Capillary Permeability Coefficient Research Articles

Effects of nano-SiO2 and nano-Al2O3 on mechanical and durability properties of cement-based materials: A comparative study

In order to explore the all-round influence of nano-SiO2 (NS) and nano-Al2O3 (NA) on cement-based materials, especially the small dosage and compound effect, the single and combined effects of NS and NA on mechanical and durability properties of cement-based materials were investigated. The contents of nanomaterials were 0.5%, 1.0%, 2.0% and 3.0% of the binder by weight, respectively. Results show that setting time could be shortened by introducing NS and NA except single-doped 2% and 3% NA and binary combination NS + NA at 3%. In addition, all hardened mortar systems with nanomaterials exhibited positive strength growth rate compared to control group. Especially, the compressive strength growth rates of mortars containing NS after 3 days were 10.5%, 27.09%, 26.78% and 42.13%, respectively, with the increase of NS content from 0.5% to 3%. In terms of durability, the charge passed, weight loss and capillary permeability coefficient decreased by adding small amount (0.5%) of NS and NA. And then the introducing of 0.5%NS + 0.5%NA powders at 1% reduced capillary permeability coefficient of concrete samples compared to that of 0.5%NS and 0.5%NA samples. Among all groups, the best performance was provided from NS at 1%, NA at 0.5%, and the binary combination NS + NA at 1%. Finally, the relationships between the drying rate/water absorption rate and time were given, which was conductive to study the moisture transport of nano-concrete.

Coupled effects of sustained compressive loading and freeze–thaw cycles on water penetration into concrete

AbstractThe combined action of sustained loading and freeze–thaw cycles (FTCs) plays an important role in the durability and service life of concrete exposed to the cold coastal area. Water transport is a primary factor closely pertaining to freeze–thaw damage in concrete, and the microcracks induced by sustained loading could provide a flow path to facilitate water penetration into concrete. This paper presents the results of an experimental investigation on water penetration behavior of ordinary and air‐entrained concrete (OC and AC) subjected to sustained compressive loading and FTCs. Aiming at the combined effects of low compressive stress ratio and FTCs on water transport, a series of water absorption and permeability experiments with the stress ratio of 0, 0.3, and 0.5 after various FTCs were conducted. The relative dynamic elastic modulus and mass loss were afterwards measured to characterize the frost damage within concrete. The experimental results indicated that the sustained compressive loading and frost action have significant influences on capillary water absorption and permeability for the OC and AC specimens. Both the initial coefficient of capillary absorption and water permeability coefficient increase with the increase of FTCs, while they initially decrease and later increase with the increase of compressive stress ratio.

Characterization of absorbent properties of fibers and fibrous assemblies using inclined wicking test

Inclined wicking test was carried out to characterize surface properties of fibers and dynamic absorption behaviors in fibrous assemblies. As testing samples, PET fabrics glycolized at different concentrations of sodium hydroxide were used. Inclined wicking test extended the wicking period to increase the wicking lengths and the difference between specimens, which facilitated the relative evaluation of absorbent characteristics. To investigate the surface properties of fibers in highly hydrophilic treated specimens, the wetting tension and contact angle were derived by combination of capillary pressure and permeability coefficient which were measured in the steady state. As the concentration of hydroxide increased, the wetting tension increased continually to a critical point and then decreased. From SEM analysis, high concentration of hydroxide caused cracked damage on fiber surface, which resulted in the increase of apparent contact angle due to buoyant effect in cracked surface and thus decrease of wetting tension. The equations were derived to describe inclined wicking behaviors in fibrous assemblies. Predicted wicking rates were higher than experiment ones. The equation was modified with tortuosity factor to fit the experimental data. The results reported in the research could provide useful information in designing comfort textiles.

