bluuebunny/crossref_metadata_2025 huggingface dataset:
Resistance of endothelium-dependent relaxation to elevation of O 2 − levels in rabbit carotid artery
Authors: Pagano Patrick J. , Griswold Mark C. , Najibi Soheil , Marklund Stefan L. , Cohen Richard A.
Published: December 2017

Endogenous superoxide anion[Formula: see text] interferes with the bioactivity of nitric oxide (NO) in endothelium-dependent arterial relaxation (EDR). Using the lucigenin chemiluminescence assay, we measured[Formula: see text] in the thoracic and abdominal aortas and the carotid artery of rabbits to determine whether ambient[Formula: see text] varies among the three arteries and differentially diminishes the effect of NO. Basal levels of[Formula: see text] were significantly higher in carotid arteries than in the thoracic aorta [23 ± 6.1 vs. 3.9 ± 1.4 chemiluminescence units (CU); P < 0.05], whereas EDR in response to ACh (10−8–10−5M) was not significantly different on ANOVA. After treatment with the superoxide dismutase (SOD) inhibitor diethyldithiocarbamate (DDC; 10 mM), [Formula: see text] levels were significantly elevated, becoming greater in the carotid artery and abdominal aorta than in the thoracic aorta (185 ± 31.2 and 202 ± 40.3 vs. 89 ± 18 CU; P < 0.05). DDC significantly reversed EDR in the thoracic aorta but not in the carotid artery; at 10−6M ACh, the decrease seen with DDC was 48 ± 6.2 vs. 6.8 ± 8.0% of maximal relaxation in the thoracic aorta and carotid artery, respectively. In the thoracic aorta, exogenous SOD reversed the inhibition of EDR caused by DDC. Moreover, DDC/[Formula: see text]-resistant EDR in the carotid artery was ablated by the addition of nitro-l-arginine methyl ester (300 μM; P < 0.05), an NO synthase inhibitor, consistent with peroxynitrite or an[Formula: see text]-resistant NO donor being involved in carotid relaxation. Indeed, exogenous peroxynitrite caused similar relaxation of the carotid artery and thoracic aorta, which was unaffected by DDC. Our studies show a greater production of nitrite and[Formula: see text] per unit area by the carotid artery, suggesting a greater amount of their product peroxynitrite. These findings support the hypothesis that peroxynitrite is the relaxing agent that resists high [Formula: see text] in the carotid artery.
Integrin signaling, free radicals, and tyrosine kinase mediate flow constriction in isolated cerebral arteries
Authors: Madden Jane A. , Christman Norbert J. T.
Published: December 2017

Isolated, cannulated, and pressurized (100 mmHg) middle cerebral arteries from adult cats were perfused intraluminally at rates from 0 to 4 ml/min with heated and gassed physiological saline solution. An electronic system held pressure constant by changing outflow resistance. The arteries constricted 18.1 ± 0.95% in response to flow and depolarized from −54 ± 0.51 to −40 ± 1.26 mV ( P < 0.05). Constriction was independent of a functional endothelium but was eliminated by superoxide dismutase or tyrosine kinase inhibitors. Luminal perfusion with a synthetic extracellular matrix Arg-Gly-ASP (RGD) peptide that binds with integrin significantly reduced constriction to flow. Neither reducing intraluminal pressure nor increasing tone or shear stresses altered constriction to flow. Flow-induced constriction did not impede the ability of the arteries to dilate to hypercapnia, and inhibiting flow-induced constriction did not alter contractile responses to other agonists. These data suggest that, in vitro, middle cerebral arteries constrict to flow through a mechanism involving free radicals and tyrosine kinase and that flow shear stresses resulting in constriction are transduced by integrin signaling.
Comparison of SERCA1 and SERCA2a expressed in COS-1 cells and cardiac myocytes
Authors: Sumbilla Carlota , Cavagna Marco , Zhong Lilin , Ma Hailun , Lewis David , Farrance Iain , Inesi Giuseppe
Published: December 2017

Cultured COS-1 cells, as well as chicken embryonic and neonatal rat cardiac myocytes, were infected with recombinant adenovirus vectors to define limiting factors in the expression and Ca2+transport function of recombinant sarcoplasmic-endoplasmic reticulum Ca2+(SERCA) isoforms. Titration experiments showed that all COS-1 cells and myocytes in culture could be infected by an adenovirus titer of 10 plaque-forming units (pfu) per seeded cell. Raising the adenovirus titer further yielded higher protein expression up to an asymptotic limit for functional, membrane-bound SERCA protein. The asymptotic behavior of SERCA expression was not transcription related but was due to posttranscriptional events. The minimal (−268) cardiac troponin T (cTnT) promoter was a convenient size for adenovirus vector construction and manifested tight muscle specificity. However, its efficiency was lower than that of the nonspecific cytomegalovirus (CMV) promoter. At any rate, identical maximal levels of SERCA expression were obtained with the CMV and the cTnT promoter, as long as the viral titer was adjusted to compensate for transcription efficiency. A maximal threefold increase of total SERCA protein expression over the level of the endogenous SERCA of control myocytes was reached (a sevenfold increase compared with the endogenous SERCA of the same infected myocytes due to reduction of endogenous SERCA after infection). In contrast with previous reports [Ji et al. Am. J. Physiol. 276 ( Heart Circ. Physiol. 45): H89–H97, 1999], a higher kinetic turnover was demonstrated for the SERCA1 compared with the SERCA2a isoform as shown by a 5.0- versus 2.6-fold increase in calcium uptake rate accompanying maximal expression of recombinant SERCA1 or SERCA2a, respectively. This information is deemed necessary for studies attempting to modify myocardial cell function by manipulation of SERCA expression.
Met5-enkephalin protects isolated adult rabbit cardiomyocytes via δ-opioid receptors
Authors: Takasaki Yasushi , Wolff Roger A. , Chien Grace L. , van Winkle Donna M.
Published: December 2017

