bluuebunny/crossref_metadata_2025 huggingface dataset:
Cellular mechanisms of delayed recovery of excitability in ventricular tissue
Authors: Joyner R. W. , Ramza B. M. , Osaka T. , Tan R. C.
Published: December 2017

It is well established that ventricular tissue, under some conditions, exhibits the phenomenon of postrepolarization refractoriness (PRR) in which the tissue excitability is depressed after an action potential. We have done parallel experiments on rabbit papillary muscles and on isolated rabbit ventricular cells to explain the cellular basis of this phenomenon, using elevated extracellular K+ concentration ([K+]o) (8 mM) to depolarize the tissue and the isolated cells. For isolated cells, we could separately measure cellular excitability (the inverse of the cellular current threshold) and the cellular responsiveness (the ability of the cell to generate inward current after excitation has occurred). We present two hypotheses that could explain the magnitude and time course of tissue PRR in terms of either changes in cellular excitability or changes in cellular responsiveness. We show that, although small changes in cellular excitability do occur, the predominant cellular mechanism for tissue PRR is the time course of recovery of the cellular responsiveness.
Multicompartment model for mechanics and energetics of fibrillating ventricle
Authors: Yaku H. , Goto Y. , Futaki S. , Ohgoshi Y. , Kawaguchi O. , Suga H.
Published: December 2017

We propose a new mechanical model of a fibrillating ventricle to interrelate ventricular mechanics and energetics during fibrillation. The model consists of multiple asynchronously contracting compartments with identical time-varying elastances but with different contraction phase lags. Pressures in all compartments are common, and volumes of all compartments change, keeping their sum constant in the model. We evaluated the mechanical behavior of each compartment by simulating this model on a personal computer. Results showed that each compartment contracts quasi-isobarically. We calculated the pressure-volume area (PVAc) of each compartment as a measure of the total mechanical energy generated by a contraction of the compartment. We found that the sum of PVAcs of all compartments agreed with the area (equivalent PVA; ePVA) surrounded by the end-systolic and end-diastolic pressure-volume relations and the isobaric line at the mean pressure of the fibrillating ventricle. We conclude that ePVA represents the total mechanical energy of the fibrillating ventricle model. The multicompartment model is useful for insight into the interrelation between ventricular mechanics and energetics during ventricular fibrillation.
NMR-visible ATP and Pi in normoxic and reperfused rat hearts: a quantitative study
Authors: Humphrey S. M. , Garlick P. B.
Published: December 2017

Nuclear magnetic resonance (NMR) spectroscopy detects only free, unbound metabolites. We have therefore compared the free high-energy phosphate content of isolated perfused rat hearts (determined by 31P-NMR) with the total high-energy phosphates of the same hearts (determined by chemical analysis) to determine the fractions, if any, that are NMR invisible. Aerobic perfusion (40 min at 37 degrees C, Pi-free Krebs buffer) was followed by 10, 14, or 18 min total global ischemia and 30 min reperfusion (n = 6 in each group). Fully relaxed 31P-NMR spectra (40 scans using 90 degrees pulses at 15-s intervals) were collected at various times throughout the protocol, and the signal intensities of the beta-phosphate of ATP, phosphocreatine (PCr), and Pi were quantified using methylenediphosphonate as an external standard. Hearts were freeze clamped either before ischemia or at the end of reperfusion and were chemically assayed for ATP, PCr, and Pi. After 40 min of normoxia, the ATP and PCr contents determined by NMR were almost identical to the values determined by chemical analysis. However, only 39 +/- 8% of the total Pi was NMR visible. After reperfusion, after 14 or 18 min of ischemia, the proportion of NMR-visible ATP had decreased to 64 +/- 9% (P less than 0.005). After reperfusion after 18 min ischemia, the proportion of NMR-visible Pi had increased to 76 +/- 10% (P less than 0.05). In conclusion, whereas the total cellular content of PCr is always NMR visible, ischemia-reperfusion can alter the fraction of NMR-visible ATP and Pi.
Mechanism of impaired responses of cerebral arterioles during diabetes mellitus
Authors: Mayhan W. G. , Simmons L. K. , Sharpe G. M.
Published: December 2017

The goal of this study was to determine the mechanism of impaired responses of cerebral arterioles during diabetes mellitus. To induce diabetes, rats were injected with streptozotocin. Rats were characterized as diabetic by a blood glucose of greater than 300 mg/dl. Diameter of pial arterioles was measured with intravital microscopy in nondiabetic and diabetic rats during superfusion with acetylcholine (ACh), ADP, the thromboxane (Tx) analogue U-46619, and nitroglycerin. ACh increased pial arteriolar diameter in nondiabetic rats and did not alter diameter in diameter in diabetic rats. ADP increased pial arteriolar diameter in nondiabetic rats and produced minimal changes in diameter of arterioles in diabetic rats. Tx analogue U-46619 produced similar constriction of cerebral arterioles in nondiabetic and diabetic rats. In addition, nitroglycerin produced similar dilatation of cerebral arterioles in nondiabetic and diabetic rats, suggesting that impaired dilatation of cerebral arterioles in diabetic rats was not related to nonspecific impairment of vasodilatation. Next, we examined the possibility that impaired responses of cerebral arterioles in diabetic rats in response to ACh and ADP may be related to production of a cyclooxygenase constrictor substance. Indomethacin and the TxA2-prostaglandin (PG) H2 receptor antagonist SQ 29548 restored dilator responses to ACh and ADP in diabetic rats toward that observed in nondiabetic rats. Indomethacin and SQ 29548 did not alter responses in nondiabetic rats. Thus diabetes mellitus impairs endothelium-dependent responses of cerebral arterioles. The mechanism of impaired responses of cerebral arterioles during diabetes mellitus appears to be related to the production of a cyclooxygenase constrictor substance and presumably related to stimulation of the TxA2-PGH2 receptor.
Muscle adaptations in trained rats with peripheral arterial insufficiency
Authors: Erney T. P. , Mathien G. M. , Terjung R. L.
Published: December 2017

