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PubMed1996

Myocardial uptake of thiopental enantiomers by the isolated perfused rat heart.

Myocardial uptake of thiopental enantiomers by an isolated perfused rat heart preparation was examined after perfusion with protein-free perfusate. Outflow perfusate samples were collected at frequent intervals for 20 min during single-pass perfusion with 10 micrograms/ml racemic thiopental (washin phase) and for another 45 min during perfusion with drug-free perfusate (washout phase). (+)- and (-)-thiopental concentrations were assayed by chiral high-performance liquid chromatography. Heart rate, perfusion pressure, and electro-cardiogram were also monitored. During the washin phase, there was no significant difference between the mean values of the equilibration rate constants of (+)- and (-)-thiopental enantiomers (0.44 +/- 0.07 min-1 and 0.43 +/- 0.09 min-1, respectively, P > 0.05). Mean volumes of distribution of (+)- and (-)-thiopental enantiomers were similar (6.34 +/- 1.20 and 6.45 +/- 1.29 ml/g for the washin phase and 7.22 +/- 0.71 and 7.47 +/- 0.81 ml/g for the washout phase, respectively, P > 0.05). This indicates that tissue accumulation of thiopental enantiomers in the isolated perfused rat heart was not stereoselective. Uptake of thiopental by the heart was perfusion flow rate-limited and independent of capillary permeability. These findings suggest that myocardial tissue concentration of racemic thiopental should be an accurate predictor of myocardial drug effect.

Anesthetics, Intravenous↗
PubMed1989

The multiple-indicator dilution technique for characterization of normal and retrograde flow in once-through rat liver perfusions.

The technique of normal and retrograde rat liver perfusion has been widely used to probe zonal differences in drug-metabolizing activities. The validity of this approach mandates the same tissue spaces being accessed by substrates during both normal and retrograde perfusions. Using the multiple-indicator dilution technique, we presently examine the extent to which retrograde perfusion alters the spaces accessible to noneliminated references. A bolus dose of 51Cr-labeled red blood cells, 125I-albumin, 14C-sucrose and 3H2O was injected into the portal (normal) or hepatic (retrograde) vein of rat livers perfused at 10 ml per min per liver. The outflow perfusate was serially collected over 220 sec to characterize the transit times and the distribution spaces of the labels. During retrograde perfusion, red blood cells, albumin and sucrose profiles peaked later and lower than during normal perfusion, whereas the water curves were similar. The transit times of red blood cells, albumin and sucrose were longer (p less than 0.005), whereas those for water did not change. Consequently, retrograde flow resulted in significantly larger sinusoidal blood volumes (45%), albumin Disse space (42%) and sucrose Disse space (25%) than during normal flow, whereas the distribution spaces for total and intracellular water remained unaltered. The distension of the vascular tree was confirmed by electron microscopy, by which occasional isolated foci of widened intercellular recesses and spaces of Disse were observed. Cellular ultrastructure was otherwise unchanged, and there was no difference found between normal and retrograde perfusion for bile flow rates, AST release, perfusion pressure, oxygen consumption and metabolic removal of ethanol, a substrate with flow-limited distribution, which equilibrates rapidly with cell water (hepatic extraction ratios were virtually identical: normal vs. retrograde, 0.50 vs. 0.48 at 6 to 7.4 mM input concentration). These findings suggest that the functional and metabolic capacities of the liver remain unperturbed during retrograde perfusion, rendering the technique suitable for the investigation of zonal differences in drug-metabolizing enzymes.

Albumins↗
PubMed2002

Parametric imaging of tumor perfusion using flow- and permeability-limited tracers.

PURPOSE: To quantitatively evaluate the spatial distribution of flow- and permeability-limited perfusion in MCF7 human breast cancer tumors orthotopically implanted in CD1-NU mice. MATERIALS AND METHODS: Flow-limited perfusion was derived from (2)H-MRI recorded before and after infusion of deuterated water. Permeability-limited perfusion was evaluated from GdDTPA-enhanced (1)H-MRI. RESULTS: The dominant processes in tumor perfusion, namely blood flow and capillary permeability, were mapped in orthotopically implanted MCF7 human breast cancer tumors. The dynamic data were processed according to physiological models, yielding parametric maps of intravascular volume fraction, water perfusion rate, GdDTPA permeability rate constant, and extracellular volume fraction accessible to GdDTPA. The maps exhibited the heterogeneous distribution of each perfusion parameter. Most of the tumor tissue (> or =95%) was perfused with HDO, while GdDTPA was perfused in only about 50% of it. In most loci the perfusion rate was limited by capillary permeability to GdDTPA. CONCLUSION: The results demonstrated the instructive value of tracers with different properties used in conjunction to achieve a deeper understanding of tumor perfusion capacity. This study offers tools for the accurate, noninvasive evaluation of drug delivery efficacy.

