bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of responses of neonatal sinus and AV nodes to critically timed, brief vagal stimuli
Authors: Yamasaki S. , Stolfi A. , Pickoff A. S.
Published: December 2017

We studied the responses of sinus cycle length and atrioventricular (AV) nodal conduction to brief, critically timed vagal stimuli in 25 neonatal (9.6 +/- 3.1 days) canines. Vagal stimuli were delivered to the right or left decentralized cervical vagosympathetic trunk as either a single, brief stimulus train or a repetitive, phase-coupled train with both stimulation paradigms programmed to scan the entire cardiac cycle. The effects of brief vagal stimuli on cardiac cycle length were measured while the heart was beating spontaneously, and the vagal effects on AV nodal conduction were measured while the cycle length was held constant by atrial pacing at 300 ms. Neither changes in sinus cycle length nor AV nodal conduction demonstrated classical phase dependency, i.e., a gradual increase in the magnitude of the vagal response as stimuli are delivered progressively later in the cardiac cycle until the latency period (that point in the cardiac cycle at which vagal stimulation no longer affects the next cardiac cycle) is reached. Phase-response curves (PRCs) to single and repetitive stimuli typically exhibited either a flat response or a small decrease in magnitude as the latency period of the PRC was approached. Thus the neonatal sinus and AV node PRCs exhibit a different configuration than that reported in the adult.
Effects of chronic dobutamine on cardiac mechanics and biochemistry after myocardial infarction in rats
Authors: Buttrick P. , Perla C. , Malhotra A. , Geenen D. , Lahorra M. , Scheuer J.
Published: December 2017

After myocardial infarction in rats, muscle performance in the remaining hypertrophied myocardium deteriorates and is associated with a decrease in myosin adenosinetriphosphatase (ATPase) activity and a shift to the V3 myosin heavy-chain isoform. We have previously shown in another model of hypertrophy, secondary to renovascular hypertension, that chronic intermittent adrenergic stimulation with dobutamine (Db) can prevent this biochemical adaptation. The present study was undertaken to assess the effects of chronic Db treatment on cardiac mass, function, metabolism, and myosin biochemistry in animals subjected to chronic myocardial infarction. Four groups of rats were studied: controls, animals treated with Db (2 mg/kg 2X daily for 4 wk), animals subjected to myocardial infarction and killed after 4 wk (MI), and MI animals concurrently treated with Db for 4 wk (MI-Db). The two MI groups were subdivided into those with and without congestive heart failure (CHF). Heart weight was increased by 13% with Db, unchanged in the infarct groups without CHF, and increased by 9 and 22% in the infarct groups with CHF. Db did not have any additional effect on heart weight in these later groups. Infarct weight was greatest in the animals with CHF, and viable myocardium was equivalent in all infarct groups suggesting that CHF was associated with a greater degree of hypertrophy. Ventricular performance, as assessed in an isovolumic heart apparatus, was markedly depressed in both infarct groups with CHF and was not affected by Db. Db increased myosin ATPase activity in control and infarcted animals both with and without congestive heart failure. Myosin oxygen consumption and lactate production were not adversely affected by Db.
Intracellular PO2 in individual cardiac myocytes in dogs, cats, rabbits, ferrets, and rats
Authors: Gayeski T. E. , Honig C. R.
Published: December 2017

Myoglobin (Mb) saturation in individual subepicardial myocytes was determined by cryospectroscopy in dogs, cats, ferrets, rabbits, and rats. Mb saturation within 800 microns of the epicardium is not affected by quick freezing or absorption of light by cytochromes. The PO2 in equilibrium with Mb (PMbO2) was calculated from the Mb oxydissociation curve. The minimum PMbO2 found among the 1,000 cells examined was 2.5 Torr, at least five times the critical PO2 for cytochrome turnover in myocardium. The maximum PMbO2 found was about one-half that in subepicardial venules, suggesting a large change in PO2 between capillaries and the cytosol. PMbO2 was the same in right and left ventricles and was unchanged by moderate hemodynamic stress. Median PMbO2 was remarkably uniform among species (range, 4.3-7.0 Torr in 20 animals), even though left ventricular work per minute varied approximately 200-fold, heart rate about fivefold, and arterial O2 content about twofold. Relatively uniform Mb saturation below venous PO2 should accelerate release of O2 from capillaries, promote Mb-facilitated O2 diffusion, and minimize diffusive O2 shunting.
Capillary spatial pattern and muscle fiber geometry in three hamster striated muscles
Authors: Bennett R. A. , Pittman R. N. , Sullivan S. M.
Published: December 2017

Since most oxygen exchange in muscle is thought to occur by diffusion across the walls of capillaries, it is important to determine the spatial relationship between capillaries and muscle fibers. We have extended the work of Kayar et al. (Microvasc. Res 24: 326-341, 1982) to include other statistical tests that allow one to make stronger statements regarding the spatial pattern. Data for hamsters were obtained from two sartorius, three retractor, and five soleus muscle sections. Distances between all pairs of capillaries, distances between a capillary and its first nearest neighbor for all capillaries, and distances between random tissue sample points and the closest capillary were used to test the spatial arrangement of capillaries. The null hypothesis tested of complete spatial randomness of capillary locations was rejected in favor of a regular alternative in one each of the sartorius and retractor fields and in all five soleus fields. We formulated a geometric model, composed of a space-filling array of identical hexagonal muscle fibers with capillaries placed randomly at the juncture of three fibers or between two fibers, according to the observed relative probability of those occurrences. The model simulations of muscle fibers and capillaries were then analyzed by the same statistical tests used on the histological sections. The findings were similar in both cases, providing confidence that the assumptions of the model were sufficient approximations. The results of this study provide a basis for the placement of capillaries around muscle fibers in mathematical models of oxygen transport in capillary networks.
Sensitivity of myocardial fluorodeoxyglucose lumped constant to glucose and insulin
Authors: Ng C. K. , Holden J. E. , DeGrado T. R. , Raffel D. M. , Kornguth M. L. , Gatley S. J.
Published: December 2017

