Constant Flow Conditions Research Articles

Erythropoietin Changes Contractility, cAMP, and Nitrite Levels of Isolated Rat Hearts

There is enough evidence that erythropoietin (EPO) may be involved in cardiovascular function. Therefore we have investigated the possible effects of EPO on left ventricular developed pressure, +dP/dt(max), heart rate, tissue cAMP, and nitrite levels. Isolated rat hearts were perfused under constant flow (10 ml/min) conditions with modified Krebs-Henseleit solution and recombinant human erythropoietin at doses of 100, 200, 500, and 1,000 IU/kg was administered as bolus injections. EPO at 100 IU/kg decreased, but higher doses (500 and 1,000 IU/kg) raised the developed pressure and +dP/dt(max). However, it did not affect heart rate or coronary perfusion pressure when all the respective doses were applied. EPO at 100 IU/kg increased nitrite, and at 1,000 IU/kg it raised cAMP. Our results suggest that EPO may produce dose-dependently negative and positive inotropic effects on myocardial contractility in isolated rat hearts. NO and cAMP may be involved in negative and positive inotropic effects of EPO, respectively.

Application of a geocentrifuge and sterolithographically fabricated apertures to investigations of multiphase flow in complex fracture apertures

A geotechnical centrifuge was used to investigate unsaturated multiphase fluid flow in synthetic fracture apertures under a variety of flow conditions. The geocentrifuge subjected the fluids to centrifugal forces allowing the Bond number to be systematically changed without adjusting the fracture aperture or the fluids. The fracture models were based on the concept that surfaces generated by the fracture of brittle geomaterials have a self-affine fractal geometry. The synthetic fracture surfaces were fabricated from a transparent epoxy photopolymer using sterolithography, and fluid flow through the transparent fracture models was monitored by an optical image acquisition system. Aperture widths were chosen to be representative of the wide range of geological fractures in the vesicular basalt that lies beneath the Idaho National Laboratory (INL). Transitions between different flow regimes were observed as the acceleration was changed under constant flow conditions. The experiments showed the transition between straight and meandering rivulets in smooth walled apertures (aperture width= 0.508 mm), the dependence of the rivulet width on acceleration in rough walled fracture apertures (average aperture width = 0.25 mm), unstable meandering flow in rough walled apertures at high acceleration (20 g) and the narrowing of the wetted region with increasing acceleration during the penetration of water into an aperture filled with wetted particles (0.875 mm diameter glass spheres).

Influence of TMB-8 and Thapsigargin on Vasoconstrictor Responses in the Pulmonary Vascular Bed of the Cat

The effects of 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8), a protein kinase C (PKC) inhibitor, and thapsigargin, a CaATPase inhibitor, on pressor responses were studied in the pulmonary vascular bed of the intact-chest anesthetized cat. Under conditions of constant lobar blood flow in the cat, injections of the angiotensin peptides (ANG II), norepinephrine (NE), serotonin (5-HT), Bay K 8644, and the thromboxane A2 mimic U46619 into the lobar arterial perfusion circuit caused dose-related increases in lobar arterial pressure and responses were reproducible with respect to time. Intravenous infusion of TMB-8 at 1.0 mug . kg reduced the pressor response to the ANG II and to NE. However, TMB-8 did not alter pressor responses to 5-HT, U46619, or Bay K 8644. In a separate series of experiments, the effects of thapsigargin were investigated and intravenous infusion of the CaATPase inhibitor at 1.0 mug . kg also reduced pressor responses to the ANG II and to NE but did not alter pressor responses to 5-HT, U46619, and Bay K 8644. The data provide support for the hypothesis that vasoconstrictor responses to ANG II and NE in the pulmonary vascular bed are mediated in part by the activation of protein kinase C (PKC) and sarcoplasmic reticulum CaATPase-sensitive mechanisms in the cat. The present data suggest that pulmonary pressor responses to U46619, 5-HT, and Bay K 8644 are not mediated by PKC or CaATPase activation in the pulmonary vascular bed of the cat.

