Pharmacokinetics and consistency of pericardial delivery directed to coronary arteries: direct comparison with endoluminal delivery

BACKGROUND AND HYPOTHESIS

Pharmacologic modulation of the contents of the pericardial space has been shown to influence the response of coronary arteries to balloon injury. Endoluminal (EL) local delivery of various drugs into coronaries has been found to be limited by short residence time, as well as by highly variable deposited agent concentration. We hypothesized that compounds placed into the pericardial space (P) would penetrate into coronary tissue with greater consistency than seen after EL delivery and provide for prolonged coronary exposure to agents.

METHODS AND RESULTS

125I-labeled basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), albumin, or 131I-labeled diazeniumdiolated albumin (NONO-albumin) were delivered as model/therapeutic proteins into the porcine pericardial space (n = 15 pigs) or into coronaries using an EL delivery catheter (n = 48 arteries). In subjects receiving 125I-labeled proteins, the delivery target or mid-regions of the left anterior descending (LAD) and left circumflex (LCx) arteries were harvested at 1 h or 24 h for gamma-counting and autoradiography, and fractional intramural delivery (FID) or retention measured as percent agent in 100 mg artery/agent in infusate for both time points. In the animals receiving 131I-labeled NONO-albumin, serial gamma imaging was employed to evaluate the rate of redistribution in individual animals following either pericardial or endoluminal delivery. At 1 h, FID values ranged from 0.00064 to 0.0052% for P delivery (median 0.0022%), and from 0.00021 to 6.7 for EL delivery (median 0.27%). At 24 h, FID values ranged from 0.00011 to 0.003 for P delivery (median 0.0013), and from 0.0002 to 1.4 for EL delivery. The estimated T1/2 for bFGF redistribution from the vascular tissue was 22 h (P) and 7 h (EL), respectively, while the directly determined T1/2 values for NONO-albumin redistribution from the delivery region were 22.2 h (P) and 2.5 h (EL).

CONCLUSIONS

These data show that pericardial fluid contents can access coronary arteries with intramural concentrations which typically vary by 10-15-fold, while EL delivery results in a remarkably wide intramural concentration range with up to 33,000-fold variability. The apparent redistribution rate is more rapid following EL delivery, possibly due to sustained diffusive tissue loading from the pericardial space. Pericardial delivery appears to offer substantial advantages over EL administration with respect to residence time and reproducibility.

Plasma appearance rate of intraperitoneal macromolecular tracer underestimates peritoneal lymph flow

The magnitude of peritoneal lymph flow is an issue of great controversy in peritoneal dialysis (PD) research. Because no single lymphatic duct drains the entire peritoneal cavity, peritoneal lymph flow is indirectly measured as lymphatic removal of intraperitoneal macromolecular tracer. In rats, the peritoneal clearance (K) of such a tracer is 5 times the approximately 8 microL/min determined from the tracer appearance rate in blood (Cl). The fractional contribution of tissues bordering the peritoneal cavity to the overall Cl was determined to be diaphragm, 55%; viscera, 30%; and abdominal wall, 15%. The present study determines whether direct measurement of visceral peritoneal lymph flow matches the 30% (approximately 2.5 microL/min) contribution of the visceral peritoneal lymph flow as measured indirectly by the Cl method. The mesenteric lymph duct that exclusively drains lymph from the gut, liver, and mesentery was cannulated in 15 rats, and lymph flow from the duct was collected at hourly intervals up to 6 hours under near-normal physiologic conditions and under conditions of simulated PD. Changes in mesenteric lymph flow that resulted from a challenge with 3 mL intravenous saline were captured using real-time video. We observed no significant differences between the hourly lymph volumes collected over 6 hours in naïve animals (n = 5, p > 0.05). Under conditions of simulated PD with dialysis fluid in the peritoneal cavity, the mesenteric duct lymph flow averaged 8.67 +/- 1.41 microL/min (n = 10). That flow is similar to reported data on total peritoneal Cl in rats; and 4 times the 2.5 microL/min visceral peritoneal contribution to the total peritoneal Cl. The intravenous saline challenge significantly increased mesenteric lymph duct output to 30.9 +/- 1.6 microL/min (n = 5, p < 0.01) and reduced the lymph-to-plasma concentration ratio (L/P) by 43%. The reflection coefficient for total proteins (sigma(prot)) across the intestinal capillaries as calculated from the filtration rate-dependent L/P ratio when the transcapillary fluid escape rate and the mesenteric lymph flow were both high was more than 0.87. We concluded that (A) under near-normal physiologic conditions, the mesenteric lymph duct flow is steady, but quite low; (B) under conditions of simulated PD, the mesenteric lymph duct flow increases significantly from the physiologic norm; (C) mesenteric lymph duct flow is sensitive to the peritoneal fill volume; (D) during simulated PD, the fractional visceral peritoneal lymph flow measured indirectly from plasma appearance of intraperitoneal tracer underestimates the directly measured mesenteric duct lymph flow; and (E) the increased transcapillary fluid escape rate is rapidly buffered by augmentation of mesenteric lymph duct output.

Prediction of in vivo tissue distribution from in vitro data. 2. Influence of albumin diffusion from tissue pieces during an in vitro incubation on estimated tissue-to-unbound plasma partition coefficients (Kpu)

PURPOSE

To determine the extent of albumin diffusion from tissue pieces into medium during in vitro incubations, to develop and assess the utility of mathematical models describing this effect on the estimation of tissue-to-unbound plasma partition coefficients (Kpu) of drug substances and to derive factors to correct for associated errors.

METHODS

Twelve separate tissues were obtained from rats sacrificed by cervical dislocation, 48 h after an intravenous dose of 125I-human albumin, and tissue pieces incubated to determine the efflux of albumin into media over 2 to 4 h. A mathematical model was developed to predict and correct for the effect of albumin diffusion on the measured Kpu values of drugs.

RESULTS

The model predicted that the effect of albumin diffusion from tissue pieces during in vitro incubation (ranging from 14 to 59% remaining in tissue) on Kpu values was generally minimal, except for compounds that are highly plasma bound and have a low measured Kpu. Under these circumstances, the measured Kpu substantially underestimates the true value. An equation was derived from readily available or measurable parameters to correct for this underestimation.

CONCLUSIONS

Albumin diffuses from tissue pieces into protein free media during in vitro incubations until equilibrium is reached, defined by the albumin Kpu. Model predictions indicated that for the majority of compounds albumin diffusion would have a minimal effect on the measured Kpu value and that a correction factor could be calculated to account for any deviation.

Biodistribution studies of BSA loaded gelatin microspheres after peroral application

Biodistribution studies of radiolabelled [131I]BSA loaded gelatin microspheres were carried out on BALB/c mice after peroral administration. To two groups, the radiolabelled [131I]BSA gelatin microspheres with different mean particle size, 1.196+/-1.961 and 7.028+/-1.231 microm were administered orally. To the control group, a solution of [131I]BSA was also orally administered. Biodistribution was followed periodically within 15 days as a percent of total radioactivity present in stomach, small intestine with Peyer's patches and mesentery, colon with Peyer's patches, appendix and mesentery, liver, spleen, blood, kidney, lungs and heart. The biodistribution data confirmed that uptake in mice into Peyer's patches and passage to the liver and spleen via the mesentery lymph supply and nodes, increased with decreasing particle size.

Augmentation of intrapericardial nitric oxide level by a prolonged-release nitric oxide donor reduces luminal narrowing after porcine coronary angioplasty

BACKGROUND

Nitric oxide (NO) is a potent vasodilator and antiplatelet agent that suppresses vascular smooth muscle cell proliferation. Hypothesizing that generating NO in the pericardial space would reduce luminal narrowing after coronary angioplasty without affecting systemic hemodynamics, we have determined the effect of a novel NO donor on vascular healing after balloon overstretch.

