bluuebunny/crossref_metadata_2025 huggingface dataset:
Cardiac dysfunction in terms of left ventricular mechanical work and energetics in hypothyroid rats
Authors: Ohga Yoshimi , Sakata Susumu , Takenaka Chikako , Abe Takehisa , Tsuji Tsuyoshi , Taniguchi Shigeki , Takaki Miyako
Published: March 2015

We hypothesized that cardiac dysfunction in hypothyroidism is mainly caused by the impairment of Ca2+handling in excitation-contraction coupling. To prove this hypothesis, we investigated left ventricular (LV) mechanical work and energetics without interference of preload and afterload in an excised, blood-perfused whole heart preparation from hypothyroid rats. We found that LV inotropism and lusitropism were significantly depressed, and these depressions were causally related to decreased myocardial oxygen consumption for Ca2+handling and for basal metabolism. The oxygen costs of LV contractility for Ca2+and for dobutamine in the hypothyroid rats did not differ from those in age-matched normal rats. The expression of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2) significantly decreased and that of phospholamban significantly increased. The present results revealed that changes in LV energetics associated with decreased mechanical work in hypothyroid rats are mainly caused by the impairment of Ca2+uptake via SERCA2. We conclude that the impairment of Ca2+uptake plays an important role in the pathogenesis of cardiac dysfunction in hypothyroidism.
Quantification of interventricular asynchrony during LBBB and ventricular pacing
Authors: Verbeek Xander A. A. M. , Vernooy Kevin , Peschar Maaike , Van der Nagel Theo , Van Hunnik Arne , Prinzen Frits W.
Published: March 2015

The quantification of mechanical interventricular asynchrony (IVA) was investigated. In 12 dogs left bundle branch block (LBBB) was induced by radio frequency ablation. Left ventricular (LV) and right ventricular (RV) pressures were recorded before and after induction of LBBB and during LBBB + LV apex pacing at different atrioventricular (AV) delays. Four IVA measures were validated using computer simulations on experimentally obtained pressure signals. The most robust measure for IVA was the time delay between the upslope of the LV and RV pressure signals (Δ T up), estimated by cross correlation. The induction of experimental LBBB decreased Δ T upfrom −6.9 ± 7.0 ms (RV before LV) to −33.9 ± 7.6 ms ( P < 0.05) in combination with a significant decrease of LV maximal first derivative of pressure development over time (dP/d t max). During LV apex pacing, Δ T up increased with decreasing AV delay up to +20.9 ± 14.6 ms ( P < 0.05). Interventricular resynchronization (Δ T up = 0 ms) significantly improved LV dP/d t max by 15.1 ± 5.9%. QRS duration increased significantly after induction of LBBB but did not change during LV apex pacing. In conclusion, Δ T up is a reliable measure of mechanical IVA, which adds valuable information concerning the nature of asynchronous activation of the ventricles.
Platelets activated by transient coronary occlusion exacerbate ischemia-reperfusion injury in rat hearts
Authors: Mirabet Maribel , Garcia-Dorado David , Inserte Javier , Barrabés José A. , Lidón Rosa-M. , Soriano Bernat , Azevedo Marta , Padilla Ferran , Agulló Luis , Ruiz-Meana Marisol , Massaguer Anna , Pizcueta Pilar , Soler-Soler Jordi
Published: March 2015

Platelets (Plt) accumulate in reperfused myocardium but their effect on myocardial necrosis has not been established. We tested the hypothesis that the effect of Plt depends on their activation status. Pig Plt were obtained before 48 min of coronary occlusion (pre-CO-Plt), 10 min after reperfusion (R-Plt), or after a 60-min sham operation (sham-Plt). Plt were infused into isolated rat hearts ( n = 124) and subsequently submitted to 60 min of ischemia and 60 min of reperfusion. P-selectin expression was higher ( P = 0.02) in R-Plt than in pre-CO-Plt or sham-Plt. Lactate dehydrogenase (LDH) release during reperfusion was similar in hearts receiving pre-CO-Plt, sham-Plt, or no Plt, but R-Plt increased LDH release by 60% ( P = 0.004). Activation of pre-CO-Plt with thrombin increased P-selectin expression and LDH release ( P < 0.001), and these results were unaffected by tirofiban. There was a close correlation between P-selectin expression and LDH release ( r = 0.84; P < 0.001), and myocardial Plt accumulation ( r = 0.85; P < 0.001). We conclude that the deleterious effect of Plt on reperfused myocardium depends on their activation status as represented by P-selectin expression, which is enhanced by ischemia-reperfusion.
Functional NOS 1 in the rat mesenteric arterial bed
Authors: Sullivan Jennifer C. , Giulumian Ararat D. , Pollock David M. , Fuchs Leslie C. , Pollock Jennifer S.
Published: March 2015

Previously we have demonstrated functional nitric oxide synthase (NOS) 1 in large arteries. Because resistance arteries largely determine blood pressure, this study examined whether functional NOS 1 also exists in resistance arteries. Phenylephrine (PE) contraction was measured in the absence and presence of the NOS 1 inhibitor N5-(1-imino-3-butenyl)-l-ornithine (VNIO) in isolated mesenteric resistance arteries (endothelium intact and denuded) from Sprague-Dawley rats. For NOS 1 activity and expression, the mesenteric arterial bed was separated into cytosolic and particulate fractions. NOS activity was assayed by measuring the conversion of [3H]arginine to [3H]citrulline inhibited by a nonselective NOS inhibitor or VNIO. VNIO increased PE sensitivity in endothelium-intact and -denuded arteries. In cytosolic and particulate fractions of the arterial bed, ∼40% of NOS activity was inhibited by VNIO. Immunoprecipitation and Western blot analysis revealed two NOS 1 immunoreactive bands. One band corresponded to the rat brain isoform, whereas the second was of a slightly lower molecular mass. The cytosolic fraction contained both isoforms; however, the particulate fraction had only the lower molecular mass form. These studies demonstrate the existence of functional NOS 1 in resistance arteries.
STAT signaling in ischemic heart: a role of STAT5A in ischemic preconditioning
Authors: Yamaura Genbu , Turoczi Tibor , Yamamoto Fumio , Siddqui M. A. Q. , Maulik Nilanjana , Das Dipak K.
Published: March 2015