The lumped constant (LC) that relates the steady-state phosphorylation rate of 2-[18F]-fluoro-2-deoxy-D-glucose (2-FDG) to that of glucose was determined in an isolated working rat heart model by direct assay of phosphorylation product formation. Five conditions were tested: 5 and 30 mM glucose without insulin, and 2, 3.5, and 5 mM glucose + 10 mU/ml insulin, all at high external work load. Hearts were continuously perfused with 2-FDG and tritiated glucose without recirculation. The steady-state production of tritiated water was used to monitor the glucose phosphorylation rate. Perfused hearts were freeze-clamped and extracted in perchloric acid, and 2-FDG-6-phosphate was separated from 2-FDG with a formate column. The accumulation of 2-FDG phosphorylation products in tissue was also determined from the slopes of the total tissue radioactivity time courses measured by external gamma-ray detection. Without insulin, the LC value decreased 18% as perfusate glucose concentration was increased sixfold (0.94 +/- 0.06 at 5 mM vs. 0.77 +/- 0.17 at 30 mM). With insulin, the LC rose from 0.33 +/- 0.03 at 5 mM to 1.19 +/- 0.05 at 2 mM glucose concentration. The trends can be interpreted in terms of the concept of control strength; the LC value rises as glycolysis becomes rate limited by transport into cells. This potential variability of the LC must be addressed in the quantitative interpretation of myocardial deoxyglucose studies.
Acute, reversible tricuspid insufficiency: creation in canine model
Authors: Kinney T. E. , Olinger G. N. , Sagar K. B. , Boerboom L. E.
Published: December 2017

Relatively few methods have been described for the creation of valvular insufficiency in an animal model. Those presented involve limitations such as permanent destruction of the valves or lack of control over the degree of regurgitation produced. We describe a method of acute reversible tricuspid insufficiency that can be easily created and controlled in anesthetized dogs. The model employs a wire spiral that is advanced through the atrioventricular canal from the right atrium. The spiral causes regurgitation by preventing complete apposition of the valve leaflets while permitting retrograde flow to occur through the spiral lumen. The degree of regurgitation can be controlled by the use of spirals of different sizes. Creation of tricuspid insufficiency is demonstrated by the onset of right atrial pressure V waves, a "ballooning" of the right atrium during ventricular systole, palpation of an atrial thrill, or by color Doppler echocardiography. In 14 dogs, right atrial pressure increased from a control value of 9 +/- 3 (mean +/- SD) mmHg to 10 +/- 3 and 12 +/- 3 mmHg, respectively, with spirals of 1.5 and 2.2 cm in diameter (both P less than 0.05). With the 2.2-cm spiral, aortic blood pressure decreased from a control value of 104 +/- 20 to 83 +/- 17 mmHg (P less than 0.05), and cardiac output decreased from 73 +/- 26 to 59 +/- 19 ml.min-1.kg-1 (P less than 0.05). This model is reversible, allows repeated trials of various grades of regurgitation, does not require ventriculotomy, and is relatively nonarrhythmogenic.
Transmural gradient of adenosine in canine heart during functional hyperemia
Authors: Deussen A. , Walter C. , Borst M. , Schrader J.
Published: December 2017

Effects of beta-adrenergic stimulation and atrial pacing on the transmural gradient of intracellular free adenosine were assessed in dog hearts in vivo by measurement of the accumulation of S-adenosylhomocysteine (SAH) in the presence of homocysteine (1.6 mg.kg-1.min-1 iv). Isoproterenol (0.3-0.5 micrograms.kg-1.min-1 iv for 30 min) consistently enhanced left ventricular dP/dtmax (86%), heart rate (38%), and myocardial oxygen consumption (MVO2; 62%) within 3 min while formation and release of adenosine transiently increased. Diastolic aortic pressure fell from 107 +/- 12 to 58 +/- 5 mmHg, and the transmural gradient of SAH was 1.6-, 2.5-, and 4.4-fold increased in subepi-, mid- myo-, and subendocardial layers, respectively. Adenosine formation was inversely related to diastolic aortic pressure. Maintaining aortic pressure greater than 65 mmHg only slightly enhanced venoarterial difference of adenosine despite a greater augmentation of MVO2. Pacing the heart at 209 +/- 4 beats/min enhanced MVO2 by 42% and increased subepi-, midmyo-, and subendocardial levels of SAH by 1.5-, 3.3- and 1.9-fold, respectively. These results demonstrate that in the in situ heart 1) beta-adrenergic stimulation and pacing cause an inhomogeneous transmural increase in free intracellular adenosine mainly affecting the subendocardial and midmyocardial layers; 2) diastolic aortic pressure as the driving force of coronary perfusion is of critical importance for cardiac adenosine formation; and 3) the kinetics of oxygen consumption and adenosine formation are clearly dissociated during beta-stimulation.
Effect of epinephrine or cAMP on cAMP-bound protein kinase holoenzymes in rat heart
Authors: Jiang H. , Corbin J. D.
Published: December 2017

