Transcapillary passage of albumin,effects of tissue cooling and of increases in filtration and plasma colloid osmotic pressure

‘Initial’ clearance of radiolabeled serum albumin was measured in the perfused, maximally vasodilated muscle vascular bed of rat hindquarters during tissue cooling, during increases in filtration and during changes in serum colloid osmotic pressure. Albumin clearance during ordinary serum perfusion at iso-gravimetry amounted to 0.03 ml/min x 100 g, increasing linearly with filtration rate to some 0.07 ml/minx 100 g at 0.5 ml/minx 100 g of filtration. During cooling from 36°C to 14°C both CFC and initial albumin clearance at isogravimetry decreased some 40%, in due proportion to the increased viscosity of the fluid. Increases of the colloid osmotic pressure of the perfusate correspondingly increased both the isogravimetric capillary pressure and ‘initial’ albumin clearance during isogravimetry. – It is concluded that even during isogravimetry the transmicrovascular albumin passage is to about 70 per cent due to filtration, and only some 30 per cent of transport at ordinary serum colloid osmotic pressures takes place by diffusion, both events presumably via ‘large pores’. There was no evidence that transendothelial vesicular transport should to any significant extent contribute to the passage of albumin from vessels to tissue.     

Measurement of colloid osmotic pressure in submicrolitre samples

A colloid osmometer for submicrolitre samples was constructed from solid polymethylmetacrylate and acrylnitrilmethylmetacrylate blocks, exposing a 0.85 mm diameter area of a Diaflo PM-30 ultrafiltration membrane. The unknown sample, contained in a 1-microliter glass micropipette, was applied to the membrane by suction, providing minimal exposure to air. The lower limit for successful application was 0.1-0.2 microliter. The accuracy of colloid osmotic pressure (COP) measurement depends strongly on the effective compliance of the pressure transducer. We tested three different systems: (i) A Hewlett-Packard 1280 'medical' transducer gave acceptable measurements on 1-microliter samples. In smaller samples (0.1-0.5 microliter) COP was underestimated, especially at COP greater than 10 mmHg. The equilibration time was 10-30 min. (ii) As (i), but with air pressure applied to the sample by a servoregulated pump, minimizing fluid transport through the membrane. Accurate measurements on 0.2-microliter samples were obtained in the course of 2-3 min, but the system required special instrumentation and some operating experience. (iii) An 'industrial' transducer, SensoNor AE-88o, with very low compliance, gave accurate measurements in the course of 1-3 min on samples as small as 0.1-0.2 microliter and COP up to 37 mmHg. We recommend system (iii) for samples smaller than 1 microliter.     

Transcapillary passage of albumin in mammary tumours and in normal lactating mammary glands of the rat

A triple-isotope technique was used to obtain albumin clearances and blood flow in DMBA induced mammary tumours, normal lactating mammary glands and various other tissues of the rat. Albumin clearance was high both in tumours (0.0337 ml/min/100 g) and in lactating mammary glands (0.0414 ml/min/100 g). Albumin extraction (defined as the ratio of clearance over plasma flow) was exceptionally high in tumours (23 X 10(-4)) and lactating glands (18 X 10(-4)) as compared to all other tissues (1-7 X 10(-4)). This probably reflects an increased capillary permeability to macromolecules and/or a change in the relation between blood flow and available capillary surface area, both in the physiological, hormonally induced gland and in the abnormal neoplasia derived from the same tissue. Increased extravasation of albumin, together with other changes (e.g. impaired lymph formation) may be important factors behind the production of increased tumour interstitial pressure, which tend to reduce nutritional blood flow in tumours.     