Animals↗
PubMed1996

Magnetization exchange in capillaries by microcirculation affects diffusion-controlled spin-relaxation: a model which describes the effect of perfusion on relaxation enhancement by intravascular contrast agents.

The effect of perfusion on relaxation time in tissue has only been considered for first-pass kinetics of NMR-signal after application of contrast agents. The importance of perfusion on relaxation has not yet been studied for steady state conditions, i.e., when the intravascular relaxation rate is constant in time. The aim of this study is to develop a model in which T1 relaxation is derived as a function of perfusion and intracapillary volume fraction (regional blood volume). Tissue is considered to be two-compartment system, which consists of intracapillary and extravascular space. Intracapillary relaxation differs from relaxation in the arterial system due to diffusion-exchange of magnetization from extravascular to intracapillary space. Perfusion tends to attenuate this difference and thus counteracts the effect on intracapillary relaxation. Relaxation in the extravascular and intracapillary magnetization are linked by diffusion. This dependence is presented in analytical form and a generic equation is derived. AT1 experiment is considered in which all spins of tissue and blood are inverted at the beginning. Calculations are performed for the fast exchange model of tissue. Perfusion increases relaxation enhancement of intravascular contrast agents. This effect is considerable in highly perfused tissue like myocardium. The dependence of relaxation on perfusion implies an overestimation of the regional blood volume when the calculation of the latter is based on tissue models that neglect perfusion. The model presented here is applied to predict the effect of perfusion on T1 imaging with FLASH-pulse sequences because this technique has been proven to be a powerful method to obtain T1 maps within a short time interval. For the fast exchange model, two algorithms are suggested that determine perfusion and regional blood volume from T1 imaging in the presence and absence of intravascular contrast agents.

Blood Volume↗
PubMed1996

Effect of treppe on isovolumic function in the isolated blood-perfused mouse heart.

The effects of treppe on left ventricular function in the isolated mouse heart perfused with physiological buffer or with erythrocyte-rich buffer were compared. Left ventricular systolic and diastolic pressures were measured in the isovolumically contracting (balloon in the left ventricle) mouse hearts. Hearts were isolated from 12 adult Swiss-Webster mice and perfused at constant pressure (approximately 85 mmHg) via the aorta. Perfusate consisted of non-recirculating oxygenated Krebs-Henseleit (KH) solution without or with washed cow red blood cells at a hematocrit of 20% (KH-RBC20). The measured ionized calcium concentration of the perfusates were adjusted to 2.2 mmol/l and the temperature held constant at 37 degrees C. Left ventricular systolic pressure, its derivative and diastolic pressures were recorded via a pressure transducer attached to a small latex balloon which was placed in the left ventricle through a left atrial incision. The balloon volume was adjusted to achieve an end-diastolic pressure of 4-8 mmHg. Left ventricular (LV) developed pressure averaged 111 +/- 4 (mean +/- S.E.M.) with KH alone and 108 +/- 4 mmHg with KH-RBC20 while the coronary flows were 3.1 +/- 0.18 and 0.95 +/- 0.15 ml/min respectively. In both KH solution alone and KH-RBC20, developed pressure remained relatively stable from 3 to 5 Hz while +/- dp/dt increased approximately 10% above values observed at 3 Hz. During KH perfusion with increasing stimulation rates, left ventricular pressure and +/- dP/dt, to a lesser extent, decreased while end-diastolic pressure markedly increased at stimulation rates higher than 5 Hz. However, KH-RBC20 perfusion prevented the marked increase in diastolic pressure with increasing stimulation rates (from 5 to 10 Hz). No significant difference in left ventricular developed pressure or +/dP/dt response to treppe were in evidence between groups. These results demonstrate that diastolic function of the isovolumically contracting mouse heart is sensitive to treppe and different techniques of perfusion. Buffer perfusion alone may limit accurate measurement of left ventricular diastolic properties and exacerbate changes in diastolic function, particularly under conditions of increased oxygen demand. The erythrocyte perfused mouse heart provides an in vitro model for determining cardiac function which is physiologically superior to buffer perfusion, and may be useful to investigators to assess gene influence on left ventricular function in genetically altered mice.

