Surface fluorescence of reduced pyridine nucleotide of the perfused rat kidney: interrelation between metabolic and functional states

Surface fluorescence of reduced pyridine nucleotide (PN) was recorded continously with a DC fluorormeter and correlated with changes in experimental conditions. As a light source for fluorescence excitation, an Hg arc lamp with a 340-375 nm filter in front was used; the fluorescence response of reduced PN was measured at 450-510 nm. The DC fluormeter and the Hg arc lamp were connected to the kidney by a trifurcated fiber optics light guide. Reduced PN fluorescence emission was corrected for changes in tissue opacity by a 1:1 subtraction of reflectance changes at 340-375 nm from the fluorescence (PN-deltaR). To obtain further information about the PN redox state of the total surface area of kidney cortex and to evaluate whether certain areas were insufficiently perfused, fluorescence photographs of the total surface area were taken. The results demonstrate that the described method is simple and provides specific information about the mitochondrial oxidation reduction state.

High spatial resolution measurements of organ blood flow in small laboratory animals

With the use of a newly developed Imaging Cryomicrotome to determine the spatial location of fluorescent microspheres in organs, we validate and report our processing algorithms for measuring regional blood flow in small laboratory animals. Microspheres (15-microm diameter) of four different fluorescent colors and one radioactive label were simultaneously injected into the left ventricle of a pig. The heart and kidneys were dissected, and the numbers of fluorescent and radioactive microspheres were determined in 10 randomly selected pieces. All microsphere counts fell well within the 95% expected confidence limits as determined from the radioactive counts. Fluorescent microspheres (15-microm diameter) of four different colors were also injected into the tail vein of a rat and the left ventricle of a rabbit. After correction for Poisson noise, correlation coefficients between the colors were 0.99 +/- 0.02 (means +/- SD) for the rabbit heart and 0.99 +/- 0.02 for the rat lung. Mathematical dissection algorithms, statistics to analyze the spatial data, and methods to visualize blood flow distributions in small animal organs are presented.

Imaging epicardial oxygen

Measurements of oxygen concentration and metabolic status in the heart are important to understanding the mechanisms that control cardiac respiration and its response to changing workload and substrate delivery. This paper presents images, recorded from a perfused rat heart, that reveal regional changes in concentrations of epicardial oxygen and of mitochondrial NADH in response to local ischemia, heterogeneous perfusion, and barbiturate inhibition. A fluorescence/ phosphorescence imaging system was developed to acquire digital images of oxygen concentration and NADH fluorescence from the epicardium of perfused hearts. The oxygen imaging technique is based upon quenching of Pd(II) meso-tetra(p-sulfonatophenyl)porphin phosphorescence by dissolved oxygen. Images of oxygen and NADH fluorescence provided complimentary information about oxygen supply and demand in the heart. The utility of two-dimensional measurements of the mitochondrial bioenergetic status is illustrated by the comparison of gradients for NADH and oxygen across the boundary separating locally ischemic tissue from normoxic epicardium. Images of oxygen concentration provide a powerful means for studying the dynamics of regional oxygen supply/ demand relationships in cardiac muscle.

Time resolved 3-dimensional recording of redox ratio during spreading depression in gerbil brain

Optical fluorescence and reflectance measurements have been used to map the distribution of metabolic states in three dimensions in the gerbil brain with a spatial resolution of 200 microns an a time resolution of 4-6 s. In Mongolian gerbils anesthetized with pentobarbital, the redox states of the nicotinamide adenine dinucleotide (NADH) and flavoprotein components of the electron transport chain exhibit two distinct phases during the wave of spreading depression: (1) a transient period of oxidation and (2) a prolonged period of reduction, during which the cytochromes are reduced, and the hemoglobin is predominantly in the deoxy form. These data are interpreted as indicating that the energy demand placed on the gerbil brain during such spreading depression wave is sufficient to drive the brain temporarily hypoxic.

Delineation of myocardial ischemia in an isolated blood-perfused rabbit heart preparation

Isolated perfused heart preparations provide controlled conditions for the study of myocardial respiration and metabolism. Most studies utilize a hemoglobin-free perfusate which requires high arterial oxygen tension and high coronary perfusion rate. A blood-perfused rabbit heart preparation using an "assist" rabbit to maintain blood homeostasis has been developed which is suitable for respiratory, metabolic, and spectroscopic studies of myocardial function under controlled conditions. Fluorescence emission of reduced nicotinamide adenine dinucleotide (NADH) from the surface of blood-perfused rabbit heart was photographed to delineate areas of myocardial ischemia detectable as NADH fluorescence from reduced mitochondria. Blood reperfusion of ischemic myocardium resulted in disappearance of NADH fluorescence. Reocclusion of the coronary artery resulted in the same pattern and amplitude of NADH fluorescence.

