bluuebunny/crossref_metadata_2025 huggingface dataset:
Renal effects of atrial natriuretic factor during control of the renin-angiotensin system in anesthetized dogs.
Authors: Seymour A A , Mazack E K
Published: June 2012

The contribution of the renin-angiotensin system to the natriuretic responses to intrarenal infusions of 1, 5, 25, and 125 pmol/kg/min synthetic rat atrial natriuretic peptide 101-126 was determined in one-kidney anesthetized dogs. In vehicle-treated dogs, atrial natriuretic peptide 101-126 increased fractional sodium excretion from 1.8 +/- 0.6% to a peak response of 5.1 +/- 0.9% during infusion of 25 pmol/kg/min. The peptide progressively decreased mean arterial pressure from 110 +/- 5 to 94 +/- 4 mm Hg, renal vascular resistance from 0.40 +/- 0.02 to 0.30 +/- 0.02 mm Hg/ml/min, and arterial plasma renin activity from 4.3 +/- 1.6 to 3.1 +/- 0.8 ng/ml/hr. When the renin-angiotensin system was blocked by 3 mg/kg i.v. enalaprilat, baseline pressure fell to 86 +/- 4 mm Hg, and subsequent infusions of atrial natriuretic peptide 101-126 did not affect fractional sodium excretion. The decreases in blood pressure (from 86 +/- 4 to 76 +/- 4 mm Hg) and in renal vascular resistance (from 0.27 +/- 0.03 to 0.23 +/- 0.02 mm Hg/ml/min) were also ameliorated compared with the control responses. Intravenous infusion of 2.5 ng/kg/min angiotensin II restored mean arterial pressure and potentiated the natriuretic and renal vascular responses to atrial natriuretic peptide 101-126. In two additional groups of anesthetized dogs, enalaprilat did not produce the profound hypotension and did not affect the natriuretic responses to atrial natriuretic peptide 101-126. When renal vascular resistance was elevated by intrarenal infusion of angiotensin II in enalaprilat-treated dogs, the natriuretic response was improved.(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanism of complement activation after coronary artery occlusion: evidence that myocardial ischemia in dogs causes release of constituents of myocardial subcellular origin that complex with human C1q in vivo.
Authors: Rossen R D , Michael L H , Kagiyama A , Savage H E , Hanson G , Reisberg M A , Moake J N , Kim S H , Self D , Weakley S
Published: June 2012

To evaluate whether ischemic myocardium releases molecules that react with the first component of complement, we studied cardiac lymph from eight dogs before and at intervals after coronary artery occlusion and reperfusion. Before occlusion, the dogs were injected intravenously with radiolabeled human C1q. Labeled C1q could be detected in the cardiac lymph within minutes following injection. Rabbit antisera, prepared against substances precipitated from postreprefusion cardiac lymph by anti-human C1q, also reacted with specific constituents of isolated cardiac sarcoplasmic reticulum and mitochondria. To evaluate whether mitochondria are the source of these C1q-binding proteins, we isolated intramyofibrillar and subsarcolemmal mitochondria from canine heart and incubated sonicates of these with purified C1q, immobilized on nitrocellulose. Molecules bound to the immobilized C1q were removed with 0.1% sodium dodecyl sulfate, fractionated under reducing conditions by polyacrylamide gel electrophoresis, and transferred electrophoretically to nitrocellulose paper. Antisera prepared against postreperfusion lymph reacted with a 31,000-32,000-dalton protein in these nitrocellulose paper replicas. Since this protein originates from mitochondria, binds to C1q, and is recognized by antibodies made against postreperfusion lymph, this protein is likely to be one of the subcellular constituents that, upon release from ischemic cells, activates the complement cascade. To evaluate the clinical relevance of these observations, we tested sera from 53 patients obtained 48-72 hours after hospitalization for suspected myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)
Calcium oscillations in digitalis-induced ventricular fibrillation: pathogenetic role and metabolic consequences in isolated ferret hearts.
Authors: Kusuoka H , Jacobus W E , Marban E
Published: June 2012

The pathophysiology of the ventricular fibrillation that complicates digitalis intoxication was investigated. In this and other calcium-overload states, oscillations of the intracellular free calcium concentration ([Ca2+]i) have been implicated as the cause of ventricular tachyarrhythmias. We addressed two questions: 1) Are [Ca2+]i oscillations obligatory in the pathogenesis of ventricular fibrillation during digitalis toxicity? 2) What are the metabolic consequences of [Ca2+]i oscillations? Ferret hearts (n = 20) were Langendorff-perfused at constant flow with oxygenated HEPES-buffered Tyrode's solution at 37 degrees C. Isovolumic left ventricular pressure was measured along with the extracellular electrogram or with simultaneous phosphorus nuclear magnetic resonance spectra. When strophanthidin (20 microM) was added during pacing at 3 Hz, the positive inotropic effect soon gave way to a decrease in developed force. The decrease in force was accompanied by an increase in inorganic phosphate concentration, a decrease in phosphocreatine concentration, and a slight acidosis. The rhythm changed to ventricular fibrillation after 12-25 minutes. This change was initially accompanied by further metabolic deterioration, but all metabolites reached steady state within 12-18 minutes of the onset of ventricular fibrillation. Fast Fourier transformation revealed the existence of periodic oscillations at 7-10 Hz in both the extracellular electrogram and the ventricular pressure during ventricular fibrillation. Ryanodine, an inhibitor of [Ca2+]i oscillations, abolished the pressure oscillations but not the voltage oscillations. Exposure to ryanodine significantly decreased the inorganic phosphate concentration and increased the phosphocreatine concentration (p less than 0.05) despite continuing exposure to strophanthidin. The results indicate that oscillations of [Ca2+]i are not required to sustain ventricular fibrillation, but when present, such oscillations contribute importantly to metabolic deterioration.
Effects of left ventricular loading by negative intrathoracic pressure in dogs.
Authors: Hausknecht M J , Brin K P , Weisfeldt M L , Permutt S , Yin F C
Published: June 2012

