bluuebunny/crossref_metadata_2025 huggingface dataset:
Blockade of cardiac sodium channels by lidocaine. Single-channel analysis.
Authors: Grant A O , Dietz M A , Gilliam F R , Starmer C F
Published: June 2012

The mechanism of interaction of lidocaine with cardiac sodium channels during use-dependent block is not well defined. We examined the blockade of single cardiac sodium channels by lidocaine and its hydrophobic derivative RAD-242 in rabbit ventricular myocytes. Experiments were performed in cell-attached and inside-out patches. Use-dependent block was assessed with trains of ten 200-msec pulses with interpulse intervals of 500 msec and test potentials of -60 to -40 mV. Single-channel kinetics sometimes showed time-dependent change in the absence of drug. During exposure to 80 microM lidocaine, use-dependent block during the trains was associated with a decrease in the average number of openings per step. At -60 mV, mean open time was not significantly changed (control, 1.4 +/- 0.6 msec; lidocaine, 1.2 +/- 0.3 msec, p greater than 0.05). Greater block developed during trains of 200-msec pulses compared with trains of 20-msec pulses at the same interpulse interval at test potentials during which openings were uncommon later than 20 msec (-50 and -40 mV). Prolonged bursts of channels showing slow-gating kinetics were observed both in control and the presence of 80 microM lidocaine. However, lidocaine may decrease the late sodium current by altering the kinetics of slow gating. The hydrophobic lidocaine derivative RAD-242, which has a 10-fold greater lipid solubility than lidocaine, decreased the peak averaged current during pulse train stimulation by 60% without a change in the mean open time. Our results suggest that the major effect of lidocaine during use-dependent block involves the interaction with a nonconducting state of the sodium channel followed by a failure to open during subsequent depolarization.
Atrial natriuretic factor-specific antibody as a tool for physiological studies. Evidence for role of atrial natriuretic factor in aldosterone and renal electrolyte regulation.
Authors: Rudd M A , Plavin S , Hirsch A T , Ingelfinger J R , Dzau V J
Published: June 2012

Numerous studies have shown that administration of atrial natriuretic factor (ANF) increases urinary sodium excretion and urine flow, decreases blood pressure, and inhibits renin and aldosterone release. However, the role of endogenous ANF in the regulation of renal sodium excretion, blood pressure, plasma renin activity, and aldosterone level remains to be elucidated. To examine this issue, endogenous ANF was blocked by administering rat ANF-(99-126) specific antiserum (Ab) to anesthetized rats (n = 7). Control animals received either no injection (time controls, n = 10) or preimmune serum (n = 8). Blockade of endogenous ANF caused a 28 +/- 0.09%, 47 +/- 0.08%, and 51 +/- 0.08% fall in sodium excretion at 15, 30, and 45 minutes after Ab injection (p less than 0.05, p less than 0.01, p less than 0.01, respectively). Urine flow fell 35 +/- 7% at 45 minutes after ANF inhibition (p less than 0.05). Plasma ANF levels were suppressed to undetectable levels. However, there were no changes in blood pressure throughout the experiment nor plasma renin concentration when measured at 45 minutes after Ab injection. Interestingly, plasma aldosterone concentration increased significantly (by approximately 50%, p less than 0.025), in response to Ab. Completeness of blockade was demonstrated by the absence of sodium excretion response to exogenous ANF (500 ng). In either the time control or the preimmune serum group, urinary excretion, blood pressure, plasma ANF, plasma renin concentration, and plasma aldosterone concentration were unchanged throughout the experiment. In contrast to the Ab group, a challenge with exogenous ANF (500 ng) increased sodium excretion by 2.17 mueq/min in the preimmune serum group.(ABSTRACT TRUNCATED AT 250 WORDS)
Decreased cardiac concentration of cGMP kinase in hypertensive animals. An index for cardiac vascularization?
Authors: Ecker T , Göbel C , Hullin R , Rettig R , Seitz G , Hofmann F
Published: June 2012

Cyclic GMP (cGMP) kinase is intimately involved in the regulation of vascular smooth muscle tone. Its tissue concentration was determined in normotensive and hypertensive rats by use of monospecific anti-cGMP kinase antibodies. Hearts of spontaneously hypertensive rats and renovascular (Goldblatt II) hypertensive rats contained half the concentration of cGMP kinase than those of the respective normotensive animals. The increase in blood pressure and the resulting left ventricular hypertrophy were correlated inversely with the left ventricular cGMP kinase concentration. This decrease was specific for the left ventricle and was not observed in other tissues. In addition, the cardiac concentration of cGMP kinase was unchanged in hyperthyroid animals that had comparable left ventricular hypertrophy and mild hypertension. This suggested that in severe renovascular hypertension the decrease in cardiac cGMP kinase concentration is caused by a relative lack of cardiac vessel growth during the development of hypertrophy. In agreement with this conclusion, immunohistochemistry of cardiac cross sections showed that cGMP kinase was exclusively located in cardiac vessels. In support of this localization, the maximal arterial blood flow of heart, liver, skeletal muscle, and kidney correlated excellently with the cGMP kinase content of the respective organ. These results suggest that the cGMP kinase concentration of nonsmooth muscle tissues depends on the amount of organ-specific vascular smooth muscle and may be used as an index for the vascularization of these organs.
Quantitative analysis of intercellular connections by immunohistochemistry of the cardiac gap junction protein connexin43.
Authors: Luke R A , Beyer E C , Hoyt R H , Saffitz J E
Published: June 2012

