Biomedical subjects

S H Audi

Publications and source records attributed to S H Audi.

18 recordsLinked to original sources

PubMed2002

Lung tissue mitochondrial benzodiazepine receptors increase in a model of pulmonary inflammation.

Pulmonary inflammation induced in the rabbit lung by the intravenous injection of complete Freund's adjuvant (CFA) increases the lung uptake of 14C-diazepam from the pulmonary circulation. The objective of this study was to determine the extent to which mitochondrial (or peripheral) benzodiazepine receptors (mBRs) may contribute to this increased uptake. To this end, we measured the pulmonary venous effluent concentration versus time for 14C-diazepam following its injection into the pulmonary artery of isolated perfused normal and CFA inflamed lungs with and without an inhibitor (PK11195) of diazepam binding to mBRs. The results demonstrate that this model of pulmonary inflammation is associated with an increase in lung tissue mBR. Lung tissue caspase-3 activity was also measured as one index of lung inflammation, and we found that in inflamed lungs, there was an inverse correlation between mBR density and lung tissue capase-3 activity. This is consistent with observations in other organs and a role for mBRs in apoptotic elimination of inflammatory cells in the resolution of this inflammatory response. The results suggest the potential utility of mBR ligands for noninvasive detection and/or characterization of pulmonary inflammation, e.g., via nuclear medicine methods.

Animals↗

PubMed2001

Pulmonary reduction of an intravascular redox polymer.

Pulmonary endothelial cells in culture reduce external electron acceptors via transplasma membrane electron transport (TPMET). In studying endothelial TPMET in intact lungs, it is difficult to exclude intracellular reduction and reducing agents released by the lung. Therefore, we evaluated the role of endothelial TPMET in the reduction of a cell-impermeant redox polymer, toluidine blue O polyacrylamide (TBOP(+)), in intact rat lungs. When added to the perfusate recirculating through the lungs, the venous effluent TBOP(+) concentration decreased to an equilibrium level reflecting TBOP(+) reduction and autooxidation of its reduced (TBOPH) form. Adding superoxide dismutase (SOD) to the perfusate increased the equilibrium TBOP(+) concentration. Kinetic analysis indicated that the SOD effect could be attributed to elimination of the superoxide product of TBOPH autooxidation rather than of superoxide released by the lungs, and experiments with lung-conditioned perfusate excluded release of other TBOP(+) reductants in sufficient quantities to cause significant TBOP(+) reduction. Thus the results indicate that TBOP(+) reduction is via TPMET and support the utility of TBOP(+) and the kinetic model for investigating TPMET mechanisms and their adaptations to physiological and pathophysiological stresses in the intact lung.

Acrylic Resins↗

PubMed2001

Oxygen dependency of monoamine oxidase activity in the intact lung.

Hydrogen peroxide generated by monoamine oxidase (MAO)-mediated deamination of biogenic amines has been implicated in cell signaling and oxidative injury. Because the pulmonary endothelium is a site of metabolism of monoamines present in the venous return, this brings into question a role for MAO in hyperoxic lung injury. The objective of this study was to evaluate the O(2) dependency of the MAO reaction in the lung. To this end, we measured the pulmonary venous effluent concentrations of the MAO substrate [(14)C]phenylethylamine and its metabolite [(14)C]phenylacetic acid after the bolus injection of either phenylethylamine or phenylacetic acid into the pulmonary artery of perfused rabbit lungs over a range of PO(2) values from 16 to 518 Torr. The apparent Michaelis constant for O(2) was approximately 18 microM, which is more than an order of magnitude less that measured for purified MAO. The results suggest a minimal influence of high O(2) on MAO activity in the normal lung and demonstrate the importance of measuring reaction kinetics in the intact organ.

Animals↗

PubMed2000

Transport and reaction at endothelial plasmalemma: distinguishing intra- from extracellular events.