There are many factors, both intrinsic and extrinsic to the left ventricle, that can affect its function when negative intrathoracic pressure is imposed. In this study, we examined whether the left ventricular response to the afterload imposed by negative intrathoracic pressure was similar to that imposed by partial aortic constriction. We used steady-state right heart bypass to control pulmonary venous return to the left ventricle and reflex blockade to maintain constant heart rate and contractility. To impose negative intrathoracic pressure we used a pressure chamber fitted over a midsternal thoracotomy, which allowed steady negative pressure to be applied to all intrathoracic surfaces. Left ventricular volumes were measured from biplane cineradiograms of multiple 1-mm markers implanted in the left ventricular midwall. With cardiac output and heart rate constant, we compared the left ventricular response to two different levels of negative intrathoracic pressure and to increasing aortic pressure by partial aortic constriction. In each case, negative intrathoracic pressure produced a rise in the left ventricular end-systolic and end-diastolic volumes as well as transmural pressures similar to the effects of partial aortic occlusion. Thus, when cardiac output, heart rate, and contractility are maintained constant and all external restraints on the left ventricle are removed, the left ventricle responds in a similar manner to an increase in hydraulic load whether produced by a decrease in intrathoracic pressure or by partial aortic occlusion.
Technique for measuring regional two-dimensional finite strains in canine left ventricle.
Authors: Villarreal F J , Waldman L K , Lew W Y
Published: June 2012

We developed a technique to measure regional two-dimensional deformations in the myocardium. Three piezoelectric crystals were implanted in a triangular array in the left ventricular anterior midwall in six anesthetized dogs. Each crystal was used in a dual function, to both transmit and receive ultrasonic signals from the other two crystals. In this manner, the three segment lengths of the crystal triangle throughout the cardiac cycle were simultaneously recorded. The orientation of the crystal triangle with reference to the left ventricular long and minor axes was determined. The orientation and three segment lengths of the crystal triangle were used to calculate the circumferential strain E11, the longitudinal strain E22, the in-plane shear strain E12, and the mutually perpendicular principal strains E1 and E2. Also, the orientation of the first principal direction or the in-plane angle was determined, which was defined as the angle between the first principal direction (E1) and the circumferential direction (0 degree). This information fully describes the regional two-dimensional myocardial deformations. This technique was applied to measure regional myocardial deformations at three different left ventricular end-diastolic pressures (LVEDP) of 2 +/- 1 (mean +/- SD), 8 +/- 1, and 17 +/- 2 mm Hg. The first principal direction at end-systole was oriented away from the circumferential direction at low LVEDP (-43 +/- 21 degrees) but became progressively closer in each animal to the circumferential direction as LVEDP increased to mid (-26 +/- 18 degrees) and high (-14 +/- 13 degrees) levels. The end-systolic ratio E11/E1 was 0.6 +/- 0.2 at low LVEDP, but increased toward unity in each animal to 0.9 +/- 0.1 at mid and high LVEDP. Thus, at low LVEDP, the greatest systolic deformation occurred in a direction different from the circumferential orientation. Therefore, circumferential strain measurements (E11) significantly underestimated the greatest systolic deformation (E1). However, as LVEDP increased, the first principal direction rotated closer toward the circumferential orientation, and circumferential strain measurements adequately estimated the greatest systolic deformation. Nevertheless, the presence of significant amounts of shortening along either the longitudinal (E22) or the second principal direction (E2) in the midwall necessitated the use of the two-dimensional method. The change in end-diastolic configuration as LVEDP increased from 1 +/- 1 to 16 +/- 1 mm Hg was also examined. Unlike the end-systolic data, the end-diastolic first principal direction did not deviate significantly from the circumferential direction at any LVEDP.(ABSTRACT TRUNCATED AT 400 WORDS)
Reactivity of isolated porcine coronary resistance arteries to cholinergic and adrenergic drugs and transmural pressure changes.
Authors: Nakayama K , Osol G , Halpern W
Published: June 2012

The reactivity of porcine intramyocardial resistance arteries (223 +/- 7 micron i.d., n = 30) was investigated with a pressurized in vitro preparation. Diameter changes in response to acetylcholine and to adrenergic drugs and dynamic changes in transmural pressure changes were investigated. Acetylcholine produced concentration-dependent constrictions, causing maximal reductions of 71 +/- 3% in lumen diameter, with EC50 values averaging 1.9 X 10(-7) M (n = 7). These responses were inhibited by atropine (10(-7) M) and therefore were mediated by muscarinic receptors. In addition, acetylcholine did not elicit relaxation in nine out of 10 vessels precontracted with U46619 (10(-7) M). Norepinephrine and epinephrine never produced constrictions (n = 6) even in the presence of propranolol (10(-6) M). Both norepinephrine and isoproterenol caused dose-dependent relaxations in acetylcholine-precontracted vessels, with IC50 values of 8.2 X 10(-7) M (n = 5) and 6.6 X 10(-8) M (n = 6), respectively. These relaxations were suppressed by propranolol. Between transmural pressures of 10 and 90 mm Hg, there was no intrinsic myogenic tone (n = 7). In addition, the vessels responded only passively to sudden pressure changes of 40 mm Hg. In all vessels, the functional integrity of the endothelium was verified by relaxations to substance P (10(-8) M) and/or bradykinin (10(-8) M).(ABSTRACT TRUNCATED AT 250 WORDS)
Selective functional characteristics of rate-induced fatigue in rabbit atrioventricular node.
Authors: Billette J , Métayer R , St-Vincent M
Published: June 2012