We recently demonstrated that ischemic preconditioning (PC) induced by cyclic episodes of short duration of ischemia and reperfusion potentiates a signal transduction cascade involving Janus kinase (JAK) 2 and signal transducer and activator of transcription 3 (STAT3). A rapid activation of JAK and several STATs, including STAT3, STAT5A, and STAT6 also occurred during myocardial ischemia and reperfusion. This study sought to examine whether STAT5A and STAT6 were also involved in PC. Two different animal models were used: isolated perfused working rat hearts and STAT5A and STAT6 knockout mouse hearts. The results of our study indicated phosphorylation of STAT 5A and STAT6 in the preconditioned myocardium. Tyrphostin AG490, a JAK2 inhibitor, or 4-amino-5-(4-methylphenyl)-7-( t-butyl)-pyrazolo-3,4-d-pyrimidine (PPI), a Src kinase blocker, blocked STAT5A phosphorylation, whereas STAT6 phosphorylation was blocked only with tyrphostin. As expected, significant cardioprotection was achieved in the preconditioned heart as evidenced by reduced myocardial infarct size and decreased number of apoptotic cardiomyocytes. PC-mediated cardioprotection was partially abolished when hearts were pretreated with tyrphostin, PPI, or LY-294002, a phosphatidylinositol (PI)-3 kinase inhibitor. Studies with STAT5A and STAT6 knockout mouse hearts revealed that STAT6 knockout mouse hearts, and not STAT5A knockout mouse hearts, were resistant to myocardial ischemia-reperfusion injury. The hearts from STAT5A knockout mice could not be preconditioned, whereas those from STAT6 knockout mice were easily preconditioned. The results of the present study demonstrate that STAT5A, and not STAT6, plays a role in ischemic PC. For the first time, the results also indicated a role of Src kinase pathway in STAT5A PC and PI-3 kinase-Akt pathways appear to be the downstream regulator for STAT5A-STAT6 signaling pathway.
Endothelium-dependent blunting of myogenic responsiveness after chronic hypoxia
Authors: Earley Scott , Walker Benjimen R.
Published: March 2015

Blunted agonist-induced vasoconstriction after chronic hypoxia is associated with endothelium-dependent vascular smooth muscle (VSM) cell hyperpolarization and decreased vessel-wall Ca2+concentration ([Ca2+]). We hypothesized that myogenic vasoconstriction and pressure-induced Ca2+ influx would also be attenuated in vessels from chronically hypoxic (CH) rats. Mesenteric resistance arteries isolated from CH [barometric pressure (BP), 380 Torr for 48 h] or normoxic control (BP, 630 Torr) rats were cannulated and pressurized. VSM cell resting membrane potential was recorded at intraluminal pressures of 40–120 Torr under normoxic conditions. VSM cells in vessels from CH rats were hyperpolarized compared with control rats at all pressures. Inner diameter was maintained for vessels from control rats, whereas vessels from CH rats developed less tone as pressure was increased. Pressure-induced increases in vessel-wall [Ca2+] were also attenuated for arteries from CH rats. Endothelium removal restored myogenic constriction to vessels from CH rats and normalized VSM cell resting membrane potential and pressure-induced Ca2+ responses to control levels. Myogenic constriction and pressure-induced vessel-wall [Ca2+] increases remained blunted in the presence of nitric oxide (NO) synthase inhibition for arteries from CH rats. We conclude that blunted myogenic reactivity after chronic hypoxia results from a non-NO, endothelium-dependent VSM cell hyperpolarizing influence.
Alterations of systolic left ventricular twist after acute myocardial infarction
Authors: Garot Jérôme , Pascal Olivier , Diébold Benoît , Derumeaux Geneviève , Gerber Bernhard L. , Dubois-Randé Jean-Luc , Lima João A. C. , Guéret Pascal
Published: March 2015

10.1152/ajpheart.00136.2001.—We sought to characterize the alterations of left ventricular (LV) twist after acute myocardial infarction in humans and to study their relationship to usual parameters of LV function. Systolic LV twist was measured by color tissue Doppler echocardiography (TDE) in 34 patients after anterior myocardial infarction and in 20 controls. In a subset of controls and patients, the assessment of LV twist by TDE was validated against magnetic resonance (MR) tissue tagging with good agreement between the two methods. Myocardial ischemia was responsible for a decrease in LV twist in infarct patients ( P < 0.01). The decrease in LV twist was correlated with the extent of the asynergic area and global LV function as assessed by LV cineangiography ( P < 0.001). Thus acute myocardial ischemia is responsible for a decrease in LV twist that is related to global LV function. Color TDE is a promising technique for straightforward assessment of LV twist in humans.
Effects of burst stimulation during ventricular fibrillation on cardiac function after defibrillation
Authors: Walcott Gregory P. , Melnick Sharon B. , Killingsworth Cheryl R. , Smith William M. , Ideker Raymond E.
Published: March 2015