The influence of training adaptations, induced within the active muscles of rats with peripheral arterial insufficiency, was assessed with an isolated hindlimb preparation. Femoral artery-stenosed rats, showing symptoms of intermittent claudication, were trained for 14-20 wk by running at 20-35 m/min up a 15% grade for up to approximately 1 h/day, 5 days/wk. Similar total hindlimb blood flows (12.6 ml/min) at a similar arterial O2 content (20.7 vol/100 ml) yielded similar blood flows (95-117 ml.min-1.100 g-1) and O2 deliveries (9-11 mumol.min-1.g-1) to the contracting muscle of sedentary (n = 10) and trained (n = 10) rats. Ten-minute periods of tetanic contractions (100 ms at 100 Hz each) at 4, 8, 13, 45, 60, and 90 tetani/min were used. Muscle force development was better maintained (P less than 0.001) by the trained group. Higher peak O2 consumption (P less than 0.01) of the trained (5.69 +/- 0.53 mumol.min-1.g-1) compared with the sedentary group (3.66 +/- 0.26 mumol.min-1.g-1) involved a greater O2 extraction, since delivery of O2 was not different between groups. Thus adaptations occurred within trained muscle to enhance performance and peak O2 consumption. Muscle citrate synthase activity, an index of mitochondrial content, was greater (P less than 0.005) in the trained group, with the low-oxidative white muscle section exhibiting the greatest change (approximately threefold sedentary). Adaptations in this section were probably realized functionally, since improvements in muscle performance were evident early in the contraction sequence.(ABSTRACT TRUNCATED AT 250 WORDS)
Myocardial metabolic effects of in vivo hydralazine treatment of streptozotocin-diabetic rats
Authors: Burns A. H. , Burns L. A. , Jurenka L. U. , Summer W. R.
Published: December 2017

We determined myocardial pumping capacity, glucose oxidation, and mechanical response to ischemia in streptozotocin-diabetic rats treated for 4 wk with or without hydralazine (0.5 mg/g of chow). Plasma triglycerides and cholesterol were decreased 73 and 50%, respectively, in the treated animals. Blood glucose levels were greater than 400 mg/100 g in both groups. Hearts were perfused in the working configuration with buffer containing 5 mM [U-14C]glucose. Starling curves were constructed by increasing left atrial filling pressure from 5 to 20 cm of water. Diabetic heart mechanical function was depressed compared with control and hydralazine treatment restored function to normal. Oxidation of [U-14C]glucose was comparably depressed in the treated and untreated diabetics. The provision of 1 mM dichloroacetate in the perfusate increased glucose oxidation in the hearts from hydralazine-treated rats, however. Twenty minutes of global ischemia resulted in 65% decrease in mechanical function in the hearts of hydralazine-treated group vs. 15% for hearts from nontreated diabetics. The data suggest that measures to normalize lipid metabolism may not normalize myocardial glucose oxidation or permit better mechanical recovery after ischemia in the diabetic myocardium.
Oxy- and carboxyhemoglobin saturation determination in frozen small vessels
Authors: Zhu N. H. , Weiss H. R.
Published: December 2017

A four-wavelength microspectrophotometric method has been developed to determine both O2 and CO saturation of hemoglobin in frozen small vessels. This method compensates for the nonspecific light loss related to the ice crystals and in addition can simultaneously measure both hemoglobin O2 and CO saturation in frozen blood. By using four wavelengths in the 540-580 nm range, it is possible to determine both O2 and CO saturations in frozen blood. This four-wavelength method demonstrated an accuracy of 6-8% within 95% confidence limits (SE of estimate = 3-4%) for both CO and O2 saturation determinations in frozen blood. The linear regression of the hemoglobin O2 saturation calibration was significant with an r2 value of 0.989. The linear regression of the CO saturation calibration was also significant with an r2 of 0.996. The repeatability of each measurement was on the order of 1-6%. This method also represents an accuracy within 5% for measurements in the frozen rabbit heart for both CO and O2 in vessels between 20 and 100 microns in diameter. It compares favorably with other previously reported methods. It shows a similar accuracy but requires fewer repeat measurements than the three-wavelength method. This method can provide accurate measurement of O2 and CO saturation in small frozen arterioles and venules of any organ.
Nonischemic myocardial damage induced by nonocclusive constriction of coronary artery in rats
Authors: Capasso J. M. , Li P. , Anversa P.
Published: December 2017

To determine whether reduction in coronary vessel diameter leads to alterations in cardiac function, coronary perfusion, and tissue integrity, the left coronary artery of rats was narrowed and ventricular hemodynamics measured at 3 and 5 days after surgery. Coronary artery narrowing averaged 62% and end-diastolic pressure was increased, whereas peak systolic pressure, positive change in pressure over time, stroke volume, and total peripheral resistance were decreased. However, this impairment of function was accompanied by a preservation of resting coronary blood flow (CBF), although a 43% decrease in maximal CBF was detected. Foci of reparative fibrosis and myocytolytic necrosis were found primarily in the endomyocardium and midmyocardium. These lesions were temporally distinct, corresponding to 5 days and 12- to 24-h-old forms of myocardial damage, respectively. The changes in maximal CBF correlated with the degree of stenosis, whereas the volume fraction, average cross-sectional area, and number of foci of reparative fibrosis lesions per unit area of myocardium correlated exclusively with end-diastolic pressure. In conclusion, reductions in luminal diameter of a major coronary artery not affecting resting coronary perfusion have a profound detrimental impact on cardiac performance and initiate immediate myocyte cell loss that is ongoing. Thus tissue and cellular damage may not be ischemic in nature but rather mediated by other mechanisms such as unbearable mechanical stress.
SA nodal parasympathectomy delineates autonomic control of heart rate power spectrum
Authors: Randall D. C. , Brown D. R. , Raisch R. M. , Yingling J. D. , Randall W. C.
Published: December 2017

