Extravascular Albumin Research Articles

Albumin metabolism and gastrointestinal loss of protein in chronic renal failure.

The catabolism of albumin labelled with 125I has been studied in 10 patients with advanced renal failure and in 5 with nephrotic syndrome. In 10 patients the gastrointestinal protein loss was studied simultaneously by determing the faecal excretion during 7 days of 51Cr after i.v. administration of 51Cr-labelled chromic chloride. The results were related to a control group in which 12 subjects were studied with respect to albumin catabolism and 17 with respect to the gastrointestinal protein losses. The results showed that: 1) In the two patient groups the means for serum albumin concnetration and the intravascular albumin pool, expressed as g or g/kg b.wt., were significantly decreased compared with those of the control group. 2) The two patient groups had an increased extravascular albumin pool as well as an elevated ration between extra- and intravascular pools. 3) The mean albumin catabolic rate was not increased in the renal insufficiency group, expressed as a percentage of the intravascular pool/24 h or as g/24 h. In the patients with nephrotic syndrome, however, it was significantly increased. 4) The renal insufficiency group had a mean cumulative 51Cr excretion during 7 days of 1.6+/- 0.80% of the given dose, the control group 0.63+/- 0.30%. This difference is highly significant. The patients with nephrotic syndrome did not differ from the control group.

Whole-body albumin mass and distribution in rats fed on low-protein diets.

1. From 5 weeks of age, control and experimental rats were given diets containing 210 and 31 g protein/kg respectively, and killed for analysis at 0, 2, 5, 8, 12 and 20 d after the start of the experiment. At these times estimates were made of plasma albumin concentration, plasma volume and total vascular and extravascular albumin mass. 2. Plasma albumin concentrations were significantly lower in the experimental animals when compared to controls at 8, 12 and 20 d but plasma volumes (ml/kg body-weight) tended to be greater in the former animals. Total vascular albumin mass (g/kg body-weight) was significantly less in experimental animals compared to controls at 8 and 20 d, but was significantly reduced below values at 0 d only at 20 d. 3. extravascular albumin mass (g/kg body-weight) was significantly lower in experimental animals in comparison with controls at 2, 5, 8, 12 and 20 d and significantly reduced below values at 0 d at 5, 8, 12, and 20 d. 4. Whole-body albumin mass was significantly reduced at 5, 8, 12 and 20 d when compared both with controls killed at the same time and animals killed at 0 d. Measurement of the ratio, extravascular albumin mass: vascular albumin mass indicated a significant redistribution of whole-body albumin mass at 5 and 20 d and mean values for this ratio were always lower in experimental animals than in controls. 5. It was concluded that measurement of plasma albumin concentration does not indicate the true extent of whole-body albumin losses in protein deficiency since total vascular albumin mass is, to some extent, maintained at the expense of extravascular albumin mass.

EFFECTS OF ALBUMIN AND/OR FUROSEMIDE THERAPY ON PULMONARY EDEMA INDUCED BY HYDROCHLORIC ACID ASPIRATION IN RABBITS

Aspiration of hydrochloric acid in rabbits resulted in an increased P(A-a)O2 together with increases in both lung water volume and lung extravascular albumin. This finding suggests lung damage following acid aspiration is related to changes in capillary permeability, with pulmonary edema resulting from the movement of albumin and water into the interstitial space. Therapy with albumin and furosemide together reduced the lung water and albumin accumulation and decreased P(A-a)O2. Treatment with albumin or furosemide alone was ineffective. Caution should be exercised in administering albumin alone for therapy of pulmonary edema when plasma protein is not clearly decreased, or when increased pulmonary capillary permeability is suspected.

The kinetics in vivo of the synthesis of albumin-like protein and albumin in rats.