Nonperfused or epinephrine-perfused rat hearts were used to examine the relative amounts of adenosine 3',5'-cyclic monophosphate (cAMP)-free and cAMP-bound holoenzymes of type II cAMP-dependent protein kinase (cAK). Crude tissue extracts of nonperfused hearts were chromatographed in the absence or presence of [3H]cAMP using DEAE-high-performance liquid chromatography. A partially resolved cAMP-free peak of cAK eluted at 0.17 M NaCl, and an asymmetric peak containing bound [3H]cAMP eluted at a slightly higher NaCl concentration. The first peak contained a tetrameric holoenzyme [2 regulatory (R) subunits and 2 catalytic (C) subunits]. From analysis of R-to-C ratios, the [3H]cAMP-bound peak contained a mixture of tetrameric and trimeric (R2C) forms. Both cAMP-free and cAMP-bound holoenzyme forms were virtually inactive without added cAMP under the conditions used. [3H]cAMP dissociation rate studies revealed that the bound cAMP in the peak fraction was equally distributed in the two different binding sites of the enzyme. Compared with the cAMP-free form, the cAMP-bound enzyme in the peak fraction exhibited enhanced binding in nonequilibrium [3H]cAMP binding assays. The cAMP-bound holoenzymes were estimated to represent at least 64% of the total type II cAK in control extracts, and the cAMP-free form was largely converted to the cAMP-bound forms by perfusing hearts with epinephrine.
Removal of sialic acid alters both T- and L-type calcium currents in cardiac myocytes
Authors: Fermini B. , Nathan R. D.
Published: December 2017

The whole cell configuration of the patch-clamp technique was used to test the hypothesis that the presence of sialic acid residues influences both T- and L-type Ca2+ currents (ICa,T and ICa,L) in cultured pacemaker cells isolated from the rabbit sinoatrial node. Removal of these anionic sugar moieties by neuraminidase (1.0 U/ml for 5-20 min) increased ICa,T in five of nine cells (by a factor of 2.2-5.1) and ICa,L in three of six cells (by a factor of 1.2-1.6). In cells that did not exhibit such an increase, the enzyme reduced ICa,T but had no significant effect on ICa,L. In cells that exhibited an increase in ICa,T, exposure to neuraminidase also shifted the activation curve to more negative potentials and increased the slope of the inactivation curve. The enzyme did not influence the gating of ICa,L or the rates of inactivation of either ICa,T or ICa,L. The enhancement of ICa,T and ICa,L could not be mimicked by including neuraminidase in the patch pipette or by adding a contaminant of the enzyme preparation, phospholipase C, to the bath. When external Ca2+ was replaced by Ba2+, neither ICa,T nor ICa,L was increased significantly by neuraminidase. It is proposed that by removing sialic acid residues neuraminidase might directly alter the gating of T-type Ca2+ channels. On the other hand, the increased amplitudes of ICa,T and ICa,L might be due to a rise in intracellular Ca2+.
Role of phospholipases A2 and C in myocardial ischemic reperfusion injury
Authors: Prasad M. R. , Popescu L. M. , Moraru I. I. , Liu X. K. , Maity S. , Engelman R. M. , Das D. K.
Published: December 2017

We investigated the role of phospholipase A2 (PLA2) and phospholipase C (PLC) in myocardial phosholipid degradation and cellular injury during reperfusion of ischemic myocardium. For this purpose, isolated rat hearts were perfused with isotopic arachidonic acid to label its membrane phospholipids. Hearts preperfused with antiphospholipase A2 (anti-PLA2) retained a significantly higher amount of radiolabel in phosphatidylcholine and phosphatidylinositol and a corresponding lower amount of radiolabel in lysophosphatidylcholine and nonesterified fatty acids (P less than 0.05) after 30 min of reperfusion following 30 min of normothermic global ischemia compared with hearts preperfused with nonimmune immunoglobulin G. In similar experiments, antiphospholipase C (anti-PLC)-treated hearts were associated with significantly (P less than 0.05) higher radiolabel in all phospholipids and lower radiolabel in diacyglycerol compared with nonimmune immunoglobulin G-treated hearts. Measurement of phospholipase activity in subcellular organelles of these hearts showed decreased PLA2 activity in cytosol, mitochondria, and microsomes of anti-PLA2-treated hearts and decreased PLC activity of microsomes in anti-PLC-treated hearts. Furthermore, both the antiphospholipases attenuated the release of creatine kinase and lactate dehydrogenase into perfusate and increased contractility as well as coronary flow in the reperfused hearts. Results of this study suggest that both PLA2 and PLC are involved in the degradation of phospholipids and cellular injury that occur during reperfusion of ischemic myocardium.
Stimulation of area postrema decreases blood flow to choroid plexus
Authors: Williams J. L. , Thebert M. M. , Schalk K. A. , Heistad D. D.
Published: December 2017

The goal of this study was to examine effects of stimulation of the area postrema on blood flow to choroid plexus and brain. In chloralose-anesthetized dogs, the area postrema was stimulated electrically, and arterial pressure and blood gases were maintained at control levels. We measured blood flow to brain and choroid plexus of the fourth and lateral ventricles with microspheres. Stimulation of the area postrema at 10 +/- 2 microA (means +/- SE), which was the threshold for changes in arterial pressure and heart rate, decreased blood flow to choroid plexus of the fourth and lateral ventricles by 41 +/- 11 and 51 +/- 6%, respectively (from 349 +/- 38 and 503 +/- 46 ml.min-1.100 g-1, respectively). Stimulation at high amplitudes (67 +/- 5 microA) produced only slightly greater decreases in blood flow to choroid plexus. In contrast, cerebral blood flow did not change during stimulation of the area postrema. After blockade of autonomic ganglia with intravenous chlorisondamine, stimulation of the area postrema had minimal effects on blood flow to choroid plexus. The results indicate that stimulation of the area postrema decreases blood flow to choroid plexus, probably by an autonomic mechanism. We speculate that the area postrema may play a role in regulation of volume in the central nervous system by modulating production of cerebrospinal fluid.
Myocardial adrenergic changes at two stages of heart failure due to adriamycin treatment in rats
Authors: Tong J. , Ganguly P. K. , Singal P. K.
Published: December 2017