Mechanism of action of hyaluronidase in decreasing myocardial ischemia post coronary occlusion in the isolated perfused rabbit heart

The influence of hyaluronidase (H) on subacute experimental myocardial ischemia was studied in isolated perfused rabbit hearts. Changes in ischemic area were assessed by epicardial nicotinamide adenine dinucleotide (NADH) fluorescence photography, an intrinsic high-resolution display of myocardial ischemia. Computerized determination of ischemic area was made from standardized photographs. Hyaluronidase was begun 20 minutes after coronary artery occlusion at 4 units/ml perfusate. NADH fluorophotographs were taken at 10-minute intervals up to 60 minutes of ischemia. Coronary sinus oxygen tension (PcsO2), myocardial oxygen consumption (MVO2), and coronary flow were determined. After 70 minutes, the hearts were perfused with rhodamine solution to identify areas of myocardial perfusion. In 13 H-treated hearts 54.3% +/- 3.7% (mean +/- SEM) of the nonperfused area (rhodamine stained) was ischemic (NADH fluorescent). In 14 untreated hearts 79.8% +/- 3.2% of the nonperfused area was ischemic (p less than 0.0001) and the ischemic areas were uniform. The distance between perfused and ischemic tissue was 952 +/- 78 micrometers in the H hearts and 504 +/- 35 micrometers in the untreated heart (p less than 0.0001). In the H hearts PcsO2 increased to 155% of the post-ligation control while it decreased to 79% in the untreated hearts (p less than 0.0001). MVO2 decreased in the H-treated hearts to 62%; the untreated hearts had no further change. In the H-treated hearts, coronary flow increased to 146% of the post-ligation control while it fell to 91% in the untreated group (p less than 0.0001). We conclude that H increases coronary flow while decreasing MVO2 during subacute ischemia. In H-treated hearts, significant amounts of myocardium remain normoxic within the nonperfused areas, and may potentially be salvaged after prolonged myocardial ischemia.

Optical measurements of oxygen delivery and consumption in gerbil cerebral cortex

Oxygen metabolism of the cerebral cortex of anesthetized gerbils was monitored by surface fluorescence and reflectance spectrophotometry both in vivo and in specimens freeze-trapped by the surface-freezing technique. Fiber optic light guides were used for optical coupling for determining mitochondrial flavoprotein and pyridine nucleotide fluorescence and for recording dual-wavelength reflectance spectra that indicated the levels of ferrocytochromes aa3 and c + c1 in the cortex and the oxygen saturation of cortical hemoglobin. During anoxic episodes increases in ferrocytochromes aa3 and c + c1 and in reduced pyridine nucleotides and flavoproteins were observed only when the cortical hemoglobin was more than 85% disoxygenated. Indeed the steady-state levels of oxidation-reduction of mitochondrial respiratory-chain components remained constant over a wide range of oxygen delivery, increased reduction being observed only when the fraction of inspired oxygen fell below 6%; these properties of mitochondria in vivo resemble those found in vitro. However, in normoxic animals the absorbance at 605 nm that may arise from ferri- or ferrocytochrome aa3 is larger than would be expected of purified mitochondria and may represent a pool of mitochondria that remains reduced at all levels of tissue oxygenation or a pigment not involved in oxygen metabolism.

Early ischemia after complete coronary ligation in the rabbit, dog, pig, and monkey

The character and extent of the myocardial ischemic "borderzone" was assessed in the rabbit, dog, pig, and monkey. A fluorophotographic technique permitting high resolution (+/- 50 micrometers) display of myocardial ischemia has been developed. Reduced intracellular NADH (ischemia) fluoresces and may be photographed while oxidized NAD (perfused tissue) does not. A coronary artery was ligated for 5 min in open-chest rabbits, dogs, pigs, and monkeys. A fluorescent dye was injected into the left atrium as a coronary vascular marker, and the tissue was quick-frozen. The ischemic margin was well seen and was jagged in all species. The distance from anoxic to perfused tissue (borderzone) was less than 50 micrometers in all species. A narrow "oxygen-diffusion zone" of nonperfused non-anoxic tissue is visible in isolated heart perfused with blood-free solution. The width of this zone is inversely related to myocardial oxygen consumption and is less than 50 micrometers in a working blood-perfused heart. We have not yet correlated the oxygen diffusion zone with the clinically defined salvageable borderzone. In dogs, collateral vessels provide a heterogeneous border to the ischemic region so that the canine ischemic pattern differs from that of pigs, rabbits, and monkeys.