The pulmonary endothelium is a chemical reactor that modifies blood composition in several ways, including reduction of the oxidized forms of certain redox active substances in the blood. The physiological functions of the transplasma membrane electron transport systems involved in the latter are not fully understood, but an argument is made that they are involved in antioxidant defense. In addition, the experimental approaches used to characterize the process, including studies at whole organ, cell culture, and subcellular levels, along with the use of mathematical modeling, may be representative of the physiome concept wherein a goal is the integration of information obtained at all levels of biological organization. In this article, separation of intra- and extracellular events involved in the disposition of redox active probes within the lungs is the particular example.

Animals↗

PubMed2000

Toluidine blue O and methylene blue as endothelial redox probes in the intact lung.

There is increasing evidence that the redox activities of the pulmonary endothelial surface may have important implications for the function of both lungs and blood. Because of the inherent complexity of intact organs, it can be difficult to study these activities in situ. Given the availability of appropriate indicator probes, the multiple-indicator dilution (MID) method is one approach for dealing with some aspects of this complexity. Therefore, the objectives of the present study were to 1) evaluate the potential utility of two thiazine redox indicators, methylene blue (MB) and toluidine blue O (TBO), as MID electron acceptor probes for in situ pulmonary endothelium and 2) develop a mathematical model of the pulmonary disposition of these indicators as a tool for quantifying their reduction on passage through the lungs. Experiments were carried out using isolated rabbit lungs perfused with physiological salt solution with or without plasma albumin over a range of flow rates. A large fraction of the injected TBO disappeared from the perfusate on passage through the lungs. The reduction of its oxidized, strongly polar, relatively hydrophilic blue form to its colorless, highly lipophilic reduced form was revealed by the presence of the reduced form in the venous effluent when plasma albumin was included in the perfusate. MB was also lost from the perfusate, but the fraction was considerably smaller than for TBO. A distributed-in-space-and-time model was developed to estimate the reduction rate parameter, which was approximately 29 and 1.0 ml/s for TBO and MB, respectively, and almost flow rate independent for both indicators. The results suggest the utility particularly of TBO as an electron acceptor probe for MID studies of in situ pulmonary endothelium and of the model for quantitative evaluation of the data.

Animals↗

PubMed1999

Proline in vasoactive peptides: consequences for peptide hydrolysis in the lung.

To examine the hypothesis that trans isomers of bradykinin and [Gly6]bradykinin are preferentially hydrolyzed by lung peptidases, we studied the fractional inactivation of these peptides in the perfused rat lung using a bioassay after a single-pass bolus injection and high-performance liquid chromatography after lung recirculation. In the bioassay studies, when the peptides passed through the lung, 25.6-fold more bradykinin or 7-fold more [Gly6]bradykinin was required to elicit a contraction equivalent to that produced when the peptides did not pass through the lung. In the recirculation studies, hydrolysis progress curves with rapid and slow phases were observed, with a higher fraction of bradykinin than [Gly6]bradykinin hydrolyzed in the rapid phase. Cyclophilin increased the hydrolysis rate during the slow phase for both peptides. Kinetic analysis indicated that the slowly hydrolyzed peptide fraction, presumably the cis fraction, was 0.13 for bradykinin and 0.43 for [Gly6]bradykinin with cis-trans isomerization rate constants of 0.074 and 0.049 s-1, respectively, consistent with published nuclear magnetic resonance studies.

Animals↗

PubMed1999

Detection of changes in lung tissue properties with multiple-indicator dilution.

We evaluated the potential utility of a group of indicators, each of which targets a particular tissue property, as indicators in the multiple-indicator dilution method to detect and to identify abnormalities in lung tissue properties resulting from lung injury models. We measured the pulmonary venous outflow concentration vs. time curves of [14C]diazepam, 3HOH, [14C]phenylethylamine, and a vascular reference indicator following their bolus injection into the pulmonary artery of isolated perfused rabbit lungs under different experimental conditions, resulting in changes in the lung tissue composition. The conditions included granulomatous inflammation, induced by the intravenous injection of complete Freund's adjuvant (CFA), and intratracheal fluid instillation, each of which resulted in similar increases in lung wet weight. Each of these conditions resulted in a unique pattern among the concentration vs. time outflow curves of the indicators studied. The patterns were quantified by using mathematical models describing the pulmonary disposition of each of the indicators studied. A unique model parameter vector was obtained for each condition, demonstrating the ability to detect and to identify changes in lung tissue properties by using the appropriate group of indicators in the multiple-indicator dilution method. One change that was particularly interesting was a CFA-induced change in the disposition of diazepam, suggestive of a substantial increase in peripheral-type benzodiazepine receptors in the inflamed lungs.