Performance assessment of Ultra High Performance Fiber Reinforced Cementitious Composites in view of sustainability

This paper presents a sustainability assessment for an Ultra High Performance Fiber Reinforced Cement Composite (UHPFRCC). The concrete composite was designed at Universidade Federal do Rio de Janeiro (UFRJ) and was produced from a Blast furnace slag cement, silica fume, silica flour, wollastonite, steel fibers and superplasticizer and showed superb performances in the field of rheology, material properties and durability, in comparison with regular concretes in general and other ultra high performance concretes in particular. The design of the UHPFRCC is based on the aim to achieve an ultra-compacted cementitious matrix with a skeleton of aggregates ranging from 150 to 600μm and with the packing of the granular skeleton based on the compressive packing model (CPM). The water/binder ratio of the mixture was 0.17 leading to outstanding performances of the cementitious composite. At 28days, the UHPFRCC showed a compressive strength of 162MPa, an elastic modulus of 48GPa, a tensile strength of 10MPa and an equivalent elastic post-cracking bending strength of 35MPa. The material properties´ stress–strain behaviour under compression, tension and bending were measured even as the durability related properties such as capillary water absorption, gas permeability and diffusion coefficient. In order to evaluate the material in view of its sustainability performance, a probabilistic analysis has been employed where UHPFRCC is compared with a regular Grade 40 concrete and with a low environmental impact sewage sludge concrete. From this evaluation a sustainability assessment has been employed in terms of mechanical performance, durability performance and natural materials usage. The results show that within its designated field of application the sustainability profile of UHPFRCC balances with ordinary Portland cement based concretes.

Liver Metastases From Colorectal Cancer Treated With Conventional and Antiangiogenetic Chemotherapy

The objectives of the study were to determine whether perfusion computed tomography (CT-p) and magnetic resonance diffusion-weighted imaging (MR-DWI) can allow evaluation of the effects of chemotherapy combined with antiangiogenetic treatment on liver metastases in patients with advanced colorectal cancer and to determine if changes in CT-p and MR-DWI correlate with the response to therapy as assessed by conventional Response Evaluation Criteria in Solid Tumors (RECIST). Eighteen patients with liver metastases from colorectal cancer underwent CT-p and MR-DWI before and 6 months after chemotherapy and antiangiogenetic treatment. Lesions were classified according to RECIST criteria (complete response [CR], partial response [PR], stable disease [SD], and progressive disease) and calculations of CT-p parameters including blood flow (BF), blood volume (BV), capillary permeability (CP), and MR-DWI apparent diffusion coefficient (ADC) values were performed; RECIST, CT-p, and MR-DWI measurements at baseline and follow-up were tested for statistically significant differences using the paired-samples t test. Baseline and follow-up perfusion parameters of the lesions were also compared on the basis of therapy response assessed by RECIST criteria using independent-samples t test. P < 0.05 was considered indicative of a statistically significant difference for all statistical test. Six patients (6/18; 33.3%) were classified as PR (), and the remaining 12 (12/18; 66.7%) were classified as SD. On a per-lesion basis, 2 (2/32; 6.3%) cannot be identified at follow-up, 6 (6/32; 18.8%) showed a decrease in size of more than 30%, and 24 (24/32; 75%) were substantially stable in size. No cases of progressive disease were demonstrated at follow-up. No statistically significant differences were demonstrated between PR, CR, and SD lesions for BF (P = 0.19), BV (P = 0.14), and ADC (P = 0.68) measurements, whereas CP was significantly higher in CR and PR lesions (P = 0.038). Considering differences between baseline and follow-up values, no statistically significant differences were noted between PR and CR lesions versus SD lesions for CT-p values (BF: P = 0.77; BV: P = 0.15; CP: P = 0.64). A statistically significant difference between PR and CR lesions and SD lesions was noted for ADC values (P = 0.047). Both CT-p and MR-DWI can detect therapy-induced modifications in lesion vascularization before significant changes in size are evident.

