Elevated levels of colloid osmotic pressure in cecal contents of germfree animals.

Determinations of colloid osmotic pressure in the supernatant of germfree rat cecal contents indicated substantially elevated values in comparison to those of rat blood plasma or of conventional rat cecal supernatant. The germfree cecal supernatant, under conditions of similar total osmolality, was able to draw water at a sizable rate from a polyvinylpyrollidone solution whose colloid osmotic pressure was taken to be equivalent to that of interstitial fluid. It is suggested that the water absorption inhibition which was observed in the lower bowel of germfree rodents, is in part caused by the colloid osmotic pressure gradient which exists in these animals between the luminal contents and the tissue component.     

Interstitial albumin concentration measured during growth of perivascular cuffs in liquid-filled rabbit lung.

The growth rate and albumin concentration of interstitial fluid cuffs were measured in isolated rabbit lungs inflated with albumin solution (3 g/dl) to constant airway (Paw) and vascular pressures for up to 10 h. Cuff size was measured from images of frozen lung sections, and cuff albumin concentration (Cc) was measured from the fluorescence of Evans blue labeled albumin that entered the cuffs from the alveolar space. At 5-cmH2O Paw, cuff size peaked at 1 h and then decreased by 75% in 2 h. The decreased cuff size was consistent with an osmotic absorption into the albumin solution that filled the vascular and alveolar spaces. At 15-cmH2O Paw, cuff size peaked at 0.25 h and then remained constant. Cc rose continuously at both pressures, but was greater at the higher pressure. The increasing Cc with a constant cuff size was modeled as diffusion through epithelial pores. Initial Cc-to-airway albumin concentration ratio was 0.1 at 5-cmH2O Paw and increased to 0.3 at 15 cmH2O, a behavior that indicated an increased permeability with lung inflation. Estimated epithelial reflection coefficient was 0.9 and 0.7, and equivalent epithelial pore radii were 4.5 and 6.1 nm at 5- and 15-cmH2O Paw, respectively. The initial cuff growth occurred against an albumin colloid osmotic pressure gradient because a high interstitial resistance reduced the overall epithelial-interstitial reflection coefficient to the low value of the interstitium.     

Analysis using a linear viscoelastic model of the in vitro osmotic kinetics of polydisperse synthetic colloids

This study clarifies the contribution to overall osmotic kinetics of colloid osmotic pressure (Pi) and the interaction of synthetic colloids with the membrane. Solutions (6%) of dextran with weight average molecular weight (MW(w)) 68 800 (DEX 70), dextran with MW(w) 40 000 (DEX 40), hydroxyethyl starch with MW(w) 70 000 (HES 70), gelatin with MW(w) 60 000 and albumin were tested. An osmotic flow cell fitted with membranes of molecular weight cutoff size 30 000 or 50 000 was used to measure time-dependent changes in Pi for each of these solutions. A linear viscoelastic model was fitted to the curve describing changes to Pi as a function of time. Values of total effective Pi for DEX 40 and DEX 70 were larger than those for HES 70, gelatin, and albumin. As an index of solute-solvent exchange rate at the membrane surface, these values were in the order DEX 40 > DEX 70, HES 70 > gelatin, albumin. The findings suggest that DEX 40 may be preferable for the temporary restoration of plasma volume because of a heightened initial osmotic force. In contrast, the osmotic force exerted by gelatin is slower to increase but is likely to be longer lasting in vivo as a result of the inhibition of gelatin from penetrating the capillary membrane due to its interaction with negatively charged groups in the endothelial glycocalyx.     

An hypothesis on the role of cellular colloid osmotic pressure in determining behavior of cells in vitro including anchorage dependency and maintenance of the differentiated state

