THE SYNTHESIS RATES OF TOTAL LIVER PROTEIN AND PLASMA-ALBUMIN DETERMINED SIMULTANEOUSLY IN-VIVO IN HUMANS

Although the metabolism of liver-derived plasma proteins such as album in has been extensively studied, human hepatic protein synthesis as a whole has not been well characterized, because a reproducible model fo r obtaining human liver tissue has not been available, In this study, the fractional synthesis rates of total liver protein and albumin in v ivo were determined simultaneously in nine subjects undergoing electiv e laparoscopic cholecystectomy. L-[H-2(5)]phenylalanine (45 mg/kg body wt) was administered for 10 minutes intravenously, Blood samples were collected at regular intervals for 90 minutes and a liver biopsy spec imen was taken at 35 +/- 7 minutes. The enrichments of plasma free phe nylalanine, plasma albumin, and total liver protein were measured with gas chromatography mass spectrometry (GC-MS). The fractional synthesi s rate (FSR) of total liver protein was 24.7 +/- 3.1 %/d (mean +/- SD) , and that of albumin was 5.9 +/- 1.2%/d The amount of albumin synthes ized per day (absolute synthesis rate, ASR) was 109 +/- 21 mg/kg body wt, No correlation between FSR of total Liver protein and ASR of album in was found. It is concluded that the technique of obtaining Liver ti ssue specimens during laparoscopic surgery may serve as a human in viv o model to study total liver protein synthesis, The fractional synthes is rate of total liver proteins (stationary and exported), equals appr oximately 25% of the liver protein content daily. Within the range of values of this study, the absolute synthesis rate of albumin was not c orrelated to the fractional synthesis rate of total liver protein.