METHODS AND RESULTS

Diazeniumdiolated bovine serum albumin (D-BSA; molecular weight 74 kDa, half-life for NO release 20 days) was radioiodinated and found by intravital gamma-imaging to have a longer residence time in pig pericardium than a low-molecular-weight (0.5 kDa) analogue (22 versus 4.6 hours, respectively). Intrapericardial injection of D-BSA immediately before 30% overstretch of normal left anterior descending and left circumflex coronary arteries dose dependently reduced the intimal/medial area ratio by up to 50% relative to controls treated with underivatized albumin when measured 2 weeks after intervention. Positive remodeling was also noted, which increased luminal area relative to control.

CONCLUSIONS

Perivascular exposure of coronary arteries to NO via intrapericardial D-BSA administration reduced flow-restricting lesion development after angioplasty in pigs without causing significant systemic effects. The data suggest that intrapericardial delivery of NO donors for which NO release rates and pericardial residence times are matched and optimized might be a beneficial adjunct to coronary angioplasty.

Effects of albumin supplementation on microvascular permeability in septic patients

Albumin has a stabilizing effect on endothelium and helps maintain capillary permeability to macromolecules. Critically ill patients with sepsis may have profound hypoalbuminemia, but the effect of this hypoalbuminemia on microvascular permeability is unknown. To determine the degree and potential importance of this effect, we measured the transcapillary escape rate (TER) of (125)I-labeled albumin in 12 adult patients fulfilling American College of Chest Physicians/Society of Critical Care Medicine criteria for septic shock. We measured TER over a 90-min baseline period and then repeated these measurements immediately after the rapid infusion of 200 ml of 20% albumin. At baseline, patients had a mean serum albumin concentration of 10.3 +/- 3.8 g/l, which, at 30 min after the albumin infusion, was 18.5 +/- 3.7 g/l. The baseline TER was 6.7 +/- 1.5%/h, with a postinfusion TER of 6.4 +/- 2.1%/h (P = 0.550). Albumin supplementation sufficient to nearly double serum concentrations in profoundly hypoalbuminemic septic patients had no clinically significant effect in reducing microvascular permeability.

Transcytosis inhibitor N-ethylmaleimide increases microvascular permeability in rat muscle

N-ethylmaleimide (NEM) has been claimed to markedly inhibit the transvascular passage of small proteins and albumin by interacting with the docking and fusion of plasmalemmal vesicles with their target membranes. To investigate the role of transcytosis in the transcapillary passage of albumin, we assessed the effects of NEM on (125)I-labeled radioiodinated serum albumin clearance (RISA-Cl) from blood to muscle in isolated and maximally vasodilated perfused rat hindquarters, in which vascular pressures, pre- and postcapillary resistances, and the capillary filtration coefficient (CFC) were continuously monitored. NEM (0.3-0.5 mM) caused a marked increase mainly in precapillary vascular resistance. Thus the arterial-to-venous resistance ratio in NEM-treated animals was 3.12 +/- 0.56 versus 1.66 +/- 0.17 during the control period (P < 0.05). Despite that, there was a doubling of both CFC from 0.0363 +/- 0.0028 to 0.0778 +/- 0.0101 ml x min(-1) x mmHg(-1) x 100 g(-1) (P < 0.01) and RISA-Cl, compared with the control situation, signaling markedly increased microvascular permeability. Our results strongly suggest that NEM, besides producing marked vasoconstriction, also causes damage to the capillary endothelium. Thus, instead of inhibiting transvascular transport, NEM may induce increases in the bulk transport of albumin from blood to tissue.

Comparison of cerebrospinal fluid transport in fetal and adult sheep

We quantified cerebrospinal fluid (CSF) transport (conductance) and CSF outflow resistance in late-gestation fetal and adult sheep using two methods, a constant pressure infusion method and a bolus injection technique into the lateral ventricles. No significant differences in CSF conductance (fetus 0.013 +/- 0.002, adult 0.014 +/- 0.003 ml x min(-1) x cm H(2)O(-1)) or CSF outflow resistance (fetus 83.7 +/- 9.8, adult 84.7 +/- 19.7 cm H(2)O x ml(-1) x min) were observed. To confirm CSF transport to plasma in fetal animals, (125)I- or (131)I-labeled human serum albumin (HSA) was injected into the lateral ventricles. The tracer entered fetal plasma with an average mass transport rate of 1.91 +/- 0.47% injected/h (n = 9). In two fetuses, we monitored the tracer appearance in plasma and cervical and thoracic duct lymph after injection of radioactive HSA into the ventricular CSF. As was the case in adult animals, fetal tracer concentrations increased in all three compartments over time, with the highest concentrations measured in lymph collected from the cervical lymphatics. These results 1) indicate that global CSF transport parameters in the late-gestation fetus and adult sheep are similar and 2) suggest an important role for extracranial lymphatic vessels in CSF transport before birth.

Liposomal antioxidants in combating ischemia-reperfusion injury in rat brain

Liposome-encapsulated antioxidants have been tested in vivo to prevent oxidative attack during cerebral ischemia and reperfusion. Oxidative stress is a causal factor in the neuropathogenesis of ischemic-reperfusion injury. From the therapeutic point of view free chemical antioxidants were almost ineffective to protect cerebral tissues from those oxidative attacks. Thus an attempt has been made to prevent the oxidative damage due to the cerebral ischemic insult by the introduction of chemical antioxidants, ascorbic acid and alpha-tocopherol either encapsulated or intercalated in small unilamellar liposomes. The effectiveness of antioxidant-loaded liposomes was tested against an experimental in vivo rat model of global cerebral ischemia. Oxidative free radical attack on cerebral tissues by the ischemic insult and brief reperfusion was accounted for by the amount of diene production per unit of tissue protein. Diene production in ischemic reperfused rat brain increases almost twofold over that of the normal rats. Prevention of excess diene production has been attributed to rats when they were treated either with L-ascorbic acid-encapsulated liposomes or alpha-tocopherol intercalated liposomes 2 hours prior to the cerebral ischemic insult. Complete restriction of excess diene generation has also been achieved when a mixture of alpha-tocopherol and L-ascorbic acid-encapsulated liposomes were injected 3 hours before the ischemic infraction.

Alveolar epithelial barrier functions in ventilated perfused rabbit lungs

We employed ultrasonic nebulization for homogeneous alveolar tracer deposition into ventilated perfused rabbit lungs. (22)Na and (125)I-albumin transit kinetics were monitored on-line with gamma detectors placed around the lung and the perfusate reservoir. [(3)H]mannitol was measured by repetitive counting of perfusion fluid samples. Volume of the alveolar epithelial lining fluid was estimated with bronchoalveolar lavage with sodium-free isosmolar mannitol solutions. Sodium clearance rate was -2.2 +/- 0.3%/min. This rate was significantly reduced by preadministration of ouabain/amiloride and enhanced by pretreatment with aerosolized terbutaline. The (125)I-albumin clearance rate was -0.40 +/- 0.05%/min. The appearance of [(3)H]mannitol in the perfusate was not influenced by ouabain/amiloride or terbutaline but was markedly enhanced by pretreatment with aerosolized protamine. An epithelial lining fluid volume of 1.22 +/- 0.21 ml was calculated in control lungs. Fluid absorption rate was 1.23 microl x g lung weight(-1) x min(-1), which was blunted after pretreatment with ouabain/amiloride. We conclude that alveolar tracer loading by aerosolization is a feasible technique to assess alveolar epithelial barrier properties in aerated lungs. Data on active and passive sodium flux, paracellular solute transit, and net fluid absorption correspond well to those in previous studies in fluid-filled lungs; however, albumin clearance rates were markedly higher in the currently investigated aerated lungs.