The purpose of this study was to quantify the relative roles of the canine cardiac parasympathetic and sympathetic nerves in controlling the distribution of power within the heart rate (HR) power spectrum using a highly selective surgical technique to parasympathectomize the SA node. DAta were recorded in awake dogs (n = 6) before and after the selective denervation; the animals were isolated from human contact and their behavior carefully monitored during the measurements. The average amplitude in the high-frequency (approximately 0.32 Hz) peak in the HR power spectrum decreased from a predenervation control of 2.68 +/- 1.54 (mean +/- SD, arbitrary units) to 0.07 +/- 0.06 (P less than 0.05). Corresponding resting HR increased from 80 +/- 9 to 106 +/- 16 beats/min (P less than 0.05). The low-frequency peak (approximately 0.02 Hz) also decreased from a control of 2.45 +/- 1.18 to a postparasympathectomy value of 1.25 +/- 0.92 (P less than 0.05). beta-Adrenergic blockade (propranolol, 1 mg/kg) further decreased the latter peak to 0.59 +/- 0.52 (P less than 0.05). These data directly demonstrate that the high-frequency peak of the HR power spectrum 1) results from parasympathetic control of SA nodal automaticity, while 2) the low-frequency peak reflects activity in both divisions of the autonomic nervous system.
Autoregressive analysis of aortic input impedance: comparison with Fourier transform
Authors: Kubota T. , Itaya R. , Alexander J. , Todaka K. , Sugimachi M. , Sunagawa K.
Published: December 2017

We evaluated the advantages of the autoregressive (AR) model over the conventional Fourier transform in estimating aortic input impedance. In 10 anesthetized open-chest dogs, we digitized aortic pressure and flow at 200 Hz for 51.20 s under random ventricular pacing and subdivided them into five segments. We obtained aortic input impedance over the frequency range of 0.1-20 Hz both by AR model and by Fourier transform for various lengths of data, i.e., from one to four consecutive segments. For any given data length, the impedance spectrum estimated by the AR model was smoother than that obtained by the Fourier transform. To evaluate the accuracy of the estimated impedance, we predicted instantaneous aortic pressure of the fifth segment by convolving corresponding aortic flow with the impulse response of aortic input impedance. The prediction error was less with the AR model than that resulting from Fourier transform as long as the number of the segments was less than four. We conclude that the AR model provides a more accurate estimate of aortic input impedance than does the Fourier transform when data length is limited.
Endothelium reduces DNA synthesis in isolated arteries
Authors: De Mey J. G. , Dijkstra E. H. , Vrijdag M. J.
Published: December 2017

We evaluated effects of endothelium removal and of endothelium-derived vasoactive agents on DNA synthesis and contractility in the isolated arterial wall. The experiments were performed on renal artery segments that had been 1) isolated from adult rats, 2) suspended in tissue culture for 3 days in the continuous presence of fetal calf serum, and 3) exposed for the last 24 h to 5-bromo-2'-deoxyuridine. Nuclear incorporation of this thymidine analogue was visualized by immunohistochemistry and used as an index of DNA synthesis. Tissue culture did not alter relaxing responses to guanosine 3',5'-cyclic monophosphate (cGMP)-generating agents but promoted relaxing responses to adenosine 3',5'-cyclic monophosphate (cAMP)-generating agents. It stimulated DNA synthesis in the endothelium, media, and adventitia. Mechanical removal of endothelium increased intra-arterial DNA synthesis. This was most prominent in the media. In preparations with endothelium, indomethacin and methylene blue did not enhance DNA synthesis. In segments that had been denuded of endothelium, atrial natriuretic factor, forskolin, iloprost, and prostaglandin E2, but not isobutylmethylxanthine or sodium nitroprusside, significantly reduced intra-arterial DNA synthesis. These data indicate that endothelium removal promotes the mitogenic response of the arterial wall to exogenous growth factors. This cannot be attributed to inhibitory influences of endothelium-derived relaxing factor or prostaglandins released by the endothelium under basal conditions.
Mathematical model of geometry and fibrous structure of the heart
Authors: Nielsen P. M. , Le Grice I. J. , Smaill B. H. , Hunter P. J.
Published: December 2017

We developed a mathematical representation of ventricular geometry and muscle fiber organization using three-dimensional finite elements referred to a prolate spheroid coordinate system. Within elements, fields are approximated using basis functions with associated parameters defined at the element nodes. Four parameters per node are used to describe ventricular geometry. The radial coordinate is interpolated using cubic Hermite basis functions that preserve slope continuity, while the angular coordinates are interpolated linearly. Two further nodal parameters describe the orientation of myocardial fibers. The orientation of fibers within coordinate planes bounded by epicardial and endocardial surfaces is interpolated linearly, with transmural variation given by cubic Hermite basis functions. Left and right ventricular geometry and myocardial fiber orientations were characterized for a canine heart arrested in diastole and fixed at zero transmural pressure. The geometry was represented by a 24-element ensemble with 41 nodes. Nodal parameters fitted using least squares provided a realistic description of ventricular epicardial [root mean square (RMS) error less than 0.9 mm] and endocardial (RMS error less than 2.6 mm) surfaces. Measured fiber fields were also fitted (RMS error less than 17 degrees) with a 60-element, 99-node mesh obtained by subdividing the 24-element mesh. These methods provide a compact and accurate anatomic description of the ventricles suitable for use in finite element stress analysis, simulation of cardiac electrical activation, and other cardiac field modeling problems.
Left ventricular contractility and diastolic properties in anesthetized dogs after severe burns
Authors: Suzuki K. , Nishina M. , Ogino R. , Kohama A.
Published: December 2017