Quantification of tissue fluorescein delivery and prediction of flap viability with the fiberoptic dermofluorometer

Quantitative fluorescence assessment with the fiberoptic dermofluorometer has been introduced to overcome the inadequacies of ultraviolet inspection following intravenous administration of fluorescein. Initial applications in the pedicle flap of the rat have indicated that this method can predict flap viability with reproducible precision and accuracy. This minimally invasive technique should be of considerable assistance to the evaluation of hypoperfused states in laboratory and clinical situations.

Temporal relation between onset of cell anoxia and ischemic contractile failure. Myocardial ischemia and left ventricular failure in the isolated, perfused rabbit heart

Contractile dysfunction is characteristic of the acutely ischemic myocardium. This study was undertaken to assess the temporal relations between the onset of cell anoxia and ischemic contractile failure in isolated, isovolumetric contracting rabbit hearts. High speed epicardial fluorescence photography using reduced nicotinamide adenosine nucleotide (NADH) was used to identify areas of cell anoxia. The onset of ischemia was correlated with deterioration of pressure generation over the course of sequential 60 second coronary arterial occlusions. In the isovolumetric contracting rabbit heart, areas of ischemia were detected 2 seconds after coronary occlusion. Significant reduction in peak systolic pressure occurred at 6 seconds of ischemic time and pressure continued to decrease throughout the 60 second period of coronary occlusion. NADH accumulation indicates imbalance of myocardial oxygen supply and demand and the cessation of oxygen utilization by the mitochondria. The results of this study indicate that ischemia is detectable within 1 to 2 seconds after coronary occlusion and that ischemic ventricular dysfunction occurs several seconds thereafter. Myocardial oxygen reserve is negligible.

Fluorescence mapping of mitochondrial redox changes in heart and brain

Fluorescence techniques may be utilized to map changes in the distribution of mitochondrial redox states in heart and brain during ischemic or hypoxic stress. The basis of these techniques is the intrinsic fluorescence of reduced NADH and oxidized flavoprotein in mitochondria which respond to changes in critical oxygen supply. Ischemic areas in rabbit hearts induced by coronary ligation were detected and mapped based on the increase in NADH fluorescence in the ischemic zone. The width of the jeopardized normoxic tissue surrounding the ischemic area (less than 50--350 mu) was measured by combination of fluorescein angiography and NADH fluorescence. Areas of increased NADH fluorescence in gerbil brains after carotid artery ligation or induction of spreading depression were mapped in a similar manner. Intraoperative monitoring of flavoprotein fluorescence from human cerebral cortex after superficial temporal artery middle cerebral artery (STA-MCA) anastomoses demonstrated increased rates of cortical oxidative metabolism after the surgical procedures.

Epicardial ischemia as delineated with epicardial S-T segment mapping andnicotinamide adenine dinucleotide (NADH) fluorescence photography

In isolated rabbit hearts with an experimental coronary arterial occlusion, epicardial ischemia was identified by reduced nicotinamide adenine dinucleotide (NADH) fluorescence photography, a technique that detects areas of myocardial anoxia. Epicardial S-T segment mapping was performed to evaluate the S-T segment changes across an ischemic border defined by NADH fluorescence. After S-T segment mapping and perfusion with a fluorescein dye, serial selections of the hearts revealed that the ischemic area was transmural and and the border was nearly perpendicular to the epicardial surface. As the epicardial ischemic border was approached, S-T segment elevation was first detected 3.3 mm outside the ischemic border, and increased over a transition zone 7 mm wide. S-T segment negativity was not detected immediately outside the ischemic border. It is concluded from these studies that S-T segment changes give relatively imprecise definition of an ischemic border, and that S-T segment changes across an ischemic border are not consistent with those predicted by solid angle analysis.

The nature of the copper atoms of cytochrome c oxidase as studied by optical and x-ray absorption edge spectroscopy

X-ray absorption edge spectroscopy has been used to study the copper of 1--2 mM cytochrome c oxidase in the resting oxidized, mixed-valence, and fully reduced states. A comparison was made of this protein with copper complexes and with natural and artificial copper proteins. Spectra were obtained with synchrotron radiation from the SPEAR storage ring using highly sensitive fluorescence detectors. Temperatures of -80 to -120 degrees C were employed further to improve the stability of the samples and to avoid the possibility of either auto- or photon-induced reduction of the materials, which might have occurred in previous studies. In order to characterize the valence states of the Cu and Fe components, the samples were monitored by infrared and visible spectroscopy before and after irradiation by the X-ray beam. The combination of the optical and X-ray absorption techniques has afforded a deconvolution of the four species of copper in the various states of cytochrome c oxidase and the tentative assignment of Cu alpha, the copper redox coupled to the heme alpha of cytochrome alpha, as a highly covalent type of copper and Cu alpha 3, the copper of cytochrome alpha 3, as a more ionic 'blue' type I copper. The implications of these findings upon the mechanism of action of cytochrome oxidase are briefly outlined.