In rats and rabbits, endogenous opioid peptides participate in ischemic preconditioning. However, it is not known which endogenous opioid(s) can trigger cardioprotection. We examined preconditioning-induced and opioid-induced limitation of cell death in isolated, calcium-tolerant, adult rabbit cardiomyocytes. Cells were subjected to simulated ischemia by pelleting and normothermic hypoxic incubation. Preconditioning was elicited with 15 min of simulated ischemia followed by 15 min of resuspension and reoxygenation. All cells underwent 180 min of simulated ischemia. Cell death was assessed by trypan blue permeability. Morphine protected cells, as did preconditioning; naloxone blocked the preconditioning-induced protection. Exogenous Met5-enkephalin (ME) induced protection, but exogenous β-endorphin did not. ME-induced protection was blocked by the δ-selective antagonist naltrindole. Additionally, two other proenkephalin products, Leu5-enkephalin and Met5-enkephalin-Arg-Phe, provided protection equipotent to ME. These data suggest that one or more proenkephalin products interact with δ-opioid receptors to endogenously trigger opioid-mediated protection.
Extracellular Ba2+blocks the cardiac transient outward K+current
Authors: Shi Hong , Wang Hui-Zhen , Wang Zhiguo
Published: December 2017

Ba2+is widely used as a tool in patch-clamp studies because of its ability to block a variety of K+channels and to pass Ca2+channels. Its potential ability to block the cardiac transient outward K+current ( Ito) has not been clearly documented. We performed whole cell patch-clamp studies in canine ventricular and atrial myocytes. Extracellular application of Ba2+produced potent inhibition of Itowith an IC50of ∼40 μM. The effects were voltage independent, and the inactivation kinetics were not altered by Ba2+. The potency of Ba2+was ∼10 times higher than that of 4-aminopyridine (a selective Itoblocker with an IC50of 430 μM) under identical conditions. By comparison, Ba2+blockade of the inward rectifier K+current was voltage dependent; the IC50was ∼20 times lower (2.5 μM) than that for Itowhen determined at −100 mV and was comparable to Itoas determined at −60 mV (IC50= 26 μM). Ba2+concentrations of ≤1 mM or higher failed to block ultrarapid delayed rectifier K+current. Our data suggest that Ba2+can be considered a potent blocker of Ito.
Mechanism of preserved positive lusitropy by cAMP-dependent drugs in heart failure
Authors: Tanigawa Taketo , Yano Masafumi , Kohno Michihiro , Yamamoto Takeshi , Hisaoka Takayuki , Ono Kaoru , Ueyama Takeshi , Kobayashi Shigeki , Hisamatsu Yuhji , Ohkusa Tomoko , Matsuzaki Masunori
Published: December 2017

In tachycardia-induced heart failure (HF), positive lusitropic effects of milrinone or dobutamine were assessed by evaluating the time constant of left ventricular (LV) pressure decay (τ) and Ca2+-ATPase activity of the sarcoplasmic reticulum (SR). The peak value of the positive first derivative of LV pressure (+dP/d t) was less increased, either by dobutamine (2–10 μg ⋅ kg−1 ⋅ min−1) or by milrinone (4–20 μg/kg), in HF than in control ( P< 0.05), whereas τ was shortened to an extent similar to that in control with dobutamine [ P = not significant (NS)] and to an even greater extent with milrinone ( P < 0.05). Ca2+-ATPase activity increased similarly in HF and control with dobutamine (1 μM; +11% in HF vs. +12% in control, P = NS), whereas it increased more with milrinone (1 μM; +19% in HF vs. +11% in control, P < 0.05). Ca2+-ATPase activity-cAMP relationships were shifted to the left by milrinone or dobutamine in HF compared with control. Thus, in HF, the sensitivity of Ca2+-ATPase activity to cAMP was increased on addition of cAMP-dependent inotropic agents, contributing to the preservation of positive lusitropy.
Functional role of angiotensin II type 1 and 2 receptors in regulation of uterine blood flow in nonpregnant sheep
Authors: Lambers Donna S. , Greenberg Suzanne G. , Clark Kenneth E.
Published: December 2017

The objective was to determine the receptor subtype of angiotensin II (ANG II) that is responsible for vasoconstriction in the nonpregnant ovine uterine and systemic vasculatures. Seven nonpregnant estrogenized ewes with indwelling uterine artery catheters and flow probes received bolus injections (0.1, 0.3 and 1 μg) of ANG II locally into the uterine artery followed by a systemic infusion of ANG II at 100 ng ⋅ kg−1 ⋅ min−1for 10 min to determine uterine vasoconstrictor responses. Uterine ANG II dose-response curves were repeated following administration of the ANG II type 2 receptor (AT2) antagonist PD-123319 and then repeated again in the presence of an ANG II type 1 receptor (AT1) antagonist L-158809. In a second experiment, designed to investigate the mechanism of ANG II potentiation that occurred in the presence of AT2 blockade, nonestrogenized sheep received a uterine artery infusion of L-158809 (3 mg/min for 5 min) prior to the infusion of 0.03 μg/min of ANG II for 10 min. ANG II produced dose-dependent decreases in uterine blood flow ( P < 0.03), which were potentiated in the presence of the AT2 antagonist ( P < 0.02). Addition of the AT1 antagonist abolished the uterine vascular responses and blocked ANG II-induced increases in systemic arterial pressure ( P < 0.01). Significant uterine vasodilation ( P < 0.01) was noted with AT1 blockade in the second experiment, which was reversed by administration of the AT2 antagonist or by the nitric oxide synthetase inhibitor N ω-nitro-l-arginine methyl ester. We conclude that the AT1- receptors mediate the systemic and uterine vasoconstrictor responses to ANG II in the nonpregnant ewe. AT2-receptor blockade resulted in a potentiation of the uterine vasoconstrictor response to ANG II, suggesting that the AT2-receptor subtype may modulate uterine vascular responses to ANG II potentially by release of nitric oxide.
Increased urinary excretion of uroguanylin in patients with congestive heart failure
Authors: Carrithers Stephen L. , Eber Sammy L. , Forte Leonard R. , Greenberg Richard N.
Published: December 2017