The slowly developing rate-induced prolongation in atrioventricular nodal conduction time, termed "fatigue," was selectively studied using specifically designed stimulation protocols in isolated rabbit heart preparations. A nodal recovery curve (A2H2 versus H1A2 intervals; nodal conduction time of each premature beat plotted against corresponding recovery time) was obtained before and after a stable and nearly maximum fatigue had been reached by driving the atrium for 5 minutes at a fast rate close to the upper limit of 1:1 nodal conduction. The fatigue uniformly prolonged all A2H2 intervals (12.3 +/- 1.3 msec) and systematically increased the minimum H1A2 interval at which complete nodal block occurred (24.8 +/- 4.0 msec) (p less than 0.01, n = 6). To study the rate and time dependence of fatigue, nodal conduction times were obtained during three rapid 5-minute pacings corresponding to 50%, 75%, and 100% shortening of the pacing interval in the 1:1 nodal conduction range. The respective maximum fatigue-induced increases in conduction time were 5.4 +/- 1.8, 9.0 +/- 2.7, and 12.5 +/- 2.1 msec (p less than 0.01, n = 6). However, the pacing interval had no significant effect on the time required to reach either 50% (17.1 +/- 3.5 seconds) or 90% (92.6 +/- 15.4 seconds) of the fatigue observed after 5 minutes of fast rate. At the termination of any rapid stimulation, the fatigue effect dissipated with a time course that was inverse but symmetrical to that of its induction. These findings support the existence of an independent, slow, nodal memory process by which the conduction time changes according to past events with a long time constant.
Mechanism of CO2 response in cerebral arteries of the newborn pig: role of phospholipase, cyclooxygenase, and lipoxygenase pathways.
Authors: Wagerle L C , Mishra O P
Published: June 2012

The role of phospholipase, lipoxygenase, and cyclooxygenase pathways in the mechanism of the cerebrovascular response to CO2 and H+ was investigated in newborn piglets. Responsiveness of pial arterioles, 48-206 micron diameter, to inhalation of 6% CO2 and to suffusion of acidic cerebrospinal fluid (CSF, pH = 6.84), adenosine (10(-4) M), or theophylline (10(-2) M) was studied using a closed cranial window. Pial arteriolar diameter was measured using intravital microscopy. Phospholipase inhibitors quinacrine hydrochloride (10(-4) M in CSF) and p-bromophenacyl bromide (10(-4) M in CSF) abolished the CO2 vasodilation from delta diameter = 27 +/- 5% and 28 +/- 3% during baseline to 0 +/- 4% and -1 +/- 1% following the respective inhibitors. Following administration of the cyclooxygenase inhibitor indomethacin (5 mg/kg i.v.), the CO2 response was converted from vasodilation, 31 +/- 6%, to constriction, -4 +/- 1% (p less than 0.001), while the lipoxygenase inhibitor nordihydroguaiaretic acid (2 mg/kg i.v. or 10(-4) M in CSF) augmented the pial arteriolar response to CO2 from 21 +/- 4% to 34 +/- 7% (p less than 0.005). Topical application of superoxide dismutase (40 units/ml CSF) plus catalase (40 units/ml CSF) also appeared to augment the CO2 response. Suffusion of the cortical surface with acidic CSF at constant PCO2 increased pial arteriolar diameter by 11 +/- 2% that was also abolished by indomethacin. Vasodilatory responses to topical adenosine and theophylline were not affected by indomethacin, suggesting specificity for H+ ion-related vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)
Parasympathetic coronary vasoconstriction induced by nicotine in conscious calves.
Authors: Young M A , Knight D R , Vatner S F
Published: June 2012

We studied the effects of intracoronary injection of nicotine and acetylcholine on coronary blood flow in nine conscious calves chronically instrumented to measure coronary blood flow, left ventricular (LV) and mean arterial pressure, LV dP/dt, and heart rate. Nicotine (5 micrograms/kg i.c.) elicited a biphasic response in coronary blood flow consisting of an initial vasoconstriction (phase 1; blood flow fell by 52 +/- 5.4% from a baseline of 66 +/- 7.5 ml/min) followed by vasodilation (phase 2, blood flow rose 119 +/- 12.7% above baseline). The change in coronary blood flow with nicotine was not associated with changes in LV systolic pressure, mean arterial pressure, or heart rate. The change in coronary blood flow was unaffected by combined alpha- and beta-adrenoceptor blockade with prazosin, rauwolscine, and propranolol but was abolished by either muscarinic blockade with atropine or ganglionic blockade with hexamethonium. Acetylcholine (0.5 microgram/kg i.c.), without affecting mean arterial pressure, elicited changes in coronary blood flow similar to those observed with nicotine, producing an initial phase of coronary vasoconstriction (blood flow fell by 71 +/- 4.9%) followed by vasodilation (blood flow rose by 228 +/- 20.7%). Both phases of the response to acetylcholine were abolished by muscarinic blockade but were unaffected by ganglionic blockade. When nicotine was injected into the left circumflex coronary artery, no change in blood flow was observed in the left anterior descending coronary artery, indicating the lack of involvement of global reflex pathways. These results suggest that nicotine locally stimulates parasympathetic nerves, which constrict the coronary circulation via a muscarinic mechanism.
Expression of cellular oncogenes in the myocardium during the developmental stage and pressure-overloaded hypertrophy of the rat heart.
Authors: Komuro I , Kurabayashi M , Takaku F , Yazaki Y
Published: June 2012