The purpose of defibrillation is to rapidly restore blood flow and tissue perfusion following ventricular fibrillation (VF) and shock delivery. We tested the hypotheses that 1) a series of 1-ms pulses of various amplitudes delivered before the defibrillation shock can improve hemodynamics following the shock, and 2) this hemodynamic improvement is due to stimulation of cardiac or thoracic sympathetic nerves. Ten anesthetized pigs received a burst of either 15 or 30 1-ms pulses (0.1–10 A in strength) during VF, after which defibrillation was performed. ECG, arterial blood pressure, and left ventricular (LV) pressure were recorded. Defibrillation shocks and burst pulses were delivered from a right ventricular coil electrode to superior vena cava coil and left chest wall electrodes. Sympathetic blockade was induced with 1 mg/kg timolol and trials were repeated. The first half of this protocol was repeated in two animals that were pretreated with reserpine. Heart rate (HR) after 1-, 2-, 5-, and 10-A pulses was significantly higher than after control shocks without preceding pulse therapy. Mean and peak LV pressure measurements increased 38 and 72%, respectively, following shocks preceded by 5- and 10-A pulses compared with shocks preceded by no burst pulses. Mean and peak arterial pressures increased 36 and 43%, respectively, following shocks preceded by 5- and 10-A pulses compared with shocks preceded by no burst pulses. After β-blockade, HR, mean and peak arterial pressures, and mean LV pressure were not significantly different after pulses of any strength compared with control shocks. LV peak pressure following the 10-A pulses was significantly higher than with no burst pulses but was significantly lower than the response to the 10-A pulses delivered without β-blockade. HR, mean and peak arterial pressures, and mean and peak LV pressure responses after 15 or 30 5- or 10-A pulses were similar to the responses to the same pulses after β-blockade. We conclude that a burst of 15–30 1-ms pulses delivered during VF can increase HR, arterial pressure, and LV pressure following defibrillation. β-Blockade or reserpine pretreatment prevents most of this postshock increase in HR, arterial pressure, and LV pressure.
Hypoxia-induced left ventricular dysfunction in myoglobin-deficient mice
Authors: Mammen Pradeep P. A. , Kanatous Shane B. , Yuhanna Ivan S. , Shaul Philip W. , Garry Mary G. , Balaban Robert S. , Garry Daniel J.
Published: March 2015

Myoglobin-deficient mice are viable and have preserved cardiac function due to their ability to mount a complex compensatory response involving increased vascularization and the induction of the hypoxia gene program (hypoxia-inducible factor-1α, endothelial PAS, heat shock protein27, etc.). To further define and explore functional roles for myoglobin, we challenged age- and gender-matched wild-type and myoglobin-null mice to chronic hypoxia (10% oxygen for 1 day to 3 wk). We observed a 30% reduction in cardiac systolic function in the myoglobin mutant mice exposed to chronic hypoxia with no changes observed in the wild-type control hearts. The cardiac dysfunction observed in the hypoxic myoglobin-null mice was reversible with reexposure to normoxic conditions and could be prevented with treatment of an inhibitor of nitric oxide (NO) synthases. These results support the conclusion that hypoxia-induced cardiac dysfunction in myoglobin-null mice occurs via a NO-mediated mechanism. Utilizing enzymatic assays for NO synthases and immunohistochemical analyses, we observed a marked induction of inducible NO synthase in the hypoxic myoglobin mutant ventricle compared with the wild-type hypoxic control ventricle. These new data establish that myoglobin is an important cytoplasmic cardiac hemoprotein that functions in regulating NO homeostasis within cardiomyocytes.
δ-Opioid receptor-induced late preconditioning is mediated by cyclooxygenase-2 in conscious rabbits
Authors: Kodani Eitaro , Xuan Yu-Ting , Shinmura Ken , Takano Hitoshi , Tang Xian-Liang , Bolli Roberto
Published: March 2015

Although activation of δ-opioid receptors is known to induce both early and late preconditioning (PC) against myocardial infarction, the mechanisms for this salubrious effect are unclear. Furthermore, it is unknown whether δ-opioid receptors can also induce late PC against myocardial stunning. By using conscious rabbits ( n = 120) in this study, we found that the δ-opioid receptor agonist (±)-4-{(α- R*)-α-[(2 S*,5 R*)-4-allyl-2,5-dimethyl-1-piperazinyl]-3-hydroxybenzyl}- N, N-diethylbenzamide (BW-373U86) induced late PC against myocardial stunning 24 h after treatment and that this effect was abolished by the selective cyclooxygenase-2 (COX-2) inhibitors N-[2-(cyclohexyloxy)4-nitrophenyl]methanesulfonamide (NS-398) and celecoxib. This protective effect was also abrogated by the selective δ1-opioid receptor antagonist 7-benzylidenenaltrexone, indicating that the δ1-opioid receptor is necessary for BW-373U86-induced late PC. BW-373U86 did not induce early PC against stunning. In addition, BW-373U86 induced late PC against infarction, which was blocked by NS-398. At 24 h after BW-373U86 administration, myocardial COX-2 protein expression and PGE2 and 6-keto-PGF1α levels were significantly increased. These results demonstrate that activation of δ-opioid receptors induces late PC against both stunning and infarction via a COX-2-dependent mechanism.
Olfactory bulbectomy attenuates cardiovascular sympathoexcitatory reflexes in rats
Authors: Moffitt Julia A. , Grippo Angela J. , Holmes Philip V. , Johnson Alan Kim
Published: March 2015

Bilateral removal of the olfactory lobes in rats produces a number of behavioral, endocrine, and neurochemical alterations in the brain. Little is known, however, regarding the effects of this treatment on cardiovascular function and autonomic reflexes. Male Sprague-Dawley rats underwent bilateral surgical ablation of the olfactory bulbs ( n = 10) or were sham operated ( n = 8). After 3 wk of recovery, animals were instrumented with femoral catheters and a lumbar sympathetic nerve recording electrode. After 24 h of recovery, cardiovascular responses to arterial baroreflex manipulation, air jet stress, and smoke exposure were recorded. Olfactory bulbectomized rats demonstrated attenuated sympathoexcitatory responses to hypotension, air jet stress, and smoke exposure, as well as elevated basal blood pressure, compared with sham-operated rats. These data indicate that the integrity of the olfactory bulbs in rats is important for the elicitation of normal cardiovascular and autonomic responses to a number of evocative stimuli.
Exercise training regulates SOD-1 and oxidative stress in porcine aortic endothelium
Authors: Rush James W. E. , Turk James R. , Laughlin M. Harold
Published: March 2015