Hyaluronan preserves peritoneal membrane transport properties

BACKGROUND

We have shown that intraperitoneal (i.p.) addition of hyaluronan (HA) in a single dwell study in rat could increase peritoneal fluid removal by decreasing the peritoneal fluid absorption rate. In this study, we investigated the impact of repeated use of HA on peritoneal membrane transport characteristics.

METHODS

Twelve male Sprague-Dawley rats received a once-daily i.p. injection of 25 mL 4.25% glucose dialysis solution without (HP group, n = 6) or with 0.025% HA (HA group, n = 6) for 1 week. Forty-eight hours after the last injection, a 4-hour dwell using 25 mL 4.25% glucose dialysis solution with i.p. volume marker and frequent dialysate and blood samplings was performed in each rat as well as in rats that did not receive any injection (control group, n = 8).

RESULTS

Although the i.p. volumes were significantly lower in the HP and HA groups compared to the control group, i.p. volume in the HA group was significantly higher than in the HP group. Net ultrafiltration at 4 hours was 5.6 +/- 1.3 mL, 10.2 +/- 1.8 mL, and 13.2 +/- 0.6 mL for the HP, HA, and control group, respectively. The peritoneal fluid absorption rate decreased by 45% in the HA group compared to the HP group. There was no significant difference in peritoneal fluid absorption rate between the HA and the control group. No difference was found in the direct lymphatic absorption rate between the HP and HA groups [0.010 +/- 0.003 mL/minute in the HP group and 0.011 +/- 0.004 mL/min in the HA group] although they were both higher than that of the control group (0.004 +/- 0.001 mL/min). The solute transport rates were in general significantly higher in the HP group compared to the HA and control groups, and there was no significant difference between the latter two groups, except that protein transport rate was significantly lower in the HA group compared to the control group.

CONCLUSIONS

The present study suggests that (1) repeated exposure to hypertonic glucose-based dialysis solution results in increased peritoneal solute transport rates, as well as increased peritoneal fluid absorption rates; and (2) these changes, reflecting a highly permeable peritoneal membrane, were ameliorated by repeated i.p. addition of hyaluronan. The similar changes in the direct lymphatic absorption rate in rats that received daily i.p. injection of dialysis solution suggest that direct peritoneal lymphatic absorption was not influenced by hyaluronan.

Lowering of interstitial fluid pressure after neurogenic inflammation is inhibited by mystixin-7 peptide

Soft tissue injury is accompanied by lowering of interstitial fluid pressure (P(if)), plasma protein extravasation, and edema. Inflammation was produced by electrical stimulation (ES) of the vagus and the effects of the synthetic peptide mystixin-7 (p-anisoyl-Arg-Lys-Leu-Leu-D-Thi-Ile-D-Leu-NH(2)) on P(if) were examined. Micropuncture measurement of P(if) in submucosa, without opening the trachea, was conducted on rats anesthetized with pentobarbital sodium (50 mg/kg) and euthanized with intravenous KCl. P(if) in control (intravenous saline) was -1.2 +/- 0.7 mmHg before ES and decreased to -4.7 +/- 1.0 mmHg (P < 0.01, n = 8) after ES. Mystixin-7 (10 and 20 microg/kg iv) blocked the fall in P(if) after ES (-1.1 +/- 0.3 and -0.8 +/- 0.2 mmHg, P < 0.01, n = 8 and n = 4). The 1 microg/kg dose was without effect. When trachea from animals pretreated with mystixin-7 (20 microg/kg iv) were soaked in phosphate-buffered saline (0.15 M, pH 7.4), the rate of fluid accumulation was significantly reduced. This study suggests that mystixin peptides, which have structural similarity to a fragment from laminin-alpha1 chain, may be useful tools for studying cell adhesion and factors that maintain the structural integrity of connective tissue after injury.

Brain-blood permeability: TNF-alpha promotes escape of protein tracer from CSF to blood

The objective of this study was to determine the effect of tumor necrosis factor (TNF)-alpha on the efflux of protein from the central nervous system to blood based on assessing the clearance of radiolabeled albumin from the cerebrospinal fluid (CSF) to blood in rats. (125)I-labeled human serum albumin ((125)I-HSA) was injected into a lateral ventricle, and venous blood was sampled hourly to determine the basal CSF protein clearance into the blood. After this, rats were intraventricularly infused with 10 microliter TNF-alpha and 10 microliter (131)I-HSA (n = 6) or 10 microliter saline and 10 microliter (131)I-HSA (n = 6). Venous blood was sampled hourly for 3 h. (131)I-HSA tracer recovery increased threefold in the venous blood and was significantly higher in the spleen, muscles, and skin in animals treated with TNF-alpha. No significant changes were observed in control animals treated with saline. The data suggest that TNF-alpha promotes the clearance of protein macromolecules from the CSF to the venous blood.

Cerebral blood volume measured using near-infrared spectroscopy and radiolabels in the immature lamb brain

Near-infrared spectroscopy (NIRS) is a technique that is increasingly being used for the noninvasive measurement of cerebral blood volume (CBV) in newborn infants, but it has not been fully validated against established methods. These experiments in immature lambs (gestation 92+/-1 d, mean+/-SEM) compared CBV measured using NIRS-derived estimates of oxygenated Hb (n = 5) with CBV estimated with radiolabeled indicators (125I-labeled serum albumin and 51Cr-labeled red blood cells, n = 10). Total brain CBV (mL/100 g tissue) measured using NIRS was 2.5+/-0.2 compared with 2.5+/-0.2 using radiolabels (NS). Regional tissue plasma, red blood cells, and whole blood volumes from radiolabels varied significantly (p < or = 0.05) throughout the brain. Whole blood volume (mL/100 g tissue) was largest in choroid plexus (16.2+/-2.1) and least in white matter (0.7+/-0.1) with a significant hierarchy evident among regions: choroid plexus > cerebellum > cortex > brain stem = midbrain > white matter. Regional plasma and red blood cell distributions were similar to whole blood, being highest in choroid plexus (13.0+/-1.6 and 3.2+/-0.9, respectively), and least in white matter (0.8+/-0.1 and 0, respectively). These data from the immature lamb brain indicate that total CBV measured with NIRS is essentially identical with the volumes obtained using intravascular radiolabels. Among cerebral regions, white matter contributes little to the global blood volume measured with NIRS because its red blood cell content is very low.

Uptake of positron emission tomography tracers in experimental bacterial infections: a comparative biodistribution study of radiolabeled FDG, thymidine, L-methionine, 67Ga-citrate, and 125I-HSA

The purpose of this study was to evaluate the localization of positron emission tomography (PET) tracers [2-deoxy-2-fluoro-D-glucose (FDG), thymidine, and L-methionine] in sites of bacterial infection, and to contrast this with that of other tracers. The left calf muscles of rats were infected with a suspension of Escherichia coli and the biodistribution of 18F- or 3H-FDG, 3H-thymidine, L-11C- or 3H-methionine, gallium-67 citrate (67Ga-citrate) and iodine-125 human serum albumin (125I-HSA) was determined in these animals. 3H-FDG uptake in the infectious foci was evaluated by autoradiography of histological sections. Although 18F-FDG, 67Ga-citrate, and 125I-HSA showed comparatively high uptake in the infected muscle [the percentage activity of injected dose (ID) per gram of tissue normalized for rat weight in kilogram (%ID/g)xkg at 2 h postinjection was as follows: 18F-FDG, 0.184+/-0.026 to 0.218+/-0.046; 67Ga-citrate, 0.221+/-0.016; 125I-HSA, 0. 198+/-0.019], the infected muscle to blood ratio was much higher for 18F-FDG than for 67Ga-citrate or 125I-HSA (18F-FDG, 10.31+/-0.76 to 14.89+/-2.26; 67Ga-citrate, 1.24+/-0.67; 125I-HSA, 0.20+/-0.02). The draining reactive lymph nodes also showed higher accumulation of 18F-FDG than of 67Ga-citrate or 125I-HSA. The uptake of 3H-thymidine and L-11C- or 3H-methionine in the infected muscle was lower than that of 18F- or 3H-FDG (at 2 h postinjection, 3H-thymidine = 0. 039+/-0.005 and L-3H-methionine = 0.063+/-0.007 (%ID/g)xkg. Autoradiographs showed that the highest 3H-FDG uptake was seen in the area of inflammatory cell infiltration surrounding the necrotic region. In conclusion, 18F-FDG, which rapidly accumulates in sites of bacterial infection and in reactive lymph nodes with a high target to background ratio, appears to be a promising infection detection agent.