Modelling the transmural transport of oxygen to the retina

Oxygen transport from retinal capillaries to retinal tissue is studied by use of a Krogh-type cylinder model. The retinal tissue is represented as an array of uniformly cylinders with capillaries along the axes. The model introduces the transmural transport of oxygen from the retinal capillaries to its surrounding (retinal) tissue in a hypoxia environment. Computational results for concentration distribution in the retinal tissue are presented through graphs and the effects of important model parameters: intraocular pressure, capillary wall permeability coefficient, capillary wall pressure gradient constant on the oxygen concentration distribution are depicted and discussed.

Effect of high transcapillary pressures on capillary ultrastructure and permeability coefficients in dog lung

To determine the correlation between ultrastructural and physiological changes in blood-gas barrier function in lungs transiently exposed to very high vascular pressures, we increased capillary transmural pressure (Ptm) of 6 canine isolated perfused left lower lung lobe preparations (high-pressure group) to 80.3 Torr for 3.8 min and then determined the capillary filtration (K(fc)) and osmotic reflection (sigma(d)) coefficients at a Ptm of 19.1 Torr in the ventilated lung lobes. This was followed by perfusion fixation of the lobes at a Ptm of 20.5 Torr for ultrastructural analysis. These data were compared with those obtained in six lobes in which Ptm was not transiently elevated before K(fc), sigma(d), and ultrastructural evaluation. K(fc) was higher [0.249 +/- 0.042 (SE) vs. 0.054 +/- 0.009 g. min(-1). Torr(-1). 100 g(-1); P < 0.01] and sigma(d) was lower (0.52 +/- 0.07 vs. 0.85 +/- 0.08; P < 0.01) in the high-pressure group. In contrast, although endothelial and epithelial breaks were occasionally observed in some experiments, their incidence was not increased in the high-pressure group. These data suggest that the increased transvascular water and protein flux occurred through pathways of a size not resolvable by electron microscopy after vascular perfusion-fixation at a Ptm of 20.5 Torr.

Test of a two-pathway model for small-solute exchange across the capillary wall.

We previously proposed a two-pathway model for solute and water transport across vascular endothelium (Fu, B. M., R. Tsay, F. E. Curry, and S. Weinbaum. J. Biomech. Eng. 116: 502-513, 1994) that hypothesized the existence of a continuous slit 2 nm wide along tight junction strands within the interendothelial cleft in parallel with 20 x 150-nm breaks in tight junctions. We tested this model by measuring capillary permeability coefficients (P) to a small solute (sodium fluorescein, radius 0.45 nm), assumed to permeate primarily the 2-nm small pore, and an intermediate-sized solute (FITC-alpha-lactalbumin, radius 2.01 nm) excluded from the small pore. Mean values of the paired diffusive permeability coefficients, Psodium fluorescein and PFITC-alpha-lactalbumin, were 34.4 and 2.9 x 10(-6) cm/s, respectively, after corrections for solvent drag and free dye (n = 26). These permeabilities were accounted for by transport through the large-break pathway without the additional capacity of the hypothetical 2-nm pathway. As a further test we examined the relative reductions of Psodium fluorescein and PFITC-alpha-lactalbumin produced by elevated intracellular cAMP. Within 20 min after the introduction of rolipram and forskolin, Psodium fluorescein and PFITC-alpha-lactalbumin decreased to 0.67 and 0.64 times their respective baseline values. These similar responses to permeability decrease were evidence that the two solutes were carried by a common pathway. Combined results in both control and reduced permeability states did not support the hypothesis that a separate pathway across tight junctions is available for solutes with a radius as large as 0.75 nm. If such a pathway is present, then its size must be smaller than that of sodium fluorescein.

