2) glucose oxidation was inhibited; 3) uncoupled oxygen consumption of isolated myocardial tissue was increased, and 4) sodium-potassium ATPase activity was enhanced. These results are compatible with the hypothesis that the cardiac nerves optimise efficiency. There is some evidence from cardiac transplantation studies in man that a similar effect of innervation on efficiency is present. However, examination of this concept as a postulated result of evolutionary pressure led us to reject such a hypothesis (at least in man) because such a mechanism should be irrelevant to the factors determining survival at the time of human evolution. However, the hypothesis may be tenable for the situation at some earlier evolutionary era. This could be determined, in theory, by a comparative study between species of the effect of cardiac innervation upon efficiency.
Noble
M I
MI
Charing Cross & Westminster Medical School, Chelsea & Westminster Hospital, London, England.
Drake-Holland
A J
AJ
D000818:Animals; D005075:Biological Evolution; D004285:Dogs; D006321:Heart / Q000294:innervation* / Q000502:physiology; D006801:Humans; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption; D013562:Sympathectomy