Polyclonal antisera directed against epitopes in the cytoplasmic domain of rat connexin43, the predominant cardiac gap junction protein, were used to delineate immunohistochemically the distribution of gap junctions in sections of canine left ventricle. Antigen-antibody binding and tissue structure were preserved after paraformaldehyde fixation and paraffin embedment of canine myocardium. Specific binding of antibody to the cytoplasmic surfaces of ultrastructurally identified gap junctions was confirmed with electron microscopy. Light microscopic morphometric analysis of immunostained sections in five separate experiments revealed a mean gap junction surface density of 0.0052 micron2/micron3 myocyte volume, which is consistent with previously reported values determined by use of quantitative electron microscopy. This new method permits quantitative determinations of gap junction surface density and distribution in relatively large heterogeneous areas of myocardium in which ultrastructural morphometry would be impractical. This approach should facilitate analysis of the relation between potential alterations in electrical coupling of myocytes and abnormalities of myocardial conduction occurring at the macroscopic scale in regions such as structurally heterogeneous infarct border zones.
Adenosine produces pulmonary vasoconstriction in sheep. Evidence for thromboxane A2/prostaglandin endoperoxide-receptor activation.
Authors: Biaggioni I , King L S , Enayat N , Robertson D , Newman J H
Published: June 2012

Adenosine, an intermediate product in the metabolism of ATP, is thought to produce vasodilation in all vascular beds with the exception of the kidney. Due to its theoretical potential as a pulmonary vasodilator, we studied the hemodynamic effects of adenosine in the pulmonary vasculature of chronically instrumented awake sheep. Adenosine produced significant pulmonary vasoconstriction instead of the expected vasodilatation. Bolus injections of adenosine into the superior vena cava produced a dose-dependent increase in pulmonary artery pressure that was entirely due to an increase in vascular resistance, since cardiac output decreased slightly. This effect is produced via activation of specific cell surface adenosine receptors, since it was blocked by the adenosine-receptor antagonists theophylline and dipropylsulfophenylxanthine. The cell type involved in adenosine-induced pulmonary vasoconstriction appears to be located within the lung, since vasoconstriction was blunted when adenosine was infused into the left atrium, distal to the lung. However, adenosine does not directly vasoconstrict the pulmonary vasculature, because its effect could be completely abolished by cyclooxygenase inhibition with either indomethacin or ibuprofen and by a thromboxane A2/prostaglandin endoperoxide-receptor antagonist (SQ 29,548). Adenosine-induced vasoconstriction was also greatly reduced after inhibition of thromboxane synthesis. Thus, adenosine produced pulmonary vasoconstriction through generation of a thromboxane/endoperoxide product. Whether endogenous adenosine is involved in the generation of pulmonary vasoconstriction seen in pathophysiological states remains to be determined. To our knowledge, this is the first clear evidence for adenosine-induced vasoconstriction outside the kidney and for an interaction between adenosine and eicosanoid mechanisms.
Chronotropic responses of chick atria to field stimulation after various neural crest ablations.
Authors: Kirby M L , Creazzo T L , Christiansen J L
Published: June 2012

Three models of altered autonomic innervation of the chick heart have been developed in the last few years. These include sympathetically aneural heart, parasympathetically aneural heart, and heart with cholinergic innervation reconstituted from the nodose placodes. The neural status of these hearts has been assessed by a variety of morphological and biochemical methods, but the functional status of innervation is not known. In the present study, we have used electrocardiography and field stimulation to determine the functional neural status of the three different innervation models. The RR and QTc intervals were measured to assess the dominant autonomic tone and autonomic dysfunction in the heart. Even though the RR and QTc intervals were found to be identical in sham and experimental embryos, field stimulation of superfused atria showed that the sympathetically aneural heart has functional cholinergic innervation but lacks any sympathetic response. Hearts from embryos which were parasympathetically aneural lacked a cholinergic response to field stimulation and were judged to be functionally parasympathetically aneural. Hearts with cholinergic ganglia reconstituted from the nodose placodes have normal RR and QTc intervals as well as a normal cholinergic response to field stimulation. The results indicate that these neurons are functionally indistinguishable from neural crest-derived neurons.
Alterations in collagen cross-linking impair myocardial contractility in the mouse heart.
Authors: Capasso J M , Robinson T F , Anversa P
Published: June 2012

A number of genetic disorders in humans are associated with defects in the synthesis and metabolism of collagen, which are accompanied by multiple cardiovascular disease processes. To determine whether genetically determined cross-linking abnormalities of collagen may alter cardiac function, left ventricular papillary muscles of mice with a genetic defect in the cross-linking of collagen (Movbr) were studied in vitro. With respect to controls, increases in time to peak tension, from 102 +/- 1.4 to 125 +/- 5.4 msec (p less than 0.001), and time to one-half relaxation, from 76 +/- 3.0 to 98 +/- 6.1 msec (p less than 0.05), were measured. Moreover, resting tension at the length associated with maximum developed isometric force (L) was elevated, from 11.1 +/- 1.7 to 19.3 +/- 1.1 mN/mm2 (p less than 0.001), and a similar difference was also seen throughout the physiological range of muscle lengths. In contrast, developed tension was depressed at 93-97% of L. Peak rate of tension rise and decay were diminished whereas time to peak rate of tension rise was prolonged. Isotonically, a decrease in the magnitude of peak shortening at L, from 4.0 +/- 0.5 to 2.0 +/- 0.2% (p less than 0.04), and an increase in time to peak shortening, from 100 +/- 2.3 to 129 +/- 2.8 msec (p less than 0.001), were seen. In addition, peak velocities of shortening and relengthening were diminished in the Movbr mouse heart. In conclusion, the impairment in collagen cross-linking alters cardiac mechanics by a reduction in force-generating ability and a prolongation of the timing parameters of the systolic and diastolic phases of contraction in vitro.
Effect of atrial natriuretic peptide on coronary collateral blood flow.
Authors: Foreman B , Dai X Z , Homans D C , Laxson D D , Bache R J
Published: June 2012