The incorporation of radioactivity into total protein, albumin-like protein and albumin in liver and into total protein and albumin in blood plasma, was studied for a time period of 2 h after intraportal injection of L-[1-14C]leucine. 1. In the liver, radioactivity began to increase in albumin-like protein before 2.5 min and in albumin at about 10 min after injection. In the plasma, radioactive albumin appeared at about 15 min. No albumin-like protein could be detected in the plasma. 2. Maximum radioactivity was reached first in albumin-like protein, then in hepatic albumin and finally in albumin in the blood-stream. The maximum specific radioactivity of albumin-like protein was 15 times higher than that of extravascular hepatic albumin which, in turn, was 6 times higher than that of plasma albumin. 3. The increase of radioactivity in albumin in the blood corresponded almost quantitatively to the decrease of radioactivity in albumin-like protein. 4. It is concluded that the albumin-like protein is the precursor of albumin in vivo. It is converted into albumin 5-6 min before the appearance of newly synthesized albumin in the blood-stream.

Extravascular albumin in bone tissue.

1. The amount of albumin in extravascular tissue fluid in bone, kidney, intestine, skin and muscle and in plasma of young rabbits has been measured by radial immunodiffusion. 2. The majority of extravascular albumin in kidney, intestine, skin and muscle is exchangeable with plasma albumin, whereas in bone, only the proportion which is in tissue fluid is readily exchangeable; the remaining fraction in calcified matrix is more permanently fixed. 3. About 27% of the albumin in young bone is in tissue fluid, about 57% in calcified matrix and about 16% is intravascular. The total amount of extravascular albumin per unit mass of bone is similar to that found in soft tissues. 4. The volume of intravascular plasma in tissues was determined in two ways: from 51Cr-erythrocyte radioactivity and the venous haematocrit and from the '5 min 125I-fibrinogen space'. 5. The rate of egress of albumin from blood vessels has been estimated from the initial slope of the ratio of extravascular radioactivity in the tissue to plasma radioactivity plotted against time after injection of 125I-albumin. 6. The rate of clearance of the albumin in extravascular tissue fluid in bone is approximately once every hour. This is more rapid than in skin and muscle, comparable with intestine and less rapid than in kidney. 7. The amount of albumin incorporated into calcified matrix of bone per day is calculated to be less than 0-5% of the total albumin passing through the tissue fluid of bone per day.

Effects of long-term low protein diet on albumin metabolism in chronic uremia.

The effects of long-term low protein diet on albumin metabolism of uremic patients were evaluated. Studies were performed on 62 patients divided into two groups depending on the duration of the diet (35 subjects from 6 to 30 days, 27 subjects from 6 months to 5 years). All patients received a diet containing at least 20 g of high biological value proteins per day. Albumin catabolism and distribution were measured by the two-tracer technique, after simultaneous i.v. injection of 131I-human serum albumin and of free 125I-iodide. Albumin synthesis was directly determined in 10 patients by two tracers, 14C-carbonate and 131I-albumin, according to the xanthydrol technique for specific activities of urea and albumin guanido carbon in plasma. The main features of albumin metabolism observed in both groups studied were: normal intravascular albumin mass, marked reduction of extravascular and total albumin pools, with proportionally reduced catabolism. No significant turnover difference was found between the first group and the patients on diet from 0.5 to 5 years, thus suggesting that dietary treatment per se is not responsible for the albumin depletion observed in chronic uremia.

Kinetics of Taurocholate Uptake by the Perfused Rat Liver

The uptake of taurocholate (TC) by the perfused rat liver was studied by the multiple indicator dilution technique using single injections of 14-C-labeled TC and 99m-Tc-labeled albumin. For determination of the intra- and extravascular space, 51-Cr-labeled erythrocytes and albumin were used. TC was found to be distributed into an extravascular space equivalent to that of albumin. Analysis of the dilution curves, according to Goresky (Am J Physiol 207:13-26, 1964), revealed that the initial TC uptake rate increased with increasingly TC dose in a nonlinear fashion, exhibiting saturation kinetics which obeyed the Michaelis-Menten equation. The initial maximal uptake rats (Vmax) was found to be 32.5 nmoles per s and g of liver, a value exceeding the maximal steady state capacity (Tm) for excretion of TC into the bile. The half-saturation constant (Km) was 90.6 nmoles per g of liver, indicating that this system is operating far from saturation at physiological levels of bile acids in portal blood.