Proto-oncogenes have been revealed to participate in normal cell proliferation as well as in cell transformation. Since cardiac myocytes are terminally differentiated, they cannot divide except in the fetal period. To determine the role of cellular oncogenes in the growth of the heart, the expression pattern of eight cellular oncogenes during the developmental stage and pressure-overloaded hypertrophy of the rat hearts were examined in vivo. Northern blot analysis was performed with eight oncogene probes (myc, fos, Ha-ras, src, erbA, erbB, sis, myb). Pressure overload increased the levels of cellular (c-) fos, c-myc, and c-Ha-ras. An increase of c-fos and c-myc was detected at 30 minutes and 2 hours, respectively; the levels peaked at 8 hours, and they returned to baseline by 48 hours after aortic constriction. However, the level of c-Ha-ras showed a gradual increase. During the course of development, the expression of c-myc was detectable only in the embryonic stage, whereas the expression of c-fos was not detected in the fetal period, was increased after birth, and peaked in 200-day-old adults. The expression of c-Ha-ras was almost the same throughout the development. Cellular oncogenes were expressed in the heart in response to pressure overload and in a stage-specific manner. These results suggest that cellular oncogenes may participate in the normal developmental process and hypertrophy of hearts and that the cellular hypertrophy induced by pressure overload may share a similar mechanistic pathway with cell proliferation.
Stimulation of muscarinic receptors raises free intracellular Ca2+ concentration in rat ventricular myocytes.
Authors: Korth M , Sharma V K , Sheu S S
Published: June 2012

The effect of carbachol on free intracellular calcium concentration, ([Ca2+]i) and on intracellular hydrogen concentration (pHi) was determined from fluorescence signals obtained from rat ventricular myocytes. Application of carbachol (300 mumol/l) to quin2-loaded myocytes bathed in 2 mmol/l Ca2+-containing solution caused [Ca2+]i to increase within 7-10 minutes from 182 +/- 9 to 212 +/- 11 nmol/l (n = 4). Carbachol acted via stimulation of muscarinic receptors because atropine (1 mumol/l) either prevented or abolished the increase in [Ca2+]i. Carbachol also produced a positive inotropic effect in rat papillary muscles contracting isometrically at a frequency of 0.5 Hz and enhanced contracture in resting preparations in the presence of high extracellular Ca2+ concentration ([Ca2+]o) (20 mmol/l). The effect of carbachol on [Ca2+]i was dependent on [Ca2+]o. In the presence of 10 mmol/l [Ca2+]o, the increase in [Ca2+]i was about two times that elicited by carbachol when bath [Ca2+]o was 2 mmol/l. Reduction of [Ca2+]o to 50 mumol/l abolished the carbachol effect but did not prevent caffeine-induced Ca2+ release. The carbachol-induced rise in [Ca2+]i remained unchanged in the presence of either 10 mmol/l caffeine or 1 mumol/l ryanodine. In the absence of extracellular Na+ concentration [( Na+]o), carbachol no longer produced an increase in [Ca2+]i of cardiomyocytes and failed to enhance Na+-withdrawal contracture of the rat papillary muscle. In contrast to the effect on [Ca2+]i, carbachol did not produce any change in pHi as determined from fluorescence signals obtained from rat ventricular myocytes loaded with 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein.(ABSTRACT TRUNCATED AT 250 WORDS)
Expression of ventricular-type myosin light chain messenger RNA in spontaneously hypertensive rat atria.
Authors: Kumar C , Saidapet C , Delaney P , Mendola C , Siddiqui M A
Published: June 2012

Using cloned DNA probes specific for two isoforms of cardiac myosin light chains (MLCs), nonphosphorylatable MLC1 and phosphorylatable, regulatory MLC2, we have observed that the MLC1 messenger RNA of ventricular type does not appear in detectable amounts in atrial cells of either normotensive Wistar-Kyoto rat strain (WKY) or spontaneously hypertensive rat strain (SHR). The messenger RNA of regulatory isoform of ventricular MLC2, on the other hand, is found in threefold excess in atria of SHR relative to that of age-matched WKY. The increased level of MLC2 messenger RNA is present even in 6-week-old SHR atria where there is no established overloading of the heart. Thus, it appears that the increased expression of the regulatory MLC2 gene in SHR atrial cells is a predetermined event, which, most likely, participates in functional adaptation of the myocardium in response to pressure overload and subsequent hypertrophy.
Elevations in arterial pressure induce the formation of spontaneous action potentials and alter neurotransmission in canine ileum arteries.
Authors: Smeda J S , Daniel E E
Published: June 2012