Vascular oxidative stress contributes to endothelial dysfunction. Aerobic exercise training improves vascular function. The purpose of this study was to test the hypothesis that exercise training would improve the balance of antioxidant to prooxidant enzymes and reduce markers of oxidative stress in aortic endothelial cells (AEC). Female Yucatan miniature pigs either remained sedentary (SED) or were exercise trained (EX) for 16–19 wk. EX pigs had increased AEC SOD-1 protein levels and Cu/Zn SOD activity of the whole aorta compared with SED pigs. Protein levels of other antioxidant enzymes (SOD-2, catalase) were not affected by exercise training. Protein levels of p67phox, a subunit of the prooxidant enzyme NAD(P)H oxidase, were reduced in EX vs. SED AEC. These EX adaptations were associated with lower AEC malondialdehyde levels and decreased phosphorylation of ERK-1/2. Endothelial nitric oxide synthase protein, protein nitrotyrosine content, and heme oxygenase-1 protein were not different in EX vs. SED pigs. We conclude that chronic aerobic exercise training influenced both antioxidant and prooxidant enzymes and decreased indexes of oxidative stress in AEC. These adaptations may contribute to improved endothelial function with exercise training.
Overexpression of phospholemman alters contractility and [Ca2+]itransients in adult rat myocytes
Authors: Song Jianliang , Zhang Xue-Qian , Carl Lois L. , Qureshi Anwer , Rothblum Lawrence I. , Cheung Joseph Y.
Published: March 2015

Previous studies showed increased phospholemman (PLM) mRNA after myocardial infarction (MI) in rats (Sehl PD, Tai JTN, Hillan KJ, Brown LA, Goddard A, Yang R, Jin H, and Lowe DG. Circulation 101: 1990–1999, 2000). We tested the hypothesis that, in normal adult rat cardiac myocytes, PLM overexpression alters contractile function and cytosolic Ca2+concentration ([Ca2+]i) homeostasis in a manner similar to that observed in post-MI myocytes. Compared with myocytes infected by control adenovirus expressing green fluorescent protein (GFP) alone, Western blots indicated a 41% increase in PLM expression after 72 h ( P < 0.001) but no changes in Na+/Ca2+exchanger, SERCA2, and calsequestrin levels in myocytes infected by adenovirus expressing GFP and PLM. At 5 mM extracellular [Ca2+] ([Ca2+]o), maximal contraction amplitudes in PLM-overexpressed myocytes were 24% ( P < 0.005) and [Ca2+]itransient amplitudes were 18% ( P < 0.05) lower than control myocytes. At 0.6 mM [Ca2+]o, however, contraction and [Ca2+]itransient amplitudes were significantly ( P < 0.05) higher in PLM-overexpressed than control myocytes (18% and 42%, respectively); at 1.8 mM [Ca2+]o, the differences in contraction and [Ca2+]itransient amplitudes were narrowed. This pattern of contractile and [Ca2+]itransient abnormalities in PLM-overexpressed myocytes mimics that observed in post-MI rat myocytes. We suggest that PLM overexpression observed in post-MI myocytes may partly account for contractile abnormalities by perturbing Ca2+fluxes during excitation-contraction.
Ovariectomy increases mitogens and platelet-induced proliferation of arterial smooth muscle
Authors: Bracamonte M. P. , Rud K. S. , Owen Whyte G. , Miller V. M.
Published: March 2015

Experiments were designed to determine how ovariectomy modulates mitogenic factors in platelets and how these factors affect proliferation of coronary arterial smooth muscle. Platelet-derived growth factors (PDGFABand PDGFBB), transforming growth factors (TGF-β1and TGF-β2), and vascular endothelial growth factor (VEGF165) were quantified in platelet lysates and platelet-poor plasma from adult gonadally intact and ovariectomized female pigs by ELISA. Proliferation of cultured coronary arterial smooth muscle cells (SMCs) from both groups of pigs was determined in response to autologous or heterologous platelet lysates. Platelet concentrations of PDGFBB, but not PDGFAB, TGF-β1, and TGF-β2, increased with ovariectomy. VEGF165was not detected in platelets from either group. Proliferation of SMCs from ovariectomized females was significantly greater on exposure to autologous or heterologous platelet lysates than proliferation of SMCs from intact females. These results indicate that ovariectomy increases concentrations of PDGFBBin platelets. Higher levels of PDGFBBin platelets in synergy with other platelet-derived products could contribute to increased proliferative arterial response to injury after ovariectomy.
Cardiac function and metabolism in Type 2 diabetic mice after treatment with BM 17.0744, a novel PPAR-α activator
Authors: Aasum Ellen , Belke Darrell D. , Severson David L. , Riemersma Rudolph A. , Cooper Marie , Andreassen Morten , Larsen Terje S.
Published: March 2015