A new approach to evaluate the final effect of parenteral nutrition.

In patients who had undergone gastric operations, the efficacy of a parenteral rehabilitation with plasma, human albumin and Aminofusin L forte was determined by assessing the extravascular albumin pool. The intravenous administration of Aminofusin L forte thus proved to be today's safest and quickest method of protein rehabilitation.

Albumin and water fluxes during cardiopulmonary bypass

If cardiopulmonary bypass is done with a hypooncotic prime, the initial fall in colloid osmotic pressure in the patient is followed by an incomplete compensatory rise. The mechanism of this rise has been investigated by studying the time course of the specific activity and the concentration of 125 I albumin activity in the plasma. Albumin specific activity fell at a rate greater than that measured in the control subjects, thus indicating an increased influx of albumin into the circulating blood volume. The concentration of labeled albumin in the patients, in sharp contrast to that in the control subjects, rose during bypass. This indicated an efflux of water from the circulating blood volume. It is concluded that both albumin influx and water efflux contribute to the rise in colloid osmotic pressure during bypass. It is further concluded that at the end of bypass approximately 40 per cent of the rapidly exchangeable extravascular albumin pool will have been transferred to the intravascular compartment, while approximately 1 L. of water will have been added to the interstitial fluid.

Pulmonary extravascular chloride space and albumin content in adult dogs and puppies.

Extract: The extravascular chloride space and albumin content of the lungs were determined in 6 adult dogs and 10 puppies. 125I-labeled human serum albumin was administered and its concentration in lung tissue was determined after equilibration with the total body albumin pool. The blood content of the lung was determined by 51Cr erythrocyte tagging, and the extravascular fluid volume by 36Cl dilution. Total water in the lung was measured by drying the lungs to constant weight. The interstitial albumin concentration, assuming uniform distribution in the chloride space, averaged 1.0 g/100 ml interstitial fluid in the adult dogs and 0.62 in the puppies; the difference between these means is statistically significant. These interstitial albumin concentrations are considerably lower than lymph protein concentrations in lung reported previously. Speculation: These data support the notion that a large net absorptive gradient of colloid osmotic pressure is present across the fluid-exchanging vessels of the lung. In view of the relatively low level of pulmonary capillary hydrostatic pressure, the application of Starling's law of capillary exchange to these data indicates that interstitial hydrostatic pressure is substantially subatmospheric [12]. Although consistent with recent measurements of interstitial pressure using perforated capsules [9], this line of argument must be considered speculative because of uncertainty as to the distribution of protein in the interstitial fluid. Information is lacking as to the mechanism whereby the protein concentration of lymph is increased relative to that of capillary filtrate or the interstitial fluid. This could occur if the hydrostatic pressure within the lymph channels were significantly higher than the surrounding interstitial pressure. The maintenance of a low protein concentration in the interstitial fluid, by virtue of limited protein filtration and efficient lymphatic removal, would constitute an important barrier against pulmonary edema formation. The present study suggests that this barrier may be more effectively maintained in the immature than in the mature animal, thus counterbalancing the increased tendency for fluid filtration in the immature lung reported previously [13].

Influence of albumin on the extravascular distribution of unconjugated bilirubin.