To clarify the mechanisms of a prompt decrease in cardiac output following burns, we studied left ventricular (LV) contractility and distensibility after full-thickness 50% total body surface area burns in anesthetized dogs during a 6-h postburn period. Contractility was assessed from the end-systolic pressure-volume relationship (ESPVR) and the stroke work-end-diastolic volume relationship (the preload recruitable stroke work relationship; PRSW). LV chamber distensibility was also assessed from the end-diastolic pressure-volume curve. The PRSW slopes in the burn group showed a significant decrease compared with those in the control group (P less than 0.05), indicating burn-impaired contractility. The ESPVR shifted significantly rightward without changes in its slope after burns (P less than 0.02). This also suggested that contractility was depressed by burns. On the other hand, there was no significant change in the indexes of chamber distensibility between the two groups. We therefore concluded that burns decreased contractility as well as preload but did not change end-diastolic distensibility during this early postburn period.
Cellular electrophysiology of neonatal and adult rabbit atrioventricular node
Authors: Hewett K. W. , Gaymes C. H. , Noh C. I. , Ross B. A. , Thompson R. P. , Buckles D. S. , Gillette P. C.
Published: December 2017

Adult and neonatal rabbit atrioventricular node (AVN) preparations were studied using transmembrane and surface electrogram recordings. Action potentials were categorized into four types, atrionodal (AN), nodal (N), “high” nodo-His (NH) (HNH), and “low” NH (LNH), according to their action potential characteristics and their location within the A-H interval. The electrophysiological parameters of the lower three regions were identical between the two age groups. Action potentials from the neonatal AN region were lower in amplitude and maximum diastolic potential than they were in the adult. The N cell action potential parameters did not differ between the two age groups, however, there did appear to be qualitative differences. AVN conduction times (A-H intervals) were the same in both age groups, as were the antegrade and retrograde refractory periods, and the Wenckebach intervals. Pacemaker activity was significantly greater in the neonates than in the adults and, in 11 of 13 neonatal preparations, originated in the AN region or higher. In 13 of 14 adult preparations, pacemaker activity resided within the AVN.
Characterization of the depressor effect of intrathecal endothelin in anesthetized rats
Authors: Han S. P. , Chen X. L. , Westfall T. C. , Knuepfer M. M.
Published: December 2017

Intrathecal administration of 1–100 pmol endothelin-1 in urethan-anesthetized rats elicited a dose-dependent decrease in arterial pressure and a modest bradycardia. The depressor response was associated with a sustained hindquarters vasodilation and a modest transient mesenteric vasoconstriction, indicating disparate effects on regional vascular resistance. In contrast, renal sympathetic nerve activity was unaffected except at the highest dose of endothelin-1 (100 pmol). The depressor effect of intrathecal endothelin is unlikely to be due to spinal ischemia produced by vasoconstriction, since a much greater dose of endothelin was needed to produce an increase in spinal vascular resistance compared with the dose necessary to produce hindquarters vasodilation and the depressor effect. Unlike intravenous administration, intrathecal endothelin-1 and endothelin-3 produced indistinguishable effects on arterial pressure, heart rate, renal sympathetic nerve activity, spinal blood flow, and spinal vascular resistance, suggesting that the spinal neuronal endothelin receptors may be less selective than those in the blood vessels. The centrally mediated depressor effect and the selective regional hemodynamic actions of intrathecal endothelin suggest a role of spinal endothelin in regulating cardiovascular function.
Effect of salt-induced hypertension on microvascular pressures in skeletal muscle of Dahl rats
Authors: Boegehold M. A.
Published: December 2017

The purpose of this study was to determine the effect of salt-induced hypertension on the microvascular pressure profile in skeletal muscle. Measurements were made in the spinotrapezius muscle of anesthetized Dahl salt-sensitive (DS) rats fed either a high- (7%) or low-normal (0.45%)-NaCl diet for 4 wk. Age-matched Dahl salt-resistant (DR) rats on high- or low-normal salt diets were also studied. The high-salt diet had no effect on either arterial or microvascular pressures in DR rats. DS rats maintained on high salt developed arterial hypertension accompanied by a pressure increase of 49% in the feed arterioles and 31% in the transverse arterioles. Hypertensive DS rats exhibited a greater pressure drop across the small arteries, arcade arterioles, and distal arterioles, indicating that each of these segments contributes to increased whole organ resistance. Pressures in the collecting and draining venules were not elevated in DS on 7% NaCl, suggesting that increased precapillary resistance in salt-induced hypertension effectively shields the skeletal muscle capillary and venular networks from high hydrostatic pressures.
Increased negativity of interstitial fluid pressure during the onset stage of inflammatory edema in rat skin
Authors: Reed R. K. , Rodt S. A.
Published: December 2017

