Abstract
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 modification 1 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 hours to give the percent of solids; the remainder was used for determination of the total creatinine content by the method of Rose, Helmer and Chanutin. 2 Because of the variable amount of edema produced during the perfusion, it was thought desirable to calculate the results in terms of the dry weight.
In the control hearts, the total creatinine content varied from 144 to 168, with an average of 153 mg. per 100 gm. of muscle. In terms of dry weight, there were from 753 to 868, with an average of 795 mg. per 100 gm. of dried muscle.
In the hearts perfused with Ringer-Locke solution alone, the total creatinine values ranged from 100 to 151, with an average of 123 mg. per 100 gm. of moist muscle; or, from 652 to 827, with an average of 742 mg. per 100 gm. of dried muscle.
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