Animals↗

PubMed1999

Pulmonary inflammation alters the lung disposition of lipophilic amine indicators.

Many lipophilic amine compounds are rapidly extracted from the blood on passage through the pulmonary circulation. The extent of their extraction in normal lungs depends on their physical-chemical properties, which affect their degree of ionization, lipophilicity, and propensity for interacting with blood and tissue constituents. The hypothesis of the present study was that changes in the tissue composition that occur during pulmonary inflammation would have a differential effect on the pulmonary extraction of lipophilic amines having different properties. If so, measurement of the extraction patterns for a group of lipophilic amines, having different physical-chemical properties, might provide a means for detecting and identifying lung tissue abnormalities. To evaluate this hypothesis, we measured the pulmonary extraction patterns for four lipophilic amines, [(14)C]diazepam, [(3)H]alfentanil, [(14)C]lidocaine, and [(14)C]codeine, along with two hydrophilic compounds, (3)HOH and [(14)C]phenylethylamine, after the bolus injection of these indicators into the pulmonary artery of isolated lungs from normal rabbits and from rabbits with pulmonary inflammation induced by an intravenous injection of complete Freund's adjuvant. The pulmonary extraction patterns, parameterized using a previously developed mathematical model, were, in fact, differentially altered by the inflammatory response. For example, the tissue sequestration rate, k(seq) (ml/s), per unit (3)HOH accessible extravascular lung water volume significantly increased for diazepam and lidocaine, but not for codeine and alfentanil. The results are consistent with the above hypothesis and suggest the potential for using lipophilic amines as indicators for detection and quantification of changes in lung tissue composition associated with lung injury and disease.

Algorithms↗

PubMed1998

Anatomic distribution of pulmonary vascular compliance.

Previously, the pressure changes after arterial and venous occlusion have been used to characterize the longitudinal distribution of pulmonary vascular resistance with respect to vascular compliance using compartmental models. However, the compartments have not been defined anatomically. Using video microscopy of the subpleural microcirculation, we have measured the flow changes in approximately 40-micron arterioles and venules after venous, arterial, and double occlusion maneuvers. The quasi-steady flows through these vessels after venous occlusion permitted an estimation of the compliance in three anatomic segments: arteries > 40 microns, veins > 40 microns, and vessels < 40 microns in diameter. We found that approximately 65% of the total pulmonary vascular compliance was in vessels < 40 microns, presumably mostly capillaries. The transient portions of the pressure and flow data after venous, arterial, and double occlusion were consistent with most of the arterial compliance being upstream from most of the arterial resistance and most of the venous compliance being downstream from most of the venous resistance.

Animals↗

PubMed1998

Pulmonary disposition of lipophilic amine compounds in the isolated perfused rabbit lung.

We measured the pulmonary venous concentration vs. time curves for [3H]alfentanil, [14C]lidocaine, and [3H]codeine after the bolus injection of each of these lipophilic amine compounds (LAC) and a vascular-reference indicator (fluorescein isothiocyanate-dextran) into the pulmonary artery of isolated perfused rabbit lungs. A range of flows and perfusate albumin concentrations was studied. To evaluate the information content of the data, we developed a kinetic model describing the pulmonary disposition of these LAC that was based on indicator dilution theory, and we sought a robust approach for interpreting the estimated model parameters. We found that the distribution of the kinetic model rate constants of the lipophilic amine-tissue interactions can be described by alpha, H, and psi, where alpha is a measure of the capacity of the rapidly equilibrating interactions between the lipophilic amine and the tissue; H is a measure of the equilibrium capacity of the slowly equilibrating interactions between the lipophilic amine and the tissue; and psi is the mean sojourn time. The values of alpha, H, and psi were 0.8 +/- 0.1 (SE), 0.6 +/- 0.1, and 1.6 +/- 0.5 s; 1.9 +/- 0.1, 5.3 +/- 0.4, and 5.6 +/- 0.5 s; and 1.1 +/- 0.1, 9.8 +/- 0.4, and 4.7 +/- 0.2 s for alfentanil, lidocaine, and codeine, respectively. These values for alpha, H, and psi reveal the relative dominance of the slowly equilibrating interactions for lidocaine and codeine in comparison with alfentanil. This approach to data analysis may have utility for the potential use of LAC to reveal and to quantify changes in lung tissue composition associated with lung disease.

