Plasma Protein Synthesis in the Liver: Method for Measurement of Albumin Formation in vivo

Abstract

l-Arginine labeled with carbon-14 at the guanido group was injected into rabbits, and the ratio of the rates of entry of radioactivity into the protein and urea was determined. This ratio, multiplied by the rate of arginine utilization in urea synthesis and by the ratio of protein to protein arginine weights, gives the rate of protein synthesis. The method applies to albumin and should apply to any plasma protein synthesized in those liver cells which also synthesize urea.

Effects of a short-term fast on albumin synthesis studied in vivo, in the perfused liver, and on amino acid incorporation by hepatic microsomes

“…Albumin synthesis was determined by the injection of carbonate-14C with its subsequent incorporation into the guanido carbon of arginine and, hence, into albumin. The specific activity of the carbon of urea was taken to represent that of the precursor guanido carbon of arginine as described previously (8)(9)(10).…”

“…These spaces (measured from the space of distribution of urea-14C) were determined to be about 60%o. The specific activity of this urea carbon was assumed to equal the mean specific activity of the precursor guanido carbon of arginine (8)(9)(10). The concentration of protein in plasma or perfusate was determined with a biuret-reagent (17) and protein partition with a Kern microelectrophoresis unit (18).…”

The measurement of the synthetic rate of bilirubin from hepatic hemes in patients with acute intermittent porphyria

“…If the labeled precursor-product relationship (11,12) is then applied to the hepatic pool of PBG, it follows that during a given period of time (ti-t2) the mean specific activity of carbon atoms 2 or 4 of PBG in this pool, or in urinary PBG derived from it, will be equal to the mean specific activity of any one of carbon atoms 1', 2, 3', 4, 5, 6', 7', and 8 in hepatic-synthesized bilirubin which is derived from the precursor pool of hepatic PBG. Let, as follows: Values for MB were determined from the plasma disap- (ic) pearance curve of unconjugated bilirubin-3H and the mean plasma unconjugated bilirubin concentration using the methods described by Berk et al (16).…”

“…Hence "C-labeled bilirubin and other bile pigments arising within the first few days of the administration of ALA-"C reflect the incorporation of the label into bilirubin derived from hepatic hemes; (b) hepatic porphobilinogen (PBG) is a common precursor of both urinary PBG and hepatic-synthesized bilirubin. These two conditions are essential prerequisites for applying the labeled precursor-product relationship (11,12) to the hepatic pool of PBG. According to this relationship, during a given period of time after the administration of ALA-4-"C the mean specific activity of urinary PBG would be equal to the mean specific activity of hepaticsynthesized bilirubin.…”

Protein metabolism after injury

“…Catabolic rates are usually determined in studies of about 14 d duration and in the 'non-steady state' the catabolic rate is calculated daily from the ratio of urine radioactivity to plasma specific radioactivity (McFarlane, 1964). In contrast, the determination of the rate of albumin synthesis in man may be achieved from values obtained in a period of about 6 h (Reeve, Pearson & Martz 1963;RkFarlane, 1963 (1968) found increased aggregation of liver polysomes 18 h after partial hepatectomy. T h e cxplanation for the discrepancies may be the different naturc of the trauma; partial hepatectomy will lead to a specific 'recovery' response by the liver.…”