Study on bubble formation at a submerged micro‐hole by a two‐stage model

In order to increase the accuracy of detached bubble volume prediction and to correct the theoretical weakness in models proposed previously, a modified two‐stage spherical bubble formation model is proposed in this study. This modified model takes account of an important factor, the length‐to‐diameter ratio of the micro‐hole by calculating the orifice constant with an entrance flow effect and expands the applicability of the modified model. Also, experimental tests were conducted to form bubbles at a submerged micro‐hole with diameters ranging from 60 to 1200 μm under variable pressure conditions due to continuous liquid drainage with drain rate ranging from 0.006 to 0.100 ml/s. The improved model indeed increases the ability to predict the detached bubble volume in the present study. Moreover, the results show that the condition for bubble formation in the present study could be shifted from a constant flow condition to a constant pressure condition depending on the orifice constant.

Coupled and uncoupled contaminant transport using advanced finite volume methods

In this paper, the modelling of contaminant transport through aquifers over a horizontal plane by the application of the vertex-centred edge-based finite volume scheme is presented. A complete description of the coupled set of equations and their discretisation is given, together with a description of the compact stencil model that is used in the implementation. The problems considered include convective-dispersive flow with or without pollutant decay under constant Darcy velocity flow conditions and a similar case where a slug of pollutant is injected for a finite time. The final set of problems considers the transient coupled flow of both groundwater and pollutant, which is again extended to include decay terms.

Frost Growth in Regenerative Wheels

An experimental investigation was carried out for frost growth in a desiccant-coated regenerative wheel. The test facility was set up following ASHRAE Standard 84-1991R. Temperature, relative humidity, mass flow rate, and pressure drops were measured at each measuring station. Photos of frost within energy wheel flow channels show frost accumulation. The problem of frost growth within the narrow parallel flow passages of a regenerative heat or energy rotary wheel is formulated for a very cold-temperature ventilation application. Frost growth is assumed to grow as a porous media while the wheel is exposed to warm humid airflow on the exhaust side. While the wheel is exposed to cold dry airflow on the supply side, the frost is cooled but no frost grows. This cyclic frost growth and cooling process is continued with each wheel rotation. An analytical/numerical model is developed to simulate these frost properties over the depth of the wheel and as a function of time. Simulation results are used to interpret experimental data for the early stage of frost growth on a typical energy wheel with a cold supply air temperature of −40°C, a warm exhaust temperature of 20 °C and 40% relative humidity. Pressure drop measurements across a wheel taken for constant mass flow conditions revealed some very significant fluctuations of up to 100% of original pressure drop with a period ranging from 2 to 4 min for a wheel speed of 20 rpm. Each fluctuation in pressure drop is interpreted to imply a catastrophic failure of the outer frost layer sequenced over 1–2 min throughout the wheel followed by another frost growth period on top of a slightly thicker frost base.

Coronary circulation: Nitric oxide and hypercapnic acidosis

See article by Heintz et al. [4] (pages 55–63) in this issue. In the past two decades, nitric oxide (NO), a molecule whose natural biological role was recognized in a relatively recent period [1], has gained wide credit as a possible agent of physiological and pathological reactions, including those related to the heart and the cardiovascular system. The rapidly increasing wealth of scientific evidence, however, often led to unresolved contradictory results [2], to the extent that, in a recent review on “Nitric oxide and cardiovascular function,” Kelly et al. [3] concluded that the explosion of new information over the past 5 years “has generated much light as well as smoke and heat.” The study by Heintz et al. [4] in this issue of Cardiovascular Research casts a new light on the specific role of NO in a well-known (patho)physiological response, namely, the coronary vasodilatation elicited by hypercapnia and/or acidosis. They relied on previous observations of their own [5] that suggested that the coronary vasodilator response to hypercapnia was biphasic. They argued that the mechanisms involved in the two phases could be different. The study was performed on Langendorff preparations of guinea pig hearts, either under constant pressure or under constant flow conditions, which allows disclosure of the possible role of shear stress-induced NO release that was obviously prevented in … *Tel.: +39 45 8952634; fax: +39 45 580881. Email address: antonio.cevese{at}univr.it