This study was carried out to examine the effects of atrial natriuretic peptide on coronary collateral blood flow. Studies were performed in nine adult mongrel dogs 3.4 months after embolic occlusion of the left anterior descending coronary artery had been performed to stimulate collateral vessel growth. At the time of study the anterior descending coronary artery was cannulated to allow estimation of interarterial collateral flow from measurements of retrograde blood flow. Injection of radioactive microspheres during retrograde flow collection allowed simultaneous determination of continuing tissue flow for evaluation of microvascular collateral communications. Atrial natriuretic peptide in doses of 20 and 200 micrograms administered into the left atrium resulted in 17 +/- 3.0% and 34 +/- 4.5% increases in retrograde flow, respectively (each p less than 0.01). Tissue flow in the collateral dependent myocardial region did not change in response to atrial natriuretic peptide. After the larger dose of atrial natriuretic peptide, the administration of nitroglycerin (10 micrograms/kg into the left atrium) caused no further increase of retrograde blood flow, and no further decrease of collateral vascular resistance. These data indicate that atrial natriuretic peptide causes vasodilation of moderately well-developed interarterial coronary collateral vessels.
Outward potassium currents in freshly isolated smooth muscle cell of dog coronary arteries.
Authors: Wilde D W , Lee K S
Published: June 2012

Outward membrane currents were characterized in single coronary smooth muscle cells of adult beagle dogs. The cells averaged 96.4 x 7.1 microns and had a resting potential of -50.7 mV, an input resistance of 307.9 M omega, a capacitance of 32.3 pF, and a calculated membrane surface area of 4,037 microns2. The cells contracted in response to external application of acetylcholine or high K+. In voltage clamp by use of the suction pipette method, outward current began to appear at -50 mV and reached 15.2 nA at 50 mV with a current density of 376.5 microA/cm2. The current was reduced by external tetraethylammonium, Ba2+, and internal Cs+, and its reversal potential had a Nernst relation to external K+ concentration. Elevation of external Ca2+ (Ca2+o) from 0 to 0.3 mM increased total K+ current by up to 300%; elevation of internal Ca2+ (Ca2+i) to 5 x 10(-7) M by internal perfusion increased total outward current to a similar extent, suggesting a large difference in Ca2+ transmembrane sensitivity. Total whole-cell K+ current consisted of two components: an initial time-independent current (Ii) followed by a time-dependent current (It). Ii and It were through separate K+ channels based on differences in a) sensitivity to Ca2+09b) modulation by an inward Ca2+ current, c) current amplitudes and activation kinetics, and d) responses to pharmacological agents. It was the largest component, measuring 4.5 nA in 0 mM Ca2+o but increasing to 11.9 nA in 0.3 mM Ca2+o with a steep 2.5 power function. It activated with a biexponential time course; in Ca2+o-free solution, its time course was relatively insensitive to voltage changes but became voltage sensitive in the presence of Ca2+o. Further, such sensitivity was abolished or enhanced by Co2+ or Bay K 8644, respectively. We concluded that there are two types of Ca2+-sensitive K+ currents, Ii and It, in coronary smooth muscle cells. Via an inward Ca2+ channel Ca2+o strongly modulates It, both in amplitude and kinetics.
Effects of inhibition of fatty acid oxidation on myocardial kinetics of 11C-labeled palmitate.
Authors: Wyns W , Schwaiger M , Huang S C , Buxton D B , Hansen H , Selin C , Keen R , Phelps M E , Schelbert H R
Published: June 2012

The effects of glucose and lactate infusion on palmitate oxidation were compared with the effect of 2-tetradecylglycidic acid (TDGA), an irreversible inhibitor of the carnitine acyltransferase I, in normoxic canine myocardium. The initial capillary transit retention fraction of [1-11C]palmitate and its fractional distribution between oxidation and esterification in myocardium were measured by the residue detection method after intracoronary tracer injection, as well as by effluent measurements of 11CO2, the end product of palmitate oxidation. TDGA reduced the initial capillary transit retention fraction (from 56 +/- 13% to 37 +/- 6%; p less than 0.001) and oxidation of palmitate (n = 19), as also evidenced by the decrease in the fraction of tracer released as 11CO2 from 28 +/- 5% to 6 +/- 3% (p less than 0.001). Infusion of carbohydrate (glucose or lactate; n = 6) reduced 11CO2 production from 30 +/- 7% to 7 +/- 4% (p less than 0.05) but did not alter the initial capillary transit retention fraction of tracer (59 +/- 5% vs. 56 +/- 10%; NS). The latter was due to increased esterification into neutral lipids (41 +/- 11% of injected palmitate after carbohydrate infusion versus 21 +/- 12% in control conditions), as measured from multiexponential curve fittings. When carbohydrates were given after inhibition of palmitate oxidation by TDGA (n = 7), the 11C tissue clearance kinetics were strikingly similar to those observed after carbohydrate infusion alone. Thus, enhanced metabolic trapping of [1-11C]palmitate in myocardium resulted in initial capillary transit retention fractions that were not different from control conditions (41 +/- 5% vs. 48 +/- 12%; NS) despite inhibition of oxidation. The results show that the intracellular metabolism of palmitate contributes to the control of its uptake by myocardium. The findings are consistent with inhibition of palmitate oxidation by carbohydrates occurring at the same site as TDGA.
Endothelial renin-angiotensin pathway. Adrenergic regulation of angiotensin secretion.
Authors: Tang S S , Stevenson L , Dzau V J
Published: June 2012