Animals↗
PubMed1994

Function of isolated rabbit hearts perfused with erythrocyte suspension is not stable but improvement may be feasible with hemoglobin solution.

In the present study isolated rabbit hearts were perfused with erythrocyte suspensions (hematocrit 21.5 +/- 0.5%) or hemoglobin solutions according to Langendorff with a constant flow at 37 degrees C. In preliminary experiments three types of stroma-free hemoglobin were used: unmodified, but carefully purified, stroma-free hemoglobin (SFHb), HbNFPLP which is a chemically modified Hb molecule and polyHbNFPLP which is a polymer of HbNFPLP. In hearts perfused with erythrocyte suspensions left ventricular developed pressure and oxygen consumption decreased and perfusion pressure increased steadily from the beginning of the perfusion. Dark spots appeared on the surfaces of these hearts, which were the result of extravasation of erythrocytes. As a consequence capillaries probably became obstructed, leading to reduced cardiac function. Hearts perfused with stroma-free hemoglobin solutions showed an initial increase in left ventricular developed pressure after switching from Tyrode perfusion to perfusion with hemoglobin solutions. Left ventricular developed pressure and perfusion pressure were stable for about 2 hours in hearts perfused with SFHb and were reasonable for 2 hours when the heart was perfused with HbNFPLP or more than 4 hours with polyHbNFPLP. More extensive experiments with stroma-free hemoglobin solutions when these become available in sufficient quantities have, according to the results from preliminary experiments, the potential of showing good oxygen supply resulting in reasonable cardiac function.

Animals↗
PubMed1992

Study of kidney and liver viability in the rat after exclusive aortic perfusion using intracellular ATP measurement.

To find whether the liver can be procured after exclusive aortic perfusion, three organ perfusion models were used in three groups of donor rats. Group 1 underwent liver wash-out via the portal vein; in group 2, the kidneys alone were perfused via the aorta; and group 3 underwent simultaneous aortic perfusion of liver and kidneys. All perfusion flow rates in the three groups were adjusted to physiological values. Harvested organs were transplanted and recipient animals were killed 4 h after transplantation to study liver and kidney viability by using intracellular ATP measurement. Liver ATP was lower (P < 0.005) in the portal perfusion group (group 1: 1.396 +/- 0.412) than in the aortic perfusion group (group 3: 2.181 +/- 0.061). Kidney ATP was comparable in groups 2 and 3:1.066 +/- 0.09 vs 1.059 +/- 0.273 (mumol/g) tissue). Liver cooling was quicker with portal perfusion than with the aortic flush (20 degrees C in 20 s vs 15 degrees C in 60 s). Aortic perfusion at a physiologic flow rate has no detrimental effect on renal viability studied by intracellular ATP measurement. We conclude that liver cooling via the aortic route only is a good alternative to portal perfusion and seems to give good preservation. Application of this observation to emergency procurement in humans is still the subject of controversy.

Adenosine Triphosphate↗
PubMed1993

Double luminal and vascular perfusion of chicken jejunum: studies on 3-O-methyl-D-glucose absorption.

The aims of the present study were: (1) to set up a procedure for simultaneous vascular and luminal perfusion of the chicken jejunum; (2) to assess the transport capacity of the tissue under such conditions, and (3) to study the effects of phloretin and theophylline, given through the vascular perfusate, on 3-O-methyl-D-glucose intestinal transport. The perfusion procedure described allowed the control of intestinal and vascular inflow rates and perfusion pressures so that these parameters could be adjusted to physiological values. A perfluorochemical emulsion was used as oxygen carrier for the vascular perfusate. The absorptive function of the perfused tissue was assessed by means of its ability to transport 3-O-methyl-D-glucose. Furthermore, ultrastructure preservation was evaluated by scanning and transmission electron microscopy. Results indicate that the perfused tissue kept its transport capacity and morphology intact throughout the 120-min experimental period. Moreover, no hypersecretion was observed as indicated by the constancy of perfusate volumes and perfusion pressures. Phloretin (1 mM) or theophylline (10 mM) added to the vascular perfusate markedly reduced the transfer of 3-O-methyl-D-glucose from the enterocyte to the vascular fluid without affecting the uptake from the lumen. Our results suggest that this preparation may be used as an alternative tool for the study of intestinal absorption processes in avian species, particularly when complete examination is required of the efflux of substrates from the intestinal lumen to the vascular fluid.