Is albumin synthesis regulated by the colloid osmotic pressure? Effect of albumin and dextran on albumin and total protein synthesis in isolated rat hepatocytes

Summary In order to study the influence of the colloid osmotic pressure on albumin and total liver protein synthesis, rat hepatocytes were isolated by collagenase perfusion and incubated in Krebs-Ringer-buffer for 4 h. The colloid osmotic pressure produced by different bovine serum albumin (BSA) or dextran 60 concentrations varied from 3 to 80 mm Hg. A physiological colloid osmotic pressure of 20 mm Hg was obtained with 5.7 g BSA or 3.7 g dextran 60 per 100 ml of buffer. Albumin synthesis was measured by Laurell rocket immunoelectrophoresis. Total liver protein and total secretory protein synthesis were determined by the measurement of 1-¹⁴C-leucine incorporation. Albumin synthesis was not primarily regulated by the colloid osmotic pressure as was demonstrated by a lack of inhibition after addition of BSA. There was no significant influence of the oncotic pressure on the incorporation of¹⁴C-leucine into total liver proteins. The incorporation into total secretory proteins was inhibited by an increasing colloid osmotic pressure, mediated either by BSA or dextran, suggesting an inhibition of the secretion of plasma proteins other than albumin.Abbreviations BSA bovine serum albumin - HEPES N-2-hydroxyethyl-piperazine-N'-2-ethan sulfonic acid - PPO 2,5,-Diphenyloxazol - POPOP p-Bis (2,5-phenyloxazolyl)-benzol - SEM standard error of the mean - VLDL very low density lipoproteins This work was supported by the Deutsche Forschungsgemeinschaft (We 462/4), the Swiss National Foundation for Scientific Research and the Hochschulstiftung an der Universität BernPart of this work was presented at the European Association for the Study of the Liver, Göteborg 1982     

Effect of ouabain and colloid osmotic pressure on renal tubule cell volume.

Proximal renal tubule cell volume increases in ouabain but cell swelling is limited by the tubule basement membrane (TBM) and the colloid osmotic pressure from the bath protein. We compared the effect of ouabain, external protein concentration, and TBM on cell volume of proximal convoluted (PCT), proximal straight (PST), and cortical collecting tubules (CCT). We blocked active solute transport with ouabain and evaluated cell size by measuring the outer diameter of nonperfused tubules. Proximal tubules in ouabain swelled 35-40% in isoncotic medium and 20-25% further in hyponcotic medium (0.3 g/100 ml albumin), but PCT swelled faster than PST. The CCT swelled minimally in similar mediums, indicating pronounced heterogeneity in the response of cortical nephron segments to ouabain. In the presence of ouabain, all tubules swelled extensively when we removed the TBM with collagenase. In the hyponcotic medium fluid flux across the peritubular membrane was 0.081, 0.049, and 0.030 nl/min per mm tubule length for PCT, PST, and CCT, respectively. The rates of fluid flux in PCT and PST were proportional to estimates of the respective basolateral surface areas. We suggest that differences in swelling rates between proximal segments reflect variations in surface area rather than intrinsic peritubular membrane permeability to solute and water.     

Transcapillary albumin extravasation in rat skin and skeletal muscle: effect of increased venous pressure

Plasma-to-tissue transport of radioactively labelled albumin has been used to study the effect of increased venous pressure on transcapillary albumin transport. Venous pressure was increased by inflating a balloon catheter in the inferior caval vein. Plasma-to-tissue transport of albumin was taken as the extravascular distribution space (EValb) for 125I-labelled human serum albumin (I-HSA) after 1 h. Venous pressure was increased from 2 to 20 mmHg in the experimental group. Interstitial fluid volume (IFV) was measured as the extravascular distribution space for 51Cr-EDTA. In control EValb was 9.24 X 10(-3) ml g-1 d. wt (SD = 1.28, n = 8) and 3.67 X 10(-3) ml g-1 d.wt (SD = 0.94, n = 8) in skin and skeletal muscle, respectively. Increasing venous pressure raised EValb and IFV in skin and skeletal muscle, but the increase in EValb was about 3 and 5% of the rise in IFV, resulting in capillary reflection coefficients for albumin of 0.94 in skin and 0.98 in skeletal muscle. The low transcapillary albumin transport relative to water transport is compatible with a two-pore model of transcapillary exchange where large pores (250 A) accounts for less than 5.5 and 2.5% of the total capillary filtrate of fluid in skin and skeletal muscle, respectively.     