Cultured bovine aortic endothelial cells (BAECs) express the complete renin-angiotensin system and secrete angiotensins. In this study, we examined the adrenergic influence on the secretion of angiotensins from BAECs. Angiotensins were determined by high-performance liquid chromatography and radioimmunoassay. At basal state, BAECs contain angiotensin I, angiotensin II, and angiotensin III at concentrations of 2.5 +/- 1.3, 4.8 +/- 2.3, and 3.4 +/- 1.5 pg/10(6) cells, respectively. Angiotensin I, angiotensin II, and angiotensin III concentrations in the culture medium were 8.3 +/- 4.4, 9.4 +/- 3.5, and 9.9 +/- 3.3 pg/10(6) cells, respectively. Isoproterenol (0.1-10 microM) increases secretion of angiotensins I, II, and III in a dose-dependent manner. Increase in angiotensin secretion induced by isoproterenol (10 microM) can be inhibited by beta 2-adrenoceptor antagonist ICI 118,551 (1 microM), but not by beta 1-adrenoceptor antagonist atenolol (1 microM). Forskolin (1-1,000 microM) mimics the isoproterenol-induced response. In contrast, alpha-adrenergic agonist phenylephrine (1-100 microM) inhibits the secretion. Pretreatment of BAECs with captopril (1 microM) inhibits the accumulation of angiotensin II and angiotensin III in the culture medium, but not angiotensin I. These findings suggest that BAEC production and/or secretion of angiotensins is regulated by adrenergic mechanisms.
Calcium channel blockers enhance cholesteryl ester hydrolysis and decrease total cholesterol accumulation in human aortic tissue.
Authors: Etingin O R , Hajjar D P
Published: June 2012

Calcium channel blockers (CCBs), which are used clinically for treatment of angina and hypertension, are known to inhibit calcium influx into arterial smooth muscle cells and thereby decrease smooth muscle cell contraction. In addition, they prevent cholesteryl ester (CE) accumulation, the hallmark of human atherosclerosis, in arteries of cholesterol-fed animals by cellular mechanisms that remain undefined. To assess whether CCBs enhance CE hydrolysis and reduce CE accumulation in human arterial cells, we measured activities of the CE metabolic cycle in aortic tissues that were stripped of endothelial cells and adventitia from 35 patients undergoing coronary artery bypass surgery. Patients who were treated with either nifedipine or diltiazem (n = 23) for several months demonstrated a threefold increase in arterial CE hydrolytic activities compared with untreated patients. This difference was independent of serum cholesterol levels, age, or treatment with other medications. No effects were observed on CE synthetic activity. Cyclic AMP levels in the aortic tissue of patients treated with CCBs were also significantly elevated twofold to threefold. In addition, both free and esterified cholesterol were significantly reduced in aortic tissue from patients taking CCBs compared with untreated patients. These data are the first to show that CCBs can increase CE hydrolysis in human aortic tissue by increasing intracellular cyclic AMP with resultant decrease in CE accumulation. Collectively, these findings support the hypothesis that CCBs can act as antiatherosclerotic agents in human tissue by mobilizing stored CE in the arterial wall.
Spatial heterogeneity of intracellular Ca2+ concentration in nonbeating guinea pig ventricular myocytes.
Authors: Williford D J , Sharma V K , Korth M , Sheu S S
Published: June 2012

The spatial distribution of intracellular Ca2+ concentration was determined by fluorescent digital imaging microscopy in fura-2-loaded quiescent cardiac myocytes isolated from guinea pig ventricle. Fluorescent ratio images revealed discrete as well as clustered bright fluorescent spots ("hot spots"), which occupied approximately 20-50% of an individual cell's area. The fluorescent intensity and the area of the hot spots were increased by agents that deplete Ca2+ in the sarcoplasmic reticulum, namely, ryanodine (20-40 nM) and caffeine (5-15 mM). However, when cells were exposed to agents that deplete mitochondrial Ca2+, such as the protonophore, carbonyl cyanide m-chlorophenyl-hydrazone (CCCP, 100-300 nM), or the inhibitor of electron transport, antimycin A (4-40 nM), the fluorescent intensity and the area of the hot spots were reduced. These results indicate that the spatial distribution of intracellular Ca2+ concentration in the ventricular myocytes of guinea pig is quite heterogeneous. The ability of CCCP and antimycin A, but not of caffeine and ryanodine, to reduce the fluorescent intensity in the hot spots implies that Ca2+ compartmentation in the mitochondria is largely responsible for the intracellular Ca2+ heterogeneity seen in the present study.
Stimulation of phospholipid N-methylation by isoproterenol in rat hearts.
Authors: Taira Y , Panagia V , Shah K R , Beamish R E , Dhalla N S
Published: June 2012