Uroguanylin is a small-molecular-weight peptide that activates membrane-bound receptor-guanylate cyclases in the intestine, kidney, and other epithelia. Uroguanylin has been shown to participate in the regulation of salt and water homeostasis in mammals via cGMP-mediated processes, bearing a distinct similarity to the action of the atriopeptins, which play a defined role in natriuresis and act as prognostic indicators of severe congestive heart failure (CHF). The objectives of this study were to measure the urinary levels of uroguanylin and the circulating plasma levels of atrial natriuretic peptide (ANP) in healthy individuals ( n = 53) and patients with CHF ( n = 16). Urinary excretion of uroguanylin was assessed by a cGMP accumulation bioassay employing human T84 intestinal cells. In individuals without CHF, the concentration of uroguanylin bioactivity was 1.31 ± 0.27 nmol cGMP/ml urine and 1.73 ± 0.25 μmol cGMP/24-h urine collection. The urinary bioactivity of uroguanylin in males (1.74 ± 0.55 nmol cGMP/ml urine; n = 27) tended to be higher than the excretion levels in females (0.94 ± 0.16 nmol cGMP/ml urine; n = 26) over a 24-h period but did not achieve statistical significance. Both male and female groups showed 24-h temporal diurnal variations with the highest uroguanylin levels observed between the hours of 8:00 AM and 2:00 PM. The circulating level of ANP was 12.1 ± 1.6 pg/ml plasma and did not significantly vary with respect to male/female population or diurnal variation. In patients with CHF, the concentration of plasma ANP and urinary uroguanylin bioactivity increased substantially (7.5-fold and 70-fold, respectively, both P≤ 0.001) compared with healthy levels. Uroguanylin was purified from the urine of CHF patients and shown to be the bioactive, COOH-terminal, 16 amino acid portion of the human prouroguanylin protein. The increased urinary uroguanylin excretion observed during CHF may be an adaptive response to this cardiovascular pathophysiology.
Glucose-insulin-potassium preserves systolic and diastolic function in ischemia and reperfusion in pigs
Authors: Zhu Peili , Lu Li , Xu Ya , Greyson Clifford , Schwartz Gregory G.
Published: December 2017

Clinical and experimental studies have suggested benefit of treatment with intravenous glucose-insulin-potassium (GIK) in acute myocardial infarction. However, patients hospitalized with acute coronary syndromes often experience recurrent myocardial ischemia without infarction that may cause progressive left ventricular (LV) dysfunction. This study tested the hypothesis that anticipatory treatment with GIK attenuates both systolic and diastolic LV dysfunction resulting from ischemia and reperfusion without infarction in vivo. Open-chest, anesthetized pigs underwent 90 min of moderate regional ischemia (mean subendocardial blood flow 0.3 ml ⋅ g−1 ⋅ min−1) and 90 min reperfusion. Eight pigs were treated with GIK (300 g/l glucose, 50 U/l insulin, and 80 meq/l KCl; infused at 2 ml ⋅ kg−1 ⋅ h−1) beginning 30 min before ischemia and continuing through reperfusion. Eight untreated pigs comprised the control group. Regional LV wall area was measured with orthogonal pairs of sonomicrometry crystals. GIK significantly increased myocardial glucose uptake and lactate release during ischemia. After reperfusion, indexes of regional systolic function (external work and fractional systolic wall area reduction), regional diastolic function (maximum rate of diastolic wall area expansion), and global LV function (LV positive and negative maximum rate of change in pressure with respect to time) recovered to a significantly greater extent in GIK-treated pigs than in control pigs (all P < 0.05). The findings suggest that the clinical utility of GIK may extend beyond treatment of acute myocardial infarction to anticipatory metabolic protection of myocardium in patients at risk for recurrent episodes of ischemia.
Resolution of smooth muscle and endothelial pathways for conduction along hamster cheek pouch arterioles
Authors: Bartlett Iain S. , Segal Steven S.
Published: December 2017

In the cheek pouch of anesthetized male hamsters, microiontophoresis of Ach (endothelium-dependent vasodilator) or phenylephrine (PE; smooth muscle-specific vasoconstrictor) onto an arteriole (resting diameter, 30–40 μm) evokes vasodilation or vasoconstriction (amplitude, 15–25 μm), respectively, that conducts along the arteriolar wall. In previous studies of conduction, endothelial and smooth muscle layers of the arteriolar wall have remained intact. We tested whether selective damage to endothelium or to smooth muscle would disrupt the initiation and conduction of vasodilation or vasoconstriction. Luminal (endothelial) or abluminal (smooth muscle) light-dye damage was produced within an arteriolar segment centered 500 μm upstream from the distal site of stimulation; conducted responses (amplitude, 10–15 μm) were observed at a proximal site located 1,000 μm upstream. Endothelial damage abolished local responses to ACh in the central segment without affecting those to PE. Nevertheless, ACh delivered at the distal site evoked vasodilation that conducted through the central segment and appeared unhindered at the proximal site. Smooth muscle damage inhibited responses to PE in the central segment and abolished the conduction of vasoconstriction but did not affect conducted vasodilation. We suggest that for cheek pouch arterioles in vivo, vasoconstriction to PE is initiated and conducted within the smooth muscle layer alone. In contrast, once vasodilation to ACh is initiated via intact endothelial cells, the signal is conducted along smooth muscle as well as endothelial cell layers.
Quantification of eNOS mRNA in the canine cardiac vasculature by competitive PCR
Authors: Fulton David , Papapetropoulos Andreas , Zhang Xiaoping , Catravas John D. , Hintze Thomas H. , Sessa William C.
Published: December 2017

