Quantitative study on creatine metabolism in sheep tissues

Creatine metabolism was quantitated in sheep tissues by measurement of the amount of creatine and creatinine flowing into and out of various tissues using multi-catheterized sheep. The results showed that sheep derived no creatine from the digestive tract. The total renal clearance of creatine plus creatinine was about 18 mmoles per day. Daily creatine synthesis in the sheep was some 15 mmoles, of which 80% occurred in the liver. There was a daily uptake of about 5.4 mmoles of creatine and an output of 7.8 mmoles of creatinine by the hindlimbs of the sheep. This difference suggests that the skeletal muscle may be able to synthesize a significant amount of creatine. However, creatine metabolism in the heart, lung and brain was much less active.