1. [3H]Bilirubin and 131I-labelled albumin were given simultaneously to six healthy adults by intravenous route and the amounts in the plasma were measured for several days. Multicompartmental analysis of the data showed that the rate of movement of [3H]bilirubin from the plasma into the extrahepatic extravascular space was 29·7 ± 7·3% (mean ± SEM) of the plasma pool/h, whereas the rate of movement of 131I-labelled albumin from plasma into the extravascular space was only 7·2 ± 1·0% of the plasma pool/h. 2. [14C]Bilirubin was found to equilibrate throughout the body of a child with the Crigler-Najjar syndrome within 24 h of intravenous administration, whereas 131I-labelled albumin required 4–5 days in human subjects. 3. Multicompartmental analysis of the plasma data in the six healthy adults indicated that the mass of material in the extrahepatic extravascular space relative to that in plasma was greater for unconjugated bilirubin than for albumin. 4. Studies of the tissue distribution of unconjugated bilirubin in homozygous Gunn rats demonstrated that the organs which comprise the rapidly exchanging extravascular albumin pool (liver, kidney and intestine) accumulated unconjugated bilirubin in excess of their albumin content, whereas lesser amounts of unconjugated bilirubin were accumulated in the tissues which make up the slowly exchanging extravascular albumin pool (muscle, fat and skin). 5. These findings indicate that unconjugated bilirubin moves more rapidly between plasma and extrahepatic extravascular sites than can be accounted for by transport bound to albumin. They also indicate that extravascular binding of unconjugated bilirubin includes tissue sites, as well as extravascular albumin.

Distribution of extravascular albumin in liver: Estimation by a fluorimetric dye-binding technique

A simple procedure for assay of albumin in liver is quoted. The technique depends on a fluorescent-binding product with ANSA, and has a comparatively low coefficient of variation of 6.4%. The results when corrected for vascular albumin content agree with those obtained from other methods, both for estimates of extravascular albumin and for microsomal, newly synthesized albumin. Accuracy, as measured by recovery of albumin added to liver homogenate, was 98–100%.

Effect of irradiation on tumor microvascular permeability to macromolecules.

In C3H mouse Gardner lymphosarcoma, we have demonstrated an increase in the extravascular albumin space 48 hours after delivering 3,000 rads of irradiation. This observation has implications for organ radiobiology in that the microvascular effect could alter radiation response in tumors. This effect may be time dependent and thus may be an extremely important consideration in dose fractionation which is not necessarily dependent on tumor cell cytokinetics. The second ramification of this observation concerns the effect of irradiation on radiotracer techniques designed to identify tumors; following irradiation, an increased macromolecular transport into the interstitial space of a tumor would be anticipated to cause increased accumulation of scanning agents which are bound to protein (e.g., gallium).

Localization of bilirubin pools in the non-jaundiced rat, with a note on bilirubin dynamics in normal human adults and in Gilbert's syndrome.

Thirty min after i.v. injection of 14C-bilirubin into normal rats, the label was distributed as follows: small intestine with contents 0.41, liver 0.15, blood plasma 0.14, skin—bone, etc.—lungs—spleen 0.30, skeletal muscle—fat depots—brain 0. Bilirubin outside liver and intestine is probably bound to extravascular serum albumin. Enterohepatic circulation of bilirubin takes place. A model is proposed for bilirubin kinetics in normal human adults and in Gilbert's syndrome.

Interaction of albumin and fusidic acid.

1. By combining the agar plate diffusion technique for determination of antibiotic activity and zone microelectrophoresis in agar gel, the activity of fusidic acid in individual serum proteins of blood and pus obtained from patients given sodium fusidate revealed albumin to be responsible for the protein binding of this antibiotic.2. Based on the assumption that only free fusidic acid is microbiologically active, the relationship between the concentration of albumin and the ratio of free to total fusidic acid was determined at four concentrations of free fusidic acid, using as test organisms four differently sensitive variants of a Staphylococcus aureus strain. At each concentration an increasing amount of albumin (0-40 mg/ml culture medium) decreased the activity of fusidic acid as determined in serial dilutions (IC50).3. The law of mass action expressed as Langmuir's adsorption isotherm was valid if a correction for the influence of albumin on the sensitivity of the strain of Staph. aureus was introduced. For other test organisms no correction is necessary. The constant in Langmuir's adsorption isotherm was K=78400+/-8200 l./mol and n=3.15 (95% confidence limits: 2.09-5.52).4. The mean blood concentration was 20.8 mug/ml and the mean pus concentration 17.2 mug/ml in nineteen sets of blood and pus samples. The ratio of pus to blood corresponds to the ratio of published values for the protein concentrations in serum and in inflammatory oedema.5. It is concluded that for albumin bound drugs the ;storage depot' of the organism also includes the fluid of the tissue spaces including the inflammatory oedema. As recent studies have revealed an extravascular albumin pool similar in size to the plasma pool, this ;storage depot' should not be neglected.