Bioluminescent response of the dinoflagellate Lingulodinium polyedrum to developing flow: Tuning of sensitivity and the role of desensitization in controlling a defensive behavior of a planktonic cell

Dinoflagellate bioluminescence is believed to serve a defensive function, decreasing grazing at night. Previous characterization of bioluminescence stimulated by fully developed flows might have underestimated the true sensitivity of bioluminescence by not observing the initial response. Also, it has been suggested that bioluminescence may be more sensitive to time-varying flow than to constant flow conditions. We used developing laminar Couette flow to characterize the sensitivity of the initial bioluminescent response of the dinoflagellate Lingulodinium polyedrum in time-varying flow. Both the absolute sensitivity (threshold) and dynamic sensitivity were consistent with that determined previously in fully developed flows, although there were differences between different cultured isolates of the same species and between those isolates and cells harvested from a unialgal bloom of the same species. When the rate of increase of shear was varied while keeping the maximum shear level similar, the threshold was independent of the rate of increase of shear. Surprisingly, the integrated bioluminescence was strongly dependent on the rate of increase of shear. The mechanism behind the preferential response to rapidly increasing shear was determined to be desensitization. Desensitization may influence which naturally occurring flows strongly stimulate bioluminescence either by allowing cells to avoid producing a primary response in certain slowly changing flows or, more generally, to avoid the cost of repeated stimulation when entrained in environmental flows containing above-threshold shears.

Modulations of shear stress-induced contractile responses and agonist-induced vasodilation in hypercholesterolemic rats

We used mesenteric arterial beds from normal rats and beef tallow-fed rats (hypercholesterolemic model) to study the interaction between the effects of viscosity-induced shear stress and agonists mesenteric vasoreactivity. Mesenteric arterial beds were perfused under constant-flow conditions (5 ml/min) via a peristaltic pump using warm oxygenated modified Krebs–Henseleit solution containing either 4% BSA to increase viscosity or 300 μM l-arginine, a NO synthase substrate. Whether beds were perfused with BSA alone or l-arginine alone as pretreatment, the methoxamine-induced contractile responses were similar to those in normal beds. However, methoxamine-induced contractile responses were significantly reduced following pretreatment with l-arginine plus BSA. These reduced responses underwent significant recovery when either tyrphostin A23 (30 μM, a tyrosine kinase inhibitor) or wortmannin (300 nM, a PI3K inhibitor) was present. The dose–response curve for methoxamine was shifted to the right and the maximum contractile response was reduced in mesenteric arterial beds from beef tallow-fed rats, but the modulation of this response induced by l-arginine plus BSA was preserved. In beef tallow-fed rats, the ACh-induced endothelium-dependent vasodilation was attenuated in both thoracic aortic strips and mesenteric arterial beds. These results suggest that in hypercholesterolemic rats, agonist-induced endothelial function is impaired, while shear stress-induced responses (tyrosine kinase- and PI3K-mediated NO production) are preserved. These abnormal vascular responses may contribute to hypertension in beef tallow-fed hypercholesterolemic model rats.

Effects of exercise training on the vascular reactivity of the whole kidney circulation in rabbits.