Interstitial fluid pressure (Pif) was measured in skin of pentobarbital-anesthetized rats during anaphylaxis toward dextran and after subdermal injection of histamine by using sharpened glass capillaries (tip diam 5–7 microns) connected to a servo-controlled counterpressure system. Control Pif averaged -1.5 mmHg (SD = 1.0). After intravenous dextran Pif in the rat paw fell transiently to -3 mmHg up to 20 min and thereafter increased to +1-2 mmHg when edema had developed. To study the full magnitude of the increased negativity of Pif, circulatory arrest was induced 1 min after dextran injection. This procedure prevents accumulation of edema that will cause underestimation of Pif. In this group Pif fell to about -10 mmHg in 20 min and remained at this level throughout the observation period of 90 min. Subdermal injection of 1–10 micrograms histamine in 10 microliters saline reduced Pif to about -6 mmHg within 5 min after injection. Injection of 10 microliters saline increased Pif by +2 mmHg. Indomethacin or cyproheptadine did not alter the response in the above situations. The increased negativity in Pif of about 6–8 mmHg will add directly to normal transcapillary net filtration pressure of 0.5 mmHg and increase the latter pressure 10–20 times.
Effect of NG-monomethyl-L-arginine on arcade arterioles of rat spinotrapezius muscles
Authors: Nakamura T. , Prewitt R. L.
Published: December 2017

The effect of the specific inhibitor of nitric oxide (NO) formation NG-monomethyl-L-arginine (L-NMMA) on resting arteriolar diameter and on actions of both endothelium-dependent and -independent vasoactive substances was investigated using intravital microscopy in rats. The spinotrapezius muscle of anaesthetized normotensive rats was suspended in a Krebs-Henseleit bath containing tetrodotoxin (3 x 10(-7) M), indomethacin (2.8 x 10(-5) M), and propranolol (10(-6) M) to block sympathetic nerve conduction, prostacyclin formation, and beta-adrenergic receptors, respectively. Acetylcholine (ACh), nitroprusside (NP), norepinephrine (NE), phenylephrine (PE), and guanabenz (GB) were topically applied before and after superfusion of L-NMMA (10(-5) to 10(-4) M). Superfusion of L-NMMA reduced arteriolar diameter and caused dose-dependent increases in arteriolar tone. The onset of action of L-NMMA was nearly immediate. L-NMMA inhibited vasodilator responses to the endothelium-dependent vasodilator ACh but not to the endothelium-independent NP. NE induced dose-related vasoconstriction that was significantly potentiated by L-NMMA. These effects were partially reversed by addition of L-arginine (10(-3) M). Potentiation of vasoconstriction elicited by NE was still observed after inhibition of alpha 1-adrenoceptors with prazosin, but potentiation was abolished by the alpha 2-adrenoceptor antagonist yohimbine. L-NMMA potentiated arteriolar vasoconstriction elicited by the alpha 2-adrenergic receptor agonist GB but not by the alpha 1-adrenoceptor agonist PE. These findings with L-NMMA suggest that resting diameter of arterioles is modulated by endogenous NO biosynthesis and that endothelium-dependent vasodilators act through the formation of endogenous NO to exert their action in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)
Skeletal muscle metabolism in heart failure in rats
Authors: Arnolda L. , Brosnan J. , Rajagopalan B. , Radda G. K.
Published: December 2017

31P nuclear magnetic resonance (NMR) was used to examine the metabolism of skeletal muscle in rats 6-8 wk after myocardial infarction (MI). These in vivo measurements were supplemented by measurement of creatine, phosphocreatine (PCr), and ATP in freeze-clamped muscle using high-performance liquid chromatography (HPLC) and assays of key muscle enzymes to better define the muscle abnormality observed in heart failure. Resting PCr/(PCr + Pi) and pH were similar in MI rats and controls. Rats with MI had lower pH and PCr/(PCr + Pi) than controls during sciatic nerve stimulation at 1 and 2 Hz. These changes were more severe in rats with large (greater than or equal to 46%) infarcts, and changes in pH and PCr/(PCr + Pi) were correlated with infarct size. Free [ADP] in vivo was estimated from the NMR and HPLC measurements. [ADP] was increased in rats with large infarcts during nerve stimulation, implying a defect in oxidative metabolism. Citrate synthase, a mitochondrial enzyme, was reduced in rats with large MI. Citrate synthase levels were correlated with changes in PCr/(PCr + Pi) at 2 Hz. The NMR changes in skeletal muscle can be explained by reduced oxidative capacity of skeletal muscle, and this proposition is supported by the demonstration of reduced citrate synthase levels in skeletal muscle of rats with large infarcts.
Sustained effects of endothelin-1 on rabbit, dog, and rat pulmonary circulations
Authors: Barnard J. W. , Barman S. A. , Adkins W. K. , Longenecker G. L. , Taylor A. E.
Published: December 2017

Effects of endothelin-1 (10(-8) M) on the pulmonary vascular resistance-compliance profile were examined in isolated blood-perfused rabbit, dog, and rat lungs using occlusion techniques. Capillary permeability was assessed by filtration coefficient (Kfc). Cyclooxygenase products were assessed by radioimmunoassay. In rabbit lungs, endothelin-1 increased all resistances except large vein; ibuprofen reversed the constriction. Endothelin-1 decreased total vascular compliance (CT), which was reversed by ibuprofen. Cyclooxygenase products were unchanged by endothelin-1 or endothelin-1 plus ibuprofen. In dog lungs, large vein resistance increased after endothelin-1; ibuprofen increased large arterial resistance. Endothelin-1 decreased CT and middle compartment compliance, and endothelin-1 plus ibuprofen decreased large vessel compliance (CLV). Ibuprofen reversed the endothelin-1 increase in plasma 6-oxo-prostaglandin F1 alpha. In rat lungs, ibuprofen reversed the endothelin-1 increase in small arterial resistance. Endothelin-1 decreased CLV, and endothelin-1 plus ibuprofen returned the compliance to baseline values. Ibuprofen potentiated the endothelin-1 increase in plasma prostanoids. Endothelin-1 plus indomethacin increased vascular resistance and blocked prostaglandin production. Kfc was increased only in rat lung after endothelin-1 plus ibuprofen. In summary, endothelin-1 increased pulmonary vascular resistance, which was attenuated by prostacyclin in dogs and rats. In rabbits, the resistance increase was reversed by ibuprofen.
Polyethylene glycol-conjugated superoxide dismutase fails to blunt postischemic reactive hyperemia
Authors: Helfaer M. A. , Kirsch J. R. , Haun S. E. , Moore L. E. , Traystman R. J.
Published: December 2017