Intravenous endotoxin does not increase tissue extravasation of albumin in rats

BACKGROUND

It is unclear whether activation of the inducible nitric oxide synthase (iNOS) increases or decreases the extravasation of plasma.

METHODS

Chloralose anaesthetised male Wistar rats received E. coli lipopolysaccharide (LPS), 3 mg kg-1 i.v., or the corresponding volume of saline, 3 or 5 h before the end of the experiment. Mean arterial pressure (MAP) and heart rate (HR) were recorded. Tissue clearance of radio-labelled albumin, during the last 2 h of each experiment, was determined by a double-isotope method. In separate animals, the serum concentration of nitrite and nitrate was determined, 5 h after LPS or the solvent.

MAIN RESULTS

LPS initially decreased MAP and lastingly increased HR. In the 3-h LPS animals (n = 8), tissue plasma clearance was lower in the heart and calf muscle and increased only in diaphragm, compared to corresponding control animals (n = 8). In the 5-h LPS rats, clearance was lowered (n = 8) in the entire gastrointestinal tract and in testes, compared to controls (n = 8). The serum nitrite/nitrate concentration was higher in animals given LPS (n = 6) than in controls (n = 6).

CONCLUSION

After LPS, tissue clearance of albumin was not increased in any major tissue, in spite of increased serum levels of NO end products. Apparently, after activation of iNOS, the augmented release of NO is not necessarily associated with increased albumin extravasation.

Clearance of tracer albumin from peritoneal cavity to plasma at low intraperitoneal volumes and hydrostatic pressures

OBJECTIVE

To assess the clearance of radiolabeled tracer albumin (RISA) from peritoneal cavity to plasma (Cl-->P) in rats under essentially "normal" conditions, that is, when intraperitoneal hydrostatic pressure (IPP) is subatmospheric and the intraperitoneal (IP) "free" fluid volume (IPV) is low.

METHODS

A volume of 0.3 mL of RISA was injected IP into anesthetized Wistar rats (wt = 300 g) when the IPV was approximately 2 mL (normal) or the IPV was approximately 10 mL, and IPP was either -1.8 mmHg (normal) or +1.5 mmHg (produced by an external cuff). Plasma samples (25 microL) were obtained repeatedly during the dwell, which lasted 30-300 min, after which the peritoneal cavity was opened to recover the IPV and residual IP RISA activity. The Cl-->P was assessed as the mass transfer of RISA into plasma, occurring per unit time, divided by the calculated mean IP RISA concentration (CD). The interstitial RISA space was measured as the mass of RISA accumulated, per unit tissue weight, in peritoneal tissue samples divided by the CD.

RESULTS

A markedly lower Cl-->P (2.47+/-0.67 microL/min), as well as total RISA clearance out of the peritoneal cavity (Cl), was found under "normal" conditions (an IPV of approximately 2 mL and an IPP of approximately -1.8 mmHg) compared to the situation during peritoneal dialysis (an IPV of approximately 20 mL and an IPP of +1 mmHg). Furthermore, the interstitial RISA space increased linearly over time even at negative IPPs and at an unchanging peritoneal interstitial fluid volume. At a low (normal) IPV the Cl-->P did not increase significantly with elevating IPP, and increased only marginally when tracer distribution was improved by artificial vibration of the rats. However the Cl-->P increased when larger volumes were infused to increase the total IPV.

CONCLUSIONS

It is concluded that the Cl-->P and Cl at low IPPs and IPVs are not as high as during peritoneal dialysis. Increases in Cl-->P were, however, coupled to increases in IPV. This highlights the importance of the IPV per se and of a sufficient IP tracer distribution for direct lymphatic absorption to be efficient.

Stop-flow studies of solute uptake in rat lungs

Stop-flow studies were used to characterize solute uptake in isolated rat lungs. These lungs were perfused at 8 or 34 ml/min for 10-28 s with solutions containing 125I-albumin and two or more of the following diffusible indicators: [3H]mannitol, [14C]urea, 3HOH, 201Tl+, or 86Rb+. After this loading period, flow was stopped for 10-300 s and then resumed to flush out the perfusate that remained in the pulmonary vasculature during the stop interval. Concentrations of 201Tl+ and 86Rb+ in the venous outflow decreased after the stop interval, indicating uptake from exchange vessels during the stop interval. The amount of these K+ analogs lost from the circulation during the stop interval was greater when the intervals were longer. However, losses of 201T1+ at 90 s approached those at 300 s. Because extraction continued after the vasculature had been flushed, vascular levels had presumably fallen to negligible levels during the stop interval. By 90 s of stop flow the vascular volume that was cleared of 201T1+ averaged 0.657 +/- 0.034 (SE) ml in the experiments perfused at 8 ml/min and 0.629 +/- 0.108 ml in those perfused at 34 ml/min. Increases in perfusate K+ decreased the cleared volumes of 201T1+ and 86Rb+. Uptake of [3H]mannitol, [14C]urea, and 3HOH during the stop intervals was observed only when the lungs were loaded at high flow for short intervals. Decreases in 201T1+ and 86Rb+ concentrations in the pulmonary outflow can be used to identify the fraction of the collected samples that were within exchange vessels of the lung during the stop interval and may help determine the distribution of solute and water exchange along the pulmonary vasculature.

Transcapillary transport of metaiodobenzylguanidine (MIBG) in isolated rat heart

A better understanding of transcapillary transport for tracer metaiodobenzylguanidine (MIBG) is desirable for development of tracer kinetic models that yield meaningful estimates of neuronal uptake function from tissue radioactivity time courses. This study utilized a multiple-indicator approach in Langendorff-perfused rat hearts to define transport mechanisms and determine the capillary permeability-surface area (PSc) over a broad range of flow (F). Multiple injections within the same heart at different flows allowed characterization of the PSc/F relationship within the same heart. The coefficient of variation of E for multiple injections within the same hearts at constant flow was 6 +/- 2% (3 to 6 injections in 9 hearts). In 10 hearts (4 to 6 injections per heart), flow was varied between 2.0-16.5 mL/min. PSc was found to be nearly proportional to flow in each heart (r = 0.88 +/- 0.14; slope = 0.23 +/- 0.10; intercept = 11 +/- 7 mL/min/g dry). Tissue hypoxia at low flows, as evidenced by enhanced lactate production, did not appear to influence the PSc/F relationship. Pharmacologic blockade of uptake-1 and uptake-2 had negligible affect on E or PSc as compared with flow-matched controls, although tissue retention was markedly reduced. The results show PSc of MIBG to be nearly proportional to flow but independent of specific neuronal and extraneuronal transport mechanisms and tissue hypoxia. The results are consistent with a passive diffusion process across the capillary endothelial barrier. The increase in PSc with increasing flow could reflect capillary recruitment and/or enhanced capillary permeability.