Phosphatidylethanolamine (PtdEtn) N-methyltransferase activities were studied in rat heart sarcolemmal and sarcoplasmic reticular fractions after a single intraperitoneal injection of isoproterenol (0.5-5.0 mg/kg). Three active sites (I, II, and III) for PtdEtn N-methylation were assayed by measurement of [3H]methyl group incorporation from 0.055, 10, and 150 microM S-adenosyl-L-[methyl-3H]methionine into membrane PtdEtn molecules. Total methylation activity for catalytic site I of both sarcolemma and sarcoplasmic reticulum was stimulated within 2 minutes by isoproterenol in a dose-dependent manner. Although the increased methyltransferase activity in sarcoplasmic reticulum was normalized at 10 minutes, the enzyme activity in sarcolemma was normalized at 5 minutes but was again increased at 10-30 minutes after isoproterenol injection. No changes in response to isoproterenol were seen for site II and III N-methylation activities in either membrane. Individual N-methylated phospholipids (phosphatidyl-N-monomethylethanolamine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidylcholine), which specifically formed at each site, showed similar behavior. Pretreatment of the animals with a beta-blocking drug, atenolol, for 2 days prevented the isoproterenol-induced changes in hemodynamic parameters and sarcolemmal methylation without affecting the enhanced methylation activities in sarcoplasmic reticulum. In vitro addition of cyclic AMP-dependent protein kinase (catalytic subunit) plus Mg-ATP enhanced methyltransferase activities in sarcolemma and sarcoplasmic reticulum from control hearts by 2.7- and 2.3-fold, respectively; however, under the same in vitro conditions, only about 20% activation was seen in both subcellular membranes isolated from the heart of isoproterenol-injected animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Glucose flux rate regulates onset of ischemic contracture in globally underperfused rat hearts.
Authors: Owen P , Dennis S , Opie L H
Published: June 2012

This study analyzes the importance of the source and rate of ATP production (glucose flux, glycogenolysis, and oxidative phosphorylation) in the prevention of ischemic contracture in isolated rat hearts. Ischemic contracture was initiated at about 10 minutes by buffer perfusion with nonglycolytic substrates whereas the addition of 11 mM glucose prevented contracture for 2 hours. Tissue values of ATP, phosphocreatine, and lactate could be dissociated from onset of ischemic contracture. In hearts perfused with acetate or free fatty acid, with 11 mM glucose, glycolytic ATP production was 2.3-2.8 mumol/g fresh wt/min; as initial rates of glycogenolysis fell, glycolysis was maintained by a steady increase of glucose flux to values in excess of 2 mumol ATP/g fresh wt/min. Decreasing the glucose flux by lowering the perfusate glucose or by the addition of 2-deoxyglucose precipitated ischemic contracture. When oxidative phosphorylation was further reduced by hypoxia, glucose still prevented ischemic contracture; however, when oxidative phosphorylation dropped to near zero (near-anoxic) rates, glycolysis was inhibited, and glucose could only delay ischemic contracture to about 45 minutes. Combined ATP production rates could be dissociated from contracture. The metabolic parameter that correlated best with prevention or delay of ischemic contracture was the rate of glycolytic flux from glucose, which in this model of global low-flow ischemia had to accelerate to provide a rate of ATP production from glucose in excess of 2 mumol/g fresh wt/min within 30 minutes of the start of ischemia to prevent ischemic contracture.
Attenuation of vasopressin-mediated coronary constriction and myocardial depression in the hypoxic heart.
Authors: Boyle W A , Segel L D
Published: June 2012

To investigate the ability of arginine vasopressin (AVP) to compete with metabolic vasodilatory factors in the coronary circulation, we examined the coronary vascular and myocardial effects of AVP in isolated working rat hearts during normoxic and hypoxic perfusion. In normoxic hearts, AVP treatment (777 +/- 67 pg/ml) reduced coronary flow by 38.4 +/- 2.6%. Myocardial function was also significantly decreased by AVP whereas efficiency significantly increased. In contrast, the same dose of AVP administered to hypoxic hearts resulted in substantially smaller effects on coronary flow (-11.5 +/- 2.8%), myocardial function, and efficiency. In hearts treated first with AVP and then with hypoxia, the greater degree of coronary vasodilation compared with that observed in hearts treated with hypoxia alone also indicated an antagonizing effect of hypoxia on AVP-mediated coronary constriction. It was also noted that the hypoxia treatment alone resulted in reductions of O2 supply and consumption identical to those produced by AVP treatment during normoxia. However, hypoxia was associated with a significantly greater effect on myocardial function and, in contrast to the effect of AVP, a marked reduction in efficiency. The rate of lactate release was greater during hypoxia alone (2.07 +/- 0.08 mumol/min) than with AVP treatment during normoxia (0.76 +/- 0.05 mumol/min). These results indicate that the effect of AVP on the coronary vessels, as well as its effect on the myocardium, is significantly attenuated during hypoxia. In addition, AVP-constricted vessels appear to retain considerable vasodilatory reserve despite evidence of ischemic conditions. Thus, although the effects of AVP resemble ischemia, the increased efficiency and the relatively small effect of AVP on contractile function, as well as the preserved vasodilatory reserve, suggest otherwise. A physiological explanation for these observations is proposed wherein the constricting effects of AVP modulate the effects of autoregulatory factors such that blood flow requirements are minimized while allowing preservation of adequate blood flow for vital tissue function.
Role of oxygen-derived free radicals in acute angiotensin II--induced hypertensive vascular disease in the rat.
Authors: Wilson S K
Published: June 2012