3-O-Methylglucose↗
PubMed1995

Hyperthermic isolated limb perfusion increases circulating levels of inflammatory cytokines.

Hyperthermic isolated limb perfusion is an established method of treatment for regionally advanced melanoma. Recent studies suggest that exogenously administered cytokines potentiate tumor response in patients with in-transit melanoma. We hypothesized that isolated limb perfusion induces an immunogenic response characterized by increased circulating levels of cytokines in the pump circuit, potentially contributing to the antitumor effect. We obtained blood samples from the perfusion circuit and systemic circulation at various intervals from patients undergoing isolated chemotherapeutic perfusion for melanoma. Samples were analyzed for serum cytokine profiles by enzyme-linked immunosorbent assay. When compared with baseline values, significant increases in serum levels of interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor (TNF) occurred within the perfusion circuit during isolated limb perfusion (P < 0.05). In addition, there was a corresponding increase in IL-8 within the systemic circulation at the 60-min interval (P < 0.05), suggesting some degree of leakage from the isolated circuit due to the extremely high levels of IL-8 in the perfusion circuit. A transient but insignificant decrease in circulating levels of neutrophils was also observed during the perfusion process, which may be attributed to margination. Increased levels of cytokines IL-6, IL-8, and TNF occurred within the isolated circuit during hyperthermic limb perfusion and may contribute to tumor response seen in patients treated with isolated limb perfusion.

Antineoplastic Combined Chemotherapy Protocols↗
PubMedDate not supplied

Association of liposomes with the isolated perfused rabbit heart.

Liposomes were prepared from a mixture of either phosphatidylcholine (PC) and cholesterol (Ch) (7:2) (neutral), PC, dicetylphosphate and Ch (4:1:3) (negative), or PC, stearylamine and Ch (4:1:3) (positive). In addition, as the lipid phase-liposomal marker, 3H- or 14C-Ch was added. Alternatively, 14C-labelled mannitol, glucose or inulin was used as the aqueous phase-marker in some experiments. The liposomes were purified by Sephadex gel chromatography and by using microfilter. After 4 h of sonication, 95% of the total liposomes were found to be smaller than 1.2 microns. The entrapment volume was calculated to be 0.9-1.2 microliters/mumole of lipid. The ratio of lipid radioactivity and aqueous phase-radioactivity, which were found in a non-filtrable portion of the perfusate, remained constant during a heart-perfusion period of 30 min, indicating that the liposomes were stable during the experimental period. The wash-out experiment indicated that the liposomes were distributed in a space of the perfused heart nearly as large as the mannitol space. The liposomes were rapidly taken up by the heart during perfusion in a Langendorff manner. The positive liposomes were taken up by the perfused nonischemic heart at a greater rate than were the negative liposomes. The results with perfused ischemic hearts were equivocal. The liposomal label was found to be distributed unequally in the subcellular fractions, namely, relatively greater amounts (per mg protein) of liposome-bound radioactivity of Ch or mannitol were found in the microsomal fraction than in the mitochondrial or cytosolic fractions of the perfused heart. This distribution pattern was not influenced by the electrical charge of liposomes or by the oxygenation state of the heart perfusion. The accumulation of the liposomal label in the microsomal fraction found in the heart perfusion experiment could not be observed in the experiment in which tissue slices were incubated in the presence of liposomes, or in the experiment in which free mannitol was administered in the heart perfusion.

Animals↗
PubMed2003

Preliminary results of intermittent retrograde cerebral perfusion during proximal aortic arch surgery.