Arterial segments (less than 250 micron o.d.) excised from canine ileum were mounted in a chamber that permitted arterial transmural pressure (TMP) to be altered and measured. Subsequently, the periarterial nerves were field stimulated with single pulses (0.1 msec, 70 V), and the resting membrane potential (Em) as well as the nerve-mediated alterations in smooth muscle Em were measured using intracellular microelectrodes at TMPs between 0 and 160 mm Hg. The resting Em was greatest at TMPs of 40 mm Hg (-54.7 +/- 2.6 mV) and depolarized as the TMP was increased, reaching a value of -44.8 +/- 3.1 mV at 160 mm Hg. At TMP greater than or equal to 60 mm Hg, a proportion of the preparations exhibited spontaneous electrical activity (SA) consisting of constant rhythmic oscillations in Em or action potentials (APs) or of trains of rhythmic APs that progressively decreased in amplitude, interrupted by periods of hyperpolarization. SA stopped when the TMP was lowered to 40 mm Hg and was reestablished when the TMP was reelevated to TMPs above 60 mm Hg. Nerve stimulation evoked excitatory junction potentials (ejps) or APs. At constant stimulus parameters, ejps of maximum amplitude having the greatest rate of potential rise and fall were produced at TMP of 100 mm Hg. At TMPs greater than 100 mm Hg or less than 100 mm Hg, the amplitude and the rate of rise and fall of the ejps decreased. Ejps formed in response to a constant single pulse stimulus (0.1 msec, 70 V) elicited APs only at TMPs greater than or equal to 60 mm Hg. Neither ejps nor APs were inhibited by alpha-receptor-blocking agents. These studies indicate that the TMP at which an artery is maintained plays an important role in determining the resting Em, the occurrence of spontaneous action potentials, and the alterations in Em associated with nerve stimulation.
Monensin turns on microtubule-associated translocation of secretory granules in cultured rat atrial myocytes.
Authors: Iida H , Barron W M , Page E
Published: June 2012

We have studied the effect of monensin on microtubule-associated translocation of atrial secretory granules in 5-7-day-old cultures of atrial myocytes from adult rats. Atrial granules and microtubules were localized by immunofluorescent microscopy of myocytes double-labeled with primary antibodies against atrial natriuretic polypeptide (ANP) and alpha-tubulin. In control myocytes, fluorescence due to atrial granules was predominantly localized to the perinuclear region containing the Golgi complex. After exposure for 30 minutes to monensin (0.5-5.0 microM), myocytes transiently contained conspicuous linear arrays of atrial granules associated with cytoplasmic microtubules. Thereafter, ANP fluorescence accumulated in subsarcolemmal foci at the cell periphery, while perinuclear ANP fluorescence faded. The monensin-induced redistribution of atrial granules was observable in both serum-containing and serum-free media and was unaffected by reducing external Ca2+ to low values, by inhibition of sarcoplasmic reticulum Ca2+ release with ryanodine, or by both. The redistribution was prevented by pretreatment with nocodazole, which fragmented microtubules and scattered Golgi complexes and the associated atrial granules throughout the cytoplasm. Radioimmunoassay showed that monensin seemingly decreased the rate of ANP secretion into the medium from 0.15 to 0.11 fmol/(hr.myocyte). These results suggest that monensin turns on microtubule-associated translocation of atrial granules from the perinuclear areas to the cell periphery by modifying the interaction between microtubules and atrial granules. Monensin also promotes movement of atrial granules along the microtubules but does not accelerate the release of ANP.
Activation block and trapping of penticainide, a disopyramide analogue, in the Na+ channel of rabbit cardiac Purkinje fibers.
Authors: Carmeliet E
Published: June 2012

The blocking mechanism of the Na+ channel by penticainide, a disopyramide analogue, was studied in rabbit cardiac Purkinje fibers. Na+ channel activity was measured directly by recording the slowly inactivating Na+ current or indirectly by measuring Vmax. The two-microelectrode technique was used to measure currents under voltage-clamp conditions or to impose different degrees and durations of depolarizing pulses. The experimental results show 1) that penticainide exerted a pronounced use-dependent block not dependent on the duration of the depolarizing pulse, 2) that no block was observed in the absence of stimulation, even when the membrane was depolarized by conditioning prepulses, and 3) that recovery was slower the more negative the holding potential but could be accelerated by repeating the depolarizing pulse; there was not only use-dependent block but also use-dependent unblock. It is concluded that penticainide binds to the open Na+ channel and is trapped when the activated channel returns to the rested state.
Failure of glycogen depletion to improve left ventricular function of the rabbit heart after hypothermic ischemic arrest.
Authors: Lagerstrom C F , Walker W E , Taegtmeyer H
Published: June 2012

We tested the hypothesis that depletion of glycogen prior to myocardial ischemia diminishes lactate buildup and improves functional recovery on reperfusion in the isolated rabbit heart. Cardiac glycogen was reduced either by substituting N2 for O2 in the perfusate or by perfusion with substrate-free solution, before the onset of ischemia. Hearts were subjected to either 30 minutes of normothermic (37 degrees C) or 60 minutes of hypothermic (4 degrees C) ischemia followed by 30 minutes of reperfusion with oxygenated Krebs-Henseleit buffer. Function was assessed by measuring peak left ventricular pressure at end-diastolic pressures ranging from 0 to 20 mm Hg. N2 perfusion for 15 minutes lowered myocardial glycogen by 60% and decreased ATP and phosphocreatine (p less than 0.001). Glycogen depletion did not decrease lactate accumulation during ischemia, but it impaired recovery with reperfusion (-46%, p less than 0.05). N2 perfusion for 5 minutes also reduced glycogen by 60%, but energy-rich phosphates were not reduced and functional recovery was still impaired (-40%, p less than 0.05). Perfusion with substrate-free medium diminished glycogen by 33% (p less than 0.05). Although lactate accumulation was significantly reduced (-45%, p less than 0.05), recovery following reperfusion was not improved. The results suggest that preservation of glycogen stores, but not the prevention of lactate buildup during ischemia, is beneficial for the recovery of function with reperfusion.
Certain beta-blockers can decrease beta-adrenergic receptor number: II. Down-regulation of receptor number by alprenolol and propranolol in cultured lymphoma and muscle cells.
Authors: Hughes R J , Mahan L C , Insel P A
Published: June 2012