The goal of the present study was to develop a competitive PCR assay to measure changes in the expression of endothelial nitric oxide synthase (eNOS) mRNA levels throughout the canine vascular tree. A partial sequence of canine eNOS cDNA (1.86 kb), inducible NOS (1.95 kb), and neuronal NOS (1.16 kb) was cultured from canine aortic endothelial cells, LPS-treated canine splenic vein endothelial cells, and from canine left ventricle, respectively. Competitor eNOS cDNA (eNOS-C) was constructed via recombinant PCR. Thus, with the use of a standard curve competitive PCR with eNOS-C, the amount of eNOS mRNA in 500 ng of total RNA was greatest in the circumflex > right coronary artery > left anterior descending coronary artery > aorta. The isolation of coronary microvessels from the left ventricle was associated with an enrichment of endothelial cell markers such as eNOS, von Willebrand factor, and caveolin-1, an observation supported by the detection of up to 15-fold higher levels of eNOS mRNA in coronary microvessels relative to the larger arteries. The ability to quantify changes in eNOS mRNA levels throughout the canine vasculature should provide greater insight into the molecular mechanisms of how this gene is regulated in physiological and pathophysiological states.
Phosphorylation of phospholamban and troponin I in β-adrenergic-induced acceleration of cardiac relaxation
Authors: Li Li , Desantiago Jaime , Chu Guoxiang , Kranias Evangelia G. , Bers Donald M.
Published: December 2017

Activation of cAMP-dependent protein kinase A (PKA) in ventricular myocytes by isoproterenol (Iso) causes phosphorylation of both phospholamban (PLB) and troponin I (TnI) and accelerates relaxation by up to twofold. Because PLB phosphorylation increases sarcoplasmic reticulum (SR) Ca pumping and TnI phosphorylation increases the rate of Ca dissociation from the myofilaments, both factors could contribute to the acceleration of relaxation seen with PKA activation. To compare quantitatively the role of TnI versus PLB phosphorylation, we measured relaxation rates before and after maximal Iso treatment for twitches of matched amplitudes in ventricular myocytes and muscle from wild-type (WT) mice and from mice in which the PLB gene was knocked out (PLB-KO). Because Iso increases contractions, even in the PLB-KO mouse, extracellular [Ca] or sarcomere length was adjusted to obtain matching twitch amplitudes (in the presence and absence of Iso). In PLB-KO myocytes and muscles (which were allowed to shorten), Iso did not alter the time constant (τ) of relaxation (∼29 ms). However, with increasing isometric force development in the PLB-KO muscles, Iso progressively but modestly accelerated relaxation (by 17%). These results contrast with WT myocytes and muscles where Iso greatly reduced τ of cell relaxation and intracellular Ca concentration decline (by 30–50%), independent of mechanical load. The Iso treatment used produced comparable increases in phosphorylation of TnI and PLB in WT. We conclude that the effect of β-adrenergic activation on relaxation is mediated entirely by PLB phosphorylation in the absence of external load. However, TnI phosphorylation could contribute up to 14–18% of this lusitropic effect in the WT mouse during maximal isometric contractions.
Serotonin 5-HT7receptors mediate relaxation of porcine pial veins
Authors: Ishine Takaaki , Bouchelet Isabelle , Hamel Edith , Lee Tony J. F.
Published: December 2017

Isolated porcine pial veins in the presence of active muscle tone have been shown to exhibit rhythmic contractions (RC) that are inhibited by serotonin (5-HT) in a concentration-dependent manner. The 5-HT inhibition of RC is mediated by an as yet unidentified 5-HT receptor subtype located on the vascular smooth muscle. 5-carboxamidotryptamine, which is a potent but nonselective agonist at 5-HT7receptors, has been shown to be the most potent inhibitor of RC in porcine pial veins. Therefore, the present study was designed to determine if the 5-HT-mediated inhibition of RC in pial veins is mediated by 5-HT7receptors and if 5-HT7receptor mRNA is expressed in endothelium-denuded pial veins; the study was done with the use of an in vitro tissue bath and RT-PCR techniques. Our findings indicated that 5-HT inhibition of RC in porcine pial veins was prevented by 5-HT7-receptor antagonists (clozapine, pimozide, and LY-215840) in a concentration-dependent manner. Furthermore, a strong PCR signal for the 5-HT7receptor was consistently detected in endothelium-denuded pial veins. Sequence analysis of the amplified products confirmed their high degree of homology with the porcine and/or human 5-HT7-receptor gene. Taken together, these data suggest that the 5-HT-induced inhibition of RC in porcine pial veins is at least in part mediated by 5-HT7receptors located on the venous smooth muscle.
Modeling short-term interval-force relations in cardiac muscle
Authors: Rice J. Jeremy , Jafri M. Saleet , Winslow Raimond L.
Published: December 2017

This study employs two modeling approaches to investigate short-term interval-force relations. The first approach is to develop a low-order, discrete-time model of excitation-contraction coupling to determine which parameter combinations produce the degree of postextrasystolic potentiation seen experimentally. Potentiation is found to increase 1) for low recirculation fraction, 2) for high releasable fraction, i.e., the maximum fraction of Ca2+released from the sarcoplasmic reticulum (SR) given full restitution, and 3) for strong negative feedback of the SR release on sarcolemmal Ca2+influx. The second modeling approach is to develop a more detailed single ventricular cell model that simulates action potentials, Ca2+-handling mechanisms, and isometric force generation by the myofilaments. A slow transition from the adapted state of the ryanodine receptor produces a gradual recovery of the SR release and restitution behavior. For potentiation, a small extrasystolic release leaves more Ca2+in the SR but also increases the SR loading by two mechanisms: 1) less Ca2+-induced inactivation of L-type channels and 2) reduction of action potential height by residual activation of the time-dependent delayed rectifier K+current, which increases Ca2+influx. The cooperativity of the myofilaments amplifies the relatively small changes in the Ca2+transient amplitude to produce larger changes in isometric force. These findings suggest that short-term interval-force relations result mainly from the interplay of the ryanodine receptor adaptation and the SR Ca2+loading, with additional contributions from membrane currents and myofilament activation.
Functional expression of NOS 1 in vascular smooth muscle
Authors: Brophy Colleen M. , Knoepp Louis , Xin Jingdong , Pollock Jennifer S.
Published: December 2017