Changes in myocardial norepinephrine (NE) levels, turnover, uptake, and release in rats were examined at two stages of cardiac dysfunction induced by adriamycin (ADR) given intraperitoneally in six equal doses over a period of 2 wk for a cumulative dose of 15 mg/kg. At 3 wk posttreatment, ADR-treated animals showed no changes in left ventricular systolic pressure (LVSP), aortic systolic pressure (ASP), and aortic diastolic pressure (ADP) but left ventricular end-diastolic pressure (LVEDP) was significantly higher. At 6 wk posttreatment, LVSP, ASP, and ADP were significantly lower and LVEDP remained elevated. Animals in both ADR-treated groups showed signs of congestive heart failure as indicated by ascites, congestive liver, and elevated LVEDP. Structural changes typical of ADR cardiomyopathy were more pronounced in the 6-wk group. In vivo hemodynamic as well as in vitro muscle function response to different concentrations of epinephrine was depressed in its duration as well as extent in both 3- and 6-wk ADR-treated groups. Myocardial NE levels were increased in the 3-wk group but were depressed in the 6-wk group. NE turnover was faster in both 3- and 6-wk ADR groups, uptake was increased only in the 6-wk group, and release was unchanged. These data show increased cardiac sympathetic tone at both stages of ADR-induced congestive heart failure.
Calcium is released from the junctional sarcoplasmic reticulum during cardiac muscle contraction
Authors: Moravec C. S. , Bond M.
Published: December 2017

We have used electron-probe microanalysis (EPMA) to address the question of Ca2+ release by junctional sarcoplasmic reticulum (JSR) as well as Ca2+ regulation by mitochondria (MT) during cardiac muscle contraction. Hamster papillary muscles were rapidly frozen during relaxation or at the peak rate of tension rise (+dT/dt). Total Ca2+ content was measured by EPMA in the JSR, within a MT, over the A band, and in the whole cell, in nine cells per animal (five animals per group). JSR Ca2+ content was found to be significantly lower in muscles frozen at the peak of contraction [7.3 +/- 1.3 (mean +/- SE) mmol Ca2+/kg dry wt] than in those frozen during relaxation (12.5 +/- 1.9 mmol Ca2+/kg dry wt; P less than 0.01), suggesting that Ca2+ is released from this storage site during cardiac muscle contraction. In contrast, MT Ca2+ content did not change significantly during contraction (0.4 +/- 0.1 mmol/kg dry wt) compared with relaxation (0.1 +/- 0.2 mmol/kg dry wt). A third group of muscles was frozen during relaxation after pretreatment with 10(-7) M ryanodine. Ca2+ content of the JSR was significantly decreased (P less than 0.01) in this group of muscles, (6.4 +/- 1.8 mmol/kg dry wt) compared with those frozen during relaxation in the absence of the drug. This suggests that the intracellular storage site with a decreased Ca2+ content in muscles frozen at the peak of contraction is the ryanodine-releasable store. These results provide the first direct measurement of the Ca2+ content of both JSR and MT during a normal cardiac muscle contraction and demonstrate that Ca2+ is released from the JSR during muscle contraction.
Endothelium-dependent hyperpolarization elicited by adenine compounds in rabbit carotid artery
Authors: Chen G. , Suzuki H.
Published: December 2017

Electrical responses of the membrane of intimal and adventitial smooth muscle cells of the rabbit carotid artery to ATP, ADP, AMP, and adenosine were recorded. In intimal cells, these compounds hyperpolarized the membrane. Mechanical removal of the endothelium altered the responses to ATP and ADP to one of a transient depolarization, with no alteration of the response to AMP and adenosine. In the adventitial cells, ATP and ADP produced a transient depolarization, whereas AMP and adenosine produced a sustained hyperpolarization, irrespective of the presence or absence of the endothelium. In tissues with an intact endothelium, 5'-adenylylimidodiphosphate tetralithium salt and alpha,beta-methylene ATP (mATP) transiently depolarized the membrane in these smooth muscles. In case of stabilization with mATP, only hyperpolarization was generated by ATP, in an endothelium-dependent manner. Our interpretation of these observations is that 1) ATP and ADP depolarize smooth muscle membrane by a direct action and hyperpolarize the membrane indirectly through the release of endothelium-derived hyperpolarizing factor, 2) AMP and adenosine hyperpolarize the membrane, independently of the endothelium, and 3) ATP receptors present on the endothelial cell membrane differ from those on smooth muscle membrane.
Cardiovascular reflexes evoked by histamine stimulation of the stomach
Authors: Stebbins C. L. , Theodossy S. J. , Longhurst J. C.
Published: December 2017