Correlation of standardized serum protein determinations with calculated and measured colloid osmotic pressure

The colloid osmotic pressure (COP) was measured on the serum of 250 individuals (healthy persons and patients) using a commercial oncometer. The total serum protein concentrations were measured by five methods, and the serum albumin concentrations were measured by four methods. The protein determinations were standardized as recommended by the Study Group on Proteins of the AACC Committee on Standards. The measured COP (mCOP) was correlated with each of the nine analytically determined protein concentrations. The mCOP also was correlated with a COP calculated (cCOP) from the Landis-Pappenheimer equation: cCOP = 2.1 (total protein [TP]) + 0.16 (TP)2 + 0.009 (TP)3. The authors found excellent linear correlations between mCOP and total protein concentration, and between mCOP and albumin concentration, when the protein determinations were standardized properly. The correlation between mCOP and protein concentrations was as good as the correlation between mCOP and cCOP in all cases. The serum albumin as determined by the DuPont ACA and mCOP gave the best linear relationship (r = 0.940) of the methods tested. Using the linear regression equation of albumin (ACA) versus mCOP, we were able to predict a cCOP to within +/- 3 mmHg for more than 95% of all samples tested.     

Effects of maintaining normal plasma colloid osmotic pressure on renal function and excretion of sodium and water after major surgery. A randomized study

A prospective, randomized study of patients undergoing abdominal aortic surgery was undertaken to determine the effects of maintaining normal plasma colloid osmotic pressure (COPp) on postoperative renal function and excretion of water and electrolytes. Two groups of 13 patients were given whole blood transfusions to replace blood loss. One group (ALB) received 80 g albumin on the day of operation and 20 g albumin the following three days. The other group (NON-ALB) received no extra albumin. The glomerular filtration rate (GFR) did not change significantly from preoperative values on the first or fourth postoperative day in any of the groups. The differences between the groups were non-significant. COPp could not be correlated to either GFR or sodium or fluid balances. Postoperative sodium and water retention was found to depend on the amount of infused sodium. Unexplained fluid shifts to a "third space" did not occur. Administration of albumin in addition to quantitative blood loss replacement is unnecessary and expensive.     

Transcapillary extravasation rate of albumin in rat skeletal muscle. Effect of motor activity

Transcapillary extravasation of albumin in hindlimb and neck skeletal muscle of rats was determined as extravascular plasma equivalent volumes (I-HSAev), 1-168 h after a single intravenous injection of radiolabelled human serum albumin (I-HSA). One experimental group was immobilized in pentobarbital anaesthesia for the first 8 h after injection of I-HSA. With longer extravasation periods, the rats then woke up and moved freely. In the other experimental group, injections were made in ether anaesthesia allowing the rats to move freely within 10 min after injection. One hour after injection, I-HSAev in the immobilized group averaged 1.5 10(-3) ml g-1 in neck and hindlimb muscle. In the mobile group, I-HSAev was two to three times higher than in the immobilized rats up to 12 h in both muscle groups (P less than 0.05). At 24 h and later I-HSAev was similar in mobile and immobile rats (P greater than 0.05). The I-HSAev increased up to 48 h, levelling off at about 0.06 and 0.08 ml g-1 in hindlimb and neck skeletal muscle, respectively. Corresponding interstitial albumin concentration, calculated from steady-state I-HSAev and interstitial fluid volume (51Cr-EDTA space), averaged 48% and 34% of plasma albumin concentration, respectively.     

Interstitial colloid osmotic and hydrostatic pressures in human subcutaneous tissue during early stages of heart failure

Subcutaneous oedema is a common finding in heart failure. However, some patients have reduced cardiac pump function without oedema. The aim of this study was to investigate whether local mechanisms in subcutaneous tissue contribute to oedema prevention. A reduction in interstitial colloid osmotic pressure (pii) and a rise in interstitial fluid hydrostatic pressure (Pi) will both counteract a rise in capillary filtration caused by heart failure. Cardiac catheterization was done in 22 angina pectoris patients without visible oedema. Two days later pii was measured with a wick method and Pi was measured with a wick-in-needle method. Both parameters were measured in subcutaneous tissue on thorax at heart level and on the ankle. Plasma volume was determined by 125I-albumin and extracellular volume measured with 35SO4. Parameters of cardiac pump function ranged from normal to clearly pathological values. Mean pii was 13.0 mmHg on thorax and 8.3 mmHg on the ankle. Pi averaged -2.1 mmHg on thorax and -1.5 mmHg on the ankle. Statistically significant (P less than 0.05) correlations were found between pii on thorax and left ventricular end diastolic pressure (rs -0.40) and pii on thorax and cardiac index (rs 0.42). Pi was positively correlated to right atrial pressure (rs 0.50). Body fluid volumes were normal or moderately reduced. The study shows that a reduction in cardiac pump function is associated with a reduction in pii and a rise in Pi. These changes may help to prevent oedema formation in the early stages of heart failure.     