OBJECTIVE: Continuous retrograde cerebral perfusion during aortic arch surgery is associated with cerebral edema. In this report, we describe the clinical use of a new type of intermittent retrograde cerebral perfusion. SUBJECTS AND METHODS: Fourteen patients with a Stanford type A dissection were included in this study. With the usual method of retrograde cerebral perfusion, about 2,500 mL venous blood is drained from bicaval cannulae into a hard-shell reservoir, and oxygenated blood is perfused through the superior vena caval cannula. The flow rate is 300 mL/min. After about 15 min, retrograde perfusion is discontinued, and drainage from the bicaval cannulae is restarted. When a bloodless field is necessary, perfusion also is discontinued. RESULTS: Two to seven cycles of intermittent retrograde cerebral perfusion were administered (average, 3.1+/-0.4, mean+/-SD). The total retrograde perfusion time was 36.0+/-1.9 min which was equivalent to 74.8% of the circulatory arrest time. No patient developed edema of the upper body. The time to wake-up was 3 to 14 h (average, 6.5+/-1.0 h). No patient suffered any neurologic complications even though the time of circulatory arrest was greater than 60 min in four cases. Head magnetic resonance imaging or computed tomography was performed in 12 cases, and no evidence of hypoxic brain injury was detected. CONCLUSIONS: Our clinical experience using a moderate amount of intermittent retrograde cerebral perfusion is superior to continuous retrograde cerebral perfusion for protecting the brain during aortic arch surgery.

Adult↗
PubMed1997

Cerebral protection using retrograde cerebral perfusion during hypothermic circulatory arrest.

BACKGROUND: Retrograde cerebral perfusion through the superior vena cava (SVC) has been proposed to protect the brain from ischaemic injury during profound hypothermic circulatory arrest (PHCA). Its contribution to cerebral protection is unclear. Furthermore, the addition of anaesthetic or vasodilating agents to the SVC perfusate to enhance brain protection, has never been described. METHODS: In three patients undergoing repair of the ascending aorta utilizing PHCA, the upper body was retrogradely perfused with cold (16 degrees C) blood through the SVC by the cardiopulmonary bypass pump. Electroencephalographic activity was monitored using a computerized electroencephalographic monitor (Cerebro Trac 2500, SRD). Perfusion pressure was measured at a port in the cannula connector. Etomidate or thiopentone was injected into the SVC perfusate to arrest reappearing electroencephalographic activity. Nitroglycerin or nitroprusside was injected into the perfusate to increase retrograde flow and maintain a constant perfusion pressure. RESULTS: During PHCA periods of up to 61 min, recurrent electroencephalographic activity was abolished by the retrograde administration of small boluses of etomidate (total 50 mg) or thiopentone (total 500 mg). Nitroprusside (100 micrograms) and nitroglycerin (2 micrograms.kg-1.min-1) increased retrograde flow from 220 to 550 and 660 ml.min-1, respectively, while maintaining perfusion pressure (25-26 mmHg). Recovery from anaesthesia and surgery was uneventful, with no adverse neurological sequelae. CONCLUSION: Injection of anaesthetic agents into the retrograde SVC perfusate during PHCA, can suppress reoccurring electroencephalographic activity and retrograde injection of vasodilators can facilitate an increase in perfusion. It is suggested that both may augment brain protection.

Aged↗
PubMed1990

Reproducible vasodilatation by platelet-activating factor in blood- and Krebs-perfused rat kidneys is albumin-dependent.

The vasodilator effect of platelet-activating factor (PAF) and its reproducibility was determined in rat kidneys perfused in situ with blood or in isolated kidneys perfused with Krebs solution or Krebs plus 0.25% bovine serum albumin (BSA) at 3 ml/min. Dilatation was measured as inhibition of the increase in perfusion pressure produced by stimulation of the renal nerves or by infusion of noradrenaline. PAF, in saline and 0.25% BSA, was infused into the perfusate at 0.05 ml/min to produce eight incremental consecutive concentrations from 3 x 10(-11) to 10(-7). Two sets of PAF infusions were made during nerve-stimulated responses followed by one set during noradrenaline infusion. With blood perfusion, PAF consistently produced dose-dependent dilatation and 3 x 10(-9) M reduced nerve-stimulated responses to 52% of control. This effect was reproduced by a second infusion. However in Krebs-perfused kidneys the effect of the first PAF infusion was not consistent, with responses either not affected or reduced only at the lower doses so that the mean maximum decrease was only 10% and the vasodilatation was not dose-dependent. The second PAF infusion invariably had no effect. On the other hand perfusion with Krebs and 0.25% BSA produced consistent and dose-dependent inhibition of vasoconstriction which was reproduced by a second infusion. PAF was effective at 10-fold lower doses in Krebs-albumin perfused compared to blood-perfused kidneys. These results indicate that exogenous PAF is a potent and reproducible dilator of the rat renal vasculature perfused with blood or Krebs-albumin solution but not albumin-free Krebs solution.