Rolipram and Isoproterenol Reverse Platelet Activating Factor-Induced Increases in Pulmonary Microvascular Permeability and Vascular Resistance

Platelet activating factor (PAF) is an important mediator of pulmonary microvascular endothelial cell (PMVEC) injury in sepsis. Membrane receptors for PAF have been identified on PMVECs and mediate its actions at least in part by protein kinase C activation. Since rolipram, a family IV cyclic AMP phosphodiesterase inhibitor, and isoproterenol, an adenylate cyclase activator, both reverse ischemia-reperfusion-induced lung permeability, we studied the effects of these agents on PAF-induced pulmonary microvascular permeability. The isolated rat lung model was used in which lungs were ventilated and buffer perfused at constant flow while suspended from a force transducer to monitor lung weight along with arterial ( P a) and venous ( P v) pressures. Control lungs ( n = 6) were infused with PAF (40 nmole/kg) via an arterial port and the capillary permeability coefficient ( K f,c) was determined at 0, 15, and 60 min. The remaining lungs were randomized for infusion with either rolipram ( n = 4, 20 μmole/kg) or isoproterenol ( n = 4, 5 μmole/kg) via an arterial port 30 min after injury with PAF. In the rolipram- and isoproterenol-treated groups, the K f,c was determined 15 and 60 min postinfusion with these agents. The control group showed significant elevation in the K f,c and total pulmonary resistance ( R t). At 15 and 60 min, rolipram and isoproterenol reversed PAF injury as shown by the significant improvement in the K f,c and R t. These findings support the concept that increased cyclic AMP is an important mediator in the reversal of PAF-increased PMVEC permeability and pulmonary resistance.

Pulmonary capillary dynamics and fluid distribution after burn and inhalation injury

A non-linear macroscopic mathematical model is described for the simulation of the different mechanisms that regulate the pulmonary capillary dynamics in patients with thermal injury. The techniques used in the construction of the model are those of ‘system's dynamics’. This model has been incorporated into a patient simulator, which makes it possible to analyse the fluid and protein exchanges in a burn patient. The regulating mechanisms involved are: the pulmonary circulation, the fluid and protein transfer between the plasma and the interstitial space at the pulmonary capillary level, and the pulmonary lymphatic system. As a result of the sensitivity analyses of the model we propose that, for the simulation of the effects of an inhalation injury at the pulmonary capillary level, the parameters to be altered will be the pulmonary capillary permeability coefficient for proteins and the pulmonary capillary surface damaged by the injury. To verify the validity and utility of the model, the clinical progress of a series of burn patients with lung injuries has been compared with the results obtained using simulation.

Improved lung preservation using a dimethylthiourea flush

The purpose of this study was to evaluate the ability of dimethylthiourea (DMTU), a low molecular weight hydroxyl free radical scavenger, to improve preservation of the lung for transplantation. Following preservation, 15 isolated canine left lower lobes were reperfused for 90 min with autologous blood. Five group I lobes served as controls and were not subjected to ischemia prior to reperfusion. Five group II lobes were flushed and submerged in a cold Euro-Collins solution and stored for 4 hr at 4°C prior to reperfusion. Group III lobes were flushed with a 20 m M DMTU-enhanced Euro-Collins solution, stored for 4 hr, and then reperfused. The isogravimetric method was utilized to determine the capillary permeability coefficient ( K fc) for the reperfused lobes. The K fc values were 0.10 ± 0.01, 0.17 ± 0.01, and 0.10 ± 0.008 ml/min/mm Hg/100 g lung for groups I, II, and III, respectively ( P < 0.01 II vs I, III). Extravascular lung water values in the reperfused lobe were 4.44 ± 0.45, 6.57 ± 0.38, and 5.23 ± 0.22 ml/g blood free dry lung weight for groups I, II, and III ( P < .05, II vs. I, III). Lung lipid peroxidation, measured as thiobarbituric acid-reactive material, was higher in group II, 146 ± 6 nmole/g, than in either group I, 90 ± 5 nmole/g, or group III, 91 ± 4 nmole/g ( P < 0.01). The results indicate that the addition of DMTU improves hypothermic lung preservation by reducing lipid peroxidation and edema formation upon reperfusion.

Interstitial distribution of charged macromolecules in the dog lung: a kinetic model.