The hyperlipidemia of the nephrotic syndrome. Relation to plasma albumin concentration, oncotic pressure, and viscosity

Although hyperlipidemia is a common feature of the nephrotic syndrome, the distribution of cholesterol among the plasma lipoproteins and the mechanism of the enhanced hepatic synthesis of lipoprotein lipids are not well understood. We studied the distribution of cholesterol among the plasma lipoproteins, as well as the relation between total cholesterol and plasma albumin concentration, oncotic pressure, and viscosity in 20 consecutive adult patients with uncomplicated nephrotic syndrome. The total plasma cholesterol (mean +/- S.D., 302 +/- 100 mg per deciliter [7.8 +/- 2.6 mmol per liter]) and low-density-lipoprotein cholesterol concentrations (215 +/- 89 mg per deciliter [5.6 +/- 2.3 mmol per liter]) were elevated in most patients, but the high-density-lipoprotein cholesterol level was normal or low (46 +/- 18 mg per deciliter [1.2 +/- 0.5 mmol per liter]) in 95 per cent of the patients. Thus, many hypercholesterolemic patients with unremitting nephrotic syndrome may be at increased risk for atherosclerotic heart disease. A significant inverse correlation was found between the total plasma cholesterol concentration and both the plasma albumin concentration (r = -0.528) and the plasma oncotic pressure (r = -0.674), but not the plasma viscosity (r = +0.319). Enhanced hepatic synthesis of lipoprotein lipids may be stimulated by a decreased plasma albumin concentration or oncotic pressure but does not appear to be due to changes in plasma viscosity.     

Mucopolysaccharide osmotic pressure in the measurement of interstitial pressure.

Subatmospheric pressures were recorded from cotton wicks inserted into Wharton's jelly of human umbilical cords (mean=-7.6+/-5.0 (SD) cmH2O; n=10). Hyaluronate concentrations (mean=0.69+/-0.30 g/100 g) and wick pressures correlated negatively (r=-0.825; P less than 0.01) but calculated hyaluronate osmotic pressures (mean=4.0+/-2.7 cmH2O) were insufficient to explain the full wick pressure. In model systems composed of asbestos fibers (mean radius=0.5 micron) and 0.9% saline, subatmospheric pressures were recorded which varied with the volume of saline added. When hyaluronate (1 g/100 g) was substituted for saline, lower wick pressures were recorded at each volume. The pressure lowering effect of hyaluronate was not seen in a matrix of glass fibers (mean radius=1.0 micron). It is suggested that the effect of hyaluronate in asbestos fibers is due to its immobilization by the matrix and the consequent development of osmotic pressure recorded via the wick. In the coarser glass-fiber matrix, hyaluronate was not immobilized and therefore had no osmotic effect. These experiments support the hypothesis that subatmospheric interstitial pressures result from osmotic pressure of immobilized mucopolysaccharide macromolecules.     

The ontogeny of the onset of drinking and plasma osmotic pressure regulation

Pertinent behavioral and physiological variables related to the development of the onset of drinking were measured in albino rats of both sexes between 14 and 100 days of age. Under ad libitum conditions all variables studied were found to increase as a function of age. Following a subcutaneous 16% NaCl injection mean latency to drink was found to range from 4.6-9.5 min across ages. Plasma osmolality levels at the initiation of drinking were found to increase as a function of age and were found to be elevated over ad libitum levels by a relatively constant magnitude. The onset of drinking across ages was associated with 2.8-6.6% increase in plasma osmolality. These data suggest that although absolute levels of ad libitum osmolality increase from birth to maturity, the threshold increase in osmolality required for the initiation of drinking remains quite constant.