We have used two different cultured cell lines--S49 lymphoma cells and BC3H-1 muscle cells--to examine the regulation of beta-adrenergic receptors by receptor antagonists. Rather than an increase ("up-regulation") of receptor number that such antagonists often produce, we found that certain beta-blockers elicit a decrease ("down-regulation") of beta-adrenergic receptors. Alprenolol and propranolol, but not sotalol or ICI 118,551, at concentrations of 10-100 nM down-regulated beta-adrenergic receptors 20-70% following 16-20 hours of treatment of S49 or BC3H-1 cells. Several observations suggest that this phenomenon depends upon beta-receptor interaction, including stereoselectivity [(-)-enantiomers more potent than (+)-enantiomers], blockade of the effect by ICI 118,551, absence of down-regulation of alpha-adrenergic receptors in BC3H-1 cells, and lack of a decrease in beta-adrenergic receptor-independent (forskolin-stimulated) cyclic AMP accumulation in S49 cells. The possibility of retained antagonist interfering with receptor measurement was precluded by the fact that the antagonist-induced decrease in receptor number required several hours incubation and occurred without a prominent change in receptor affinity. The ability of the beta-blockers to elicit down-regulation did not correlate with hydrophobicity of the drugs. Antagonist-induced down regulation of beta-adrenergic receptors did not occur in S49 lymphoma cells that lack the alpha-subunit of Gs, the guanine nucleotide-binding regulatory protein, thus implying a requirement for receptor-alpha s interaction in eliciting beta-receptor down-regulation.(ABSTRACT TRUNCATED AT 250 WORDS)
Response of human coronary arteries to aggregating platelets: importance of endothelium-derived relaxing factor and prostanoids.
Authors: Förstermann U , Mügge A , Bode S M , Frölich J C
Published: June 2012

Epicardial human coronary arteries (HCA) were obtained during heart transplantation. Strip preparations were mounted for isometric tension recording. Tension was induced with prostaglandin F2 alpha (0.3-3 microM). Aggregating human platelets (10(7)/ml and 10(8)/ml) caused marked relaxation if the endothelium of the HCA was intact, but produced modest additional constriction if the endothelium was removed. The endothelium-dependent relaxations to platelets were slightly enhanced in the presence of methysergide (1 microM) or after treatment of the platelets with the thromboxane synthase inhibitor dazmegrel (1 mM, 30 minutes). Relaxations to platelets were markedly inhibited or abolished in the presence of apyrase (1 unit/ml), after selective pretreatment of HCA with gossypol or methylene blue (both 30 microM, 30 minutes), or after addition of hemoglobin (20 microM) to the organ bath. Pretreatment of HCA (not the platelets) with aspirin (30 microM, 30 minutes) had no significant effect on platelet-induced relaxations. Adenosine 5'-diphosphate (0.1-100 microM) induced marked relaxations in endothelium-intact and much smaller relaxations in endothelium-denuded HCA. A low concentration (10 nM) of serotonin (5-HT) produced modest endothelium-dependent relaxations, higher concentrations (0.1-1 microM) led to increases in tension (also in the presence of endothelium). The thromboxane A2 mimetic U44069 (1-100 nM) was the most potent constrictor of HCA irrespective of the presence or absence of endothelium. After inhibition of thromboxane synthase, platelets produced large amounts of prostaglandins E2 and F2 alpha. Both prostaglandins constricted HCA, which can explain the limited effects of dazmegrel.(ABSTRACT TRUNCATED AT 250 WORDS)
Muscarinic cholinergic-receptor stimulation of specific GTP hydrolysis related to adenylate cyclase activity in canine cardiac sarcolemma.
Authors: Fleming J W , Watanabe A M
Published: June 2012

One component of muscarinic receptor inhibition of the function of cardiac ventricles is mediated by the inhibition of activated adenylate cyclase activity in sarcolemma. We have shown previously that muscarinic agonists inhibit GTP- but not Gpp(NH)p-activated adenylate cyclase activity, and various studies in other tissues indicate that nonhydrolyzable GTP analogues prevent inactivation of the enzyme. These data have suggested a role for GTP hydrolysis in the mechanism of inhibition of adenylate cyclase. The present study demonstrates that purified canine cardiac sarcolemma displays high-affinity GTPase activity that is reciprocally related to adenylate cyclase activity. The high-affinity GTPase activity was stimulated by muscarinic agonists and blocked by atropine. Furthermore, the one-half maximal effects of oxotremorine for binding to muscarinic receptors, stimulation of high-affinity GTPase activity, and inhibition of adenylate cyclase activity were similar. Muscarinic stimulation of GTPase activity and inhibition of adenylate cyclase activity required functional activity of the pertussis toxin (IAP) substrate(s). Treatment of sarcolemmal membranes with IAP attenuated the ability of oxotremorine to both stimulate high-affinity GTPase activity and inhibit adenylate cyclase activity. These studies indicate that muscarinic receptor stimulation of high-affinity GTPase activity dependent on functional IAP substrate(s) is closely linked to the mechanism of muscarinic inhibition of adenylate cyclase activity.
Cardiac response to pressure overload in the rat: the selective alteration of in vitro directed RNA translation products.
Authors: Boheler K R , Dillmann W H
Published: June 2012