This study examined the potential for histamine to cause cardiovascular reflexes when applied to the serosal or mucosal surface of the stomach. Thus, in chloralose-anesthetized cats, histamine was applied to the serosal surface of the stomach in concentrations ranging from 0.5 to 1,000 micrograms/ml. This resulted in graded increases in mean arterial pressure (MAP), maximal left ventricular pressure over time (dP/dt), and heart rate ranging from 9 +/- 4 to 30 +/- 3 mmHg, 450 +/- 103 to 1,710 +/- 610 mmHg/s, and 2 +/- 1 to 13 +/- 4 beats/min, respectively. Histamine stimulation of the gastric serosa evoked a greater pressor response than that observed when the same concentration of histamine (100 micrograms/ml) was applied to the gastric mucosa (43 +/- 7 vs. 13 +/- 3 mmHg, respectively). In six cats, celiac ganglionectomy abolished the previously observed cardiovascular response to histamine stimulation of the serosal surface of the stomach. When the gastric serosa was treated with the H1-receptor antagonist diphenhydramine (1 mg/ml) (n = 5), the cardiovascular response to histamine was abolished. In five other cats, administration of the H2-antagonist ranitidine (1 mg/ml) had no effect on the histamine-induced responses. When indomethacin (2-5 mg/ml), was applied to the serosal surface of the stomach (n = 6), histamine-induced increases in MAP and dP/dt were attenuated. However, application of PGE2 (1 microgram/ml) restored these two responses. These results suggest that histamine stimulates H1-receptors in the gastric wall to cause reflex cardiovascular responses that are dependent, in part, on the local production of prostaglandins.
Postexcitatory depression of baroreceptors in dogs with experimental heart failure
Authors: Wang W. , Chen J. S. , Zucker I. H.
Published: December 2017

The phenomenon of postexcitatory depression (PED) of baroreceptors is related to augmentation of Na(+)- K(+) -adenosinetriphosphatase (ATPase) activity. To provide additional evidence to support the hypothesis that dogs with chronic heart failure have augmented Na(+) -K(+) -ATPase activity in baroreceptor endings, the present study was undertaken to compare the duration of the PED of carotid sinus baroreceptors from normal and heart failure dogs. The effect of perfusion of the carotid sinus with a cardiac glycoside was also investigated. Eight normal and six dogs with experimental heart failure induced by ventricular pacing (250 beats/min for approximately 5 wk) were used in this study. Dogs were anesthetized, and the carotid sinus was isolated and perfused. Single baroreceptor units from the carotid sinus nerve were recorded, and the duration of the PED was measured. The relationship between the magnitude of the pressure steps and the duration of PED was determined. Duration of PED was significantly prolonged in the heart failure group at each pressure step (range from 2.7 to 9.0 s compared with 0.5 to 2.9 s in normal dogs). For the relationship between the duration of the pressure step and duration of PED, the heart failure dogs exhibited a markedly longer duration of PED than the normal dogs (range from 2.3 to 12.4 s compared with 0.5 to 5.3 s in normal dogs). Perfusion of the carotid sinus with very low doses of ouabain decreased the duration of PED in the heart failure dogs; however, there was no such effect in the normal dogs. These data are consistent with the view that baroreceptor membranes have increased Na(+) -K(+) -ATPase activity in heart failure(ABSTRACT TRUNCATED AT 250 WORDS)
Acetylcholine-induced release of endothelium-derived relaxing factor from lymphatic endothelial cells
Authors: Ohhashi T. , Takahashi N.
Published: December 2017

Ring segments of dog thoracic ducts precontracted with a high concentration of norepinephrine (NE) relaxed in a concentration-dependent manner in response to acetylcholine (ACh) or sodium nitroprusside (SNP). Pretreatment with atropine inhibited the ACh-induced relaxation in a competitive manner. The Schild plot showed a slope of 1.1 +/- 0.2 and a pA2 value of 10.4 +/- 0.4 (n = 6 ring segments). Removal of endothelium caused a complete inhibition of the ACh-induced relaxations in precontracted dog thoracic ducts. ACh, which failed to relax precontraction of the ring segment when mounted separately, induced relaxation in the same preparation when it was mounted as a "sandwich" with the longitudinal strip. The ACh-induced relaxations in the lymphatic preparations with endothelium were suppressed or abolished by pretreatment with oxyhemoglobin (10(-6) and 10(-5) M), methylene blue (10(-6) and 10(-5) M), and NG-monomethyl-L-arginine (3 x 10(-5) M), but the relaxations were unaffected by aspirin (10(-5) M). Pretreatment with methylene blue (10(-5) M) also caused a significant reduction of the SNP-induced relaxations in the precontracted thoracic ducts. It may be concluded that ACh-induced relaxation in dog thoracic ducts precontracted with NE is mediated by high-affinity muscarinic receptors in the lymphatic endothelial cells. Also, stimulation of the endothelial muscarinic receptors liberates a transferable endothelium-derived relaxing factor, which results in the relaxation of the lymphatic smooth muscles via the accumulation of cellular guanosine 3',5'-cyclic monophosphate.
Effect of occluding one umbilical artery on placental oxygen transport
Authors: Wilkening R. B. , Meschia G.
Published: December 2017

Placental O2 transport was studied in seven fetal lambs before and after occluding one of the two umbilical arteries. Ethanol was used to measure uterine and umbilical blood flows using the steady-state transplacental diffusion method. Blood samples were drawn from umbilical artery, umbilical vein, both uterine veins, and maternal artery and analyzed for blood flow indicator, O2 content, PO2, PCO2, and pH. Occlusion reduced the placental mass and the uterine blood flow, which was available for transplacental exchange, to 49.5 and 46.5% of control, respectively. After occlusion, fetal blood pressure increased 38%, total umbilical blood flow decreased 25%, total fetal O2 uptake decreased 26%, fetal blood flow to the unoccluded placenta increased 52%, and the O2 flux from unoccluded placenta to fetus increased 49%. This increased flux was accompanied by a decrease in the PO2 of maternal venous blood from the unoccluded placenta and an enlargement of the transplacental PO2 gradient, resulting in a marked drop in umbilical venous PO2 (28.3 to 17.7 Torr). This evidence supports the hypothesis that placental O2 diffusing capacity is a limiting factor in placental O2 transport and agrees with other studies indicating the absence of homeostatic mechanisms for preventing acute changes of PO2 in the placental circulation.
Dynamic properties of left ventricular response to changes in coronary perfusion
Authors: Sugiura S. , Hunter W. C. , Waclawiw M. A. , Sagawa K.
Published: December 2017