Alfentanil↗

PubMed1996

Impact of angiotensin-converting enzyme substrate conformation on fractional hydrolysis in lung.

We examined the hydrolysis kinetics of benzoyl-phenylalanyl-glycyl-proline (BPGP) in the isolated perfused lung and in vitro for evidence of preferential hydrolysis of the trans isomer by angiotensin-converting enzyme (ACE). Nuclear magnetic resonance spectroscopy showed that BPGP exists as cis and trans isomers in a ratio of 44:56. After a single pass through the perfused rabbit lung over a wide range of infused BPGP concentrations, 42% of the BPGP was not hydrolyzed. In single-pass bolus-injection studies, 41% of the injected BPGP was not hydrolyzed, and very little further hydrolysis occurred in a second passage of the bolus through the lungs. In rat lung recirculation and in vitro studies of BPGP hydrolysis by ACE, approximately 60% of the substrate was hydrolyzed rapidly compared with the remaining approximately 40%, and the peptidyl-prolyl cis-trans isomerase cyclophilin increased the rate of the slower phase of the reaction in both kinds of experiments. We conclude that the rapid hydrolysis phase represents primarily the hydrolysis rate of the trans isomer and the slower phase the cis-trans isomerization rate, suggesting that the trans isomer of BPGP is preferentially hydrolyzed by ACE in the perfused lung and in vitro.

Animals↗

PubMed1995

Estimation of the pulmonary capillary transport function in isolated rabbit lungs.

Recently, we presented a method for estimating the pulmonary capillary volume and transport function based on the use of a reference indicator and two or more indicators that rapidly equilibrate (radially) with the tissue (i.e., the concentrations in the vascular and extravascular spaces at a given axial location are in equilibrium) during transit through the capillaries in a bolus-injection indicator dilution method (S. H. Audi, G. S. Krenz, J. H. Linehan, D. A. Rickaby, and C. A. Dawson. J. Appl. Physiol. 77:332-351, 1994). The objectives of the present study were 1) to determine whether [14C]diazepam and [3H]alfentanil equilibrate sufficiently rapidly between the vascular space and tissue and with sufficiently different pulmonary extra-vascular mean residence times to be used in a single bolus to estimate the pulmonary capillary volume and transport function using this method and 2) to estimate the pulmonary capillary volume and transit time distribution in isolated perfused rabbit lungs. Both [14C]diazepam and [3H]alfentanil were found to be rapidly equilibrating indicators by the criteria that, over a wide range of flow rates, their respective venous effluent concentration curves were nearly congruent on a time scale normalized to the lung mean transit time for the reference indicator (fluorescein isothiocyanate dextran). In addition, at a given plasma albumin concentration, [14C]diazepam had a significantly longer extravascular mean residence time than [3H]alfentanil, e.g., at 6% plasma albumin concentration, the extravascular mean residence time of [14C]diazepam was more than twice that of [3H]alfentanil. On average, the estimated pulmonary capillary volume for a 2.7-kg was approximately 4.2 ml or approximately 44% of the total pulmonary vascular volume (9.5 ml). The relative dispersion of the pulmonary capillary transport function of the rabbit was approximately 90%.

Alfentanil↗

PubMed1994

Pulmonary capillary transport function from flow-limited indicators.