The radioisotopic assessment of regional microvascular permeability to macromolecules

Using a dual isotope technique we have identified regional characteristics of microvascular permeability to macromolecules in the rat. Much of the difference between organs is consistent with the electron microscopic observations of different capillary endothelia. Although cardiac and skeletal muscle have similar endothelial anatomy we discerned a difference in macromolecular permeability. In cardiac muscle extravascular albumin equilibrates faster to a small space. The lung has a small, rapidly equilibrating extravascular albumin pool. Skin has a very large, slowly equilibrating extravascular albumin space. Brain has a small extravascular albumin space, perhaps related to the choroid plexus which was not eliminated from our assay. The liver extravascular albumin space equilibrates in less than 5 min, consistent with prior observations and hepatic microvascular anatomy. The adrenal was characterized by a very rapidly equilibrating small extravascular albumin space. The small intestine demonstrated a remarkably low blood volume for the apparent size of the extravascular space. A dilutional intravascular space (i.e., low regional hematocrit) may have contributed to our estimate of extravascular albumin in the intestine. The kidney was characterized by a rapid movement of albumin to the extravascular compartment, which may be due in part to a loss of the label and iodine excretion.

Extravascular albumin in human tissues.

1. Extravascular albumin in human tissue was determined by direct immunochemical analysis. Samples of muscle, skin and intestinal tract obtained at surgery were extracted with a solution of 0· 9% sodium chloride plus 0· 1% desoxycholate and total albumin of the extracts was determined by radial diffusion in agarose plates containing antibody to human albumin. Occluded blood in tissues was estimated from the haemoglobin content of the extracts and the albumin due to blood calculated. This was used to obtain by difference the extravascular albumin content of the tissues. The extravascular albumin content of muscle and skin from seven patients was (mean and range) 3·6 (2·7–6·4) and 8·4 (6·5–12) mg/g, respectively. The albumin content of intestinal tissue (five patients) ranged from 4·3 to 9·0 mg/g (mean 6·3), and of stomach wall (three patients), from 3·5 to 5·4 mg/g (mean 4·4). Total extravascular albumin in humans is estimated to be at least 4 g/kg. 2. The extravascular (EV) albumin of human tissue is similar to that of rats. It is concluded that calculation of the extravascular albumin from the intercepts and slopes of the decay curve of injected radioactive iodine-labelled albumin leads to underestimation of the extravascular mass by 20–40%. The validity of the conventional multicompartmental model of albumin metabolism in the human is questioned.

Extravascular albumin mass and exchange in rat tissues.