Substances that increase intracellular calcium concentration ([Ca2+]i), such as serotonin, are known to induce vascular smooth muscle (VSM) contraction. However, increases in [Ca2+]ialso activate Ca2+/calmodulin-dependent nitric oxide synthases (NOS), which leads to increases in cGMP and activation of cGMP-dependent protein kinase (PKG). One recently identified substrate protein of PKG is the small heat shock protein, HSP20. The purpose of this study was to determine if serotonin activates a Ca2+-dependent NOS in VSM. Strips of bovine carotid arterial smooth muscle denuded of endothelium were stimulated with serotonin in the presence and absence of the nonspecific NOS inhibitor N-monomethyl-l-arginine (l-NMMA). Activation of NOS was determined by increases in cGMP and in the phosphorylation of HSP20. Immunohistochemical and Western blotting techniques were performed to identify specific NOS isoforms in bovine carotid arterial smooth muscle preparations. Serotonin stimulation led to significant increases in cGMP and in the phosphorylation of HSP20, which were inhibited by pretreatment with l-NMMA. Antibodies against NOS 1 stained the media of bovine carotid and human renal arteries, whereas antibodies against NOS 3 stained only the endothelium. Additionally, the conversion of radiolabeledl-arginine to l-citrulline NOS activity demonstrated a consistent amount of activity present in the endothelium-denuded smooth muscle preparations that was reduced by 99% with an NOS 1 specific inhibitor. Finally, an NOS 1 specific inhibitor, 7-nitroindazole, augmented contractions induced by high extracellular KCl. This study demonstrates that NOS 1 is present in VSM and may effect physiological contractile responses.
Effect of 6-wk estrogen withdrawal or replacement on myocardial ischemic tolerance in rats
Authors: McNulty Patrick H. , Jagasia Dinesh , Whiting Jennifer M. , Caulin-Glaser Teresa
Published: December 2017

Menopausal status is a risk factor for coronary artery disease death, but the mechanism underlying this association is uncertain. To test whether estrogen ameliorates the effects of acute myocardial ischemia in ways likely to translate into a mortality difference, we compared the response to brief (6-min) and prolonged (45-min) coronary occlusion in vivo in five groups (each n = 16) of rats: ovariectomized females; ovariectomized females after 6 wk 17β-estradiol replacement; male rats supplemented with estradiol for 6 wk; normal males; and normal females. Coronary occlusion produced a uniform ischemic risk area averaging 53 ± 3% of left ventricular volume. After a brief occlusion, reperfusion ventricular tachycardia/fibrillation occurred with >85% frequency in all groups. During a prolonged occlusion, ischemic ventricular tachycardia occurred in 100% and sustained tachycardia requiring cardioversion in >75% of rats in all groups. Myocardial infarct size averaged 52 ± 4% of the ischemic risk area and was similarly unaffected by gender or estrogen status. We conclude that neither short-term estrogen withdrawal, replacement, nor supplementation significantly affects the potentially lethal outcomes from acute coronary occlusion in this species.
The thyroid hormone analog DITPA restoresI to in rats after myocardial infarction
Authors: Wickenden Alan D. , Kaprielian Roger , You Xiao-Mang , Backx Peter H.
Published: December 2017

Previous studies have established that reductions in repolarizing currents occur in heart disease and can contribute to life-threatening arrhythmias in myocardium. In this study, we investigated whether the thyroid hormone analog 3,5-diiodothyropropionic acid (DITPA) could restore repolarizing transient outward K+ current ( I to) density and gene expression in rat myocardium after myocardial infarction (MI). Our findings show that I to density was reduced after MI (14.0 ± 1.0 vs. 10.2 ± 0.9 pA/pF, sham vs. post-MI at +40 mV). mRNA levels of Kv4.2 and Kv4.3genes were decreased but Kv1.4 mRNA levels were increased post-MI. Corresponding changes in Kv4.2 and Kv1.4 protein were also observed. Chronic treatment of post-MI rats with 10 mg/kg DITPA restored I to density (to 15.2 ± 1.1 pA/pF at +40 mV) as well as Kv4.2 and Kv1.4 expression to levels observed in sham-operated controls. Other membrane currents (Na+, L-type Ca2+, sustained, and inward rectifier K+ currents) were unaffected by DITPA treatment. Associated with the changes in I toexpression, action potential durations (current-clamp recordings in isolated single right ventricular myocytes and monophasic action potential recordings from the right free wall in situ) were prolonged after MI and restored with DITPA treatment. Our results demonstrate that DITPA restores I to density in the setting of MI, which may be useful in preventing complications associated with I to downregulation.
Role of a glycocalyx on coronary arteriole permeability to proteins: evidence from enzyme treatments
Authors: Huxley Virginia H. , Williams Donna A.
Published: December 2017