Severe experimental hypertension is associated with vascular hyperpermeability and cellular damage in small arteries and arterioles in rats. Oxygen-derived free radical production is also associated with increased vascular permeability and cellular injury in a variety of conditions, including ischemia-reperfusion and inflammation. To determine if free radicals play a role in the pathogenesis of hypertensive vascular disease, the free radical scavengers superoxide dismutase (SOD), catalase, SOD and catalase, and dimethyl sulfoxide (DMSO) were given to rats made acutely hypertensive with angiotensin II infusions. Untreated hypertensive and normotensive control animals were used for comparison. The effects of scavenger treatment were assessed by in vivo observations of intestinal small arteries by use of stereomicroscopy and videotape and light and transmission electron microscopy to identify and quantitate vascular lesions, and tracer particle injections to determine permeability changes. In vivo observations revealed that scavenger treatment did not alter vascular constriction patterns, vessel caliber, or blood pressures. Electron microscopy of arteries from untreated hypertensive rats showed more severe and more extensive endothelial and smooth muscle lesions, increased tracer particle penetration, and greater fibrin deposition than that found in scavenger-treated hypertensive groups. Quantitation of vascular lesions showed approximately equal reductions in smooth muscle necrosis (p less than 0.01) and fibrin deposition (p less than 0.05) in arteries from each of the scavenger-treated hypertensive groups. The results indicate that the free radical scavengers SOD, catalase, SOD-catalase, and DMSO inhibit (but do not prevent) vascular hyperpermeability and cellular damage during acute, angiotensin II--induced hypertension. These findings suggest that free radicals play a role in the pathogenesis of hypertensive vascular disease, probably by exacerbating the vascular changes initially triggered by an acute elevation in blood pressure.
Role of thromboxane A2 in the cardiovascular response to intracoronary C5a.
Authors: Stahl G L , Amsterdam E A , Symons J D , Longhurst J C
Published: June 2012

Intracoronary administration of complement component C5a induces transient decreases in coronary blood flow and regional left ventricular segment shortening, associated with intramyocardial granulocyte trapping. We evaluated the influence of a cyclooxygenase inhibitor (acetylsalicylic acid, n = 8) or a thromboxane A2/prostaglandin H2 receptor antagonist (SQ29548, n = 6) on these C5a-induced cardiovascular responses. Open-chest anesthetized pigs were instrumented to monitor heart rate, arterial blood pressure, left anterior descending coronary blood flow, regional left ventricular segment shortening, and dP/dt. Oxygen content, lactate concentration, leukocyte count, and thromboxane B2, the stable metabolite of thromboxane A2, were measured in arterial and regional coronary venous blood. Repetitive injections of intracoronary C5a (500 ng) given 60 minutes apart showed no tachyphylaxis of the hemodynamic response. However, tachyphylaxis was seen in coronary blood flow changes when injections were spaced 30 minutes apart. An increase in myocardial oxygen extraction and lactate production was observed after intracoronary C5a. Administration of acetylsalicylic acid (50 mg/kg i.v.) attenuated C5a-induced decreases in coronary blood flow (-8 +/- vs. -3 +/- 1 ml/min) and regional left ventricular segmental shortening (-10 +/- 3% vs. -2 +/- 1%) and blocked the maximal increase in coronary venous thromboxane B2 (2.0 +/- 0.1 vs. 0.2 +/- 0.1 pmol/ml plasma). Furthermore, SQ29548 (30 micrograms/kg/min) reduced C5a-induced changes in coronary blood flow (-13 +/- 2 vs. -4 +/- 2 ml/min) and segmental shortening (-14 +/- 2% vs. -3 +/- 1%). Neither cyclooxygenase inhibition nor thromboxane A2/prostaglandin H2 antagonism blocked the decrease in coronary venous granulocyte count.(ABSTRACT TRUNCATED AT 250 WORDS)
Substance P is released from the endothelium of normal and capsaicin-treated rat hind-limb vasculature, in vivo, by increased flow.
Authors: Ralevic V , Milner P , Hudlická O , Kristek F , Burnstock G
Published: June 2012

The rat hind-limb vasculature releases substance P when subjected to a rapid increase in flow through the vascular bed. This release also occurs during high flow after rats have been capsaicinized, when loss of substance P-containing nerve fibers was verified by immunohistochemistry. Air treatment, a procedure shown by transmission electron microscopy to have removed endothelial cells from the arteries but not arterioles or capillaries of the hind-limb preparations, eliminated this release. Thus, the substance P released is unlikely to arise from perivascular nerves but rather from arterial endothelial cells.
Excitation-contraction coupling in postischemic myocardium. Does failure of activator Ca2+ transients underlie stunning?
Authors: Kusuoka H , Koretsune Y , Chacko V P , Weisfeldt M L , Marban E
Published: June 2012

To elucidate the mechanism of contractile dysfunction in postischemic ("stunned") myocardium, time-resolved measurements of intracellular free Ca2+ concentration ([Ca2+]i) were made using gated 19F nuclear magnetic resonance in seven perfused ferret hearts loaded with the fluorinated Ca2+ indicator 5F-BAPTA. Left ventricular developed pressure decreased to 65 +/- 3% (mean +/- SEM) of control after 15 minutes of global ischemia at 37 degrees C. In stunned myocardium, diastolic [Ca2+]i (0.24 +/- 0.03 microM) was not changed from control (0.18 +/- 0.03 microM, p greater than 0.10), but peak [Ca2+]i (1.03 +/- 0.13 microM) was paradoxically higher than that in control (0.61 +/- 0.06 microM, p less than 0.02). The slope of the relation between developed pressure and Ca2+ transient amplitude in stunned myocardium was significantly lower than that in control (p less than 0.05), even after normalization by maximal Ca2(+)-activated pressure. These results indicate that contractile failure in stunned myocardium is due to a decrease in the myofilament sensitivity to Ca2+ as well as to the previously identified decrease in maximal Ca2(+)-activated force; failure of activator Ca2+ delivery cannot be implicated. The increase in the amplitude of Ca2+ transients would require that more ATP be spent in Ca2+ sequestration; thus, decreased efficiency of energy utilization in stunned myocardium would result.
Molecular and particulate depositions for regional myocardial flows in sheep.
Authors: Bassingthwaighte J B , Malone M A , Moffett T C , King R B , Chan I S , Link J M , Krohn K A
Published: June 2012