Hearts from diabetic db/ db mice, a model of Type 2 diabetes, exhibit left ventricular failure and altered metabolism of exogenous substrates. Peroxisome proliferator-activated receptor-α (PPAR-α) ligands reduce plasma lipid and glucose concentrations and improve insulin sensitivity in db/ db mice. Consequently, the effect of 4- to 5-wk treatment of db/ db mice with a novel PPAR-α ligand (BM 17.0744; 25–38 mg · kg−1· day−1), commencing at 8 wk of age, on ex vivo cardiac function and metabolism was determined. Elevated plasma concentrations of glucose, fatty acids, and triacylglycerol (34.0 ± 3.6, 2.0 ± 0.4, and 0.9 ± 0.1 mM, respectively) were reduced to normal after treatment with BM 17.0744 (10.8 ± 0.6, 1.1 ± 0.1, and 0.6 ± 0.1 mM). Plasma insulin was also reduced significantly in treated compared with untreated db/ db mice. Chronic treatment of db/ db mice with the PPAR-α agonist resulted in a 50% reduction in rates of fatty acid oxidation, with a concomitant increase in glycolysis (1.7-fold) and glucose oxidation (2.3- fold). Correction of the diabetes-induced abnormalities in systemic and cardiac metabolism after BM 17.0744 treatment did not, however, improve left ventricular contractile function.
Changes in extracellular collagen matrix alter myocardial systolic performance
Authors: Baicu Catalin F. , Stroud Jason D. , Livesay Virginia A. , Hapke Elizabeth , Holder Jennifer , Spinale Francis G. , Zile Michael R.
Published: March 2015

The purpose of this study was to test the hypothesis that acute disruption of fibrillar collagen will decrease myocardial systolic performance without changing cardiomyocyte contractility. Isolated papillary muscles were treated either with plasmin (0.64 U/ml, 240 min) or untreated and served as same animal control. Plasmin treatment caused matrix metalloproteinase activation and collagen degradation as measured by gelatin zymography, hydroxyproline assays, and scanning electron microscopy. Plasmin caused a significant decrease in myocardial systolic performance. Isotonic shortening extent and isometric developed tension decreased from 0.17 ± 0.01 muscle length (ML) and 45 ± 4 mN/mm2 in untreated muscles to 0.09 ± 0.01 ML and 36 ± 3 mN/mm2 in treated muscles ( P < 0.05). However, plasmin treatment (0.64 U/ml, 240 min) did not alter shortening extent or velocity in isolated cardiomyocytes. Acute disruption of the fibrillar collagen network caused a decrease in myocardial systolic performance without changing cardiomyocyte contractility. These data support the hypothesis that fibrillar collagen facilitates transduction of cardiomyocyte contraction into myocardial force development and helps to maintain normal myocardial systolic performance.
Female rats are protected against fructose-induced changes in metabolism and blood pressure
Authors: Galipeau Denise , Verma Subodh , McNeill John H.
Published: March 2015

The objective of this study was to determine whether the effects of a fructose diet, which causes hyperinsulinemia, insulin resistance, and hypertension in male rats, are dependent on sex. Blood pressure was measured via the tail-cuff method, and oral glucose tolerance tests were performed to assess insulin sensitivity. Blood pressure in female rats did not differ between fructose-fed and control rats at any time point (126 ± 5 and 125 ± 3 mmHg at week 9 for fructose-fed and control rats, respectively) nor was there a difference in any metabolic parameter measured. Furthermore, the vascular insulin resistance that is present in male fructose-fed rats was not observed. After ovariectomy, fructose caused a significant change in systolic blood pressure from baseline compared with fructose-fed ovary-intact rats (change of 21 ± 5 vs. −2 ± 4 mmHg). The results demonstrate that females do not develop hypertension or hyperinsulinemia upon fructose feeding except after ovariectomy, suggesting that female sex hormones may confer protection against the effects of a fructose diet.
Short-term insulin treatment and aortic expressions of IGF-1 receptor and VEGF mRNA in diabetic rats
Authors: Kobayashi Tsuneo , Kamata Katsuo
Published: March 2015

We investigated the relationship between the changes in vascular responsiveness and growth factor mRNA expressions induced by 1-wk treatment with high-dose insulin in control and established streptozotocin (STZ)-induced diabetes. Aortas from diabetic rats, but not those from insulin-treated diabetic rats, showed impaired endothelium-dependent relaxation in response to ACh (vs. untreated controls). The ACh-induced nitrite plus nitrate (NOx) level showed no significant difference between controls and diabetics. Insulin treatment increased NOx only in diabetics. In diabetics, insulin treatment significantly increased the aortic expressions of endothelial nitric oxide synthase (eNOS) mRNA and VEGF mRNA. The expression of IGF-1 mRNA was unaffected by diabetes or by insulin treatment. In contrast, the mRNA for the aortic IGF-1 receptor was increased in diabetics and further increased in insulin-treated diabetics. In aortic strips from age-matched control rats, IGF-1 caused a concentration-dependent relaxation. This relaxation was significantly stronger in strips from STZ-induced diabetic rats. These results suggest that in STZ-diabetic rats, short-term insulin treatment can ameliorate endothelial dysfunction by inducing overexpression of eNOS and/or VEGF mRNAs possibly via IGF-1 receptors. These receptors were increased in diabetes, perhaps as result of insulin deficiency.
Assessment and consequences of the constant-volume attribute of the four-chambered heart
Authors: Bowman Andrew W. , Kovács Sándor J.
Published: March 2015

The constant-volume hypothesis regarding the four-chambered heart states that total pericardial volume remains invariant throughout the cardiac cycle. Previous canine studies have indicated that the pericardial volume remains constant within 5%; however, this hypothesis has not been validated in humans using state-of-the-art technology. The constant-volume hypothesis has several predictable functional consequences, including a relationship between atrial ejection fraction and chamber equilibrium volumes. Using cardiac magnetic resonance (MR) imaging (MRI), we measured the extent to which the constant-volume attribute of the heart is valid, and we tested the accuracy of the predicted relationship between atrial ejection fraction and chamber equilibrium volumes. Eleven normal volunteers and one volunteer with congenital absence of the pericardium were imaged using a 1.5-T MR scanner. A short-axis cine-loop stack covering the entire heart was acquired. The cardiac cycle was divided into 20 intervals. For each slice and interval, pericardial volumes were measured. The slices were stacked and summed, and total pericardial volume as a function of time was determined for each subject. In the normal subjects, chamber volumes at ventricular end diastole, end systole, and diastasis were measured. Pericardial volume remained invariant within 5 ± 1% in normal subjects; maximum variation occurred near end systole. In the subject with congenital absence of the pericardium, total heart volume, defined by the epicardial surface, varied by 12%. The predictions of the relationship between atrial ejection fraction and chamber equilibrium volumes were well fit by MRI data. In normal subjects, the four-chambered heart is a constant-volume pump within 5 ± 1%, and constant-volume-based modeling accurately predicts previously unreported physiological relationships.
Fractal and periodic heart rate dynamics in fetal sheep: comparison of conventional and new measures based on fractal analysis
Authors: Koshino Takahiro , Kimura Yoshitaka , Kameyama Yoshinobu , Takahashi Takeshi , Yasui Tomoharu , Chisaka Hiroshi , Sugawara Junichi , Okamura Kunihiro
Published: March 2015