To determine the dynamic property of cardiac function response to alterations in coronary perfusion, we varied coronary arterial pressure (CAP) sinusoidally around one of four mean CAP levels with a constant amplitude at several frequencies in isolated, isovolumically contracting canine heart preparations. From the frequency spectrum of the peak left ventricular pressure (PLVP) response, we arrived at a phenomenological model with two components coupled in parallel and estimated the parameter values. One component is a first-order delay system having a short time constant (approximately 1 s) and a small gain (range 0.08-0.16); it probably represents a hydraulic effect of coronary perfusion. The other component is a second-order delay system with longer time constants (approximately 15 and 6 s) and a larger gain (range 0.14-0.69); this probably represents a metabolic effect. The gain value of the slow component varied inversely with the mean CAP level, and studies with adenosine suggested that this dependence was due to the coronary autoregulation. The model prediction of the transient responses of PLVP to step changes in CAP agreed reasonably well with those experimental data of transient responses obtained in the identical hearts but not used to determine the model parameter values.
Macromolecule permeability of coronary and aortic endothelial monolayers under energy depletion
Authors: Watanabe H. , Kuhne W. , Spahr R. , Schwartz P. , Piper H. M.
Published: December 2017

The dependence of macromolecule permeability (MP; indicator fluorescein isothiocyanate-labeled albumin) of endothelial cells on their energetic state was investigated using confluent monolayers of rat coronary microvascular endothelial cells and porcine aortic macrovascular endothelial cells. When oxidative and glycolytic energy productions were inhibited (5 mM KCN plus 5 mM 2-deoxy-D-glucose) 90% of the endothelial ATP contents were lost within 15 min, followed by a progressive increase of MP, disintegration of the actin cytoskeleton, and the opening of intercellular gaps. Elution of the blocker and a subsequent 3-h incubation in complete culture medium reversed the effects of 2-h metabolic blockade, completely for MP and partially for ATP levels. Coronary microvascular and aortic macrovascular endothelial cells responded similarly to energy depletion and repletion, the microvascular cells being more sensitive. The results demonstrate that 1) energetic inhibition augments endothelial macromolecule permeability when both oxidative and glycolytic energy production are inhibited, 2) increased macromolecule permeability in energy-depleted endothelial monolayers is caused by the opening of intercellular gaps, and 3) endothelial cells reversibly tolerate up to 2 h of almost complete ATP depletion.
Effects of area postrema stimulation on neurons of the nucleus of the solitary tract
Authors: Hay M. , Bishop V. S.
Published: December 2017

Previous studies have suggested that neurons of the area postrema may modulate cardiovascular function through an interaction at the level of the nucleus of the solitary tract (NTS). Using an in vitro brain slice preparation of the rabbit medulla, the present study investigated the electrophysiological and pharmacological effects of area postrema stimulation on NTS neuronal activity. In the majority of neurons tested (85.7%), electrical stimulation of the area postrema consistently produced either single or multiple action potentials in NTS neurons. Latency values for neurons showing single spike responses to area postrema stimulation ranged from 3.0 to 17.0 ms with an average latency of 9.3 +/- 4.3 ms. The average threshold for area postrema activation of these nonspontaneously active NTS neurons was 99.8 +/- 12 microA with a stimulus threshold range between 15 and 200 microA (n = 53). Perfusion of the slice with phentolamine (1.0 microM) or yohimbine (200 nM) blocked the area postrema-evoked action potentials, whereas perfusion of the slice with prazosin (200 nM) had no effect. These findings suggest that area postrema neurons do modulate NTS neuronal activity and that this modulation results in an increase in NTS neuronal activation.
Oxidative changes in hypoxic rat heart tissue
Authors: Park Y. , Kanekal S. , Kehrer J. P.
Published: December 2017

Reactive O2 species appear to be generated both during hypoxia and at reoxygenation, but it has not been established whether these species interact with heart tissue and cause injury. Oxidative changes were evaluated in isolated rat heart perfused with Krebs-Henseleit medium containing 10 mM glucose and 2.5 mM calcium. After 5–10 min hypoxia, tissue glutathione (GSH) decreased while glutathione disulfide (GSSG), protein carbonyls, and thiobarbituric acid reactive substances (TBARS) increased compared with controls. Similarly, sarcolemmal and sarcoplasmic reticular Ca-ATPase activity (an enzyme susceptible to oxidative inactivation) decreased in response to 10 min hypoxia. These changes were more pronounced after 60 min of hypoxia when protein-GSH mixed disulfides were also increased. There were no further oxidative changes after 4 min reoxygenation when the release of lactate dehydrogenase (LDH) was maximal. Myocardial protein thiol and alpha-tocopherol contents were not significantly changed by either hypoxia or reoxygenation. Mitochondria also exhibited oxidative changes but with more pronounced increases in GSSG and mixed disulfides. There was no change in GSH or GSSG efflux into the coronary effluent during hypoxia, although, in parallel with LDH release, both increased after reoxygenation. Diamide (200 microM), t-butylhydroperoxide (20 microM), or purine (2.3 mM) + xanthine oxidase (0.01 U/ml) were infused for 10 min. Except for large diamide-induced changes in protein thiols and mixed disulfides, the magnitude of the changes produced by these oxidants was similar to those produced by hypoxia. These data show that changes consistent with oxidative processes occur in whole heart and mitochondria in response to hypoxia. The absence of marked signs of oxidation at reoxygenation suggest that enzyme release at this time is unrelated to oxidative stress.
Lung hyaluronan during development: a quantitative and morphological study
Authors: Allen S. J. , Gunnar Sedin E. , Jonzon A. , Wells A. F. , Laurent T. C.
Published: December 2017