The osmotic problems involved when cells are isolated from tissues are analyzed. Evidence is considered which indicates that in vivo the Na pump is operating at maximal or near maximal rates and that this depends on low leak rates for salts and water due to various aspects of the tissues structure. Dispersion of the tissue results in breakdown of these barriers on free diffusion and the isolated cell is subjected to an enormous increase in passive influx due to colloid osmotic pressure without being able to increase its pumping rate to the extent needed to maintain volume control. It is proposed that the primary problem the cell faces in vitro is to compensate for the effective increase in its colloid pressure, e.g. the colloid osmotic pressure excess, emerging with the breakdown of the tissue structure. The finding that most normal cells have to adhere to a surface in order to grow or "anchorage dependency" is analyzed in terms of the way adhesion and spreading result in changes in ion and water movements into cells enabling them to achieve fluid balance in the face of the colloid pressure excess. It is also proposed that the differentiated state is more dependent on colloid osmotic balance than proliferation. The failure of conditions used in tissue culture to compensate adequately for the colloid pressure excess results in limiting the amount of protein which can be synthesized, dissipation of cellular energy, and changes in orientation of cellular components which contribute directly to the loss of differentiation which occurs during growth in vitro.     

Semipermeability of the nuclear membrane in the intact cell

The osmotic properties of nuclei in intact cells were studied by injecting solutions into the cytoplasm of amphibian oocytes. Subsequent changes in nuclear volume were recorded photographically. The injection of solutions containing polyvinylpyrrolidone or bovine serum albumin caused changes in nuclear volume which were related to the colloid osmotic pressure of the solution injected. The concentration in which no significant nuclear volume change occurred (the isotonic range) was 1.0 to 1.5 per cent polyvinylpyrrolidone (2.0 to 3.75 x 10(-4)M). 2 per cent bovine serum albumin had no significant effect on nuclear volume, whereas 4 per cent caused a significant decrease. The significance of these findings is discussed in terms of the permeability characteristics of the nuclear membrane.     

Continuous measurement of protein osmotic pressure in blood and lymph of sheep

We have continuously measured protein osmotic pressure of blood and lymph in sheep to compare two kinds of needle osmometers (rigid and flexible) with a membrane osmometer (Wescor). We also compared the averaged values of the continuous measurement with osmotic pressure calculated from total protein and albumin fraction, using the Yamada equation. The rigid-needle and membrane osmometers showed excellent correlation (y = 1.00x + 0.06; r greater than 0.99). The flexible-needle osmometer tended to overestimate osmotic pressure (avg 16%). We used the rigid-needle osmometer for continuous measurements of protein osmotic pressure of blood and lymph in anesthetized or unanesthetized sheep to observe changes in protein osmotic pressure of blood and lymph through the three different interventions. The relationship between the theoretical values (x) and the continuous measurements (y) of osmotic pressure was good (y = 0.99x + 0.16, r = 0.97), but after various interventions, the continuously measured protein osmotic pressure tended to exceed the calculated measurements. The continuous measurement should be monitored with spot samples measured in a stationary osmometer or by calculation of osmotic pressure from total protein concentration and albumin fraction.     

Conservation of blood plasma fluids in hamadryas baboons after thermal dehydration

After 2 days of water deprivation in a warm climate, Papio hamadryas baboons lost 10% of their body mass, 12.5% of their total body water (3H2O) space, but only 4% of their plasma volume [Evans blue (EB) space]. Hematocrit and hemoglobin concentration as well as blood viscosity and blood pressure were not affected by thermal dehydration. Plasma colloid osmotic pressure (COP) in the dehydrated animals was, however, 8 Torr higher than in fully hydrated baboons. Total mass and concentration of plasma albumin, and protein concentration increased after dehydration. Both half times (T 1/2) of EB and T 1/2 of 131I-serum albumin were twice as high as in the dehydrated animal than in the fully hydrated ones. Incorporation rate of L-[3H]leucine in the plasma proteins was similarly higher in the dehydrated animals. The capacity of the P. hamadryas baboon to maintain its plasma volume at the expense of losses from other body fluid compartments is related to an increase in the blood COP that is brought about by a more efficient retention of albumin and an increase in its rate of synthesis.     