Determination of volumetric cerebrospinal fluid absorption into extracranial lymphatics in sheep

We estimated the volumetric clearance of cerebrospinal fluid (CSF) through arachnoid villi and extracranial lymphatics in conscious sheep. Catheters were inserted into both lateral ventricles, the cisterna magna, multiple cervical lymphatics, thoracic duct, and jugular vein. Uncannulated cervical vessels were ligated. 125I-labeled human serum albumin (HSA) was administered into both lateral ventricles. 131I-HSA was injected intravenously to permit calculation of plasma tracer loss and tracer recirculation into lymphatics. From mass balance equations, total volumetric absorption of CSF averaged 3.37 +/- 0.38 ml/h, with 2.03 +/- 0.29 ml/h (approximately 60%) removed by arachnoid villi and 1.35 +/- 0.46 ml/h (approximately 40%) cleared by lymphatics. With projected estimates for noncannulated ducts, total CSF absorption increased to 3.89 +/- 0.33 ml/h, with 1.86 +/- 0.49 ml/h (48%) absorbed by lymphatics. Additionally, we calculated total CSF drainage to be 3.48 +/- 0.52 ml/h, with 54 and 46% removed by arachnoid villi and lymphatics, respectively, using previously published mass transport data from our group. We employed estimates of CSF tracer concentrations that were extrapolated from relationships observed in the study reported here. We conclude that 40-48% of the total volume of CSF absorbed from the cranial compartment is removed by extracranial lymphatic vessels.

Clearance of albumin by cortical bone and marrow

Male Sprague-Dawley rats, approximately 300 g, were anesthetized. The jugular vein and carotid artery were cannulated and the left femoral vein was exposed. The femoral vein was then ligated, and 2 minutes later albumin, labeled with 125I, was injected. The albumin was allowed to equilibrate in the vascular system for 3 minutes, and then 1 group of animals was euthanized. Further groups of animals were euthanized after 15, 30, and 60 minutes. Tibias were removed from both legs together with samples of muscle and liver. The tibias were separated into diaphyseal cortex, marrow, and proximal and distal ends. All tissue samples and terminal blood samples were counted for radioactivity, and volumes of distribution were calculated. In cortical bone the volume distribution increased from an initial value of 12.9 +/- 1.1 microL/g to 18.6 +/- 2.5 microL/g at 30 minutes in the control leg (mean +/- standard error of the mean, n = 5). In the congested leg, the volume of distribution increased from 10.6 +/- 0.6 to 19.6 +/- 2.1 microL/g during the same time interval. The difference in rate of increase between the congested and control leg was not statistically significant. Albumin seemed to equilibrate within 3 minutes within the marrow. The data are consistent with the hypothesis that macromolecular transport in the interstitial fluid of cortical bone is coupled to convectional flow from endosteal to periosteal surface. This data may help to understand mechanisms by which venous hypertension has been shown to stimulate bone growth and fracture repair, and also the distribution of bone density changes observed after prolonged exposure to microgravity.

Accelerated clearance of albumin from the osteoarthritic knee: implications for interpretation of concentrations of "cartilage markers" in synovial fluid

OBJECTIVE

The magnitude of articular cartilage destruction or repair in osteoarthritic (OA) joints has been deduced in some studies from the synovial fluid (SF) concentration of proteins derived from the extracellular matrix of the cartilage, without regard to the low grade synovitis that is often present in this disease. We examined the clearance kinetics of albumin, as a surrogate for cartilage derived proteins, from OA and control joints in an established canine model.

METHODS

Twelve weeks after the left anterior cruciate ligament of 6 normal dogs was transected, 131I albumin (RISA) was injected into the contralateral (control) knee. Surface radioactivity was monitored for 7 h, and SF was then aspirated to determine the SF RISA concentration and leukocyte count, and calculate the volume of distribution (VD) and clearance of RISA. One week later, RISA was injected into the cruciate deficient knee and these measurements were repeated, then the intensity of synovial inflammation and severity of cartilage changes of OA in both knees were assessed.

RESULTS

Synovitis and articular cartilage ulceration were seen only in the cruciate-deficient OA knee, in which the mean SF leukocyte count (1570/mm3), thickness of the synovial intima (mean = 30 microns), and severity of synovial mononuclear cell infiltration (mean = 13,500 cells/mm2) significantly exceeded those in the contralateral knee (850/mm3, 13 microns, 1400 cells/mm2; p < or = 0.01 in each case). In each dog, RISA VD in the OA knee was higher than in the contralateral knee (mean = 9.2 +/- 3.6 and 3.7 +/- 0.9 ml, respectively; p = 0.008) and RISA clearance rate in the OA knee exceeded that in the contralateral knee (3.8 +/- 1.5 and 1.4 +/- 0.3 microliters/min, respectively; p = 0.009).

CONCLUSION

Accelerated clearance of protein from the OA joint with low grade synovitis could significantly affect the SF concentration of cartilage derived proteins. Therefore, inferences about the effect of a therapeutic agent on cartilage metabolism based upon changes in the concentration of a protein in serial samples of OA SF may be misleading unless protein clearance kinetics have been determined.

Drainage of CSF through lymphatic pathways and arachnoid villi in sheep: measurement of 125I-albumin clearance

We investigated lymphatic drainage pathways of the central nervous system in conscious sheep and quantified the clearance of a cerebrospinal fluid (CSF) tracer into lymph and blood. In the first group of studies, 125I-HSA was injected into the lateral ventricles of the brain or into lumbar CSF and after 6 h, various lymph nodes and tissues were excised and counted for radioactivity. Multiple lymphatic drainage pathways of cranial CSF existed in the head and neck region defined by elevated 125I-HSA in the retropharyngeal/cervical, thymic, pre-auricular and submandibular nodes. Implicated in spinal CSF drainage were mainly the lumbar and intercostal nodes. In a second group of experiments, multiple cervical vessels and the thoracic duct were cannulated and lymph diverted from the animals. Transport of tracer through arachnoid villi was taken from recoveries in venous blood. Following intraventricular administration, the 6 h recoveries of 125I-HSA in the lymph (sum of cervical and thoracic duct) and blood were 8.2% +/- 3.0 and 12.5% +/- 4.5 respectively and at 22 h, 25.1% +/- 6.9 and 20.8% +/- 4.1 respectively. When 125I-HSA was injected into lumbar CSF, the 6 h recoveries of tracer in thoracic duct and blood were 11.6% +/- 2.7 and 16.3% +/- 3.7 respectively. Total lymph and blood recoveries were not significantly different in any experiment. We conclude that the clearance of 125I-HSA from the CSF is almost equally distributed between lymphatic and arachnoid villi pathways.

Transport of tracer albumin from peritoneum to plasma: role of diaphragmatic, visceral, and parietal lymphatics

Using a technique to acutely seal off various parts of the peritoneal membrane surface, with or without evisceration, we investigated the role of diaphragmatic, visceral, and parietal peritoneal lymphatic pathways in the drainage of 125I-labeled albumin (RISA) from the peritoneal cavity to the plasma during acute peritoneal dialysis in artificially ventilated rats. The total RISA clearance out of the peritoneal cavity (Cl) as well as the portion of this Cl reaching the plasma per unit time (Cl--> P) were assessed. Under non-steady-state conditions, the Cl was fivefold higher than the Cl--> P. Evisceration caused a 25-30% reduction in both Cl--> P and Cl. Sealing of the diaphragm, however, reduced the Cl--> P by 55% without affecting the Cl. A further reduction in the Cl--> P was obtained by combining sealing of the diaphragm with evisceration, which again markedly reduced the Cl. However, the greatest reduction in the Cl was obtained when the peritoneal surfaces of the anterior abdominal wall were sealed off in eviscerated rats. The discrepancy between the Cl and the Cl--> P can be explained by the local entrance of fluid and macromolecules into periabdominal tissues, where fluid is rapidly absorbed through the capillary walls via the Starling forces, while macromolecules are accumulating due to their very slow uptake by tissue lymphatics under non-steady-state conditions. Of the portion of the total Cl that rapidly entered the plasma, conceivably by lymphatic absorption, 55% could be ascribed to diaphragmatic lymphatics 30% to visceral lymphatics, and only some 10-15% to parietal lymphatics.