Exercise training is known to improve vasodilating mechanisms mediated by endothelium-dependent relaxing factors in the cardiac and skeletal muscle vascular beds. However, the effects of exercise training on visceral vascular reactivity, including the renal circulation, are still unclear. We used the experimental model of the isolated perfused rabbit kidney, which involves both the renal macro- and microcirculation, to test the hypothesis that exercise training improves vasodilator mechanisms in the entire renal circulation. New Zealand White rabbits were pen confined (Sed; n = 24) or treadmill trained (0% grade) for 5 days/wk at a speed of 18 m/min during 60 min over a 12-wk period (ExT; n = 24). Kidneys isolated from Sed and ExT rabbits were continuously perfused in a nonrecirculating system under conditions of constant flow and precontracted with norepinephrine (NE). We assessed the effects of exercise training on renal vascular reactivity using endothelial-dependent [acetylcholine (ACh) and bradykinin (BK)] and -independent [sodium nitroprusside (SNP)] vasodilators. ACh induced marked and dose-related vasodilator responses in kidneys from Sed rabbits, the reduction in perfusion pressure reaching 41 +/- 8% (n = 6; P < 0.05). In the kidneys from ExT rabbits, vasodilation induced by ACh was significantly enhanced to 54 +/- 6% (n = 6; P < 0.05). In contrast, BK-induced renal vasodilation was not enhanced by training [19 +/- 8 and 13 +/- 4% reduction in perfusion pressure for Sed and ExT rabbits, respectively (n = 6; P > 0.05)]. Continuous perfusion of isolated kidneys from ExT animals with N(omega)-nitro-L-arginine methyl ester (L-NAME; 300 microM), an inhibitor of nitric oxide (NO) biosynthesis, completely blunted the additional vasodilation elicited by ACh [reduction in perfusion pressure of 54 +/- 6 and 38 +/- 5% for ExT and L-NAME + ExT, respectively (n = 6; P < 0.05)]. On the other hand, L-NAME infusion did not affect ACh-induced vasodilation in Sed animals. Exercise training also increased renal vasodilation induced by SNP [36 +/- 7 and 45 +/- 10% reduction in perfusion pressure for Sed and ExT rabbits, respectively (n = 6; P < 0.05)]. It is concluded that exercise training alters the rabbit kidney vascular reactivity, enhancing endothelium-dependent and -independent renal vasodilation. This effect seems to be related not only to an increased bioavailability of NO but also to the enhanced responsiveness of the renal vascular smooth muscle to NO.

Sensitivity of the Neuronal Network Biosensor to Environmental Threats

It is widely acknowledged that there is a critical need for broad-spectrum environmental threat detection. While cells/tissue-based biosensors have been discussed for many years as a means of meeting this critical need, these kinds of systems have met with logistic concerns, in particular with regard to stability. Our group has been working with cultured neuronal networks, which have the capacity to respond to a wide range of neuroactive compounds and are sufficiently robust to be shipped to end users. The basis of operation involves extracellular recording using thin-film microelectrode arrays where spontaneous bioelectrical activity, that is, spike firing, can be monitored in a noninvasive manner conducive for potentially long-term measurements. This work describes the current status of our efforts for the fabrication of a portable biosensor that incorporates cultured neuronal networks grown over standardized microelectrode arrays. Based on our protocol for aqueous phase sample introduction under constant flow conditions, minimal variation in mean spike rate is observed, consistent with temporal stability, such that changes of>10% are readily distinguished. To demonstrate the capability of this system, changes are reported in mean spike rate and network synchronization resulting from exposure to different model environmental threats, cadmium and strychnine. The sensitivity of this assay approach and implications of the experimental findings for environmental threat detection are discussed.

Performance of immobilized moss in the removal of137Cs and90Sr from actual low-level radioactive waste solutions

The efficiency of immobilized moss as a bio-sorbent for the removal of 137Cs and 90Sr radionuclides from actual low-level radioactive waste (LLW) solutions was investigated. Preliminary batch experiments with the moss (Funaria hygrometrica) for the sorption of Cs and Sr have shown a pH dependent binding trend from pH 1–13, with maximum binding between pH 5–10. Time dependence of the batch studies showed that a contact time of 30 minutes was sufficient to reach equilibrium. Column experiments for the sorption of Cs and Sr by moss after immobilizing in polymer silica matrix demonstrated that the sorbent is capable of removing considerable amounts of Cs and Sr from actual LLW solutions under constant flow conditions. The adsorption capacity was estimated to be 8.5 mg/g for Cs and 15 mg/g for Sr. These sorbed metal ions from the column could be leached out using 0.20M nitric acid. The regenerated sorbent exhibited relatively the same initial binding capacity of both Cs and Sr even after 3 cycles of reuse.