We tested the hypothesis that superoxide dismutase (SOD) conjugated with polyethylene glycol (PEG-SOD) would alter hyperemia following complete global cerebral ischemia. Thirty minutes before ischemia pentobarbital-anesthetized piglets were assigned to receive 3 ml of either PEG-SOD (10,000 U/ml; n = 10), an equivalent concentration of PEG (n = 10), or saline (n = 10) in a randomized and blinded manner. Cerebral ischemia was sustained for 10 min by cross-clamping the ascending aorta. Measurements of cerebral blood flow (radiolabeled microspheres) and oxygen consumption were made before ischemia and at 2, 4, 8, 12, and 15 min of reperfusion. Plasma SOD activity was higher in PEG-SOD-treated piglets (134 +/- 8 U/ml) than in PEG or saline-treated piglets (less than 5 U/ml). All groups and all brain regions demonstrated postischemic hyperemia. There were no differences in blood flow between groups at any time point in any region. At 2 min of reperfusion, blood flow to cerebrum rose from 31 +/- 4 to 88 +/- 9 ml.min-1.100 g-1 (saline), 44 +/- 6 to 102 +/- 17 ml.min-1.100 g-1 (PEG), and 31 +/- 3 to 83 +/- 16 ml.min-1.100 g-1 (PEG-SOD). During reperfusion cerebral oxygen consumption was not different from preischemic values in any group. In conclusion, we demonstrated that exogenously administered PEG-SOD raises serum SOD activity but does not alter the patterns of early cerebral blood flow or metabolic recovery after 10 min of complete global cerebral ischemia in piglets.
Inhibition of Ca(2+)-ATPase of vascular smooth muscle sarcoplasmic reticulum by reactive oxygen intermediates
Authors: Suzuki Y. J. , Ford G. D.
Published: December 2017

Effects of reactive oxygen intermediates generated by hypoxanthine plus xanthine oxidase on the Ca(2+)-adenosinetriphosphatase (ATPase) of sarcoplasmic reticulum from bovine aortic smooth muscle were studied. Exogenous hypoxanthine (0.1-100 microM) plus xanthine oxidase (10 mU/ml) produced an hypoxanthine concentration-dependent inhibition of the Ca(2+)-ATPase. The inhibition could be completely blocked by superoxide dismutase (100 U/ml) but not by either mannitol (20 mM) or deferoxamine (100 microM). Direct addition of hydrogen peroxide in the micromolar range did not cause significant inhibition. These results suggest that superoxide is the primary damaging species. Cysteine blocked this inhibition, suggesting possible involvement of sulfhydryl groups in the inhibition mechanism. Additionally, 1.16 +/- 0.17 mU/g wet wt of xanthine oxidase activity was detected in the postnuclear supernatant of bovine aortic smooth muscle, suggesting the existence of a possible intracellular source of superoxide. This value was calculated to be approximately 5 mU/ml by using a usual value of vascular smooth muscle cellular volume. Thus the level of endogenous xanthine oxidase in vascular smooth muscle is comparable with the level of exogenous xanthine oxidase used in the present study. These findings suggest a potential role of xanthine oxidase-generated superoxide in oxidative damage to vascular smooth muscle during a number of pathophysiological conditions.
Oxygen metabolite effects on creatine kinase and cardiac energetics after reperfusion
Authors: Banerjee A. , Grosso M. A. , Brown J. M. , Rogers K. B. , Whitman G. J.
Published: December 2017

Noninvasive 31P nuclear magnetic resonance measurements indicate that during the initial reperfusion phase myocardial tissue contents of phosphocreatine (PCr) recover rapidly, while ATP levels remain low and recover slowly. There is also a burst of H2O2 during the first 10 min of reperfusion, as indicated by the in vivo inactivation of catalase that occurs only when H2O2, and the inactivator 3-aminotriazole (AMT), are simultaneously present. Neither H2O2 production nor CK inactivation was discernable after ischemia alone. In excitable tissue the PCr and ATP pools are equilibrated by the enzyme creatine kinase (CK), but myocardial CK activity is decreased by 20% after reperfusion, though not by simple washout. Extrapolating from the well-known air sensitivity of CK, we find that limited exposure in vitro to small concentrations of H2O2 can markedly diminish CK activity. We postulate that failure of certain CK isoenzymes at energy-using termini may decouple the relative rates of PCr production and ATP regeneration and hence cause elevated PCr-to-ATP ratios. The assumptions of 1) CK equilibrium during the reperfusion period to calculate free ADP levels and 2) cardiac recovery deduced from the elevation of PCr levels may require reexamination.
Turbulent pressure fluctuations on surface of model vascular stenoses
Authors: Loree H. M. , Kamm R. D. , Atkinson C. M. , Lee R. T.
Published: December 2017