Animals↗
PubMed1988

Hypoxic vasoconstriction in blood and plasma perfused lungs.

Isolated lungs of pigs, cats and rats were perfused in situ with blood and with plasma at constant flow rate. The experiments were specifically designed to compare the intensity of the hypoxic pressor response (HPR) during blood and plasma perfusion. Ventilation of the lungs with 6.0% O2 during perfusion with blood, elevated the inflow pressure (Pa) from 18.9 +/- 1.5 to 35.8 +/- 2.0 mm Hg in pig lungs, from 12.9 +/- 0.5 to 17.9 +/- 1.1 mm Hg in rat lungs, and from 12.6 +/- 0.8 to 19.2 +/- 1.5 mm Hg in cat lungs. In comparison during perfusion of the lungs with plasma, the HPR was larger in pig lungs (Pa increased from 16.9 +/- 2.0 to 42.3 +/- 2.7 mm Hg), smaller in rat lungs (Pa increased from 10.2 +/- 0.9 to 11.4 +/- 1.2 mm Hg), and also smaller in cat lung (Pa increased from 9.9 +/- 1.2 to 11.9 +/- 1.2 mm Hg). The site of HPR in blood perfused cat lobes was primarily in the middle segment (arterial and venous technique) and remained in the middle segment (although blunted) during plasma perfusion. The vascular pressure-flow relationship in pig lungs showed that during blood perfusion, both the slope and intercept rose during hypoxia; these changes were similar but greater during plasma perfusion. Measurement of thromboxane A2 and prostacyclin in the lung effluent revealed no relation to intensity of the HPR or to the difference in the HPR in blood and plasma perfused lungs. Thus the absence of red blood cells (RBCs) may have been responsible for the difference in the HPR during blood and plasma perfusion; in rats and cats, RBCs appear to be essential for the full expression of the HPR, in contrast, the HPR in pigs does not require the presence of the RBCs. Possible explanations for these differences are suggested.

Animals↗
PubMed1992

Hepatic glutathione concentrations and the release of pyrrolic metabolites of the pyrrolizidine alkaloid, monocrotaline, from the isolated perfused liver.

We have examined the relationship between the metabolism of the pyrrolizidine alkaloid, monocrotaline, and glutathione concentration in the isolated, perfused rat liver. On perfusion of monocrotaline (300 microM) through the isolated liver, high concentrations (1.1 mM) of its metabolite glutathionyldehydroretronecine are released into bile, while much lower amounts (4.86 microM; 0.05 mumol/g liver) accumulate in the perfusate over a 1 hr perfusion period. Metabolite concentration in both the bile and perfusate increase when the level of monocrotaline perfused is increased to 900 microM. Metabolite release is also elevated in livers pretreated with phenobarbital. Monocrotaline perfusion lowered glutathione concentrations in the liver from 30 min onwards. Livers from animals treated with buthionine sulfoximine or chloroethanol showed much lower glutathione levels after 60 min perfusion. Livers from chloroethanol-treated (but not buthionine sulfoximine-treated) animals showed significantly lower release of pyrroles into the bile on perfusion with monocrotaline, but there is no effect on the rate of build-up of pyrrolic metabolites in the perfusate. We conclude that hepatic glutathione concentrations and the release of pyrrolic metabolites of monocrotaline mutually interact. Exposure of the liver to monocrotaline reduces glutathione concentrations, while marked depletion of liver glutathione concentration leads to a decrease in the release of monocrotaline metabolites.

Animals↗
PubMed1984

Properties and regulation of a trans-plasma membrane redox system of perfused rat heart.