Hyaluronan, an important constituent of developmental interstitium in fetal lungs, mediates cell-to-cell interactions and thereby directs migrating cells. Furthermore, because of the polyionic nature of the molecule, hyaluronan forms open, hydrated matrices that provide channels for migrating cells. This hydrated matrix undergoes contraction before birth. However, continued growth of the lung in the perinatal period requires newly synthesized hyaluronan. This study's purpose was to elucidate the changes in lung hyaluronan concentration and distribution in the perinatal period. We studied rabbits at days -6, -4, -2, -1, 0, +2, and +4 with respect to term, as well as adult rabbits. We found that hyaluronan concentration was highest in the youngest fetuses studied [682 +/- 115 micrograms/g dry wt (means +/- SD)]. However, hyaluronan concentration decreased to 129 +/- 12 micrograms/g dry wt just before birth then returned to 366 +/- 111 micrograms/g dry wt at day +4; these values were similar to adult values. We found hyaluronan staining decreased during late gestation, particularly in the interalveolar region. In the postnatal period, hyaluronan staining increased in the visceral pleura and, to a lesser extent, beneath the epithelium of the bronchioles. Hyaluronan did not reaccumulate in the interalveolar region in the postnatal period. Our data suggest a change in the predominant role of lung hyaluronan during the perinatal period. Before term, hyaluronan facilitates morphogenesis. However, hyaluronan's major role in neonatal lung is most likely in regulation of fluid balance in interstitium.
Interactions of area postrema and solitary tract in the nucleus tractus solitarius
Authors: Hay M. , Bishop V. S.
Published: December 2017

The nucleus tractus solitarius (NTS) receives information from both area postrema (AP) and peripheral afferents. It is, therefore, one likely site of interaction between AP and peripheral afferent fibers. The present study's purpose was to determine the influence of AP stimulation on solitary tract-induced modulation of NTS neuronal activity. With the use of an in vitro rabbit brain slice preparation, extracellular recordings were made from 58 NTS neurons in which action potentials were evoked by both solitary tract and AP stimulation. In the majority of the cells tested, simultaneous stimulation of solitary tract and AP, at voltage levels that evoked no action potentials when stimulated separately, resulted in production of either single or multiple action potentials. In 27 units, stimulation levels to the solitary tract and to the AP were adjusted such that their respective separate stimulations produced an NTS action potential less than 30% of the time. When the two inputs were stimulated together, simultaneous stimulations produced an NTS action potential 100% of the time, suggesting a facilitatory interaction between the AP and the solitary tract on NTS neuronal activity. In nine cells, perfusion of the slice with clonidine induced a facilitation of solitary tract-evoked NTS response to a level similar to that seen during simultaneous stimulation of the solitary tract with the AP. Application of the alpha 2-adrenergic receptor antagonist yohimbine blocked the ability of both clonidine and AP to facilitate the solitary tract-evoked response. These results support a possible interaction between AP and peripheral afferents and suggest that AP stimulation facilitates effects of solitary tract activation at the level of the NTS.
Left ventricular ejection activation in the in situ heart
Authors: Igarashi Y. , Cheng C. P. , Little W. C.
Published: December 2017

We tested, in the in situ heart, the hypothesis that the end-systolic pressure (ESP) of small ejecting contraction (EC) is greater than that of an isovolumic contraction (IC) with a similar end-systolic volume. We produced ECs with varying amounts of ejection by partial aortic occlusion while measuring left ventricular pressure, one or two left ventricular dimensions (anteroposterior and septal-lateral), and aortic flow. In 11 dogs, we plotted ventricular pressure against the time integral of aortic flow of ECs and IC with the same end-diastolic anteroposterior dimension. The end-systolic pressure-volume line was drawn from the peak isovolumic pressure-volume point tangential to the left upper corner of the pressure-volume loop of ECs. The slope of the tangential line of the middle EC, whose stroke volume was 51 +/- 8% of that of the control EC, was decreased by 54 +/- 16% compared with that of the control EC. In eight dogs with two pairs of crystals, left ventricular volume was controlled by partial vena caval occlusion, and ICs were produced by total aortic occlusion. The end-systolic pressure of small ejections exceeded (11.3 +/- 7.7 mmHg, P less than 0.01) those of isovolumic contractions with the same end-systolic cross-sectional area, whereas the end-systolic pressure of beats with large ejections was similar (-9.4 +/- 14.4 mmHg, P = NS) to an IC with the same end-systolic cross-sectional area. We conclude that the end-systolic pressure-volume point of beats with a small ejection is located above the isovolumic end-systolic pressure-volume relation in the in situ dog left ventricle.
Heparin promotes the formation of extracardiac to coronary anastomoses in a canine model
Authors: Unger E. F. , Sheffield C. D. , Epstein S. E.
Published: December 2017

