Total Creatinine Content of Perfused Rabbit Hearts

In our efforts to determine the part played by creatine and its possible precursors in heart muscle metabolism, we perfused isolated rabbit hearts in Dawson's modification1 of the Gunn-Locke apparatus. We used oxygenated Ringer-Locke solution to which 0.1% dextrose was added in one apparatus, and in the other the same solution plus 0.1% glycocoll. About 250 cc. of each mixture was placed in the reservoirs, and that which perfused through the coronaries was collected and returned automatically to the reservoirs and oxygenated by an oxygen pump system.Thirty isolated rabbit hearts, or 15 pairs, were perfused from 1 to 5 hours, beating spontaneously, or stimulated at the rate of 60 per minute when spontaneous contraction was too slow. Thirteen isolated hearts were perfused for a minute each in order to wash the blood from the coronary system, and used as controls. All hearts were weighed, cleaned of fat and connective tissue, and the ventricular muscle minced. Part of the tissue was dried at 105°C. for 22 ho...