Turbulence frequently develops when blood passes through a stenosis. To study the hypothesis that turbulence near a plaque surface can cause pressure fluctuations that may promote plaque rupture, models of intravascular stenoses were studied. Experimental conditions simulated peak flow in the coronary and carotid arteries through a stenosis of 80 or 90% diameter reduction and into a region where the plaque had widened distally to a 50-75% stenosis. For symmetric stenoses at carotid artery flow rates, peak pressure fluctuations were observed 1-1.5 upstream diameters distal to the stenosis, but there were no significant turbulent pressure fluctuations at coronary artery flow rates. Stenosis asymmetry strongly increased the intensity of turbulent pressure fluctuations at flows simulating carotid flow and resulted in significant pressure fluctuations for coronary flow conditions. Increasing stenosis severity from 80 to 90% increased the root mean square pressure fluctuations 3.6-fold. These studies predict peak to peak pressure fluctuations of 15 mmHg in a 90% asymmetric coronary stenosis; it is possible that turbulence may play a role in acute damage of atherosclerotic plaques, particularly in asymmetric stenoses.
Characterization of AT2 angiotensin II receptors in rat anterior cerebral arteries
Authors: Tsutsumi K. , Saavedra J. M.
Published: December 2017

Quantitative autoradiography using the agonist 125I-Sar1-angiotensin II was used to localize and characterize angiotensin II (AT) receptors in the anterior cerebral artery of the male rat. This artery showed a moderately high number of AT receptors, localized throughout the arterial wall. The number of receptors was higher (125 +/- 7 fmol/mg protein) in arteries from young 2-wk-old rats compared with those in adult 8-wk-old rats (43 +/- 2 fmol/mg protein). In the anterior cerebral artery, AT binding was insensitive to displacement with the selective AT1 antagonist DuP 753 but was readily displaced by the selective AT2 antagonist CGP-42112 A (concentration eliciting 50% of maximum inhibition: 6 +/- 1 x 10(-10) M). This indicated that the AT receptors in the cerebral artery were of the AT2 subtype. Our observations suggest that AT may exert its effects on cerebral circulation by stimulation of AT2 receptors and that these receptors may play a role during cerebrovascular development.
Glibenclamide attenuates adenosine-induced bradycardia and coronary vasodilatation
Authors: Belloni F. L. , Hintze T. H.
Published: December 2017

The effects of the ATP-sensitive K(+)-channel blocker glibenclamide on the cardiovascular responses to adenosine in dogs were determined. Adenosine (0.01-20 mumol/kg iv) caused coronary vasodilatation, arterial hypotension, and bradycardia in dogs with either combined beta-adrenergic and muscarinic receptor blockade or with bilateral cervical vagotomy plus beta-adrenergic receptor blockade. The 50% effective dose for adenosine-induced coronary dilatation was increased from 0.13 +/- 0.04 mumol/kg in the control state to 1.1 +/- 0.5 mumol/kg after 2 mg/kg of glibenclamide (P less than 0.001). Adenosine at 5 mumol/kg reduced heart rate by 19 +/- 5% from a baseline of 158 +/- 6 beats/min in five anesthetized dogs. After glibenclamide (10 mg/kg), this dose of adenosine failed to cause a significant change in heart rate. The arterial hypotensive effects of adenosine were also attenuated by glibenclamide. Thus glibenclamide inhibited adenosine-induced bradycardia, hypotension, and coronary dilatation. On the other hand, glibenclamide did not affect the reductions in heart rate caused by vagus nerve stimulation. The mechanism of this adenosine antagonism is not known but, in the case of bradycardia, it does not appear to involve any of the steps shared in common by both adenosine-induced and vagal responses of the sinoatrial node.
Analysis of lymphatic protein flux data. V. Unique PS products and sigma dS at low lymph flows
Authors: Reed R. K. , Townsley M. I. , Korthuis R. J. , Taylor A. E.
Published: December 2017

The selectivity of the capillary membrane to protein (osmotic reflection coefficient, sigma d) can be measured at high transcapillary volume flow when the capillary membrane can be considered as a true sieve. However, the diffusive capacity of the membrane (permeability-surface area product, PS) for macromolecules has not been directly measured, only estimated by assuming that transcapillary volume flow was zero. Based on unique properties of the Peclet number, a parameter that describes the ratio of solute convective flux relative to diffusive capacity, we have developed three new techniques using lymph protein fluxes to estimate a unique PS product that is independent of transcapillary fluid flux. Two of these techniques require a measure of sigma d when the ratio of protein concentration in lymph relative to plasma is equal to (1- sigma d), which occurs at high capillary filtration rates. However, the third method allows both sigma d and the PS product to be determined at relatively low lymph flow rates, eliminating the need for high capillary pressures to determine sigma d. For each protein, these techniques yield an estimate of PS and sigma d for the total membrane. However, by analysis of several different sized proteins and estimation of small- and large-pore volume flows, sigma d and PS can be determined separately for the small- and large-pore pathways. These techniques for estimating sigma d and PS were evaluated by modeling the total solute flux of albumin and immunoglobulins G and M in a heteroporous membrane.
Effect of H+ on ATP-regulated K+ channels in feline ventricular myocytes
Authors: Cuevas J. , Bassett A. L. , Cameron J. S. , Furukawa T. , Myerburg R. J. , Kimura S.
Published: December 2017