We developed a canine model for the in vivo utilization of angiogenesis factors to promote revascularization of a collateral-dependent area of the heart and assessed the potential of heparin in this preparation. Ameroids were placed on the proximal left anterior descending coronary artery (LAD) of 29 dogs, and the left internal mammary artery (IMA) was implanted in an intramyocardial tunnel in proximity to the LAD. A tube positioned in the distal IMA provided a continuous retrograde infusion directly into the vessel from an implanted pump. Heparin (15 or 150 U/h) or saline vehicle was infused. After 8 wk, regional myocardial blood flow was assessed in the anesthetized state during adenosine-induced vasodilatation, before and during occlusion of the IMA. The IMA provided a greater proportion of maximal collateral flow in heparin-treated dogs (22 +/- 5%, n = 17) than in saline-treated dogs (9 +/- 2%, n = 12, P less than 0.05). Thus continuous infusion of heparin promotes the formation of collaterals between the extracardiac artery and the myocardial circulation, establishing the feasibility of targeting angiogenic agents for myocardial revascularization.
Relationship of cerebral and myocardial intracellular pH to blood pH during hypothermia
Authors: Swain J. A. , McDonald T. J. , Robbins R. C. , Balaban R. S.
Published: December 2017

The regulation of tissue pH during hypothermia is important for cellular homeostasis. The present study was undertaken to determine the relationship between blood pH and intracellular pH in the brain and heart during hypothermia in sheep and to compare these data with those in humans. Intracellular pH (pHi) was determined by 31P nuclear magnetic resonance (NMR) spectroscopic data collected from the heart and brain of sheep during cardiopulmonary bypass (CPB). Alpha-stat and pH-stat blood pH management schemes were compared. When the blood pH was held constant (pH stat), the pHi of the heart increased from 7.01 +/- 0.01 at 37 degrees C to 7.18 +/- 0.02 at 26 degrees C, and the pHi of the brain increased from 7.04 +/- 0.02 at 37 degrees C to 7.23 +/- 0.02 at 26 degrees C and to 7.32 +/- 0.04 at 20 degrees C. Alpha-stat pH management resulted in similar increases in pH to that found with pH-stat [heart: 7.00 +/- 0.02 at 37 degrees C to 7.19 +/- 0.03 at 26 degrees C; brain: 7.07 +/- 0.02 at 37 degrees C to 7.29 +/- 0.02 at 26 degrees C, and 7.32 +/- 0.03 at 20 degrees C]. The tissue pH of the heart in humans showed similar findings during blood pH-stat regulation.(ABSTRACT TRUNCATED AT 250 WORDS)
Nonlinearity of indexes of left ventricular performance: effects on estimation of slope and diameter axis intercepts
Authors: Toombs C. F. , Vinten-Johansen J. , Yokoyama H. , Johnston W. E. , Julian J. S. , Cordell A. R.
Published: December 2017

The slope and diameter axis intercept (D0) of the linear indexes end-systolic pressure-diameter relation (ESPDR), maximum of the first derivative of left ventricular pressure (dP/dtmax)-end-diastolic diameter relation (dP/dtmax-Ded), and dimensional preload-recruitable stroke work relation (PRDSW) are used to describe left ventricular performance. We tested the hypothesis that nonlinearity in these indexes would preclude accurate estimation of slope and D0. In nine pentobarbital-anesthetized dogs, right heart bypass was used to obtain a wide range of pressure-minor axis diameter (sonomicrometry) points from which the three indexes were derived. For ESPDR and dP/dtmax-Ded, a nonlinear fit (y = ax2 + bx + c) approximated the data better than a linear fit, with significant nonlinearity toward the diameter axis (a = -10.28 +/- 3.42 and -111.2 +/- 26.2, respectively, P less than 0.05). Although linear D0 was significantly less than nonlinear D0, this difference was overcome by the diameter intercept at a midrange value of end-systolic pressure or dP/dtmax. PRDSW demonstrated no significant nonlinearity (a = -4.40 +/- 3.53, P = 0.86) but extrapolation to D0 demonstrated linear and nonlinear differences. We conclude that 1) ESPDR and dP/dtmax-Ded demonstrate significant nonlinearity, while PRDSW is well-approximated by a linear fit over a large range of data points; and 2) extrapolation of D0 is inaccurate in all three indexes, while a midrange intercept is independent of the model used to fit the data. Left ventricular performance may be more accurately described by linear slope and midrange diameter intercept over comparable ranges of data.
Hyperpolarization of arterial smooth muscle induced by endothelial humoral substances
Authors: Chen G. , Yamamoto Y. , Miwa K. , Suzuki H.
Published: December 2017

A sandwich preparation was obtained by placing a segment of the endothelium-free guinea pig coronary artery over the intact carotid artery with the objective being to determine whether the endothelium-dependent hyperpolarization by acetylcholine chloride (ACh) is mediated by a humoral factor. ACh hyperpolarized the sandwiched coronary smooth muscle membrane, the amplitude being larger than that of the carotid artery and smaller than that of the intact coronary artery. When spontaneously active smooth muscles (stomach antrum or portal vein) were used as the donor tissue, no electrical signal was transducted to the overlying coronary smooth muscles. In the sandwiched coronary artery, the ACh-induced hyperpolarization was not inhibited by ouabain, indomethacin, or nitroarginine. Pinacidil hyperpolarized the coronary smooth muscle membrane; the responses were inhibited by glybenclamide but not by tetraethylammonium chloride (TEA). The ACh-induced hyperpolarization was inhibited by TEA but not by glybenclamide. These results suggest that the ACh-induced hyperpolarization is mediated by an endothelium-derived humoral substance (endothelium-derived hyperpolarizing factor). Possible contribution of Ca-dependent K channels, but not ATP-sensitive K channels, to the endothelium-derived hyperpolarizing factor-induced hyperpolarization was considered.