Whereas the glycocalyx of endothelial cells has been shown to influence solute flux from capillary microvessels, little is known about its contribution to the movement of macromolecules across the walls of other microvessels. We evaluated the hypothesis that a glycocalyx contributes resistance to protein flux measured in coronary arterioles. Apparent solute permeability ( Ps) to two proteins of different size and similar charge, α-lactalbumin (α-lactalb) and porcine serum albumin (PSA), was determined in arterioles isolated from the hearts of 43 female Yucatan miniature swine. Pswas assessed in arterioles with an “intact” glycocalyx under control conditions and again after suffusion with adenosine (Ado, 10−5M, n = 42 arterioles, N = 29 pigs). In a second set of experiments ( n = 21 arterioles, N = 21 pigs) arteriolar Pswas determined before and after perfusion with enzyme (pronase or heparinase), which was used to digest the glycocalyx. Pswas assessed a third time on those microvessels after exposure to Ado. Consistent with the hypothesis, Psfor PSA ([Formula: see text]) and Psfor α-lactalb ([Formula: see text]) increased from basal levels following enzyme treatment. Subsequent suffusion with Ado, a significant metabolite known to alter coronary vascular smooth muscle tone and permeability, resulted in a significant reduction of basal [Formula: see text] in both untreated and enzyme-treated arterioles. Furthermore, in untreated arterioles, [Formula: see text] was unchanged by Ado suffusion, whereas Ado induced a pronounced reduction in[Formula: see text] of enzyme-treated vessels. These data demonstrate that in intact coronary arterioles an enzyme-sensitive layer, most likely at the endothelial cell surface, contributes significantly to net barrier resistance to solute flux.
Diabetes abolishes ischemic preconditioning: role of glucose, insulin, and osmolality
Authors: Kersten Judy R. , Toller Wolfgang G. , Gross Eric R. , Pagel Paul S. , Warltier David C.
Published: December 2017

Recent evidence indicates that hyperglycemia is an important risk factor for the development of cardiovascular disease. We tested the hypothesis that myocardial infarct size is related to blood glucose concentration in the presence or absence of ischemic preconditioning (PC) stimuli in canine models of diabetes mellitus and acute hyperglycemia. Barbiturate-anesthetized dogs were subjected to a 60-min period of coronary artery occlusion and 3-h reperfusion. Infarct size was 24 ± 2% of the area at risk (AAR) for infarction in control dogs. PC significantly ( P < 0.05) decreased the extent of infarction in normal (8 ± 2% of AAR), but not diabetic (22 ± 4% of AAR), dogs. Infarct size was linearly related to blood glucose concentration during acute hyperglycemia ( r = 0.96; P < 0.001) and during diabetes ( r= 0.74; P < 0.002) in the presence or absence of PC stimuli. Increases in serum osmolality caused by administration of raffinose (300 g) did not increase infarct size (11 ± 3% of AAR) or interfere with the ability of PC to protect against infarction (2 ± 1% of AAR). The results indicate that hyperglycemia is a major determinant of the extent of myocardial infarction in the dog.
Translational inhibition of E-selectin expression stimulates P-selectin-dependent neutrophil recruitment
Authors: Ostrovsky Lena , Carvalho-Tavares Juliana , Woodman Richard C. , Kubes Paul
Published: December 2017

Although known for its role in hemostasis, there is a growing body of evidence that thrombin can induce leukocyte recruitment and contribute to the inflammatory response. An in vitro parallel-plate flow chamber was used to systematically examine thrombin-induced neutrophil interactions with human endothelium. Stimulation of endothelial cells with thrombin (1 U/ml) resulted in an immediate, P-selectin-dependent increase in neutrophil rolling and adhesion that was comparable in magnitude to optimal levels of histamine (the classical inducer of P-selectin). However, thrombin, but not histamine, induced a delayed (4 h) E-selectin-dependent rolling similar to that of tumor necrosis factor-α, suggesting that thrombin has the unique ability to recruit neutrophils by an early P-selectin and a delayed E-selectin pathway. Surprisingly, inhibition of E-selectin expression with the general protein synthesis inhibitor cycloheximide induced P-selectin expression 4 h after thrombin stimulation. Cycloheximide and thrombin (4 h) induced sufficient P-selectin-dependent rolling to recruit as many neutrophils as were recruited with 4 h of stimulation with thrombin alone. Histamine in the presence of cycloheximide or cycloheximide alone did not evoke the P-selectin response at 4 h, suggesting that this was not due to direct cycloheximide induction of P-selectin. Treatment of endothelium with tumor necrosis factor-α (an E-selectin inducer) and cycloheximide also eliminated E-selectin expression but, much like thrombin, induced P-selectin expression and neutrophil recruitment. In conclusion, inhibition of E-selectin via protein synthesis inhibition activates the protein synthesis-independent pathway of P-selectin expression to support adequate leukocyte recruitment.
Role of peroxynitrite in altered fetal-placental vascular reactivity in diabetes or preeclampsia
Authors: Kossenjans Wilhelm , Eis Annie , Sahay Rashmi , Brockman Diane , Myatt Leslie
Published: December 2017

Oxidative stress may increase production of superoxide and nitric oxide, leading to formation of prooxidant peroxynitrite to cause vascular dysfunction. Having found nitrotyrosine residues, a marker of peroxynitrite action, in placental vessels of preeclamptic and diabetic pregnancies, we determined whether vasoreactivity is altered in these placentas and treatment with peroxynitrite produces vascular dysfunction. The responses of diabetic, preeclamptic, and normal placentas to increasing concentrations of the vasoconstrictors U-46619 (10− 9–10− 7M) and ANG II (10− 9–10− 7M) and the vasodilators glyceryl trinitrate (10− 9–10− 7M) and prostacyclin (PGI2; 10− 8–10− 6M) were compared as were responses to these agents in normal placentas before and after treatment with 3.16 × 10− 4 M peroxynitrite for 30 min. Responses to both vasoconstrictors and vasodilators were significantly attenuated in diabetic and preeclamptic placentas compared with controls. Similarly, responses to U-46619, nitroglycerin, and PGI2, but not ANG II, were significantly attenuated following peroxynitrite treatment. The presence of nitrotyrosine residues confirmed peroxynitrite interaction with placental vessels. Overall, our data suggest that peroxynitrite formation is capable of attenuating vascular responses in the human placenta.
Myofibrillar disruption in hypocontractile myocardium showing perfusion-contraction matches and mismatches
Authors: Sherman Andrew J. , Klocke Francis J. , Decker Robert S. , Decker Marlene L. , Kozlowski Karen A. , Harris Kathleen R. , Hedjbeli Sascha , Yaroshenko Yuri , Nakamura Sakie , Parker Michele A. , Checchia Paul A. , Evans Daniel B.
Published: December 2017