The physiological significance of spectral and fractal components of spontaneous heart rate (HR) variability in the fetus remains unclear. To examine the relationship between circadian rhythms in different measures of HR variability, R-R interval time series obtained by fetal ECGs were recorded continuously over 24 h in five pregnant sheep at 116–125 days gestation. Conventional measures of short-term (STV) and long-term variability (LTV), low-frequency (LF; 0.025–0.15 cycles/beat) and high-frequency (HF; 0.2–0.5 cycles/beat) spectral powers, the LF-to-HF ratio, and fractal dimension values were calculated from 24-h ECG recordings and quantified every 60 min. STV, LTV, and LF and HF spectral powers were minimal during the day but increased significantly to their highest values at night. We found a significant positive correlation between these measures, whereas the cosinor method showed significant similarity between their circadian rhythm patterns. Fetal R-R intervals also exhibited fractal structures. Fetal HR variability had a fractal structure, which was similar between day and night. These results suggested that the circadian rhythms exhibited by STV and LTV during the day were mainly due to changes in frequency components rather than to fractal components of fetal HR fluctuation.
Acrolein-induced vasomotor responses of rat aorta
Authors: Tsakadze Nina L. , Srivastava Sanjay , Awe Sunday O. , Adeagbo Ayotunde S. O. , Bhatnagar Aruni , D'Souza Stanley E.
Published: March 2015

Acrolein is a highly reactive aldehyde pollutant and an endogenous product of lipid peroxidation. Increased generation of, or exposures to, acrolein incites pulmonary and vascular injury. The effects of acrolein on the vasomotor responses of rat aortic rings were studied to understand its mechanism of action. Incubation with acrolein (10–100 μM) alone did not affect the resting tone of aortic vessels; however, a dose-dependent relaxation of phenylephrine-precontracted aortic rings was observed. Acrolein-induced relaxation was slow and time dependent and the extent of relaxation after 100 min of application was 44.7 ± 4.1% (10 μM), 56.0 ± 5.6% (20 μM), 61.0 ± 7.9% (40 μM), and 96.1 ± 2.1 (80 μM), respectively, versus 14.2 ± 3.3% relaxation in the absence of acrolein. Acrolein-induced vasorelaxation was prevented by endothelial denudation and was abolished on pretreatment with the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester, the guanylyl cyclase inhibitor 1 H-[1,2,4]oxidazolo[4,3- a]quinoxaline-1-one, or the cyclooxygenase inhibitor indomethacin. Inhibition of K+ channels (by tetrabutylammonium) or Na+-K+-ATPase (by ouabain) did not significantly prevent acrolein-mediated vasorelaxation. Exposure to acrolein in the presence or absence of other compounds elicited slow wave vasomotor effect in 77% of aortic vessels versus 1.4% in control. Vasomotor responses were also studied on aortic rings prepared from rats fed 2 mg · kg–1 · day–1 acrolein for 3 alternate days by oral gavage. These vessels developed a significantly lower contractile response to phenylephrine compared with controls. Together, these results indicate that acute acrolein exposure evokes delayed vasorelaxation due to a nitric oxide- and prostacyclin-dependent mechanism, whereas in vivo acrolein exposure compromises vessel contractility.
Maternal dexamethasone treatment alters myosin isoform expression and contractile dynamics in fetal arteries
Authors: Hai Chi-Ming , Sadowska Grazyna , Francois Louise , Stonestreet Barbara S.
Published: March 2015

We tested the hypothesis that maternal glucocorticoid treatment modulates 17-kDa myosin light chain (myosin LC17) isoform expression and contractile dynamics in fetal ovine carotid arteries. In the single course group, ewes received 6 mg dexamethasone or placebo over 48 h. In the repeated course group, ewes received 6 mg dexamethasone or placebo weekly for 5 wk. In response to 1 μM phenylephrine, arteries from fetuses of dexamethasone-treated ewes exhibited biphasic contractions, characterized by an intermediate relaxation phase. The relaxation rate constant was significantly higher in arteries from the fetuses of dexamethasone than placebo-treated ewes. The observed biphasic contractions suggest the appearance of functional sarcoplasmic reticulum in the arteries from the fetuses of dexamethasone-treated ewes. The myosin LC17aisoform expression was lower in the arteries from the fetuses of the placebo-treated ewes than in those from the ewes. Repeated maternal administration of dexamethasone induced an almost twofold increase in myosin LC17aisoform expression in the fetal arteries. In contrast, maternal myosin LC17a isoform expression was not affected by dexamethasone treatment. We speculate that dexamethasone-induced increases in fetal myosin LC17aisoform expression represent accelerated differentiation of a subpopulation of vascular smooth muscle cells from the fetal to adult phenotype.
Improved oxygenation in ischemic hamster flap tissue is correlated with increasing hemodilution with Hb vesicles and their O2 affinity
Authors: Contaldo Claudio , Schramm Sören , Wettstein Reto , Sakai Hiromi , Takeoka Shinji , Tsuchida Eishun , Leunig Michael , Banic Andrej , Erni Dominique
Published: March 2015