Perfusión hipotérmica del riñón aislado: respuesta hidrodinámica y bioquímica al perfil de aplicación de la presión

Hydrodynamic and biochemical adaptation to perfusion pressure profile in isolated hypothermic renal perfusion ObjectivesTo evaluate hydrodynamic, biochemical and pathologic consequences of positive forced pressure on hypothermic isolated renal perfusions in comparison to softly progressive administration of perfusion solution. Material & methods16 hypothermic experimental pig renal perfusion o 180 min completed under constant flow conditions. A vacuum computer-controlled pump was used. A comparison was performed of the results obtained by two groups of organs (forced perfusion pressure -I.B.- and soft perfusion pressure -I.S.). ResultsEven though perfusion flor did not offer significant differences among both groups at the end of the procedure, I.B. group showed medium perfusion pressure and renal vascular resistance values significantly higher. Nitric oxide metabolites concentration was also greater in I.B. group. Finally, these kidneys showed more tubular cell aedema and glomerular shrinkage in comparison to I.S. group. ConclusionSharp and forced hypothermic perfusion of the isolated kidney don’t increase flow perfusion values. Inversely, hydrodynamic and pathologic results are worst in comparison to soft and progressive organ perfusion.

'Brink DepthDischarge' Relationship for SpatiallyVaried Flows in Pipes

In view of the selfcalibrating feature, the brink depth generated at the entrance to a freelydischarging drop structure in a prismatic open channel is widely used for estimating channel discharge. Laboratory investigations on this subject have been performed for both subcritical and supercritical flows in differentshaped prismatic channels. However, these studies have examined the brink depthdischarge relationship for constant channel flow conditions only. This research investigates the brink depthdischarge relationship for circular pipes carrying subcritical spatiallyvaried flows (SVF) with discharge increasing in the flow direction. Results indicate that for this type of SVF the brink ratio (BR) is: (i) closer to unity than that for constant discharge, and (ii) offers reasonable accuracy in regards to estimating SVF in a circular pipe section.

Flow monitoring and permeability measurement under constant and transient flow conditions

This paper considers the technique of diverging radial flow for the measurement of the in-plane permeability of isotropic or in-plane orthotropic porous media. Various causes for discrepancies and errors in the permeability thus determined are studied and finally a design for the experimental conditions and an experimental protocol is developed to minimise sources of errors. Numerical analysis methodologies are developed for flow under transient conditions through isotropic and orthotropic porous media, where in the latter case the flow ellipse axes may or may not coincide with the laboratory axes. Finally, these methodologies are validated by comparing the permeability data derived under transient flow with permeability data derived under constant injection pressure conditions.

On-line continuous measurement of particle size using electrostatic sensors

The development of a reliable, cost-effective instrument for on-line particle sizing remains a challenging area worldwide. This paper presents the design and evaluation of a new electrostatic sensor combined with a novel digital signal processing algorithm for the on-line continuous measurement of the mass median size of particles in a dilute-phase pneumatic suspension. Key design aspects of the constituent elements of the sensor, including a wire-mesh electrode, signal conditioning electronics and digital signal processing algorithm are described. Experimental results obtained using a typical range of particulate materials demonstrate that, under constant mass flow conditions, the processed output of the sensor is capable of indicating the mass median particle size with a relative error no greater than 15%. A critical appraisal of the technique, including advantages and limitations, is also included.

The impact of hydrochemical boundary conditions on the evolution of limestone karst aquifers