Chronically instrumented dogs underwent 2- or 5-h regional reductions in coronary flow that were followed, respectively, by balanced reductions in myocardial contraction and O2consumption (“hibernation”) and persistently reduced contraction despite normal myocardial O2consumption (“stunning”). Previously unidentified myofibrillar disruption developed during flow reduction in both experimental models and persisted throughout the duration of reperfusion (2–24 h). Aberrant perinuclear aggregates that resembled thick filaments and stained positively with a monoclonal myosin antibody were present in 34 ± 3.8% (SE) and 68 ± 5.9% of “hibernating” and “stunned” subendocardial myocytes in areas subjected to flow reduction and in 16 ± 2.5% and 44 ± 7.4% of subendocardial myocytes in remote areas of the same ventricles. Areas of myofibrillar disruption also showed glycogen accretion and unusual heterochromatin clumping adjacent to the inner nuclear envelope. The degrees of flow reduction employed were sufficient to reduce regional myofibrillar creatine kinase activity by 25–35%, but troponin I degradation was not evident. The observed changes may reflect an early, possibly reversible, phase of the myofibrillar loss characteristic of hypocontractile myocardium in patients undergoing revascularization.
Resistance to myocardial ischemia in five rat strains: is there a genetic component of cardioprotection?
Authors: Baker John E. , Konorev Eugene A. , Gross Garrett J. , Chilian William M. , Jacob Howard J.
Published: December 2017

There is a need to develop new and more consistent animal models of cardioprotection. Traditionally, outbred dogs, rabbits, and rats have been studied. We determined resistance to ischemia in isolated hearts from inbred strains of rats. Hearts from inbred rats: SS/Mcw (Dahl S, Dahl salt-sensitive), DA/Hsd (Dark Agouti), LEW/Hsd (Lewis), and BN/SsN/Mcw (Brown Norway); and from an outbred rat: Hsd:WIST (Wistar) were subjected to 27 min of global, no-flow ischemia, followed by 3 h of reperfusion. Infarct size in the Brown Norway rat was 2.5 times less than that observed in the Dahl S rat, with the Dark Agouti, Lewis, and Wistar rats intermediate in response. Hearts from Brown Norway rats were also most resistant to ischemia in terms of postischemic enzyme leakage and contractile and vascular function compared with other strains. The average polymorphism rate between strains revealed that such strains were genetically diverse. This study demonstrates strain differences in resistance to myocardial ischemia, suggesting these rats could be used to study a genetic and/or environmental basis for these differences and to provide new animal models for the physiological study of cardioprotection.
Contribution of cytochrome P-450 ω-hydroxylase to altered arteriolar reactivity with high-salt diet and hypertension
Authors: Frisbee Jefferson C. , Falck John R. , Lombard Julian H.
Published: December 2017

The present study evaluated the contribution of cytochrome P-450 ω-hydroxylase in modulating the reactivity of cremaster muscle arterioles in normotensive rats on high-salt (HS) and low-salt (LS) diet and in rats with reduced renal mass hypertension (RRM-HT). Changes in arteriolar diameter in response to ACh, sodium nitroprusside (SNP), ANG II, and elevated O2 were measured via television microscopy under control conditions and following cytochrome P-450 ω-hydroxylase inhibition with 17-octadecynoic acid (17-ODYA) or N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS). In normotensive rats on either LS or HS diet, resting tone was unaffected and arteriolar reactivity to ACh or SNP was minimally affected by cytochrome P-450 ω-hydroxylase inhibition. In RRM-HT rats, cytochrome P-450 ω-hydroxylase inhibition reduced resting tone and significantly enhanced arteriolar dilation to ACh and SNP. Treatment with 17-ODYA or DDMS inhibited arteriolar constriction to ANG II and O2 in all the groups, although the degree of inhibition was greater in RRM-HT than in normotensive animals. These results suggest that metabolites of cytochrome P-450 ω-hydroxylase contribute to the altered reactivity of skeletal muscle arterioles to vasoconstrictor and vasodilator stimuli in RRM-HT.
Vagus nerve is involved in lack of blood reflow into sinusoids after rat hepatic ischemia
Authors: Nishida Toshirou , Ueshima Shigeyuki , Kazuo Hiromu , Ito Toshinori , Seiyama Akitoshi , Matsuda Hikaru
Published: December 2017

Although recovery of microcirculation is an important determinant for ischemia-reperfusion injury, little information is available about hepatic blood flow after ischemia. To examine regulatory mechanisms of postischemic hepatic microcirculation, we studied the sinusoidal blood flow after portal triad clamping of rat livers for 5, 15, or 30 min. Hepatic tissue blood flow and erythrocyte blood flow in sinusoids were measured using a laser-Doppler flowmeter and an intravital microspectroscope, respectively. There was a time of no blood flow (lag time) in sinusoids after declamping, dependent on the ischemic time. Cholinergic blockade agents eliminated the lag time, whereas nerve stimulation at the hiatus esophagus or on the hepatoduodenal ligament during reperfusion prolonged it. Chemical denervation with 10% phenol or surgical denervation on the hepatoduodenal ligament eliminated the lag time. The prolongation of lag time by nerve stimulation was completely abrogated by truncal vagotomy. These results suggest that the cholinergic vagus nerve is involved in causing the lag time of sinusoidal blood flow in hepatic ischemia-reperfusion.
Vagal modulation of the heart and central hemodynamics during handgrip exercise
Authors: Kluess Heidi A. , Wood Robert H. , Welsch Michael A.
Published: December 2017