A mathematic model was constructed to investigate conflicting physiologic data concerning the charge effect of continuous capillaries to macromolecules in the lung. We simulated the equilibration kinetics of lactate dehydrogenase (MR 4.2 nM) isozymes LDH 1 (pI = 5.0) and LDH 5 (pI = 7.9) between plasma and lymph using previously measured permeability coefficients, lung tissue distribution volumes (VA) and plasma concentrations (CP) in lung tissue. Our hypothesis is that the fixed anionic charges in interstitium, basement membrane, and cell surfaces determine equilibration rather than charged membrane effects at the capillary barrier, so the same capillary permeability coefficients were used for both isozymes. Capillary filtration rates and protein fluxes were calculated using conventional flux equations. Initial conditions at baseline and increased left atrial pressures (PLA) were those measured in animal studies. Simulated equilibration of isozymes over 30 h in the model at baseline capillary pressures accurately predicted the observed differences in lymph/plasma concentration ratios (CL/CP) between isotopes at 4 h and equilibration of these ratios at 24 h. Quantitative prediction of isozyme CL/CP ratios was also obtained at increased PLA. However, an additional cation selective compartment representing the surface glycocalyx was required to accurately simulate the initial higher transcapillary clearances of cationic LDH 5. Thus experimental data supporting the negative barrier, positive barrier, and no charge barrier hypotheses were accurately reproduced by the model using only the observed differences in interstitial partitioning of isozymes without differences in capillary selectivity.

Microvascular exchange of albumin

The transcapillary exchange of albumin was examined in seven rabbits using plasma disappearance curves and black box kinetic analysis. From the experimental data and the Renkin and Kedem-Katchalsky equations it was found that the average whole body diffusional capillary permeability coefficient for albumin was 24 × 10 −8 cm/sec as the total whole body capillary permeability-surface area product was 0.0739 ml/100 g · min (surface area estimate 50 cm 2/g). The convective components of the net albumin tracer flux was found to be 15%, and the pure permeation ratio of influx to outflux ( R = 0.61) of systemic albumin was reduced to 0.57. The solvent drag component of either unidirectional flux relative to the permeative component was 0.037. The Casley-Smith hypothesis of solvent drag convection up a gradient across the capillary membrane could not be verified as possible. It is emphasized that the so-called transcapillary escape rate is an arbitrary rate constant which cannot be attributed to reflect any physiological process, especially not the transcapillary exchange of albumin.

Glomerular hemodynamics in moderate Goldblatt hypertension in the rat.

Glomerular hemodynamics were studied by micropuncture technique in the unclipped kidney in rats in which modest two kidney Goldblatt hypertension was maintained for 4 weeks and in normotensive controls. Both groups ingested less than 2 mEq Na+/day. In hypertensive rats at micropuncture, mean hydrostatic pressure was elevated both systematically (128 +/- 5 vs 113 +/- 3 mm Hg, p less than 0.05) and within glomerular capillaries (55 +/- 2 vs 48 +/- 1 mm Hg, p less than 0.05), resulting in an increase in the transglomerular hydrostatic pressure gradient (40 +/- 2 vs 33 +/- 1 mm Hg, p less than 0.05). The glomerular capillary permeability coefficient, however, was decreased in the hypertensive rats (0.063 +/- 0.017 vs 0.115 +/- 0.011 nl/s/g kw/mm Hg, p less than 0.05), resulting in no change in nephron filtration rate 38.9 +/- 2.3 vs 39.0 +/- 2.5 nl/min/g kw). Nephron plasma flow also remained unchanged (154 +/- 10 vs 140 +/- 7 ml/min/g kw). In separate studies in this model of hypertension, saralasin infusion demonstrated a peripheral effect of circulating angiotensin II which was increased over controls. Kidney mass and GFR were not different between clipped and unclipped kidneys. No consistent abnormalities were observed by light or electron microscopy either in glomeruli or in vessels in the unclipped kidney. This study demonstrates that glomerular hemodynamics may be altered early in the course of modest hypertension in this model without altering blood flow or filtration rate. The decrease in glomerular capillary area and/or permeability (LpA) in the hypertensive rats could be either a result of the increased effect of circulating angiotensin II or the direct effect of glomerular capillary hypertension.

