Further Rabbit Heart Perfusion Experiments with Amino-Acids

We have previously reported 1 our studies on the creatine content of rabbit heart muscle after perfusion of the coronary system with oxygenated Ringer-Locke solution plus glycocoll in a Dawson-Gunn-Locke apparatus. We found that a further modification of the method was necessary in order to maintain the perfusate at a satisfactory pH level. The cause of the greater part of the fall in pH was found to be the CO₂ produced by the heart's metabolism. In order to remove this absorbed and diffusible CO₂, an aerating agitating lift for the perfusate was devised with the use of a suction pump instead of oxygen pressure. The perfusate was then reoxygenated in the reservoir in the constant temperature bath just above the heart cannulae.

It was found that the creatine content of the heart muscle dropped when the pH of the perfusion fluid was allowed to fall below 7.3–7.5 (Table I). When the estimated pH of the fluid in the myocardial vessels was maintained within these limits, however, failure was postponed for several hours. Eventually there accumulated in the perfusate a non-volatile acid metabolite, lactic acid on the basis of the qualitative test, which caused an agitation-irreversible drop in the pH. In the presence of myocardial infarcts the non-volatile acid metabolites early forced down the pH and lead to a sharp loss in creatine and early failure.

We have previously 1 noted that perfusion of the isolated rabbit heart with Ringer-Locke solution, until it stopped in failure after several hours, resulted in a uniform drop in the creatine content of he heart muscle. Furthermore, we found that under similar circumstances the addition of glycocoll failed to prevent this creatine loss. This finding has been confirmed in a larger series of hearts perfused under more constant conditions made possible by the modified method described above.