Blood pressure and continuous electrocardiogram recordings were obtained from 12 participants during spontaneous breathing (SB1), dynamic handgrip exercise at 20% (HG20) of maximal voluntary contraction (MVC), and spontaneous breathing (SB2) and dynamic handgrip exercise at 60% (HG60) of MVC. Repeated-measures ANOVAs were used to examine the effects of the exercise conditions on mean arterial pressure (MAP), on mean standard deviation (SDNN), and on the coefficient of variation of R-R intervals. The mean R-R interval responded to exercise in an intensity-dependent manner. SDNN decreased with exercise but was not intensity dependent. Coefficient of variation decreased during HG20, and MAP increased following HG60. These data are consistent with the notion that changes in cardiovascular function with low-intensity exercise are primarily mediated by parasympathetic withdrawal, and as exercise intensity increases, additional cardiovascular reactivity is mediated by increased sympathetic outflow. The change in the coefficient of variation from rest to exercise was unique in comparison to the changes in SDNN, and this merits further investigation.
Effects of diminished expression of connexin43 on gap junction number and size in ventricular myocardium
Authors: Saffitz Jeffrey E. , Green Karen G. , Kraft William J. , Schechtman Kenneth B. , Yamada Kathryn A.
Published: December 2017

Gap junction number and size vary widely in cardiac tissues with disparate conduction properties. Little is known about how tissue-specific patterns of intercellular junctions are established and regulated. To elucidate the relationship between gap junction channel protein expression and the structure of gap junctions, we analyzed Cx43 +/− mice, which have a genetic deficiency in expression of the major ventricular gap junction protein, connexin43 (Cx43). Quantitative confocal immunofluorescence microscopy revealed that diminished Cx43 signal in Cx43 +/− mice was due almost entirely to a reduction in the number of individual gap junctions (226 ± 52 vs. 150 ± 32 individual gap junctions/field in Cx43 +/+ and +/− ventricles, respectively; P < 0.05). The mean size of an individual gap junction was the same in both groups. Immunofluorescence results were confirmed with electron microscopic morphometry. Thus when connexin expression is diminished, ventricular myocytes become interconnected by a reduced number of large, normally sized gap junctions, rather than a normal number of smaller junctions. Maintenance of large gap junctions may be an adaptive response supporting safe ventricular conduction.
Endothelin-induced cardiac myocyte hypertrophy: role for focal adhesion kinase
Authors: Eble Diane M. , Strait James B. , Govindarajan Geetha , Lou Jueren , Byron Kenneth L. , Samarel Allen M.
Published: December 2017

Endothelin-1 (ET) produces neonatal rat ventricular myocyte (NRVM) hypertrophy and activates focal adhesion kinase (FAK) in other cell types. In the present study, we examined whether ET activated FAK in NRVM and whether FAK was necessary and/or sufficient for ET-induced NRVM hypertrophy. Chronic ET-1 stimulation (100 nM, 48 h) increased protein-to-DNA and myosin heavy chain (MHC)-to-DNA ratios and stimulated the assembly of newly synthesized MHC into sarcomeres. ET-1 also induced the assembly of focal adhesions and costameres, as evidenced by increased phosphotyrosine, FAK, and paxillin immunostaining. Acutely, ET treatment rapidly increased tyrosine phosphorylation of FAK and paxillin. FAK was also activated by phorbol 12-myristate 13-acetate (2 μM, 5 min). Pretreatment with chelerythrine (5 μM) or rottlerin (10 μM) completely blocked ET-induced FAK phosphorylation, indicating that protein kinase C activation was upstream of ET-induced FAK activation. In contrast, ET-induced FAK activation was not affected by blocking calcium influx via L-type voltage-gated calcium channels. Adenoviruses (Adv) containing FAK and FAK-related nonkinase (FRNK) were used to specifically define the role of FAK in ET-induced hypertrophy. ET stimulation failed to increase total protein-to-DNA or MHC-to-DNA ratios or to stimulate sarcomeric assembly in myocytes infected with Adv-FRNK. However, Adv-FAK alone did not increase total protein-to-DNA or MHC-to-DNA ratios and failed to increase the number or size of myofibrils as evidenced by double immunofluorescence labeling for MHC and FAK. Thus, although FAK is necessary for ET-induced NRVM hypertrophy, other ET-generated signals are also required to elicit the hypertrophic phenotype.
A new method of long-term preventive cardioprotection usingLactobacillus
Authors: Oxman Tatyana , Shapira Michal , Diver Adriana , Klein Rodica , Avazov Natalie , Rabinowitz Babeth
Published: December 2017

Potential long-term cardioprotection was investigated in an extensive experimental study. Lactobacillus cultivation components (LCC) were administered intravenously in anesthetized rats 1, 7, and 21 days before global ischemia (GI). GI was produced by full stop flow in isolated Langendorff-perfused hearts for 20 min and was followed by reperfusion. Control animals were injected with saline. LCC reduced reperfusion tachyarrhythmia significantly and improved functional recovery of the ischemized rat heart. These beneficial effects were associated with reduction of release of norepinephrine (NE) and prostacyclin at the first minute of reperfusion, activation of myocardial catalase, and overexpression of 70-kDa heat stress protein (HSP-70) at ischemia and reperfusion ( P < 0.05). This cardioprotection was documented up to 21 days after a single injection of LCC. Thus Lactobacillus cultivation components are new nontoxic materials that produce marked long-term cardioprotection against ischemia-reperfusion damage. This effect is attributed to an activation of the cellular defense system, manifested by activation of the antioxidant pathway and by expression of protective proteins. NE is involved in this process, and the data also suggest a role for prostacyclin in this model of cardioprotection. The potential of LCC and related compounds working through similar mechanisms in the prevention and therapy of various ischemic heart syndromes should be explored.