As cardiac hypertrophy develops, total cardiac RNA and protein synthesis increase significantly. We have identified specific messenger RNAs that change in predominance with the induction of pressure-overload-stimulated cardiac hypertrophy. Total cardiac RNA was isolated from rats either undergoing cardiac hypertrophy secondary to subdiaphragmatic aortic constriction or subjected to sham surgery. The products translated in vitro were separated by two-dimensional gel electrophoresis and quantitated. The translation of four proteins decreased while the translation of four others increased in preparations from hypertrophied hearts compared with those from sham-treated rats. Two isoforms of creatine kinase M were translated in vitro. Only one of these isoforms decreased with cardiac hypertrophy, suggesting that the transcriptional or translational control for creatine kinase is much more complex than previously believed. Finally, since only eight of over 700 different translation products changed in relative predominance with cardiac hypertrophy, we conclude that the accumulation of existing RNA and protein products is the primary adaptive process responsible for cardiac hypertrophy.
Effects of ouabain and isoproterenol on left ventricular diastolic function during low-flow ischemia in isolated, blood-perfused rabbit hearts.
Authors: Lorell B H , Isoyama S , Grice W N , Weinberg E O , Apstein C S
Published: June 2012

Myocardial ischemia causes both systolic and diastolic dysfunction. A variety of positive inotropic agents with different subcellular mechanisms may be used clinically in an attempt to reverse ischemic contractile failure. We tested the hypothesis that two inotropic agents, isoproterenol (a beta-adrenergic agonist) and ouabain (a sodium pump inhibitor), might have different effects on left ventricular (LV) diastolic function during ischemic failure despite an equivalent inotropic effect. Isolated isovolumic (balloon-in-LV) blood perfused rabbit hearts were paced at constant physiological heart rate (4 Hz), given either no drug (controls, n = 7), isoproterenol (n = 7), or ouabain (n = 7), and then subjected to 6 minutes of low flow ischemia (75% reduction of baseline coronary flow). The doses of isoproterenol and ouabain were selected to produce equivalent modest inotropic effects (15% increase in LV + dP/dt) in each heart during baseline perfusion conditions. During the ischemic period, there was a marked decrease in contractility, and neither isoproterenol nor ouabain demonstrated a positive inotropic effect relative to the control group. However, these agents had markedly different effects on diastolic chamber distensibility (assessed by end-diastolic pressure at constant LV volume) during ischemia. In the control and isoproterenol groups, diastolic chamber distensibility did not change during the ischemic period. In contrast, ouabain treatment resulted in a marked decrease in diastolic chamber distensibility during ischemia; this change was not completely reversible during the 10-minute reperfusion period. The mechanism by which ouabain decreased diastolic chamber distensibility relative to isoproterenol was assessed indirectly. The ouabain and isoproterenol groups were subjected to equivalent degrees of ischemia as assessed by oxygen supply/demand imbalance; during ischemia, each drug group did not differ with regard to myocardial perfusion rates, determinants of myocardial oxygen demand (heart rate, LV developed pressure, LV + dP/dt), myocardial oxygen consumption, lactate production, and ATP and creatine phosphate content. We therefore inferred that the greater decrease in diastolic distensibility in the ouabain group was not due to a greater metabolic severity of ischemia. These observations are consistent with a mechanism of cytosolic calcium overload induced by ouabain, resulting in persistent active myofilament tension development throughout diastole, to cause the observed decrease in diastolic chamber distensibility during ischemia in the ouabain group.(ABSTRACT TRUNCATED AT 400 WORDS)
Pulmonary vascular responses to forebrain stimulation in the cat.
Authors: Hyman A L , Dempesy C W , Fontana C , Richardson D E , Rieck R W , Kadowitz P J
Published: June 2012

The effects of forebrain stimulation on the pulmonary vascular bed were investigated in the intact-chest cat under conditions of controlled blood flow and constant left atrial pressure. When pulmonary vascular tone was raised to a high steady level, direct electrical stimulation of the forebrain elicited a biphasic change in lobar arterial pressure. The response was characterized by an initial transient increase in lobar arterial pressure that was followed by a prolonged secondary decrease in pressure. When a delay coil was added to the extracorporeal perfusion circuit, the secondary vasodilator response was separated into initial brief and delayed prolonged components, suggesting that it was mediated in part by the release of a humoral factor. The entire response to forebrain stimulation was abolished by cervical cord section or freezing. The initial constrictor response and early brief dilator response were not blocked by classic pharmacological blocking agents. The delayed humorally mediated vasodilator response was blocked by propranolol or ICI 118551, indicating that it was mediated by a circulating factor with beta 2-stimulating properties. The delayed vasodilator response was associated with a large increase in arterial epinephrine levels, and this rise in plasma epinephrine was not altered by propranolol. The present data suggest that electrical stimulation of the forebrain causes a prolonged pulmonary vasodilator response that is mediated by way of a descending pathway, which results in a large rise in arterial epinephrine levels.
[3H]-8-cyclopentyl-1,3-dipropylxanthine binding to A1 adenosine receptors of intact rat ventricular myocytes.
Authors: Martens D , Lohse M J , Schwabe U
Published: June 2012