The deposition of microspheres in small tissue regions is not strictly flow dependent. In comparison with the soluble flow marker 2-iododesmethylimipramine (IDMI), deposition of 16.5-microns microspheres was mildly but systematically biased into high flow regions of rabbit hearts (Bassingthwaighte JB, Malone MA, Moffett T-C, King RB, Little SE, Link JM, Krohn KA. Am J Physiol 1987;253 (Heart Circ Physiol 22):H184-H193). To examine the possibility of bias in larger hearts, a similar study was undertaken in sheep. 141Ce- and 103Ru-labeled 16.5-microns microspheres in one syringe and 125I- and 131I-DMI in another syringe were injected simultaneously into the left atrium of five open-chest sheep while obtaining reference blood samples from the femoral artery. In six other sheep, one microsphere type and one IDMI were used. Hearts were removed 1 minute after injection, cut into approximately 254 pieces averaging 217 mg, and regional deposition densities calculated for each tracer from the isotopic counts. Correlations in the five animals between the two differently labeled IDMIs and between the two microspheres were both greater than or equal to 0.98. In all 11 sheep, scatter plots of microsphere deposition densities versus IDMI densities showed that differences between microspheres and IDMI had substantially more scatter (0.84 less than r less than 0.98) but were not random. Microsphere depositions tended to be lower than IDMI depositions in low flow regions and higher in high flow regions, in accord with the expected bias that at a bifurcation a microsphere is most likely to enter the branch with higher flow. There was less bias ascribable to endomyocardial/epicardial maldistribution. Thus, while microsphere depositions appear to err systematically with respect to flow when the regions of interest are small enough that the diameters of their arterioles are only a few times those of the microspheres, microspheres are, in sheep as in rabbits, adequate for estimating regional flows.
Endothelium and myocardial protecting actions of taprostene, a stable prostacyclin analogue, after acute myocardial ischemia and reperfusion in cats.
Authors: Johnson G , Furlan L E , Aoki N , Lefer A M
Published: June 2012

The effects of taprostene, a synthetic prostacyclin analogue, were investigated in a 6-hour model of myocardial ischemia (MI) with reperfusion in anesthetized cats. Taprostene (100 ng/kg/min) was infused intravenously starting 30 minutes postocclusion of the left anterior descending coronary artery followed by reperfusion 1 hour later, and the cats were observed for an additional 4.5 hours. Taprostene infusion resulted in significantly lower plasma creatine phosphokinase activities at every time from 3 to 6 hours for the MI + taprostene group compared with the MI + vehicle group and were not significantly different when compared with sham MI controls. The areas at risk, expressed as a percentage of the total left ventricular weights, were not significantly different between the MI groups. However, the necrotic area expressed as a percentage of the myocardial area at risk was significantly lower in the taprostene-treated cats compared with the untreated MI group (p less than 0.01). Cardiac myeloperoxidase activities indicated that significantly fewer neutrophils were attracted to the area at risk and to the ischemic zone of the MI + taprostene cats when compared with the MI cats given only the vehicle. Data from isolated left anterior descending coronary artery ring preparations removed from hearts after 6 hours of ischemia indicated that the endothelium was damaged by ischemia-reperfusion injury in the untreated cats. However, endothelial dysfunction was not observed in circumflex coronary arteries of ischemic cats or in coronary rings isolated from MI + taprostene cats. Thus, taprostene exerted a significant cardioprotection in cats subjected to ischemia and reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)
Reduced L-type calcium current in the embryonic chick heart with persistent truncus arteriosus.
Authors: Creazzo T L
Published: June 2012

Calcium currents were examined in an experimental model in the embryonic chick heart with a congenital malformation known as persistent truncus arteriosus. This is a severe defect characterized by failure of conotruncal and aorticopulmonary septation of the embryonic heart tube. As a result, no separation into the aortic and pulmonary arteries occurs, and there is a common outflow tract. The hearts with persistent truncus arteriosus had a 26% greater ventricular to whole embryo weight, which indicated that the ventricles were enlarged. Both the low-threshold T-type (ICa.T) and the 1,4-dihydropyridine-sensitive L-type (ICa.L) Ca2+ currents were present in the ventricular myocytes from hearts at day 11 of incubation. However, day 11 hearts with persistent truncus arteriosus showed a twofold reduction in the peak magnitude of ICa.L at a test potential of + 10 mV without a concomitant reduction in the number of L channels detected by 1,4-dihydropyridine antagonist [(+)[3H]PN200-110] and agonist (Bay K 8644) receptor binding. The results indicated that an L channel regulatory mechanism other than protein synthesis was affected. These changes are consistent with responses to conditions of excessive hemodynamic burden that have been characterized in adult hearts.
Experimental and modeling study of the excitability of carotid sinus baroreceptors.
Authors: van Brederode J F , Seagard J L , Dean C , Hopp F A , Kampine J P
Published: June 2012