1. Extravascular albumin in carcass, skin and gut of rats was extracted and the albumin content estimated by several methods. Assay by electrophoresis on acrylamide gel, by immunodiffusion and by radioimmunoassay were in essential agreement. The method used previously, precipitation with antibody followed by alcohol-TCA extraction, underestimates the amount of albumin in tissue extracts, because extraction from the antibody precipitate is not complete. This method is valid, however, for specific activity determination. 2. Normal rats contain from 500 to 650 mg of albumin per 100 g body weight. Of this, 20–25% is in the circulation, 35–40% in the carcass (mainly but not exclusively muscle), 20–25% in skin and 10% in gut. 3. The extracellular water of muscle, carcass, skin and gut was estimated from the distribution of mannitol and sulphate. With the exception of gut, both methods agreed closely. Extracellular, extravascular water constitutes about 23% of the body weight of 150–200 g rats. The extracellular water in muscle is about 20% and in skin, 40%. In gut the extracellular water cannot be estimated reliably by these compounds. 4. Muscle contains about 3·5 mg/g of extravascular albumin; skin and gut, 7–8 mg/g. The concentration of extravascular albumin in extracellular water of muscle and skin is 1620 mg/ml, or 5060% of the concentration in plasma. In the small intestine the concentration of albumin is higher, possibly similar to that in plasma. 5. In rats with severe aminonucleoside nephrosis, body albumin was depleted to 100–200 mg/100 g. Of this, 15–25% was in plasma, 50% in carcass, and about 15% in skin. Ascitic fluid contained only a few mg of albumin. 6. The specific activity of extravascular albumin of tissues was followed after intravascular injection of 125I- or 131I-labelled albumin. The specific activity of carcass albumin increases rapidly, becoming equal to that in plasma after less than 2 days. The specific activity of albumin in skin increases much more slowly and becomes equal to that of plasma after 4 days. Labelling of albumin of gut is even slower. The specific activities in tissue never exceed that in plasma. 7. In severely nephrotic rats, specific activities in carcass and skin become equal to that in plasma within 2–3 days and remain equal thereafter. Specific activity of albumin in ascitic fluid increases to reach values as much as sixteen-fold those in plasma. 8. The extravascular pool, as calculated by multicompartmental analysis from the slopes and intercepts of the plasma curve, is about equal to that in plasma and in severely nephrotic rats is less than that in plasma. Discrepancies between calculated and observed extravascular albumin masses is by a factor of 3 in normal rats and 10 or more in severely nephrotic rats. 9. Specific activity of extravascular albumin as calculated from multicompartmental analysis is 1·5 times that in plasma in normal rats and at least six times that in plasma in severely nephrotic rats. Actually, the specific activities in extravascular and vascular albumin ultimately become and remain equal. 10. It is concluded that the multicompartmental model of vascular pool exchange with one or two extravascular pools is not valid for rats and probably not for other animal species.

Ocular vascular permeability. Effect of systemic administration of bacterial endotoxin.

Intravenously administered bacterial endotoxin induces an acute marked alteration in ocular vascular permeability in the rabbit. This effect was measured using a dual radioisotope technique employing red blood cells labeled with Ferrie chloride Fe 59 and human serum albumin labeled with iodine 131. Sites of vascular leakage were identified by a topographic analysis utilizing carbon particles systemically. Ocular blood volume was unchanged until 12 hours after endotoxin when a 50% rise was noted. Extravascular protein (extravascular albumin space—EVAS) was seven times greater than in the normal rabbit at two to four hours, twice as great at 12 hours, and was returning to normal at 24 hours. Leakage was primarily in ciliary processes, and by 12 hours, these were markedly edematous. The HSA 131 I content in the aqueous was only a partial indication of the extent of the vascular permeability change.

Changes in the blood volume of the rabbit with age.

1. The changes in blood haemoglobin concentration, great vessel haematocrit value, red cell volume, plasma volume and total blood volume have been studied in rabbits from birth to 4 months of life.2. The plasma volumes were measured with [(131)I]human serum albumin and/or rabbit serum [(14)C]albumin. Red cell volumes were measured with [(51)Cr]-rabbit red blood cells. Blood volumes were also calculated from carbon clearance curves.3. The haemoglobin concentration and the great vessel haematocrit value fell during the first 11 days of life. The great vessel haematocrit value was then not significantly different from the value at 4 months; whereas the haemoglobin concentration fell further until 22 days, when it started to rise towards the concentration at 4 months.4. The true plasma volume could not be accurately measured during the first 48 hr of life by the injection of labelled albumin since it rapidly equilibrated with an extravascular albumin space. As the ratio of the whole body haematocrit to the great vessel haematocrit (F(cells)) did not appear to change with age the plasma volume at this time was best obtained by calculation from the red volume and corrected great vessel haematocrit.5. The blood volume fell significantly during the first 4 months of life due to significant falls in the red cell and plasma volumes.