The purpose of the present study was the identification of A1 adenosine receptors in intact rat ventricular myocytes, which are thought to mediate the negative inotropic effects of adenosine. The adenosine receptor antagonist [3H]-8-cyclopentyl-1,3-dipropylxanthine was used as radioligand. Binding of the radioligand to intact myocytes was rapid, reversible, and saturable with a binding capacity of 40,000 binding sites per cell. The dissociation constant of the radioligand was 0.48 nM. The adenosine receptor antagonists 8-cyclopentyl-1,3-dipropylxanthine, "xanthine amine congener," and theophylline were competitive inhibitors with affinities in agreement with results obtained for A1 receptors in other tissues. Competition experiments using the adenosine receptor agonists R-N(6)-phenylisopropyladenosine, 5'-N-ethylcarboxamidoadenosine, and S-N(6)-phenylisopropyladenosine gave monophasic displacement curves with Ki values of 50 nM, 440 nM, and 4,300 nM, which agreed well with the GTP-inducible low affinity state in cardiac membranes. The low affinity for agonists was not due to agonist-induced desensitization, and correlated well with the corresponding IC50 values for the inhibition of cyclic AMP accumulation by isoprenaline. It is suggested that only a low affinity state of A1 receptors can be detected in intact rat myocytes due to the presence of high concentrations of guanine nucleotides in intact cells.
Time-dependent increase in left ventricular contractility following acute volume loading in the dog.
Authors: Lew W Y
Published: June 2012

Acute volume alterations were produced in eight anesthetized dogs to determine if the contractility of the left ventricle is partially volume-dependent. Pressures were measured in the left ventricle with a micromanometer and regional ventricular function was measured with sonomicrometers implanted in the midwall of the anterior, lateral, and posterior left ventricle. Regional end-systolic pressure-length relations (ESPLR) were determined with transient venae cavae occlusions. The ESPLR data were fitted to a quadratic equation, then end-systolic lengths were compared at matched end-systolic pressures at multiple time periods after the acute load alterations. Bilateral vagotomy, carotid sinus denervation, and stellate ganglion denervation were performed to prevent reflex alterations in contractility. The heart was paced at a constant rate. In seven animals, dextran was infused intravenously over 77 +/- 23 seconds (+/- SD) to increase left ventricular end-diastolic pressure from 5 +/- 2 to 13 +/- 3 mm Hg and peak pressures from 113 +/- 11 to 147 +/- 18 mm Hg. The end-diastolic lengths increased 14 +/- 6% in the anterior, 9 +/- 2% in the lateral, and 12 +/- 4% in the posterior segments. The ESPLR was measured immediately (77 +/- 23 seconds), early (3 +/- 1 minutes), and late (10 +/- 2 minutes) after initiation of the volume load. In all three regions, there was a significant time-dependent leftward shift in the ESPLR. From 1 to 10 minutes after the volume load, the regional end-systolic lengths decreased by a mean of 4-6% when compared at a matched end-systolic pressure of 96 +/- 10 mm Hg, and decreased by 7-9% when compared at a matched pressure of 139 +/- 20 mm Hg. The end-systolic lengths immediately after the volume load were not significantly different from the control value (compared at a matched end-systolic pressure) but were significantly shorter 10 minutes after the volume load. The leftward shift of the ESPLR represented a true increase in contractility and not merely a recovery from a transient myocardial depression. A similar leftward shift in the ESPLR occurred in four animals after release of a partial venae cavae occlusion, producing an acute volume load without acute hemodilution. Acute volume loads in four animals treated with propranolol also produced a leftward shift in the ESPLR, ruling out the possibility that a time-dependent increase in circulating catecholamines was responsible for the alterations in contractility. In five animals, the ESPLR shifted to the right after a transient (1-2 minutes) decrease in venous return.(ABSTRACT TRUNCATED AT 400 WORDS)
In vivo determination of the force of leukocyte-endothelium adhesion in the mesenteric microvasculature of the cat.
Authors: House S D , Lipowsky H H
Published: June 2012

Quantitative estimates of the force of adhesion between leukocytes and endothelium were obtained from in vivo hemodynamic measurements in small venules of cat mesentery during topical application of the chemotactic compound N-formyl-methionyl-leucyl-phenylalanine (FMLP). Simultaneous measurements of upstream to downstream pressure drop, red cell velocity, microvessel hematocrit, and vessel diameter and length permitted application of the principles of momentum conservation to calculate the forces acting upon a leukocyte during adhesion to the endothelium. For venules ranging in diameter from 23 to 49 micron, the ratio of force (acting in the vessel axial direction) to wall shear stress on the endothelium fell from 14.6 X 10(-6) in small venules to 2.3 X 10(-6) dynes per dyne/cm2 in large venules; reflecting the larger pressure drops and forces attendant to greater lumen obstruction in the smaller venules. The equilibrium force representative of a balance between fluid shear stresses on the leukocyte and those at its site of contact with the endothelium ranged from 1.1 to 76.1 X 10(-5) dynes for wall shear stress ranging from 2 to 25 dynes/cm2; with venules with greater wall shear stresses having the greater leukocyte-endothelium shear force. Within individual venules, however, the force acting on a single leukocyte varied inversely with wall shear stress, most likely due to white blood cell deformation, which leads to a lessening of shear stress on the surface of the white blood cell.