High potassium diets reduce endothelial permeability in stroke-prone spontaneously hypertensive rats

1. High potassium (K) diets are known to prevent hypertensive arterial lesions and reduce stroke incidence without affecting blood pressure. 2. To elucidate the mechanism of this beneficial effect, we studied the effect of K supplementation on the extravasation of plasma albumin in high NaCl-fed stroke-prone spontaneously hypertensive rats (SHRSP). Increased permeability of the endothelium to macromolecules is assumed to be an early manifestation of vascular injury. 3. The disappearance of intravenously injected [125I]-albumin was examined in SHRSP rats fed high NaCl diets containing either 0.5% normal K or 2.1% high K for 5 weeks. 4. The bodyweight, blood pressure, plasma volume and urinary protein excretion were not significantly different between the two SHRSP groups. 5. The high K SHRSP showed a slower plasma albumin disappearance rate than the normal K SHRSP (10.3 vs 14.7%/h, P < 0.004). The albumin radioactivity remaining in the aortic wall and in the brain after removing blood after perfusion was lower in the high K SHRSP than in the normal K SHRSP (aorta, -20%, P < 0.02; brain, -26%, P < 0.04). 6. These results suggest that the high K diet reduced the endothelial permeability to albumin in high NaCl-fed SHRSP rats. High K diets may have a protective effect against endothelial dysfunction and thereby contribute to the reduction of vascular lesion formation and stroke incidence.

Intraperitoneal fluid volume changes during peritoneal dialysis in the rat: indicator dilution vs. volumetric measurements

In order to validate the single injection RISA (125I human serum albumin) indicator diluation technique for assessing the alterations in intraperitoneal (i.p.) dialysate volume (IPV) which occur vs. time [V(t)] during peritoneal dialysis (PD), the RISA dilution technique was compared to V(t) determinations using a direct volume recovery method in Wistar rats. Sixteen milliliters of either 1.36 or 3.86% Dianeal or 0.9% NaCl were used as dialysis fluids in exchanges lasting between 1 and 360 min. Approximately 4% (4.41 +/- 0.59 (SE; n = 8) for 1.36% Dianeal and 4.07 +/- 0.72 (n = 4) for 3.86% Dianeal) of the RISA dose given intraperitoneally was lost from the dialysate during the first 1(-1.5) min after instillation, conceivably due to rapid tracer adsorption to peritoneal surfaces. Following the initial instant tracer loss and RISA dilution due to a residual volume (3.07 +/- 0.18 ml; n = 12), RISA disappeared at a fractional rate (FDR) of 2.10 +/- 0.14 x 10(-3) min-1 and 1.67 +/- 0.09 x 10(-3) min-1, during the first 30 min for 1.36 and 3.86% Dianeal, respectively. The overall FDR was 1.33 +/- 0.10 x 10(-3) and 0.707 +/- 0.082 x 10(-3) min-1 for 1.36% Dianeal (0-150 min) and 3.86% Dianeal (0-360 min), respectively, while the overall (0-150 min) FDR for the NaCl exchanges was 1.40 +/- 0.21 x 10(-3) min-1. These values correspond to RISA clearances out of the peritoneal cavity (KE) of 29.2 +/- 1.8, 22.1 +/- 1.6, and 25.7 +/- 2.4 microliter x min-1 for 1.36 and 3.86% Dianeal and 0.9% NaCl, respectively. The KE value for 3.86% Dianeal was significantly (p < 0.05) lower than for the two dialysates with lower osmolality. The slightly enhanced FDR of RISA during the first 30 min was partly due to the presence of nonprotein-bound free iodine in the RISA preparation used, and also to an enhanced disappearance of albumin during the first portion of the dwell. V(t) data from individual experiments using the RISA dilution technique (RISA curves) were analyzed by computer-aided nonlinear least-squares regression analysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Regional CNS uptake of blood-borne nerve growth factor

Nerve growth factor (NGF), in addition to being a neurotrophic substance, has effects on the endocrine and immune systems. For example, intravenous injection of NGF results in a cascade of events leading to an increase in glucocorticoid secretion. While this response appears to be mediated centrally, there has been no evidence that circulating NGF has access to the CNS. Using intravenous injections of 125I-NGF, we find specific uptake at 1 hr but none at 6 hr, into homogenates of the basal forebrain, cerebellum, frontal cortex, hippocampus, and olfactory bulb. By autoradiography, uptake is localized to circumventricular organs, deep layers of the cerebellum, and all layers of the hippocampal region CA1, but not the dentate gyrus. Thus, uptake of blood-borne NGF could affect the hypothalamic-pituitary-adrenal axis via binding to NGF receptors present in the hippocampus. However, the sources of endogenous NGF, the mechanism of access through the blood-brain barrier, the eventual fate of NGF entering from the blood, and the physiological significance of this uptake remain to be elucidated.

Indomethacin reduces ischemia-induced alteration of blood-brain barrier transport in piglets

Cerebral ischemia-reperfusion (Isc-Rep) alters blood-brain barrier (BBB) transport properties in piglets. Pretreatment with superoxide dismutase and catalase partially attenuates these effects. Activated O2 species produced with Isc-Rep in piglets are generated via prostaglandin (PG) H synthase. This experiment determines if products of PGH synthase alter BBB transport of sodium and albumin. Piglets anesthetized with nitrous oxide and halothane were divided into four groups: 1) control, 2) indomethacin (5 mg/kg iv) with no Isc-Rep, 3) Isc-Rep alone, and 4) Isc-Rep after pretreatment with indomethacin (Indo). Regional transfer coefficients (Kin) and regional cerebral blood flow (microspheres) were measured at 2 h reperfusion after 20 min total global cerebral ischemia. Kin values are represented as absolute values and also relative to blood flow to account for any changes in perfusion caused by ischemia and/or Indo. Indo alone did not alter sodium or albumin transfer compared with control animals. Isc-Rep alone caused a significant increase in sodium and albumin transport compared with all other groups (control cerebral sodium Kin was 18.2 +/- 2.7 cm3.g-1.s-1.10(6) vs. 32.9 +/- 3.1 for Isc-Rep, P < 0.05). In contrast, there was no significant difference in sodium or albumin transfer with Isc-Rep after Indo pretreatment (e.g., cerebral sodium Kin was 22.0 +/- 2.0 for Isc-Rep after Indo) compared with the control or Indo alone groups. Indo pretreatment effectively attenuates increased BBB transport of both sodium and albumin following cerebral ischemia. We conclude that products of PGH synthase are involved in BBB alterations of protein and cation transport that follow the early stages of cerebral reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Partial deuteration and blood-brain barrier (BBB) permeability

Boron neutron capture therapy (BNCT) is one method of radio-surgery used for malignant brain tumor. The theory of this method is based on the nuclear reaction that occurs when boron-10 is radiated with and absorbs neutrons. When treating deep-seated brain tumor, partial deuteration of body water is used to improve the penetration of neurons into the tissue. In order to investigate the change in the BBB function under partial deuteration, we measured brain water content and the permeability of protein. Wistar rats were given 99% heavy water (approx. 10% of body weight/day) as drinking water. On the day of the experiment, all animals received 125-I labeled albumin as a tracer of protein. Light water in the control group or heavy water (D2O) in the experimental group was given by drip infusion for 60 min. Heavy water was measured by infrared spectroscopic analysis. Water content was measured by the freeze-dry method. The radioactivity of 125-I was determined with a gamma scintillation counter. Mean values of D2O concentration in the tissue were 17.9-36.5%. Water content increased in the cortex in all animals. The ratio of 125-I in the brain tissue to blood showed significant differences between the control group and animals deuterated to more than 30% of body water. Brain tissue deuterated over 10% showed a mild leakage of water, indicating the early stage of brain edema. Deuteration higher than 30% caused a leakage of protein, which might indicate the leakage of boron compound from the vessels into the normal brain tissue.