Alterations of myocardial capillary permeability by albumin in the isolated, perfused rabbit heart.

1. Capillary permeability-surface area products for 22Na, 51Cr-EDTA (mol. wt. 357), [57Co]cyanocobalamin (mol. wt. 1353) and 125I-labelled insulin (mol. wt. approximately or equal to 6000) were measured using the single-passage, multiple-tracer dilution technique in isolated rabbit hearts perfused at constant flows between 0.2 and 4.7 ml. min-1 . g-1. 2. In hearts perfused with a Krebs-Ringer solution containing bovine albumin (10 g . l . -1), the permeability-surface area products for 51Cr-EDTA and [57Co]cyanocobalamin increased as the perfusion rate increased, but reached constant values at flows above 2 ml . min-1 . g-1. For 125I-labelled insulin a diffusion-limited value of 0.06 +/- 0.02 ml . min-1 . g-1 (mean +/- S.E., n = 10) was measured at significantly lower perfusion rates. As the value for 22Na increased continuously with increments in flow, only a flow-limited value could be estimated. 3. When hearts were initially perfused with albumin (10 g . l . -1) and then with an albumin-free Krebs-Ringer solution, a significant increase in the permeability-surface area for 22Na, 51Cr-EDTA and [57Co]cyanocobalamin was observed. 4. In hearts perfused with albumin capillary permeability coefficients calculated for 22Na, 51Cr-EDTA. [57Co]cyanocobalamin and 125I-labelled insulin were respectively: 10.5, 3.5, 2.1 and 0.21 x 10(-5) cm.sec-1. 5. These findings confirm that bovine albumin reduces the permeability of myocardial capillaries to hydrophilic solutes of varying molecular sizes and this effect may be the result of an interaction of albumin with the pathways for transcapillary exchange.

Intracapillary events in osmotic weight transients

In osmotic transient experiments on perfused organs the time course of the concentrations of both test and resident buffer solutes within the capillary must be known in order to give an adequate description of the underlying events leading to the observed weight changes. In accompanying papers ( G. Bloom and J. A. Johnson, 1981, Microvasc. Res. 22, 64–79, J. A. Johnson and G. Bloom, 1981, Microvasc. Res. 22, 80–92), we describe a model for osmotic transients based on the assumption that both test and buffer solute concentrations within the capillary are constant. In this paper we determine the magnitude and time course of solute concentration changes within the capillary and show the effect of inserting these values into our model in place of the previously assumed constant concentrations. In particular we show what effect these changes in solute concentration have on our estimates of capillary osmotic reflection coefficients (σ) and permeability coefficients ( P) for inulin and sodium chloride. A mathematical analysis is presented which describes the concentration as a function of time as the new solution moves through the following segments of the fluid pathway preceding the heart capillaries: (1) the tubing conduits to the heart; (2) the mixing chamber of the aortic bulb; (3) the precapillary vascular system. This analysis is combined with that of J. A. Johnson and T. A. Wilson (1966, Amer. J. Physiol. 210, 1299–1303) on the axial profile of capillary concentration caused by solute movement across the capillary wall. A mathematical analysis of the intracapillary buffering which could arise due to sieving of resident solute at the capillary wall is presented in an appendix. We find that perfusion rates similar to those that we employ in our experimental system enable us to obtain valid estimates of PA and σ. Significantly lower perfusion rates do not yield valid results.

