13CO2 Peak Value of [formula omitted]-[1-13C]phenylalanine Breath Test Reflects Hepatopathy

Abstract

Background. Using a rat model of hepatectomy, we investigated whether the severity of hepatopathy could be quantitatively measured from changes in expiratory 13CO2 levels after intravenous administration of l-[1-13C]methionine or l-[1-13C]phenylalanine.Materials and Methods. Under nembutal anesthesia, 30 mg/kg l-[1-13C]phenylalanine or 40 mg/kg l-[1-13C]methionine was administered to rats through the femoral vein, and expiratory 13CO2 levels were measured for 15 min. A 30, 70, or 90% hepatectomy was performed. In the control group, simple laparotomy was performed. Breath test was conducted 20 min after laparotomy. We examined the correlation of the total 13CO2 output over 15 min or peak 13CO2 level with liver weight/body weight (%).Results. In breath test graphs, l-[1-13C]methionine did not show any peak level during measurement. l-[1-13C]phenylalanine showed a specific peak level 6 ± 1 min after administration. The correlation coefficient between total 13CO2 output over 15 min after l-[1-13C]methionine administration and liver weight/body weight was 0.922 (P < 0.001). The correlation coefficient between total 13CO2 output over 15 min after l-[1-13C]phenylalanine administration and liver weight/body weight was 0.883 (P < 0.001). The correlation coefficient between peak l-[1-13C]phenylalanine level and liver weight/body weight was highest, 0.927 (P < 0.001).Conclusion. In a breath test with intravenously administered l-[1-13C]methionine or l-[1-13C]phenylalanine, hepatopathy could be quantitatively evaluated by measuring expiratory 13CO2 levels over 15 min. After administration of l-[1-13C]phenylalanine, hepatopathy could be quantitatively evaluated in a short period by measuring the peak expiratory 13CO2 level.