Two and three dimensional display of myocardial ischemic "border zone" in dogs

It is intuitively apparent that the ultimate fate of reversibly damaged, peri-ischemic "border zone" tissue should relate to individual patient survival. The purpose of this study was: (1) to describe a technique of assessing the adequacy of epicardial and myocardial oxygenation, and (2) to examine the extent and character of the peri-ischemic "border zone" in the dog after coronary arterial ligation. A diagonal branch of the left anterior descending coronary artery was ligated in four anesthetized open chest, neurohormonally intact dogs. The same diagonal coronary artery was ligated in six isolated perfused canine heart preparations in which coronary partial pressures of oxygen and carbon dioxide, pH, blood flow and temperature were fixed. The ischemic zones were rapidly frozen and reduced nicotinamide adenine dinucleotide (NADH) fluorescence photographs were taken of the epicardium and at 0.5 mm depths into the myocardium. The distinction between perfused and ischemic myocardium is not apparent with the naked eye or natural light photography. Epicardial and myocardial oxidation-reduction status is well seen with NADH fluorophotography. In both the intact and perfused heart preparations the NADH-fluorescent (ischemic) border is jagged along all edges. Islands of perfused nonfluorescent tissue appear within the ischemic border. The transition between NADH-fluorescent ischemic cells and adjacent non-fluorescent tissue is less than 0.1 mm. The ischemic border is narrow. The distance between homogeneously NADH-fluorescent tissue and homogeneously nonfluorescent tissue (across the zone of island normoxia or microheterogeneity) may be as wide as 6 to 8 mm.

Display of epicardial ischemia by reduced nicotamide adenine dinucleotide fluorescence photography, electron microscopy, and ST segment mapping

Reduced nicotinamide adenine dinucleotide (NADH) fluorescence photography, a technique of assessing myocardial ischemia, was correlated with ischemia as identified by ST segment mapping and electron microscopy (EM) in 25 Langdneorff perfused rabbit hearts following coronary occlusion. Nicotinamide adenine dinucleotide (NAD), a component of the intramitochondrial electron transport chain, becomes reduced during periods of ischemia (NADH). NADH fluoresces when excited by ultraviolet light. NAD does not. All three techniques were compared to assess their resolution of the "border zone" between ischemia and nonischemic myocardium. The border zone defined by NADH fluorescence is 0.1 mm or less. Areas of high NADH fluorescence invariably revealed ST segment elevation, whereas minimally fluorescent areas did not. St segment mapping yields a border zone of approximately 7 mm. Areas of high NADH fluorescence following 1 hour of ischemia displayed severe damage on EM as compared to matched controls. A zone of intermediate ultrastructural damage is identified in a 1 mm biopsy taken between fluorescent and nonfluorescent myocardium. This evidence confirms epicardial NADH fluorescence photography as an assay of myocardial ischemia. This high resolution technique delineates a border zone of narrow dimensions as compared with ST segment mapping.

Evaluation of cardiac ischemia by NADH fluroescence photography

A direct, noninvasive method of assessing the oxidation-reduction potential of an intramyocardial respiratory chain component is described. The technique is based on the differences in spectral properties between the oxidized and reduced forms of nicotinamide adenine dinucleotide (NADH). The tissue surface fluorescence from intracellular NADH may be measured and documented photographically. Noose occlusion of a coronary artery produced detectable NADH fluorescence in 15 seconds in the subtended ischemic epicardium. This fluorescence of reduced pyridine nucleotide resolved following 60 seconds of reperfusion of the ischemic myocardium. The reduction of epicardial NADH with ischemia is a rapid and reversible process. A subsequent noose reocclusion resulted in a reproducible pattern of fluorescence. The technique of NADH fluorescence photography appears superior to current methods of assessing tissue oxygen supply:demand.

