Sidney S. Schreiber

Albumin synthesis in cirrhotic subjects with ascites studied with carbonate-14C

The synthesis of serum albumin was measured in 19 patients with cirrhosis of the liver and ascites. Carbonate-(14)C was used to label the guanido carbon of arginine in albumin.18 of the patients had the diagnosis of cirrhosis confirmed by biopsy and/or by the presence of esophageal varices. Seven patients with albumin synthesis rates of 42-105 mg/kg per day demonstrated the lowest serum cholesterol esters and highest serum glutamic oxalacetic transaminase (SGOT) levels, while the seven patients whose albumin synthesis rates ranged from 203-378 mg/kg per day, had significantly higher cholesterol ester levels and significantly lower values for SGOT. The serum albumin levels were equally depressed in all patients. In patients with cirrhosis and ascites albumin production was found to be normal or elevated in seven of the 19 subjects, and only markedly depressed in seven patients, in spite of the fact that the serum albumin level was depressed in all patients.

Ethanol, acetaldehyde, and myocardial protein synthesis

The cause of alcoholic myocardiopathy is unknown. The effects of acute exposure to ethanol or its metabolite acetaldehyde on protein synthesis in working, intact, guinea pig hearts in vitro were studied utilizing lysine-(14)C perfusion. Ethanol at 250 mg/100 ml, a level sufficient to markedly inhibit hepatic production of albumin, did not alter cardiac function, the equilibration of the intracellular free lysine pool in either ventricle, or the incorporation of lysine-(14)C into protein. Thus, in controls and ethanol-perfused hearts, the incorporation of lysine in 3 hr was 44.1+/-1.5 and 42.8+/-1.2 mumoles lysine/g protein N for the right ventricles and 25.6+/-1.0 and 24.3+/-0.8 for the left ventricles, respectively. Only at lethal levels, 1500 mg/100 ml ethanol, was protein synthesis depressed. Acetaldehyde 3.5 mg/100 ml (0.8 mM) effected a markedly positive chronotropic and inotropic effect on the perfused heart and slightly depressed equilibration of the intracellular free lysine pool. However, determinations of protein incorporation of lysine-(14)C based on intracellular lysine-(14)C specific activities showed a significant decrease from control right and left ventricle values, to 27.1+/-2.8 and 14.9+/-1.9. Propanalol, which abolished the chronotropic effect, did not prevent the inhibition of protein synthesis. The studies suggest that acetaldehyde, which inhibits cardiac protein synthesis in vitro, may play a role in alcoholic myocardiopathy by interfering with normal myocardial protein synthesis.

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

Carbonate-(14)C was used to label the hepatic intracellular arginine pool and direct measurement of albumin synthesis was made in six rabbits before and after an 18-36 hr fast. 18 perfusion studies were performed with livers derived from fed and fasted rabbits (18-24 hr). Microsomal amino acid-incorporating ability with leucine-(3)H and phenylalanine-(14)C was compared in 17 studies, using microsomes isolated from livers taken from fed and fasted rabbits and from isolated perfused livers whose donors were fed and fasted. Albumin synthesis is rapidly inhibited by fasting. Albumin synthesis decreased 33% in vivo and 53% in the perfused liver. The microsomes from perfused livers taken from fed animals did not demonstrate a significantly reduced capacity to incorporate leucine-(3)H or phenylalanine-(14)C into protein. Microsomes derived from perfused and nonperfused livers whose donors were fasted incorporated 32-54% less tracer than microsomes obtained from fed donor rabbits. Microsomes separated from perfused livers removed from fed and fasted rabbits responded to polyuridylic acid stimulation and phenylalanine-(14)C incorporation rose from 58 to 171%. An 18-36 hr fast inhibits albumin production in vivo and in the perfused liver. The microsomal system is less active in the fasted state and perfusion per se does not inhibit the microsomal response.

Alcohol-induced depression of albumin synthesis: reversal by tryptophan

The influence of alcohol on albumin synthesis was studied in the isolated perfused rabbit liver. Carbonate-(14)C was used to label the intracellular arginine pool which serves as the precursor of both the carbon of urea and the guanido carbon of arginine in albumin. The control group synthesized albumin at a rate of 33 mg/100 g of wet liver weight during 2.5 hr of perfusion. When alcohol, 220 mg/100 ml, was added to the perfusate, albumin synthesis decreased to between 7 and 11 mg, less than one-third the control rate. The addition of 10 mM tryptophan to perfusates containing alcohol prevented most of the inhibitory effects and albumin synthesis increased to average 24 mg. Further, the addition of alcohol to the perfusate decreased the hepatic protein/DNA ratio from 70 to 54 and the RNA/DNA ratio from 2.3 to 1.8, changes equivalent to those seen after a 24 hr fast. The addition of tryptophan to the perfusate prevented these findings in both instances. Endoplasmic membrane-bound polysomes were examined for aggregation. Alcohol decreased the quantity of heavier aggregates. Reaggregation occurred when tryptophan was added but quantitative changes in albumin synthesis could not be related to the degree of reaggregation.

Alcoholic cardiomyopathy II. The inhibition of cardiac microsomal protein synthesis by acetaldehyde

Abstract Previous studies in this laboratory had shown that while ethanol at levels of 200 to 300 mg 100 ml had no effect on cardiac protein synthesis, acetaldehyde ( 3.5 mg 100 ml or 0.8 m m ) markedly inhibited cardiac protein synthesis in the intact heart in vitro. In order to localize further the action of acetaldehyde and to separate the protein synthetic effects from contractile function, studies on cell free systems with cardiac muscle microsomes were carried out at concentrations of acetaldehyde seen in humans after moderate ethanol ingestion. There was a significant reduction of microsomal protein synthesis even at these levels of acetaldehyde. Thus, with an acetaldehyde concentration of 0.53 mg 100 ml (0.12 m m ) the protein synthesis was reduced to 52 ± 5.3% of the control microsomes. With acetaldehyde concentrations of 0.13 to 0.26 mg 100 ml (0.03 to 0.06 m m ), the microsomal protein synthesis was 65 ± 8.6% of the controls. The differences from the controls were statistically significant. These data show that at concentrations seen in humans following ethanol ingestion, acetaldehyde interferes with normal cardiac protein synthesis independent of contractile action and thus may play a role in the ultimate development of ethanolic cardiomyopathy.