Ferricyanide was reduced to ferrocyanide by the perfused rat heart at a linear rate of 78 nmol/min per g of heart (non-recirculating mode). Ferricyanide was not taken up by the heart and ferrocyanide oxidation was minimal (3 nmol/min per g of heart). Perfusate samples from hearts perfused without ferricyanide did not reduce ferricyanide. A single high-affinity site (apparent Km = 22 microM) appeared to be responsible for the reduction. Perfusion of the heart with physiological medium containing 0.5 mM ferricyanide did not alter contractility, biochemical parameters or energy status of the heart. Perfusate flow rate and perfusate oxygen concentration exerted opposing effects on the rate of ferricyanide reduction. A net decreased reduction rate resulted from a decreased perfusion flow rate. Thus, the rate of supply of ferricyanide dominated over the stimulatory effect of oxygen restriction; the latter effect only becoming apparent when the oxygen concentration was lowered at a high perfusate flow rate. Whereas glucose (5 mM) increased the rate of ferricyanide reduction, pyruvate (2 mM), acetate (2 mM), lactate (2 mM) and 3-hydroxybutyrate (2 mM) each had no effect. Insulin (3 nM), glucagon (0.5 microM), dibutyryl cyclic AMP (0.1 mM) and the beta-adrenergic agonist ritodrine (10 microM) also had no effect, however, the alpha 1-adrenergic agonist, methoxamine (10 microM), produced a net increase in the rate of ferricyanide reduction. It is concluded that a trans-plasma membrane electron efflux occurs in perfused rat heart that is sensitive to oxygen supply, glucose, perfusion flow rate, and the alpha-adrenergic agonist methoxamine.

Adenosine Diphosphate↗
PubMed1985

Effects of insulin on the metabolism of the isolated working rat heart perfused with undiluted rat blood.

Working rat hearts were perfused with either buffer or with defibrinated, undiluted rat blood dialyzed to remove vasoconstrictor factors. With precautions taken for sterility in the preparation of the perfusate and the apparatus, hearts were obtained which were stable as judged by stroke rate and cardiac output. In these hearts, cardiac output and coronary flow averaged 46.0 and 1.7 ml/g heart per min, respectively. Perfusion with erythrocyte-free buffer depressed cardiac output by 30%, while coronary flow averaged 8.8 ml/g of heart per min. The mean stroke rate of blood-perfused hearts was 300 beats/min but only 240 beats/min during buffer perfusion. In blood-perfused hearts, insulin did not alter stroke rate but significantly lowered coronary flow. The hormone caused a transient increase in cardiac output in hearts perfused with buffer. Insulin did not alter glucose uptake in buffer-perfused hearts but increased lactate release in perfusions with blood. Both serum fatty acids and triacylglycerol fatty acids were significant metabolic fuels in hearts perfused with undiluted blood. The preparation described would appear to be potentially useful for the study of myocardial metabolism in vitro.

Animals↗
PubMed1985

Obtaining local SAR and blood perfusion data from temperature measurements: steady state and transient techniques compared.

A series of analyses and experiments was performed to determine the extent that SAR and blood perfusion information can be extracted from steady state temperature values and from transient temperature measurements following a step change in applied power. Multiple local temperature measurements were made in canine thighs heated by 2450 MHZ microwaves to evaluate two parameters: the local absorbed power in the tissue, and the local "effective blood perfusion." The theoretical bases for these calculations are presented in order to identify their underlying assumptions and to obtain a unified basis for comparison of the various calculation methods used by previous investigators. From energy balance considerations it can be shown that the local absorbed power can be obtained from either the rate of increase of temperature following a step increase in power, or from the rate of decrease in temperature immediately following a step decrease in power. These theoretical observations are verified experimentally by comparing the SAR results at fixed positions in canine thighs as calculated from both increasing and decreasing power steps. For decreasing power steps, the resulting decreasing temperature curves can also be used to calculate an effective blood perfusion rate if thermal conduction is included. Alternatively, this same effective blood perfusion rate can be calculated from steady state data. (These two approaches have been used by previous investigators to determine "blood perfusion" values. We have added the modifier "effective" to specifically denote the presence of thermal conduction effects in such perfusion calculations.) From our experimental results and theoretical calculations it appears that differences between the predictions of the two calculation methods arise from changing thermal conduction values during the cooling period of the thermal clearance method. The steady state calculation approach is easier to apply than the washout method, but it requires the additional knowledge of the local SAR value. It is important to realize that effective blood perfusion values calculated using thermal techniques are subject to large errors under conditions where thermal conduction is important, unless this conduction is explicitLy included in the calculation. Such effective blood perfusion values should not be quantitatively compared to values calculated from non-thermal techniques that are not affected by thermal conduction. Unless such conduction effects are known to be negligible, effective perfusion values are only qualitative indicators of the presence of changes in blood perfusion.

Absorption↗