Effects of crystalloid and colloid fluids on extravascular lung water in hypoproteinemic dogs

We compared the effect of crystalloid to colloid fluid infusion on extravascular lung water (EVLW) in hypoproteinemic dogs. Plasmapheresis was used to decrease plasma colloid osmotic pressure (COP) to less than 40% of its base-line level. Five animals were then infused with 0.9% sodium chloride (saline), five with 5% human serum albumin (albumin), and five with 6% hydroxyethyl starch (hetastarch) to increase the pulmonary arterial occlusive pressure by 10 Torr in comparison to the postplasmapheresis level for a 5-h study interval. On completion of the procedure, the lungs were harvested and EVLW measured by the blood-free gravimetric technique. Three to six times the volume of saline compared with albumin or hetastarch (P less than 0.001) was infused. In the saline animals, COP was decreased to 3.3 +/- 1.3 Torr, whereas COP was increased to 18.1 +/- 1.4 Torr in albumin animals (P less than 0.001) and 20.1 +/- 1.6 Torr in the hetastarch group (P less than 0.001). The saline-treated dogs developed gross signs of systemic edema. The EVLW was 8.1 +/- 0.9 ml/kg in saline animals compared with 5.3 +/- 2.1 ml/kg in the albumin (P less than 0.05) and 4.1 +/- 1.4 ml/kg in the hetastarch (P less than 0.01) groups. These data indicate that crystalloid fluid infusion during hypoproteinemia is associated with the development of both systemic and pulmonary edema.     

Plasma volume, albumin and globulin concentrations and their intravascular masses. A comparative study in endurance athletes and sedentary subjects.

Plasma volume, hematocrit, intravascular protein concentration, colloid osmotic pressure and the intravascular mass of proteins were measured in 49 sedentary subjects and 40 endurance athletes (long-, middle distance runners, cyclists). The plasma volume in sedentary subjects was 42.7(35.8-51.7) ml/kg body weight (BW) as compared to 54.6(46.7-65.9) ml/kg BW in athletes. The protein concentrations were 71.0 (66.5-77.1) g/l in sedentary subjects and 69.0 (64.8-75.2) g/l in athletes. The respective numbers for the hematocrit were 44.6 (40.1-49.25)% and 42.8 (38.2-49.6)%, for the colloid osmotic pressure 38.0 (36.0-40.5) cm H2O (n=35) and 30.0 (25.0-34.4) cm H2O (n=31), for the intravascular mass of proteins 3.09 (2.45-4.01) g/kg BW and 3.75 (3.31-4.67) g/kg BW. All differences were statistically significant at least on the 5% level. The physiological consequences for athletes of having a lower hematocrit and lower protein concentration but a higher intravascular mass of proteins (+22%) for their waterbalance as well as for their dietary protein intake are discussed. Endurance exercise stimulates mainly the synthesis of albumin and globulins produced by the liver resulting in an expansion of the PV. The protein synthesis of the RES does not seem to respond to exercise stimulus.     

The colloid osmotic pressures of invertebrate body fluids.

Colloid osmotic pressures of the body fluids of twenty invertebrate species were measured directly. The results, which are generally lower than predicted values for the same species, pertain to several physiological questions: (1) they do not quantitatively explain the frequently observed hyperosmoticity of body fluids in species believed to be osmoconformers, indicating that the condition cannot be merely a consequence of a Gibbs-Donnan equilibrium; (2) the excess of hydrostatic over colloid osmotic pressure is very small. This result supports the hypothesis that the oxygen transport function of bloods with extracellular haemocyanins and haem proteins is limited by their colligative properties; (3) the pressure relationships and the absence of colloid osmotic activity in urine indicates that filtration contributes to urine formation in several species.     

Osmotic reflection coefficient for total plasma protein in lung microvessels

The osmotic reflection coefficient (sigma) for total plasma proteins was estimated in 11 isolated blood-perfused canine lungs. Sigma's were determined by first measuring the capillary filtration coefficient (Kf,C in ml X min-1 X 100g-1 X cmH2O-1) using increased hydrostatic pressures and time 0 extrapolation of the slope of the weight gain curve. Kf,C averaged 0.19 +/- 0.05 (mean +/- SD) for 14 separate determinations in the 11 lungs. Following a Kf,C determination, the isogravimetric capillary pressure (Pc,i) was determined and averaged 9.9 +/- 0.5 cmH2O for all controls reported in this study. Then the blood colloids in the perfusate were either diluted or concentrated. The lung either gained or lost weight, respectively, and an initial slope of the weight gain curve (delta W/delta t)0 was estimated. The change in plasma protein colloid osmotic pressure (delta IIP) was measured using a membrane osmometer. The measured delta IIP was related to the effective colloid osmotic pressure (delta IIM) by delta IIM = (delta W/delta t)0/Kf,C = sigma delta IIP. Using this relationship, sigma averaged 0.65 +/- 0.06, and the least-squares linear regression equation relating Pc,i and the measured IIP was Pc,i = -3.1 + 0.67 IIP. The mean estimate of sigma (0.65) for total plasma proteins is similar to that reported for dog lung using lymphatic protein flux analyses, although lower than estimates made in skeletal muscle using the present methods (approximately 0.95).     