The objective of this study was to examine the use of rapidly diffusing (flow-limited) indicators for estimating the pulmonary capillary blood volume (i.e., fraction of the lung blood volume wherein the diffusible indicators equilibrate with the tissue) and the capillary transit time distribution. Supporting theory and an application to experimental data are presented. The theory leads to the following equations, which relate the mean transit time (t), the variance (sigma 2), and the third central moment (m3) of the capillary transport function, hc(t), to the moments of the venous concentration-time curves for a vascular reference indicator, CR(t), and a flow-limited diffusible indicator, CD(t), after a bolus injection of the indicators upstream from an organ: sigma 2D - sigma 2R = ([1 + (te/tc)]2-1)sigma 2c and m3D-m3R = ([1 + (te/tc)]3-1)m3c, where te = tD - tR and tc is capillary t. The moments of hc(t) can be estimated if the injected bolus includes, along with the vascular reference indicator, at least two flow-limited diffusible indicators, each with a different te. A least-squares optimization procedure can then be used to specify the moments of hc(t). This approach was applied to isolated dog lung lobes with [14C]-diazepam as the diffusible indicator. The tissue-to-perfusate partition coefficient for [14C]diazepam could be adjusted to any desired value by altering the perfusate albumin concentration. Thus, by making a number of injections, each at a different perfusate albumin concentration, data were obtained in a manner equivalent to making one injection with a number of flow-limited diffusible indicators, each with a different te. On average, the estimated capillary volume and mean transit time were approximately 48% of the total lobar volume and mean transit time, and the relative dispersion of the hc(t) was approximately 75%.

Animals↗

PubMed1992

A method for analysis of pulmonary arterial and venous occlusion data.

Recently, we presented a compartmental model of the pulmonary vascular resistance (R) and compliance (C) distribution with the configuration C1R1C2R2C3 (J. Appl. Physiol. 70: 2126-2136, 1991). This model was used to interpret the pressure vs. time data obtained after the sudden occlusion of the arterial inflow (AO), venous outflow (VO), or both inflow and outflow (DO) from an isolated dog lung lobe. In the present study, we present a new approach to the data analysis in terms of this model that is relatively simple to carry out and more robust. The data used to estimate the R's and C's are the steady-state arterial [Pa(0)] and venous [Pv(0)] pressures, the flow rate (Q), the area (A2) encompassed by Pa(t) after AO and the equilibrium pressure (Pd) after DO, and the average slope (m) of the Pa(t) and Pv(t) curves after VO. The following formulas can then be used to calculate the 2 R's and 3 C's: [Pa(0) - Pv(0)]/Q = R1 + R2 = RT, R1C1 congruent to to A2/[Pa(0) - Pd], R1 congruent to [Pa(0) - Pd]/Q, Q/m = C1 + C2 + C3 = CT, and C2 = CT - (RTC1/R2).

Animals↗

PubMed1991

Localization of the sites of pulmonary vasomotion by use of arterial and venous occlusion.

In this study, we present a new approach for using the pressure vs. time data obtained after various vascular occlusion maneuvers in pump-perfused lungs to gain insight into the longitudinal distribution of vascular resistance with respect to vascular compliance. Occlusion data were obtained from isolated dog lung lobes under normal control conditions, during hypoxia, and during histamine or serotonin infusion. The data used in the analysis include the slope of the arterial pressure curve and the zero time intercept of the extrapolated venous pressure curve after venous occlusion, the equilibrium pressure after simultaneous occlusion of both the arterial inflow and venous outflow, and the area bounded by equilibrium pressure and the arterial pressure curve after arterial occlusion. We analyzed these data by use of a compartmental model in which the vascular bed is represented by three parallel compliances separated by two series resistances, and each of the three compliances and the two resistances can be identified. To interpret the model parameters, we view the large arteries and veins as mainly compliance vessels and the small arteries and veins as mainly resistance vessels. The capillary bed is viewed as having a high compliance, and any capillary resistance is included in the two series resistances. With this view in mind, the results are consistent with the major response to serotonin infusion being constriction of large and small arteries (a decrease in arterial compliance and an increase in arterial resistance), the major response to histamine infusion being constriction of small and large veins (an increase in venous resistance and a decrease in venous compliance), and the major response to hypoxia being constriction of the small arteries (an increase in arterial resistance). The results suggest that this approach may have utility for evaluation of the sites of action of pulmonary vasomotor stimuli.