The aim of this study was to test the influence of oxygen affinity of Hb vesicles (HbVs) and level of blood exchange on the oxygenation in collateralized, ischemic, and hypoxic hamster flap tissue during normovolemic hemodilution. Microhemodynamics were investigated with intravital microscopy. Tissue Po2 was measured with Clark-type microprobes. HbVs with a P50 of 15 mmHg (HbV15) and 30 mmHg (HbV30) were suspended in 6% Dextran 70 (Dx70). The Hb concentration of the solutions was 7.5 g/dl. A stepwise replacement of 15%, 30%, and 50% of total blood volume was performed, which resulted in a gradual decrease in total Hb concentration. In the ischemic tissue, hemodilution led to an increase in microvascular blood flow to maximally 141–166% of baseline in all groups (median; P < 0.01 vs. baseline, not significant between groups). Oxygen tension was transiently raised to 121 ± 17% after the 30% blood exchange with Dx70 ( P < 0.05), whereas it was increased after each step of hemodilution with HbV15-Dx70 and HbV30-Dx70, reaching 217 ± 67% ( P < 0.01) and 164 ± 33% ( P < 0.01 vs. baseline and other groups), respectively, after the 50% blood exchange. We conclude that despite a decrease in total Hb concentration, the oxygenation in the ischemic, hypoxic tissue could be improved with increasing blood exchange with HbV solutions. Furthermore, better oxygenation was obtained with the left-shifted HbVs.
Carotid distensibility characterized via the isometric exercise pressor response
Authors: Myers Christopher W. , Farquhar William B. , Forman Daniel E. , Williams Todd D. , Dierks Dustin L. , Taylor J. Andrew
Published: March 2015

Distensibility of the large elastic arteries is a key index for cardiovascular health. Distensibility, usually estimated from resting values in humans, is not a static characteristic but a negative curvilinear function of pressure. We hypothesized that differences in vascular function with gender and age may only be recognized if distensibility is quantified over a range of pressures. We used isometric handgrip exercise to induce progressive increases in pressures and carotid diameters, thereby enhancing the characterization of distensibility. In 30 volunteers, evenly distributed by gender and age across the third to fifth decades of life, we derived pulsatile distensibility slopes as a function of arterial pressure for a dynamic distensibility index and compared it with a traditional static index at a reference pressure of 95 mmHg. We also assessed intima-media thickness (IMT). We found that women had greater distensibility slopes within each decade, despite comparable IMT. Furthermore, declines in distensibility slope with increasing age were correlated to increased IMT. The static distensibility index failed to show gender-related differences in distensibility but did show age-related differences. Our results indicate that gender- and age-related differences can be manifest even in young, healthy adults and may only be identified with techniques that assess carotid distensibility across a range of pressures.
Antiadrenergic effects of adenosine A1receptor-mediated protein phosphatase 2a activation in the heart
Authors: Liu Qinghang , Hofmann Polly A.
Published: March 2015

The ability of adenosine A1receptors to activate type 2a protein phosphatase (PP2a) and account for antiadrenergic effects was investigated in rat myocardial preparations. We observed that the adenosine A1receptor agonist N6-cyclopentyladenosine (CPA) significantly reduces the isoproterenol-induced increase in left ventricular developed pressure of isolated heats, and this effect is blocked by pretreatment of hearts with the PP2a inhibitor cantharidin. CPA alone or given in conjunction with isoproterenol stimulation decreases phosphorylation of phospholamban and troponin I in ventricular myocytes. These dephosphorylations are blocked by an adenosine A1receptor antagonist and by PP2a inhibition with okadaic acid. Adenosine A1receptor activation was also shown to increase carboxymethylation of the PP2a catalytic subunit (PP2a-C) and cause translocation of PP2a-C to the particulate fraction in ventricular myocytes. These results support the hypothesis that adenosine A1receptor activation leads to methylation of PP2a-C and subsequent translocation of the PP2a holoenzyme. Increases in localized PP2a activity lead to dephosphorylation of key cardiac proteins responsible for the positive inotropic effects of β-adrenergic stimulation.
Amplification of sumatriptan-induced contraction in rabbit saphenous vein but not in basilar artery
Authors: Bhattacharya Anindya , Schenck Kathryn W. , Cohen Marlene L.
Published: March 2015

The modulation of serotonin (5-HT1B/1D) receptor-induced vascular contractility by histamine and U-46619 was compared in the rabbit basilar artery and saphenous vein. In the saphenous vein, histamine (5 × 10−7 M) significantly increased the potency (from pEC50 of 6.0 to 6.8) and efficacy (from 52.3% to 88.2%) of sumatriptan. Likewise, U-46619 (5 × 10−9 M) also increased the potency (from pEC50 of 5.9 to 6.6) and efficacy (from 51.8% to 92.1%) of sumatriptan in the saphenous vein. In contrast, equieffective concentrations of histamine (10−7 M) and U-46619 (3 × 10−9 M) failed to amplify contraction to sumatriptan in the basilar artery. Contraction to sumatriptan was inhibited by nitrendipine (10−7 M) in the basilar artery but not in the saphenous vein, suggesting that different contractile signaling mechanisms are operating in these tissues. Furthermore, U-46619- and thrombin-induced contractility in the basilar artery were also not amplified by histamine, suggesting that lack of amplification of contraction in the basilar artery was not restricted to sumatriptan but was rather a characteristic of this cerebral vessel. These data suggest that in the in vivo plasma milieu sumatriptan will more markedly contract the peripheral saphenous vein than the basilar artery, a cerebral blood vessel.
Hypertension induced by blockade of ETB receptors in conscious nonhuman primates: role of ETAreceptors
Authors: Reinhart Glenn A. , Preusser Lee C. , Burke Sandra E. , Wessale Jerry L. , Wegner Craig D. , Opgenorth Terry J. , Cox Bryan F.
Published: March 2015