Effects of histamine and acetylcholine on equine digital lymph flow and composition.

We measured the flow rate and protein concentration of lymph collected from a digital lymphatic in eight anesthetized ponies. Additionally, we recorded systemic arterial pressure (Part), and small vein pressure (Psv). Control lymph flow averaged 0.068 ml/min, and contained 3.11 g/100 ml of protein with albumin/globulin ratio of 0.75. Twenty-minute local intra-arterial infusion of acetylcholine (10 mug/min.) elevated Psv but did not increase lymph flow rate or protein concentration. A 60-min local intra-arterial infusion of histamine (10 mug/min) produced a marked sustained increase in Psv and both lymph flow and protein concentration. Edema developed in the digit receiving histamine. These data support the conclusion that in the horse, as in other species, histamine edema is due primarily to a decreased transcapillary colloid osmotic pressure gradient rather than an increased transcapillary hydrostatic pressure gradient.     

Direct method for osmotic pressure measurement (author's transl)]

A new dynamic method to measure osmotic pressure was presented. The method is easy and with only a 1.8% degree of error. All determinations were done with an osmometer, equipped with three small chambers of methyl metacrilate and dialyser membranes. The central area had two capillaries: one for measuring and the other for changing dynamic pressure. The data from different albumin concentrations were satisfactory, and they agreed with published results from others. The present results indicate that osmotic pressure is an exponential function of albumin concentration.     

Interstitial fluid pressure changes in pregnant rats

In pregnant rats significant interstitial fluid pressure changes could be detected by means of capsules chronically implanted into the subcutaneous tissue. The capsular pressure increased significantly from a control value of -4.3 +/- 0.5 mmHg to -0.7 +/- 0.5 mmHg during the first period of pregnancy. Immediately before parturition the capsular pressure returned to the control level. During lactation the pressure rose as high as + 0.5 +/- 0.9 mmHg. After lactation the pressure returned again to the control value. By determining the extracellular fluid and plasma volume, as well as protein concentration in plasma and capsular fluid, the hydrostatic and colloid osmotic forces operating in the extracellular space could be analysed. It has been concluded that the observed capsular pressure changes during pregnancy are not solely of volumetric or colloid osmotic origin.     

Effects of haemorrhage on colloid osmotic pressure in the pigeon

1. Colloid osmotic pressure, plasma osmolality and plasma protein concentration, percentage composition and A/G ratio were measured before and after haemorrhage in the pigeon. 2. Colloid osmotic pressure, total protein, albumin and beta-globulin concentrations decreased significantly immediately post-haemorrhage, but were significantly elevated after one week. 3. Osmolality and A/G ratio values were significantly increased post-haemorrhage. 4. The results are discussed in relation to fluid exchange across capillaries.     

Protein washdown as a defense mechanism against myocardial edema

Myocardial edema occurs in many pathological conditions. We hypothesized that protein washdown at the myocardial microvascular exchange barrier would change the distribution of interstitial proteins from large to small molecules and diminish the effect of washdown on the colloid osmotic pressure (COP) of interstitial fluid and lymph. Dogs were instrumented with coronary sinus balloon-tipped catheters and myocardial lymphatic cannulas to manipulate myocardial lymph flow and to collect lymph. Myocardial venous pressure was elevated by balloon inflation to increase transmicrovascular fluid flux and myocardial lymph flow. COP of lymph was measured directly and was also calculated from protein concentration. Decreases occurred in both protein concentration and COP of lymph. The proportion of lymph protein accounted for by albumin increased significantly, whereas that accounted for by beta-lipoprotein decreased significantly. The change in the calculated plasma-to-lymph COP gradient was significantly greater than the change in the measured COP gradient. We conclude that the change in the distribution of interstitial fluid protein species decreases the effect of protein washdown on interstitial fluid COP and limits its effectiveness as a defense mechanism against myocardial edema formation.     