Effect of gamma-irradiation on the uptake and digestion of 125I-labeled bovine serum albumin by rat visceral yolk sac cultured in vitro

The effect of gamma-irradiation on a major nutritional function of the yolk sac (the uptake and digestion of macromolecular materials) was studied in rat visceral yolk sacs cultured in vitro being used 125I-labeled bovine serum albumin (RISA) as the tracer protein. The uptake of RISA (per g wet weight) by rat yolk sacs irradiated with doses of 5-80 Gy was essentially the same as that in the unirradiated control yolk sacs. There were no significant differences in yolk sac uptake of RISA with respect to the radiation doses or to culture period up to 18 hours after irradiation. External gamma-irradiation with 10-80 Gy does also had no effect on the extracellular release of 125I from yolk sacs which had been taken it up as RISA. The ratios of the activity in ultrafiltrates of the medium to the total activity in the medium were slightly higher at doses of 40 and 80 Gy.

Role of chronic Pseudomonas aeruginosa infection in airway mucosal permeability

The role of Pseudomonas aeruginosa infection in airway mucosal permeability was studied in 16 patients with chronic bronchitis by measuring the amounts of radiolabeled albumin in sputum. One group (A) consisted of six patients (two female, four male, 53 +/- 6 years, SEM) with chronic P aeruginosa infection for 5 +/- 0.9 years. Another group (B) consisted of ten patients (five female, five male, 67 +/- 4 years) without P aeruginosa infection for at least two years. No significant differences between groups A and B were found in the volume of sputum (63 +/- 21 ml/day in group A and 45 +/- 8 ml/day in group B, p = 0.44), the obstructive changes (FEV1 of 57 +/- 6 percent in group A and 51 +/- 4 percent in group B), or the duration of disease (19 +/- 4 years in group A and 14 +/- 4 years in group B). Saliva, sputum, and serum samples were collected at intervals of 2 h over an 8-h period, and at 24 h after intravenous administration of 131I-labeled human albumin. For counting, free 131I was removed by dialysis. Radiocounts (cpm) of saliva were significantly smaller than those of sputum or serum. The cpm from each sputum sample was divided by serum cpm at the time of each sampling. Group A showed significantly higher values in the ratio of sputum- to serum-cpm than did group B at all sampling times. Furthermore, the ratios at 2 and 4 h after 131I-albumin injection significantly correlated with sputum volume per day, whereas they did not correlate with any other factors (age, obstructive impairment, and duration of disease). These findings suggest that chronic P aeruginosa infection produces an increase in airway mucosal permeability to albumin.

A simple, dual tracer method for the measurement of transvascular flux of albumin into the lung

A simple, first-order model of albumin kinetics in the rat lung is presented and validated with a more sophisticated model. The simple model assumes that intravascular concentration of tracer albumin is constant over 30 min after injection and transvascular flux of tracer albumin is unidirectional and proportional to the permeability-surface area product (PS). 125I-albumin is injected initially and 131I-albumin at 20 min. At 30 min the rat is sacrificed and plasma and tissue samples are obtained for gamma counting. Simultaneous equations are set up for the two tracers and solved for PS and plasma volume. The accuracy of this approach is examined with data generated from a more complete model. This model uses the concepts of hydraulic conductivity, solvent drag, reflection coefficients, hydrostatic and osmotic pressures, exclusion volumes, and lymph flow, as well as PS. Based on known PS and clearance rates from the complex model, the simple model estimates tracer albumin leakage rate with less than 5% error over the range of PS encountered in rat studies.

Tissue extravasation of albumin from intraabdominal trauma in rats

Intraabdominal surgery tends to lower circulating plasma volume by mechanisms unrelated to bleeding and evaporation. In chloralose-anesthetized rats, the tissue clearance of radiolabelled albumin was determined by a double isotope method. Animals were subjected to a standardized abdominal trauma, eliciting minimal bleeding and evaporation, and others served as controls. The trauma significantly increased tissue albumin extravasation in abdominal skin, abdominal wall, pancreas, small intestine, colon, mesentery and diaphragm. Considering the mass of the respective tissues, a substantial portion of the albumin extravasation took place in the abdominal wall. No increased albumin clearance was found in extra-abdominal tissues. It is suggested that abdominal surgery decreases plasma volume by extravasation in the operation field.

Cornea fluid dynamics. II. Evidence for transport of radiolabelled albumin in rabbits by bulk flow

Transport of radiolabelled albumin in vivo has been measured in cornea. In anaesthetized rabbits, a 1-10 nl mixture of either 125I- or 131I-labelled human serum albumin and fluorescinthiocarbamoyldextran was injected with micropipettes under guidance of a fluorescent microscope. The injection sites were a spot 3 mm from limbus and the cornea centre, and the sites were localized by a template fitting the cornea exactly. Four, 12, 20 and 30 hr after the injection, the rabbits were reanaesthetized, and enucleated after being killed with an overdose of anaesthetic. The bulbi were frozen, and dissection of cornea performed in the cold room using the template described above and a stereomicroscope. Numbered samples were obtained, and isotope distribution measured. In the experiments lasting for 20 hr, about 55% of the isotope was recovered, giving a transfer coefficient of 0.4-0.5 per day. A common pattern of isotope distribution was observed independent of duration of isotope equilibration; peripherally injected isotope moved preferentially in central direction, indicating that fluid is transported by bulk flow and diffusion from peripheral to central cornea. Centrally injected isotope moved symmetrically from the injection point, as expected from transport by diffusion alone. Data from experiments with isotope injection in the cornea centre allowed the calculation of a diffusion coefficient for albumin along cornea of 2.19 x 10(-7) cm2 sec-1.

Pharmacokinetics and tissue distribution of parenterally administered human alpha-lymphotoxin in normal and meth-A tumor-bearing BALB/c mice

These in vivo studies examine the pharmacokinetics of parenterally administered purified, native human alpha-lymphotoxin (LT) in normal and Meth-A bearing BALB/c mice. We found that the lytic activity of alpha-LT was inactivated within 5 h in the blood of both normal and tumor-bearing mice in vivo. However, LT bioactivity in vitro was not affected by incubation with fresh serum. Radioiodinated LT was rapidly sequestered in the kidneys of both normal and tumor-bearing animals. Systemically administered, radioiodinated LT did not selectively localize in tumor tissues.

Initial plasma disappearance and distribution volume of [131I]albumin and [125I]fibrinogen in man

The simultaneous plasma disappearance curves of albumin and fibrinogen were recorded in eight normal subjects from 10 to 60 min following intravenous injection. Additional samples were taken at 3, 4, 5, 6 and 7 min. The initial distribution volume (IDV) of albumin calculated by semilogarithmic extrapolation to zero time was 5.56% (range 3.73-8.53) larger than that of fibrinogen, denoting an initial high-rate function of albumin efflux extending from zero to about 10 min after tracer injection. The following slower phase of the albumin curve from 10 to 60 min was found to be similar to the so-called transcapillary escape rate (TER) of single-tracer experiments. By introducing the value Cp(0) (i.e. the estimated curve height at t = 0, from the injected amount of albumin tracer divided by the IDVf), the entire initial part of the albumin curves was analysed. From this analysis the mean value of 0.0135 +/- 0.0038 min-1 was determined for initial slope, corresponding to a whole-body unidirectional albumin efflux [j(0)] of 0.0572 +/- 0.0160 ml 100 g-1 min-1. The result is about 16 times higher than normal estimates of total lymphatic albumin return, indicating a huge backflux of interstitial albumin at the whole-body capillary level. Both phases of efflux seem to reflect uptake in a variety of peripheral tissues, and the hypothesis that the second phase (TER) expresses the initial slope of albumin escape into non-liver tissues is not substantiated. Based on the difference in IDV of the tracers demonstrated, the uncritical use of albumin as a plasma volume marker is not justified.