Oxygen delivery in perfused rat kidney: NADH fluorescence and renal functional state

Changes in steady-state levels of reduced pyridine nucleotide (PN) recorded by continuous monitoring of surface fluorescence were correlated with changes in physiological function of perfused rat kidneys when subjected to anoxia, ischemia, hypothermia, variations in perfusion pressure, inhibition of Na-K ATPase, and uncoupling of oxidative phosphorylation. Biphasic responses of PN reduction and oxidation during ischemic cycles at varying temperatures and anoxic cycles at different perfusion pressures demonstrated the presence of two different cell populations in the kidney cortex, those with sufficient oxygen and those without. The magnitude of PN fluorescence change during ischemia increased with decreasing temperature demonstrating better tissue oxygenation during hypothermia. The measurement of mitochondrial NADH oxidation in the perfused kidney during transitions from CO anoxia to normoxia was made possible by flash photolytic activation of mitochondrial electron transport. The half time for NADH oxidation (125 ms) was independent of the rate of oxygen delivery while the initial rate and extent of reaction was faster and steeper, respectively, at higher perfusion pressure, due to a better tissue oxygenation and faster CO washout.

Ischemic areas in perfused rat hearts: measurement by NADH fluorescence photography

Fluorescence emission of reduced nicotinamide adenine dinucleotide (NADH) from the surface of perfused rat hearts was photographed to provide a two-dimensional recording of NADH levels. Sodium Amytal inhibition of NADH oxidation resulted in a homogeneous increase in NADH fluorescence, while lowering perfusion pressure from 55 to 10 torr caused a heterogeneous increase in NADH fluorescence, reflecting the heterogeneous oxygen delivery at this low pressure. Local ischemia resulted in a well-defined region of high NADH fluorescence that corresponded to the region of ischemic inslut. The sharp transition between the ischemic and normoxic areas demonstrated that the hypoxic interface separating the two areas must be quite small.

Infrared spectroscopic studies of carbonyl horseradish peroxidases

Infrared difference spectra, FeIIICO vs. FeIII of horseradish peroxidase isoenzymes A2 and C were recorded from 2000 to 1800 cm-1. Under alkaline conditions, pH 9, both isoenzymes exhibit two CO stretching bands, at 1938 and 1925 cm-1 for A2 and at 1933 and 1929 cm-1 for C. As the pH is lowered the low-frequency band for each isoenzyme decreases in intensity with a concommitant appearance and increase in intensity of a band at 1906 and 1905 cm-1 for the A2 and C isoenzymes, respectively. These changes conform to pK values of 6.7 for the A2 and 8.8 for the C isoenzymes of horseradish peroxidase. The interpretation of the infrared results was simplified by the observation that a linear relationship exists between the redox potential, Em7, for the FeIII/FeII system vs. the infrared CO stretching frequency, vCO, for cytochrome a3, hemoglobin, myoglobin, and cytochrome P-450 cam with substrate. This relationship suggests that the primary force altering vCO in these heme proteins is a variation in electron density at the heme iron and not direct protein interactions with the CO ligand. The horseradish peroxidase infrared bands in the 1930-cm-1 region correlate well with this relationship. The large deviation of the 1905-cm-1 band from the linear relationship and its dependence upon hydrogen ion concentration are consistent with horseradish peroxidase having a single CO binding site which can hold in two geometries, one of which contains an amino acid moiety capable of forming a hydrogen bond to the carbonyl oxygen.

Magnetic and spectroscopic probes for FeOFe linkages in hemin systems

Magnetic and spectroscopic properties of mu-oxo-bis-hemins from natural and structurally related porphyrins were investigated as probes for ascertaining the presence or absence of FeIII-O-FeIII linkages between hemin moieties of hemeproteins. Magnetic susceptibilities of solids from 2.2 to 293 degrees K were investigated. The data fit the temperature variations expected for a pair of antiferromagnetically coupled S = 5/2, iron (III) porphyrins with J values of 175, 190, 195, 205, and 210 degrees K for deuterohemins with hydrogen, vinyl, 2'-ethoxycarbonylcyclopropyl, acetyl, propionyl, and ethyl 2,4-substituents, respectively. This magnetic character is reflected in PMR spectra that exhibit resonances with far less broadening and paramagnetic shift than is the case for monomeric high-spin hemins. Only impurities are seen in EPR spectra, which serve effectively in monitoring the magnetic purity of preparations. An infrared active asymmetric stretching frequency characteristic of the FeOFe linkage can be identified by substitution of 160 by 180. Electronic spectra are highly characteristic with poorly resolved absorption bands. The substituents on the porphyrin ring exert significant, but usually not large, electronic and steric effects on these properties. Solvent effects were relatively small and no firm evidence for binding of ligands trans to bridging oxygen was found. The uniqueness of these physical properties and their low sensitivity to changes in porphyrin structure or medium facilitates the identification of mu-oxo linkage in hemins or oxidized hemeproteins.