Using patch-clamp techniques, we examined the effects of pH on properties of ATP-regulated K+ channels in single myocytes isolated from cat left ventricles. ATP-K+ channels of inside-out patches were bilaterally exposed to 140 mM K+ solutions (22 degrees C). In the absence of ATP and Mg2+, the channels had a linear current-voltage relationship during hyperpolarizing pulses (20-100 mV negative to the reversal potential) at both intracellular pH (pHi) 7.4 and 6.5, but the slope conductance was 66 +/- 2 pS at pHi 7.4 and 46 +/- 2 pS at pHi 6.5. Lowering pHi from 7.4 to 6.5 increased the mean open time (from 15.9 +/- 4.6 to 35.9 +/- 7.9 ms, P less than 0.01) but decreased the open-state probability measured at 50 mV positive to the reversal potential (from 0.35 +/- 0.04 to 0.16 +/- 0.04, P less than 0.01). However, in the presence of both 0.2 mM ATP and 1 mM MgCl2, lowering pHi from 7.4 to 6.5 increased the mean open time (from 5.0 +/- 2.6 to 17.9 +/- 5.9 ms, P less than 0.01) and the open-state probability (from 0.025 +/- 0.010 to 0.098 +/- 0.024, P less than 0.01). These data indicate that increases in intracellular H+ concentration modulate cardiac ATP-K+ channel properties. Ischemia-associated decreases in pHi may enhance the opening of cardiac ATP-regulated K+ channels and resultant action potential shortening.
Reperfusion-induced contracture develops with a decreasing [Ca2+]i in single heart cells
Authors: Koyama T. , Temma K. , Akera T.
Published: December 2017

The causal relationship between intracellular Ca2+ overloading and reperfusion-induced contracture was examined from changes in intracellular Ca2+ concentration ([Ca2+]i) at rest, changes in the magnitude and time course of intracellular Ca2+ transients, and the development of contracture. Single myocytes isolated from guinea pig hearts were subjected to the conditions mimicking ischemia and reperfusion. Ischemic condition was produced by superfusing myocytes with hypoxic substrate-free solutions containing elevated concentrations of K+, H+, and lactate as described by Ferrier et al. (Circ. Res. 56: 184-194, 1985). Changes in [Ca2+]i were estimated using fura-2 as the Ca2+ indicator. Under these conditions, twitch contractions were suppressed during simulated ischemia associated with an early and gradual rise of [Ca2+]i. The development of contracture, however, was not observed. Upon “reperfusion” of myocytes that had been subjected to 20 min of the above “ischemic” condition, the elevated [Ca2+]i declined rapidly. With the recovery of twitch contractions, contracture developed despite a substantial decrease in [Ca2+]i. These results indicate that reperfusion-induced contracture is not associated with a concomitant increase in [Ca2+]i in isolated myocytes.
Dominance of colloid osmotic pressure in renal excretion after isotonic volume expansion
Authors: Cowley A. W. , Skelton M. M.
Published: December 2017

Studies were carried out in unanesthetized dogs to determine the relative importance of neural, endocrine, and colloid osmotic pressure (COP) in the diuretic and natriuretic responses associated with volume expansion. Renal excretory responses to 30-min intravenous infusions of isotonic saline (400 ml) or whole blood (100 ml) were compared while various controllers of sodium and water excretion were either eliminated or held constant. Dogs were studied in the normal state; with plasma arginine vasopressin (AVP) fixed by intravenous infusion; with bilateral renal denervation and plasma AVP fixed; renal denervated with plasma AVP, angiotensin II, aldosterone, atrial natriuretic factor fixed; and renal denervated with these same hormones fixed and with renal arterial pressure servo-controlled at a constant level. Normal uncontrolled dogs increased sodium and water excretion nearly fourfold by the end of the saline load and excreted 85% of the load within 5 h. Urine excretion was minimally affected when the various neural and endocrine controllers were fixed or eliminated. There were no changes of mean arterial pressure with the saline volume loads, but COP fell 2.5 mmHg. Equivalent expansion of the blood volume (100 ml) with whole blood in which COP was unchanged resulted in nearly no increase of urine excretion in renal-denervated dogs with plasma hormones fixed and renal perfusion pressure held constant. We conclude that the rapid diuresis and natriuresis following isotonic volume expansion is predominantly a result of plasma protein dilution and a reduction of COP.
Neutrophils from chronic granulomatous disease fail to increase endothelial permeability
Authors: Kaslovsky R. A. , Gibbs L. , Malik A. B.
Published: December 2017

Studies of neutrophil-dependent endothelial injury were made using normal neutrophils (nl-PMN, i.e., normal polymorphonuclear neutrophils) and PMN obtained from a patient with X-linked chronic granulomatous disease (CGD-PMN). Layering of nl-PMN on bovine pulmonary microvessel endothelial monolayers (ratio 10:1) followed by challenge with phorbol 12-myristate 13-acetate (PMA; 5 x 10(-9) M) resulted in a 190% increase in 125I-labeled albumin permeability across the monolayers. Pretreatment of endothelial monolayers with tumor necrosis factor-alpha (TNF-alpha; 200 or 1,000 U/ml) further enhanced the increase in permeability after stimulation of nl-PMN with PMA. In contrast, challenge of CGD-PMN layered on endothelial cells with PMA did not increase permeability, and the effect was not enhanced by pretreating the endothelial cells with TNF-alpha. Nl-PMN, but not CGD-PMN, generated superoxide anion on stimulation with PMA (42.5 +/- 0.7 vs. 6.5 +/- 0.6 nM.10(6) PMN-1.h-1). PMA also induced degranulation of nl-PMN as measured by release of elastase (2.32 +/- 0.12 micrograms/10(6) PMN) and myeloperoxidase (173.8 +/- 1.9 U/10(6) PMN) into the medium, whereas release by CGD-PMN was markedly reduced (elastase release of 0.88 +/- 0.04 microgram/10(6) PMN and myeloperoxidase release of 82.6 +/- 19.4 U/10(6) PMN). The adherence response of nl-PMN and CGD-PMN to the endothelial cells after PMA stimulation was similar (79.5 +/- 11.8% nl-PMN and 64.0 +/- 1.9% CGD-PMN). Therefore, the PMN respiratory burst, with the resultant generation of oxidants and PMN-derived proteases, is required to increase endothelial permeability even in the face of increased endothelial adhesivity.