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.

Effects of oxygen free radical scavengers, xanthine oxidase inhibition and calcium entry-blockers on leakage of albumin after ischaemia. An experimental study in rabbit kidneys

The effect of pretreatment with various substances protecting against oxygen free radicals on the leakage of proteins across the vessel walls of rabbit kidneys induced by ischaemia has been studied. The leakage of proteins was estimated from the difference between the 120-min distribution space of [131I]albumin and the 5-min distribution space of [125I]albumin, the latter mainly measuring the intravascular volume. Neither SOD (superoxide dismutase), catalase, allopurinol or two different Ca2+ channel blockers (nifedipine, felodipine) could alone reduce the leakage induced by ischaemia. A combined pretreatment with SOD, catalase and nifedipine reduced the leakage in the cortex, and pretreatment with mannitol alone reduced the leakage in the cortex and outer stripe of the medulla. The results indicate that oxygen free radicals are involved in the leakage of proteins across the vessel walls induced by ischaemia, but that other mechanisms are involved as well.

Changes in albumin/platelet interaction with an artificial surface--due to a antibiotics, pyridoxal phosphate, and lymphocytes

Protein adsorption and platelet adhesion are two important biological processes arising at the blood prosthetic interface. The effect of certain antibiotics, namely, neomycin, gentamicin, ampicillin, penicillin-G, and streptomycin to modulate the albumin polycarbonate surface interaction was investigated using 125I albumin from a protein mixture in the presence and absence of isolated calf lymphocytes. This study also demonstrated the changes in platelet-surface adhesion with these antibiotics. The effect of pyridoxal phosphate to modulate the red blood cell-mediated platelet-surface attachment was also attempted. It appears from pyridoxal phosphate studies that pyridoxal 5'-phosphate (PLP) could modify the surface-platelet attachment. It also inhibited the fibrinogen-induced platelet adhesion. It seems, the addition of antibiotics to the polymerprotein system increased the level of surface-bound albumin variably whereas lymphocytes incubated in the medium did not affect the surface-albumin concentration with time course. These antibiotics also inhibited the surface-induced platelet adhesion to variable degrees. Our earlier studies have indicated that certain antibiotics or antiplatelet drugs can inhibit the fibrinogen binding to an artificial surface. Therefore, it may be possible that the enhanced albumin-surface concentration or reduced fibrinogen-surface binding, in the presence of these antibiotics, may itself be one of the parameter for a reduced platelet-surface attachment, which may also improve the blood compatibility of the substrate. A better understanding of the mechanism of antibiotics is needed in in vivo conditions to correlate these findings.

Transcapillary escape rate and capillary permeability to albumin in patients with Plasmodium falciparum

The transcapillary escape rate and capillary permeability to albumin were studied in five patients with Plasmodium falciparum malaria and six control subjects by using 125I-HSA. The mean transcapillary escape rate of albumin, calculated from the slope of the plasma disappearance curve of 125I-HSA, was found to be significantly higher in the malaria patients than in the control group. As the plasma volume increased while the plasma albumin concentration decreased in these patients, this resulted in a significantly higher plasma clearance and outflux of albumin from the intravascular to the extravascular compartments. Both the effective capillary pore area per unit path length available for restricted diffusion and the specific permeability coefficient of the capillary to albumin were found to be grossly elevated in the patients' group. These findings indicated that there was an increased leakage of plasma albumin in patients with P. falciparum malaria as a result of increased capillary surface area and an increased capillary permeability to albumin.

Transcapillary clearance of albumin in rat skeletal muscle monitored by external detection. Effects of alterations in capillary surface area

The effects of noradrenaline (NA)-induced vasoconstriction on the transcapillary passage of albumin was evaluated by an external detection technique, allowing repetitive measurements of albumin clearance (Cl) during various conditions (in the same animal). Six isolated rat hindquarters were perfused with serum-albumin solutions during maximal vasodilation (papaverine 90 microM) and Cl was determined at different net filtration rates (Fv) induced by elevations of venous pressure. Then, the perfusate was changed to one of similar composition but containing noradrenaline (2-4 microM), and the procedure of determining Cl vs. Fv was repeated. Tissue accumulation of [99mTc]albumin was expressed in terms of clearance, using the isogravimetric Cl of defined muscle samples during maximum vasodilation in separate experiments as reference, the latter being 0.0246 +/- 0.0012 ml min-1 per 100 g. Noradrenaline caused an increase in vascular resistance from 2 to 14 mmHg min 100 g ml-1, while the Cl vs. Fv relationship was shifted downwards in a fashion parallel with the control Cl vs. Fv curve. For Fv = 0, Cl was 0.0101 +/- 0.0014 ml min-1 per 100 g during NA challenge. The average reflection coefficient for albumin (sigma tot) was 0.92 +/- 0.01 irrespective of vascular tone. Thus, both albumin clearance and the capillary filtration coefficient (CFC) seem to vary in direct proportion to the capillary surface area available for exchange.

Blood-to-tissue transport of albumin in rat fibrosarcomas at two different implantation sites

Albumin clearance and blood flow were measured in normal tissues and in fibrosarcomas by means of a multiple tracer method in intact male rats. Sarcomas implanted in testes had higher albumin clearances than the same tumours implanted in skeletal muscle, 59 and 26 microliters min-1 per 100 g, respectively. Albumin extraction (defined as the ratio of albumin clearance to plasma flow) was found to be 1 x 10(-4) - 14 x 10(-4) in normal tissues. Fibrosarcomas in muscle showed high extractions (24 x 10(-4)), especially in the central portions (96 x 10(-4)), where the extraction was similar to that in tumours implanted in the testes (111 x 10(-4)). The high albumin extraction in poorly perfused central parts of the muscle-implanted tumours and in the similarly insufficiently perfused testicular sarcomas is probably due to an increased endothelial permeability of the exchange vessels and not to an increased capillary exchange surface area compared with the better-perfused peripheral parts of the muscle-implanted tumours. The latter tissue also had a high albumin clearance, however, in the range of that of maximally dilated skeletal muscle vasculature, possibly reflecting a large functional capillary surface area.

Effects of ischaemia on leakage of albumin in rabbit kidneys

The effect of ischaemia on the leakage of proteins across the vessel walls in rabbit kidneys was studied. The leakage of proteins was estimated from the distribution space of labelled albumin. Various methods to calculate the vascular volume yielding the true extravascular leakage were tested. The most reliable method appeared to be to use the same tracer (131I-albumin, 125I-albumin) for both estimating the leakage and the intravascular volume. One hour of ischaemia induced a drastic increase in the extravasation of proteins in the cortex and outer zone of the medulla but not in the inner zone.

Dynamics of pleural effusion estimated through urea clearance

Radioactive human serum albumin (RHSA) and urea were injected into the pleural cavity of patients with pleural effusions. The dynamics of the pleural liquid was investigated based on the volume of the pleural liquid and on the change in the concentrations of markers. RHSA concentration in the pleural liquid decreased linearly and slowly. Urea disappeared rapidly and exponentially. The analysis shows that water exchanges rapidly at the pleural capillary and that the volume of the pleural liquid is an affecting factor on the turnover of the pleural volume. The dynamics of malignant effusion was the same as that of tuberculous effusion.

Influence of some inhibitors and activators of fibrinolysis on transcapillary transport of macromolecules

The RISA transcapillary transport in the posterior paw was followed up under the influence of some substances inhibiting and activating fibrinolysis (Trasylol, EACA and Streptokinase and Salyrgan, respectively) in 11 dogs under narcosis with chloralose and the cannulation of the lymphatics in the popliteal space. It was found that EACA inhibits the transcapillary RISA transport and streptokinase activates it. Trasylol and Salyrgan produced no changes, the slope of the vanishing curve of the tracer being identical with that of the controls.