Theoretical and experimental studies on freezing point depression and vapor pressure deficit as methods to measure osmotic pressure of aqueous polyethylene glycol and bovine serum albumin solutions

For survival in adverse environments where there is drought, high salt concentration or low temperature, some plants seem to be able to synthesize biochemical compounds, including proteins, in response to changes in water activity or osmotic pressure. Measurement of the water activity or osmotic pressure of simple aqueous solutions has been based on freezing point depression or vapor pressure deficit. Measurement of the osmotic pressure of plants under water stress has been mainly based on vapor pressure deficit. However, differences have been noted for osmotic pressure values of aqueous polyethylene glycol (PEG) solutions measured by freezing point depression and vapor pressure deficit. For this paper, the physicochemical basis of freezing point depression and vapor pressure deficit were first examined theoretically and then, the osmotic pressure of aqueous ethylene glycol and of PEG solutions were measured by both freezing point depression and vapor pressure deficit in comparison with other aqueous solutions such as NaCl, KCl, CaCl(2), glucose, sucrose, raffinose, and bovine serum albumin (BSA) solutions. The results showed that: (1) freezing point depression and vapor pressure deficit share theoretically the same physicochemical basis; (2) theoretically, they are proportional to the molal concentration of the aqueous solutions to be measured; (3) in practice, the osmotic pressure levels of aqueous NaCl, KCl, CaCl(2), glucose, sucrose, and raffinose solutions increase in proportion to their molal concentrations and there is little inconsistency between those measured by freezing point depression and vapor pressure deficit; (4) the osmotic pressure levels of aqueous ethylene glycol and PEG solutions measured by freezing point depression differed from the values measured by vapor pressure deficit; (5) the osmotic pressure of aqueous BSA solution measured by freezing point depression differed slightly from that measured by vapor pressure deficit.     

Synthesis and biophysical properties of polymerized human serum albumin

The use of many plasma expanders (PEs) is often limited by undesirable side effects, such as red blood cell (RBC) aggregation (hydroxyethyl starch), nephrotoxicity (dextran), and extravasation (albumin). Despite its natural prevalence in the bloodstream, human serum albumin (HSA) can increase the risk of mortality when administered to patients with increased vascular permeability (i.e., patients suffering from burns, septic shock, and endothelial dysfunction). The harmful extravasation of HSA can be limited by polymerizing HSA to increase its molecular size. In this study, HSA was nonspecifically cross-linked with glutaraldehyde at different cross-link densities by varying the molar ratio of glutaraldehyde to HSA. The results of this study show that the weight-averaged molecular weight (MW), viscosity, and extent of RBC aggregation of polymerized HSA increases with increasing cross-link density, whereas the colloid osmotic pressure (COP) decreases with increasing cross-link density. Interestingly, circular dichroism measurements indicate that the secondary structure of HSA is unaffected by polymerization. Altogether, these results show that glutaraldehyde can effectively cross-link HSA to produce high MW polymers, yielding a novel series of potential PEs that exhibit low COP and high viscosity.     

Virial coefficients of protein solutions

An osmometer capable of measuring protein osmotic pressures up to 100 cms. of mercury pressure has been described. The principle of the osmometer is to set a given pressure and to permit the protein concentration to equilibrate with the pressure. The higher virial osmotic coefficients of egg albumin in various electrolytes and in 1 m urea as well as a function of NaCl concentration are reported. The virial coefficients of bovine serum albumin and of bovine methemoglobin in 1 m NaCl are also given. It appears that the primary cause for the departure of the osmotic pressure from ideality is due to the covolumes of the proteins.     

Colloid osmotic homeostasis in humans: intravascular oncotic energy under varying gravitational potential

From theoretical considerations it is possible to predict plasma volume—oncotic pressure changes that occur under changing gravitational or acceleration fields. The intravascular volume—colloid osmotic pressure integral has the dimensions of energy and correlates with the gravitational potential to which an individual is subjected.The postural hypotension found in returning astronauts and cosmonauts whose cardiovascular reflexes had been previously well trained can be explained in part on the basis of decreased total intravascular oncotic energy upon return from zero gravity conditions. Conversely a period of cardiovascular stress due to increased plasma volume occurs when going from higher to lower gravitational potentials.