In this study we examined the effects of blockade of a transient K+ current with 4-aminopyridine (4-AP) on the static stimulus-response relation of myelinated carotid sinus baroreceptors (n = 8), using a vascularly isolated sinus preparation in sodium thiopental-anesthetized dogs. In one class of baroreceptors (type I), which did not fire spontaneously below the pressure threshold (Pth), 4-AP (10(-5) to 10(-4) M) decreased Pth in a dose-dependent manner and transformed the stimulus-response relation from a discontinuous, hyperbolic shape to a sigmoidal, continuous curve. After exposure to 10(-4) M of 4-AP, baroreceptors were spontaneously active below Pth. These effects of 4-AP were more pronounced in baroreceptors with a high control Pth and were independent of enhanced neurotransmitter release or changes in carotid sinus distensibility. In contrast, 4-AP had relatively little effect on type II baroreceptors, which under control conditions are characterized by a continuous, sigmoidal stimulus-response curve. We believe that these effects of 4-AP on baroreceptor discharge were mediated by blockade of a transient K+ conductance that was present at the receptor spike-initiation zone. This hypothesis was examined using a mathematical model based on the Hodgkin-Huxley axon, but modified to include the transient K+ conductance. The modeling results showed that the minimum current necessary to elicit action potential firing is an extremely sensitive function of the magnitude of this K+ conductance, supporting our experimental results obtained with 4-AP. Our findings suggest that a transient K+ conductance might play a role in the determination of Pth and that differences between type I and II receptors could be the result of differences in the effectiveness of this conductance in controlling spike-initiation zone excitability.
Protective role of intracoronary fatty acid binding protein in ischemic and reperfused myocardium.
Authors: Srimani B N , Engelman R M , Jones R , Das D K
Published: June 2012

In this study, fatty acid binding protein was used to protect an ischemic heart from reperfusion injury. Isolated rat heart was preperfused in the presence of 1.4 microM liposome-bound fatty acid binding protein for 15 minutes, followed by 30 minutes of ischemia and 30 minutes of reperfusion. Our results indicated better preservation of myocardial high-energy phosphate compounds (including ATP and creatine phosphate), reduced creatine kinase and lactate dehydrogenase release from the heart, and improved coronary flow in hearts treated with fatty acid binding protein compared with untreated controls. Fatty acid binding protein enhanced reacylation of arachidonic acid into phospholipids, thereby preserving membrane phospholipids and reducing free fatty acid contents during ischemia and reperfusion. In addition, fatty acid binding protein-bound long-chain free fatty acids and their thioesters as well as carnitine esters were increased in the cytosolic compartment of the heart. These results suggest that fatty acid binding protein may be used as a possible therapeutic agent to improve myocardial function during reperfusion of ischemic heart.
Baroreceptor-heart rate reflex function before and after surgical reversal of two-kidney, one-clip hypertension in the rat.
Authors: Edmunds M E , Russell G I , Burton P R , Swales J D
Published: June 2012

Baroreflex function was studied in conscious early phase (less than 6 weeks) two-kidney, one-clip hypertensive rats before and 24 hours after surgical reversal of hypertension by removal of the constricting renal artery clip or after pharmacological reduction of blood pressure by an infusion of hydralazine or captopril. A normotensive sham-clipped group was included. Another group of two-kidney, one-clip rats was studied 3 weeks after unclipping. Baroreflex sensitivity, as assessed by the steady-state method using a graded phenylephrine infusion, mean arterial pressure, and heart rate were measured preoperatively and at 24 hours postoperatively. Two-kidney, one-clip rats were significantly hypertensive preoperatively compared with control (mean arterial pressure, 183 +/- 4 vs. 106 +/- 2 mm Hg, p less than 0.001), heart rate was similar (420 +/- 9 vs. 401 +/- 9 beats/min, p greater than 0.05), and baroreflex sensitivity was significantly reduced (0.76 +/- 0.07 vs. 1.50 +/- 0.20 msec/mm Hg; p less than 0.001). There was a minimal change in heart rate despite the fall in mean arterial pressure in all hypertensive groups, indicating resetting of the baroreflexes. At 24 hours after the operation, baroreflex sensitivity was unchanged in all groups compared with the preoperative value. By 3 weeks, baroreflex sensitivity was significantly greater than in the hypertensive two-kidney, one-clip rats before the operation and 24 hours after they were unclipped, but not compared with normotensive sham-clipped rats. Thus, although resetting occurs within 24 hours, whatever the method of blood pressure reduction, baroreflex sensitivity remains impaired at this time.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of bigeminies and paired-pulse stimulation on oxygen consumption in dog left ventricle.
Authors: Nozawa T , Yasumura Y , Futaki S , Tanaka N , Suga H
Published: June 2012

In 10 excised, cross-circulated, isovolumically beating dog left ventricles, we examined the effects of bigeminy, including paired-pulse stimulation, on cardiac oxygen consumption (VO2) and evaluated whether the VO2 versus pressure-volume area (PVA) relation obtained from regularly beating hearts in our previous studies could account for the changes in VO2 during bigeminies with various coupling intervals. The extrasystolic interval (ESI) was decreased in four steps from 300 msec (regular rhythm) to paired-pulse stimulation (less than or equal to 210 msec). The sum of ESI and the postextrasystolic interval was always held constant (600 msec); therefore, the number of excitations was 200/min at any ESI. Both VO2 and PVA were measured in four runs: a small volume run at a ventricular volume of 13 ml, a large volume of 12 ml, a calcium run in which contractility was enhanced by CaCl2 at a small volume of 12 ml, and a verapamil run in which contractility was depressed by verapamil at a large volume of 20 ml. In any run, both VO2 and PVA were unchanged at long ESIs (greater than or equal to 250 msec) from each control value at regular rhythm, but VO2 markedly increased at short ESIs (less than or equal to 230 msec). VO2s during bigeminies with various ESIs were comparable with the theoretical VO2 values that were calculated by the VO2-PVA relation at regular rhythm. However, the theoretical VO2 values underestimated the measured VO2 values at the shortest ESIs under a high volume loading and in a high contractile state. This indicates that the PVA concept can be expanded to various arrhythmias unless ESI becomes very short.