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The isolated rabbit kidney was perfused with the blood collected from the donor rabbits. in order to investigate the substrates taken up by the rabbit kidney as the fuels of energy source. Perfusion pressure was set at 150 mmHg which was within the range of autoregulation. Blood glucose was determined by the Somogyi-Nelson method, and O2 and CO2 contents in renal artery and vein were measured by the VanSlyke mercury manometric technique. Radioactivity of 14CO2 in the blood sample derived from 14C-UL-glucose was measured by use of liquid scintillation counter. Respiratory quotient (R.Q.) of rabbit kidney was calculated from the CO2 production and O2 consumption rate. Relative specific activity (R.S.A.) of CO2 was also calculated from the specific activity of plasma glucose and specific activity of CO2. The results were as follows: 1) Average renal blood flow was 1. 41 ml/min-gm kidney. 2) COs content of renal artery and vein were 13.6 mM/L and 15. 5 mM/L respectively. (AV. difference of CO2... 1.9mM/L) and O. content of renal artery and vein were 13.6 vol% and 8.3 vol%. (Av-difference of O2.., 5. 3vol%) 3) COs production rate (VCO2) was 5l. 6 uL/min-gm kidney and O2 consumption rate(VO2) was 73. 6uL,min.gm kidney. Therefore respiratory quotient of kidney was O. r3. 4) Glucose concentration in the perfused blood was 242mg% and the specific activity of plasma glucose was 4, 439 c.p.m/,mgC of glucose. 5) The specific activity of CO2 was 40c,p.m/mgC of CO2 and the relative specific activity was 0.90%. From the above results, it was concluded that glucose is almost not used as the fuel of energy source in the rabbit kidney as found in human and dog kidneys, and suggested the possibility that fats such as free fatty acids are utilized as predominant energy source.
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