The role of endothelin-B (ETB) receptors in circulatory homeostasis is ambiguous, reflecting vasodilator and constrictor effects ascribed to the receptor and diuretic and natriuretic responses that could oppose the hypertensive effects of ET excess. With the use of conscious, telemetry-instrumented cynomolgus monkeys, we characterized the hypertension produced by ETB blockade and the role of ETA receptors in mediating this response. Mean arterial pressure (MAP) and heart rate (HR) were measured 24 h/day for 24 days under control conditions and during administration of the ETB-selective antagonist A-192621 (0.1, 1.0, and 10 mg/kg bid, 4 days/dose) followed by coadministration of the ETAantagonist atrasentan (5 mg/kg bid) + A-192621 (10 mg/kg bid) for another 4 days. High-dose ETB blockade increased MAP from 79 ± 3 (control) to 87 ± 3 and 89 ± 3 mmHg on the first and fourth day, respectively; HR was unchanged, and plasma ET-1 concentration increased from 2.1 ± 0.3 pg/ml (control) to 7.24 ± 0.99 and 11.03 ± 2.37 pg/ml. Atrasentan + A-192621 (10 mg/kg) decreased MAP from hypertensive levels (89 ± 3) to 75 ± 2 and 71 ± 4 mmHg on the first and fourth day, respectively; plasma ET-1 and HR increased to 26.64 ± 3.72 and 28.65 ± 2.89 pg/ml and 113 ± 5 (control) to 132 ± 5 and 133 ± 7 beats/min. Thus systemic ETB blockade produces a sustained hypertension in conscious nonhuman primates, which is mediated by ETA receptors. These data suggest an importance clearance function for ETB receptors, one that influences arterial pressure homeostasis indirectly by reducing plasma ET-1 levels and minimizing ETA activation.
Bimodal δ-opioid receptors regulate vagal bradycardia in canine sinoatrial node
Authors: K. Jackson M. Farias , Yoshishige D. , Caffrey J. L.
Published: March 2015

Methionine-enkephalin-arginine-phenylalanine (MEAP) introduced into the interstitium of the canine sinoatrial (SA) node by microdialysis interrupts vagal bradycardia. In contrast, raising endogenous MEAP by occluding the SA node artery improves vagal bradycardia. Both are blocked by the same δ-selective antagonist, naltrindole. We tested the hypothesis that vagal responses to intranodal enkephalin are bimodal and that the polarity of the response is both dose- and opioid receptor subtype dependent. Ultralow doses of MEAP were introduced into the canine SA node by microdialysis. Heart rate frequency responses were constructed by stimulating the right vagus nerve at 1, 2, and 3 Hz. Ultralow MEAP infusions produced a 50–100% increase in bradycardia during vagal stimulation. Maximal improvement was observed at a dose rate of 500 fmol/min with an ED50near 50 fmol/min. Vagal improvement was returned to control when MEAP was combined with the δ-antagonist naltrindole. The dose of naltrindole (500 fmol/min) was previously determined as ineffective vs. the vagolytic effect of higher dose MEAP. When MEAP was later reintroduced in the same animals at nanomoles per minute, a clear vagolytic response was observed. The δ1-selective antagonist 7-benzylidenenaltrexone (BNTX) reversed the vagal improvement with an ED50near 1 × 10–21mol/min, whereas the δ2-antagonist naltriben had no effect through 10–9mol/min. Finally, the improved vagal bradycardia previously associated with nodal artery occlusion and endogenous MEAP was blocked by the selective δ1-antagonist BNTX. These data support the hypothesis that opioid effects within the SA node are bimodal in character, that low doses are vagotonic, acting on δ1-receptors, and that higher doses are vagolytic, acting on δ2-receptors.
An implantable bolus infusion pump for use in freely moving, nontethered rats
Authors: Holschneider D. P. , Maarek J.-M. I. , Harimoto J. , Yang J. , Scremin O. U.
Published: March 2015

One of the current constraints on functional neuroimaging in animals is that to avoid movement artifacts during data acquisition, subjects need to be immobilized, sedated, or anesthetized. Such measures limit the behaviors that can be examined, and introduce the additional variables of stress or anesthetic agents that may confound meaningful interpretation. This study provides a description of the design and characteristics of a self-contained, implantable microbolus infusion pump (MIP) that allows triggering of a bolus injection at a distance in conscious, behaving rats that are not restrained or tethered. The MIP is externally triggered by a pulse of infrared light and allows in vivo bolus drug delivery. We describe application of this technology to the intravenous bolus delivery of iodo[14C]antipyrine in a freely moving animal, followed immediately by lethal injection, rapid removal of the brain, and analysis of regional cerebral blood flow tissue radioactivity with the use of autoradiography. The ability to investigate changes in brain activation in nonrestrained animals makes the MIP a powerful tool for evaluation of complex behaviors.
Intramyocardial pressure measurements in the stage 18 embryonic chick heart
Authors: Chabert Steren , Taber Larry A.
Published: March 2015

Intramyocardial pressure (IMP) and ventricular pressure (VP) were measured in the trabeculating heart of the stage 18 chick embryo (3 days of incubation). Pressure was measured at several locations across the ventricle using a fluid-filled servo-null system. Maximum systolic and minimum diastolic IMP tended to be greater in the dorsal wall than in the ventral wall, but transmural distributions of peak active (maximum minus minimum) IMP were similar in both walls. Peak active IMP near midwall was similar to peak active VP, but peak active IMP in the subepicardial and subendocardial layers was four to five times larger. These results suggest that the passive stiffness of the dorsal wall is greater than that of the ventral wall and that during contraction the inner and outer layers of both walls generate more contractile force and/or become less permeable to flow than the middle part of the wall. Measured pressures likely correspond to regional variations in wall stress that may influence morphogenesis and function in the embryonic heart.