Animals↗

PubMedDate not supplied

An interpretation of 14C-urea and 14C-primidone extraction in isolated rabbit lungs.

We measured the venous concentration versus time curves of 14C-urea and 14C-primidone after rapid bolus injections of a vascular reference indicator, fluorescein isothiocyanate dextran, and one of the two 14C-labeled indicators in isolated rabbit lungs perfused with Krebs-Ringer bicarbonate solution containing 4.5% bovine serum albumin at flow rates (F) of 6.67, 3.33, 1.67, and 0.83 ml/sec and with nearly constant microvascular pressure and total lung vascular volume. When we calculated the permeability-surface area product, PS, from the 14C-urea and 14C-primidone outflow curves using the Crone model, the estimates of the PS product were directly proportional to F. However, the fractional change in the PS with flow was different for the two indicators. We also estimated the PS from the same 14C-urea and 14C-primidone data using an alternative model that includes perfusion heterogeneity, estimated in a previous study, and flow-limited and barrier-limited extravascular volumes accessible to both urea and primidone. This model was able to fit the outflow curves of either 14C-urea or 14C-primidone at all four flows studied with one flow-independent PS for each indicator. The ability of the new model to explain the 14C-urea and 14C-primidone data with no flow-dependent change in PS suggests that a change in PS with F estimated using other models such as the Crone model is not sufficient for capillary surface area recruitment.

Animals↗

PubMedDate not supplied

Accounting for the heterogeneity of capillary transit times in modeling multiple indicator dilution data.

To mathematically model multiple indicator dilution (MID) data for the purpose of estimating parameters descriptive of indicator-tissue interactions, it is necessary to account for the effects of the distribution of capillary transit times, h(c)(t). In this paper, we present an efficient approach for incorporating h(c)(t) in the mathematical modeling of MID data. In this method, the solution of the model partial differential equations obtained at different locations along the model capillary having the longest transit time provides the outflow concentrations for all capillaries. When weighted by h(c)(t), these capillary outflow concentrations provide the outflow concentration versus time curve for the capillary bed. The method is appropriate whether the available data on capillary dispersion are in terms of capillary transit time or relative flow distributions, and whether the dispersion results from convection time differences among heterogeneous parallel pathways or axial diffusion along individual pathways. Finally, we show that the knowledge of a relationship among the moments of h(c)(t), rather than h(c)(t) per se, is sufficient information to account for the effect of h(c)(t) in the mathematical modeling interpretation of MID data. This relationship can be determined by including a flow-limited indicator in the injected bolus, thus providing an efficient means for obtaining the experimental data sufficient to account for capillary flow and transit time heterogeneity in MID modeling.

Alfentanil↗

PubMedDate not supplied

Kinetics of plasma membrane electron transport in a pulmonary endothelial cell-column.

Thiazine dyes such as toluidine blue O (TBO) are reduced at the luminal endothelial surface. The purpose of this study was to determine the rate of this reaction in endothelial cells in culture. A multiple indicator dilution method was used to measure the reaction kinetics during transient passage of a TBO-containing bolus through a chromatographic column filled with bovine pulmonary arterial endothelial cells grown on microcarrier beads (cell-column). A bolus containing TBO and an inert extracellular reference indicator (FITC-Dextran) was injected upstream of the cell-column, and the indicator concentrations were measured downstream using on-line photodetection. The effects of column flow rate, PO2, and TBO concentration were studied. The fraction of TBO reduced upon passage through the cell-column decreased with increasing flow indicating that the reaction rate rather than TBO delivery controlled TBO reduction. The fraction of TBO reduced did not change with PO2 or dose in the ranges studied. TBO reduction was about 10 times that for steady state TBO sequestration by these cells which, along with the lack of a PO2 effect indicates that the rapid rate of reduction is not the rate-limiting step in steady state sequestration.

Animals↗