STUDIES ON ALBUMIN SYNTHESIS: THE EFFECTS OF DEXTRAN AND CORTISONE ON ALBUMIN METABOLISM IN RABBITS STUDIED WITH ALBUMIN-I131*

Following plasmapheresis, the depressed serum albumin concentration rapidly returns to normal (1) indicating alterations in albumin synthesis or degradation. Both dextran administration (2-6) and elevation of serum globulin levels produced by means of hyperimmunization (7, 8) are associated with hypoalbuminemia; a colloid osmotic regulatory mechanism has been suggested as responsible for the reciprocal changes in serum proteins observed after hyperimmunization (7, 9). If such a mechanism does exert control over the concentration of serum albumin, alterations of albumin metabolism either in the rate of synthesis or in the rate of degradation might be expected when osmotically active molecules other than albumin are added to the circulation. The present study represents an attempt to define, more specifically than heretofore reported, the changes in albumin metabolism resulting from such a procedure. Dextran was administered to rabbits to depress albumin concentration. After the development of hypoalbuminemia, the rates of albumin synthesis and degradation were studied and compared with control values. Cortisone acetate was then given to increase the rate of albumin degradation (10), and the rates of albumin synthesis were remeasured.

THE EFFECT OF HYPERGAMMAGLOBULINEMIA ON ALBUMIN METABOLISM IN HYPERIMMUNIZED RABBITS STUDIED WITH ALBUMIN-I131

Depressions of the serum albumin level are seen in clinical and in experimentally produced hyperglobulinemia (1-3); dextran infusions are also associated with hypoalbuminemia (4). However, the mechanisms for the production of these changes in albumin levels are not clearly defined. A colloid osmotic regulatory system has been postulated which effects control through either changes in plasma volume (1) or alterations in albumin metabolism (4). Previous studies employing dextran infusions supported the existence of a colloid osmotic regulatory mechanism in the control of serum albumin metabolism (4). The purpose of the studies reported here was to reexamine this hypothesis by measuring the rates of albumin synthesis and degradation during the development of induced hyperglobulinemia and after the attainment of this state.

Alterations in Albumin Metabolism after Serum and Albumin Infusions

The intravenous administration of whole serum or of serum albumin results in a temporary increase in the concentration of circulating protein; the rate of return toward preinfusion levels depends upon the state of protein depletion or pool size and upon the rates of synthesis and degradation of albumin (1-6). Much of the infused protein can be accounted for by increased nitrogen excretion in the urine (2-4); the remainder has been assumed to be stored in intravascular or extravascular areas (1-6). The rate of disappearance of tracer-labeled homologous and heterologous albumin from plasma has been observed to increase during the infusion of whole serum or of serum albumin (6-7). Thus, although there is an increase in protein degradation associated with at least a temporary storage of protein, observations on the changes in endogenous protein synthesis and degradation that might follow such infusions are not available. The effects of prolonged infusions of pooled homologous serum or salt-poor human serum albumin on albumin metabolism in rabbits tolerant to human albumin are reported in the present study.

Alcohol, Amino Acids, and Albumin Synthesis: II. Alcohol inhibition of albumin synthesis reversed by arginine and spermine

The effects of alcohol and spermine on albumin synthesis and polysome aggregation were studied in the isolated perfused rabbit liver system. Fed or fasted males served as donors and the perfusate contained, singly or in combination, alcohol, 200 mg per 100 ml, spermine, 1 mM, and arginine, 10 mM. The results indicate that in the presence of alcohol, using a liver from a fed donor, albumin synthesis is depressed from 16 to 6 mg per 100 g of wet liver weight per hr and the bound polysome is disaggregated. Spermine partially reaggregates the bound polysome and a combination of spermine and arginine augments albumin synthesis to the control rate. When the donor is fasted, and alcohol is present in the perfusate, the addition of spermine results in aggregated bound and free polysome patterns, whereas the combination of arginine and spermine is necessary to restimulate albumin synthesis. The results indicate that spermine plays an important role in the integrity of the polysome system and that arginine and spermine appears synergistic in maintaining albumin synthesis.

The Stimulation of Albumin Synthesis by Methadone

Elevated levels of serum albumin have been noted in patients on chronic methadone maintenance and in heroin addicts. This observation was investigated in rabbits maintained on daily methadone 4 mg per kg of body weight after a period of 3 months on increasing dosage to assure drug tolerance. Albumin distribution and metabolism were measured with tested lots of 125I rabbit albumin. Studies were made before and again after the attainment of the methadone maintenance state. Albumin distribution was altered markedly with a shift of intravascular albumin to extravascular sites. Associated with this change, the serum albumin level rose by an average of 0.5 g per 100 ml. Albumin degradation increased by 32% from 248 to 327 mg per kg per day. The total exchangeable albumin pool increased 35%, or 3.6 g. Since the exchangeable albumin pool increased in the face of an increment in albumin degradation, albumin synthesis must have increased even further to account for this change. Although the specific factors responsible for these alterations in albumin metabolism and distribution are not known at present, to date, this hyperalbuminemic hypercatabolic state is not produceable in any other clinical or experimental situation.