The early evolution of karst aquifers depends on a manifold of initial and boundary conditions such as geological setting, hydrologic properties of the initial aquifer, and petrologic properties of the rock. When all water entering at various inputs into the aquifer has equal chemical composition with respect to the system H 2O–CO 2–CaCO 3 early evolution under conditions of constant head exhibits breakthrough (BT) behaviour. If the chemical compositions of the input waters are different, deep in the aquifer where the saturated solutions mix renewed aggressiveness occurs, and additional dissolutional widening of fractures by mixing corrosion (MC) changes the hydrologic properties of the aquifer. To study the impact of MC on the evolution of karst we have modelled a simple karst aquifer consisting of a confined limestone bed, with two symmetrically located inputs at constant head and open flow conditions along the entire width at base level. To calculate dissolutional widening of the fractures the well-known dissolution kinetics of limestone was used, which is linear up to 90% of saturation with respect to calcite and then switches to a nonlinear fourth order rate law. First, two extremes are modelled: (a) Both inputs receive aggressive water of equal chemical composition with [Ca 2+]=0.75[Ca 2+] eq. In this case two channels migrate downstream with that from one input more competitive and reaching base level first, causing BT. (b) Water at both inputs is saturated with respect to calcite, but in equilibrium with different partial pressures of CO 2. Therefore, dissolution widening can occur only where these waters mix. A central channel starts to grow extending down-head until base level is reached. Flow rates through the aquifer first rise and become constant after the channel has reached base level. In the following runs these two extreme modes of karstification are combined. The waters entering have different chemical compositions and therefore different equilibrium concentrations [Ca 2+] eq. This allows MC to be active. They are also undersaturated with the inflowing solutions at concentration [Ca 2+] in= f[Ca 2+] eq where f is the ratio of saturation. In comparison to the extreme limit (a) the action of MC now creates permeability where the solutions mix and diverts the evolution of conduits into this region. Finally one conduit reaches base level and causes BT. This behaviour is found for f=0.7, 0.9, and 0.96. For solutions more close to equilibrium with respect to calcite ( f=0.99, 0.9925, and 0.995) BT behaviour is replaced by a steady increase in flow rates. In the early state as in the case of MC controlled evolution (case b) a central channel not connected to the input is created by MC and reaches base level. After this event, further increase in flow rates is caused by slow dissolutional widening by the slightly undersaturated input solutions flowing towards the central channel. Comparison of the various model aquifers at termination of the computer runs reveals significant differences in their properties caused solely by changes of the hydrochemical boundary conditions.

Effects of halothane and isoflurane on acetylcholine-induced, endothelium-dependent vasodilation in perfused rat mesenteric arterial beds.

The present study was designed to examine the effects of halothane and isoflurane on acetylcholine-induced, endothelium-dependent vasodilation in rat mesenteric arterial beds perfused at a constant flow both in vitro and in situ. In the in-vitro preparation, the mesenteric artery was cannulated and perfused (5 ml x min(-1)). The perfusion pressure was continuously monitored. Under active tone induced by methoxamine, the effects of halothane and isoflurane on the vasodilator response to acetylcholine in either the presence or absence of NG-nitro-L-arginine (L-NA), tetraethylammonium (TEA), or KCl (30 mM)-depolarization were examined. All experiments in these preparations were performed in the presence of indomethacin (10 mM). In the in-situ experimental model, rats were anesthetized with pentobarbital and the lungs were mechanically ventilated via a tracheostomy with a ventilator. The superior mesenteric artery was cannulated and used for the monitoring of the perfusion pressure. Blood shunting with constant flow (2 ml x min(-1)) from the carotid artery to the superior mesenteric artery was introduced with clamping at the immediately distal portion of the mesenteric artery branching. Following 20-min ventilation with halothane or isoflurane at 1 minimum alveolar concentration (MAC) in oxygen, acetylcholine was given from the mesenteric artery, under active tone induced by norepinephrine (100 mg x kg(-1) x hr(-1)). In the in-vitro preparation, the nitric oxide synthase inhibitor, L-NA (100 microM) did not affect vasodilations to acetylcholine (1, 10 nM), while the K+ channel inhibitor TEA (10 mM), as well as KCl (30 mM), significantly reduced these vasodilations. However, only in the presence of L-NA, TEA and KCl completely abolished the vasodilations produced by acetylcholine. The higher concentrations of halothane (2.0%, 3.0%), but neither isoflurane (3.0%) nor the lower concentration of halothane (1.0%), significantly impaired vasodilator responses to acetylcholine in the presence of L-NA, whereas the volatile anesthetics did not affect these vasodilations in the absence of L-NA. Halothane (2.0%) did not alter the vasodilation produced by acetylcholine in the presence of TEA or KCl. In the in-vivo preparation, the vasodilator effects of acetylcholine (1 and 10 nmol) were not affected by the inhalation of halothane (1.0%) or isoflurane (1.3%). These results suggest that, in resistance arteries in conditions of constant flow, halothane and isoflurane do not affect vasodilations in response to an endothelium-dependent agonist. However, in these preparations, once the enzymatic activity of nitric oxide synthase is inhibited, higher concentrations of halothane, but neither isoflurane nor the lower concentration of halothane, appear to impair endothelium-dependent relaxations, probably mediated by TEA-sensitive K+ channels.