Permeability and reflection coefficients from osmotic transients—Extravascular factors

F. F. Vargas and J. A. Johnson in 1964 and 1967 ( J. Gen Physiol. 47, 667–677; Amer. J. Physiol. 213, 87–93) published a technique for obtaining capillary permeability and reflection coefficients from the rate of weight loss of an organ undergoing an osmotic transient. The rate of weight loss was plotted versus time on semilogarithmic paper. From the intercept an estimate of the capillary reflection coefficient could be made. From the slope an estimate of the permeability coefficient could be made. We have examined this technique using a model developed by G. Bloom and J. A. Johnson (1981, Microvasc. Res. 22, 64–79). In this paper we examine the effects of factors such as interstitial and cell buffering, solvent drag, interstitial elasticity, and cell water permeability while we maintain the intracapillary concentrations constant. In a subsequent paper we relax this restraint and allow inlet and intracapillary conditions to influence the transient and thus evaluate the role they play in an osmotic weight transient. In the present paper we have found the intercept technique for obtaining the reflection coefficient to be valid. However, the slope-permeability technique has to be modified in some cases. For highly water-soluble molecules the size of inulin, or larger, an elastic factor correction must be made. This occurs because the tendency for a large transfer of fluid from the interstitium to the capillaries is opposed by an interstitial pressure drop which influences the time course of the entire process and also gives rise to a minimum in the weight vs time curve. A simple analytical model is given which agrees very well with the full computer model for these larger compounds. In the case where the test solute is identical in properties to the extracellular buffer (e.g., NaCl), the slope (rate constant) must be modified by using the total water (cellular plus extracellular) in the denominator instead of the interstitial volume. An analytical model for this type of transient is given which also agrees very well with the computer model for NaCl.

A model for osmotically induced weight transient in the isolated rabbit heart

In this paper we present a model for osmotically induced weight transients in the isolated perfused rabbit heart. The model consists of a set of lumped parameter, first-order, ordinary differential equations describing the solute and volume flow across the capillary and cell membranes. The differential equations describing the model have been solved by using a Hewlett-Packard Model HP9830 computer. The results, in terms of weight changes, solute, and solvent flows are given in graphical form. This paper has indicated the importance of diffusion, solvent drag, elastic factors, capillary sieving, interstitial pressure changes, lymph flow, transcellular (myocytal) transport, all as a function of time and related these to simultaneous weight changes. The parameters used for our model are values which have all been experimentally obtained in the isolated perfused rabbit heart. Results are presented using two small, water-soluble test molecules, inulin and NaCl, since they elicit different tissue responses to osmotic perturbation. For an inulin transient the main loss of weight occurs in the extracellular compartment. When NaCl is used as the test solute the main loss of weight is from the heart muscle cells. While complete in itself this paper is the starting point for two associated articles on factors important in the estimation of capillary permeability and reflection coefficients.

Putrescine diffusion in cat brain and capillary permeability in rat brain: Relation to CSF putrescine levels in brain tumor patients

Cerebrospinal fluid (CSF) putrescine (Pu) levels are extremely useful measures of active tumor growth in patients harboring medulloblastoma but not in patients harboring most supratentorial malignant gliomas. This study was designed to determine the diffusion coefficient (D) for Pu in cat brain and the capillary permeability coefficient (Pc) in rat brain to explain the failure of supratentorial gliomas to manifest a consistent increase in CSF Pu with progressive tumor growth. The Pc for Pu was found to be greater than the Pc for urea, while the apparent brain D for Pu was lower than that for urea. This implies that Pu crosses capillaries and enters cells more rapidly than urea, which would reduce the amount of Pu that might ultimately reach the CSF by diffusion from tumor. These data explain why CSF levels of Pu are correlated best in medulloblastoms—generally located adjacent to the CSF pathways—and why levels are correlated least in malignant supratentorial gliomas—usually located within the brain hemispheres, from which diffusion to the ventricles and into the CSF would be difficult.

ChemInform Abstract: RELATIONSHIP OF OCTANOL/WATER PARTITION COEFFICIENT AND MOLECULAR WEIGHT TO RAT BRAIN CAPILLARY PERMEABILITY

The rat brain capillary permeability coefficient was determined for 27 compounds. The relationship of permeability to octanol/water partition coefficient and molecular weight was found to be predictable for drugs with molecular weights less than 400.