Two-Phase Flow Visualization of R134A in a Multiport Microchannel Tube

Results are presented from a flow visualization investigation of a multiport microchannel tube using R134a, a medium pressure refrigerant. The study covers mass fluxes from 50-300 kg/s.m 2 and qualities ranging from 10-90%, with a 6-port microchannel tube with a hydraulic diameter of 1.5 mm under adiabatic conditions. The results from the flow visualization studies indicate that several flow configurations may exist in multiport microchannel tubes at the same time while constant mass flux and quality flow conditions are maintained. Based on these observations, development of a typical flow regime map does not appear to be an appropriate manner for describing the flow field if the flow conditions for each port are not known. Flow mapping of the fluid regimes in this multiport microchannel is accomplished by developing functions that describe the fraction of time or the probability that the fluid exists in an observed flow configuration. An application of the alternative method of flow description for pressure drop predictions in multiport channels is included.

IRL2500, A Selective ETB Antagonist for Endothelin-Induced Vasodilatation in the Pulmonary Vascular Bed in Rats

Introduction: Endothelins (ET-1 and ET-2) have vasoactive effects mediated by receptors (ETA & ETB). The objective of the present study was to determine the effect of endothelins and their antagonists on the pulmonary vascular bed in vivo. To accomplish this, we employed the unique rat model and studied the pulmonary vascular beds of intact-chest animal under conditions of constant pulmonary blood flow. Methods: Twenty-five rats were anesthetized with pentobarbital, and a specially designed balloon catheter was placed into rat's the pulmonary artery via the right jugular vein. The right lower lobe of the lung was perfused at constant flow (14 ± 0.6 ml/min) with blood removed from a cannulated carotid artery. The baseline pulmonary arterial pressure was 12.8 ± 1.1 mmHg. In order to demonstrate vasodilator responses to testing agents, the pulmonary arterial pressure was elevated to 34.8 ± 1.4 mmHg by continuous infusion of U46619, a thromboxane-like substance. The effect of various endothelin agonists and antagonists were then studied. Results: Intrapulmonary arterial injections of ET-1, IRL1620 (ETB agonist) and ET-3 produced dose-dependent vasodilator responses in the pulmonary vascular bed. At a dose of 1µg, ET-1, IRL1620 and ET-3 caused decreases in pulmonary arterial pressure of 8.1 ± 0.4 mmHg, 8.2 ± 0.3 mmHg and 7.9 ± 0.3 mmHg respectively (all significantly different from baseline, n=5, p<0.05). After pretreatment with IRL2500 (ETB antagonist, 10mg/kg, i.v.), the vasodilator responses to ET-1, IRL1620 and ET-3 at the same dose were 0.9 ± 0.1mmHg, 2.1 ± 0.3 mmHg and 1.8 ± 0.3 mmHg respectively (n=5, not significantly differ from the baseline). This data suggests that IRL2500 can block the vasodilator responses to ET-1, IRL1620 and ET-3 in the lung. Data from a different group of animal demonstrate that the vasodilator responses to ET-1, IRL1620 and ET-3 are not altered significantly by pretreatment with BQ123 (an ETA antagonist) (n=5) Conclusions: Using a new rat model, these results indicate that ET-1, IRL1620 and ET-3 dilate the pulmonary vascular bed by activation of the ETB receptor. The present data also suggest that IRL2500, as a specific ETB antagonist can be a useful pharmacological tool to study the pulmonary vascular regulation in rats. This new intact rat preparation appears to be valuable in carrying out cardiopulmonary studies in vivo.