Pig Myocardium Research Articles

The making of diabetic guinea pigs by streptozotocin and high incidence of triggered activity in the ventricular muscle.

Myoplasmic Ca2+ metabolism is reported to be impaired in diabetic rat heart. We studied the possibility that the ventricular muscles of diabetic guinea pig are prone to develop delayed afterdepolarizations (DADs) and triggered activity (TA), because DADs and TA are believed to be a possible index of increased level of intracellular Ca2+ concentration. To establish an experimental diabetic model from the guinea pig, male animals were divided into four groups: 1) control group: intracardiac injection of citrate buffer; 2) IP group: intraperitoneal injection of streptozotocin (STZ, 200 mg/kg); 3) IC group: intracardiac injection of STZ; and 4) Ins-IC group: intracardiac injection of STZ after pretreatment with insulin (20 IU/kg). We found that: 1) only in the Ins-IC group was the fasting plasma glucose concentration (determined 40 days after STZ injection) significantly higher than in the control group; 2) oral glucose tolerance test performed 40 days after treatment also showed glucose intolerance in the Ins-IC group. These findings evinced the successful making of diabetic guinea pigs by an intracardiac one-shot injection of STZ during development of insulin-induced hypoglycemia. In vitro electrophysiological experiments were performed on ventricular papillary muscle from diabetic animals (Ins-IC group) by conventional glass microelectrode techniques. Transmembrane action potentials were elicited by pulse trains with various rates (2-5 Hz) and durations (10-30 stimuli) in the presence of ouabain (1 microM) and various Ca2+ concentrations (1.8-7.2 mM). The incidence of TA in the muscles from diabetic animals was significantly higher (chi 2-test, p less than 0.05) than that from controls. The findings gave evidence that Ca2+ homeostasis in the myocardium of diabetic guinea pigs is impaired, and this may be a cause of arrhythmia.

Influence of isoproterenol on myocardial energetics. Experimental and clinical investigations.

The influence of isoproterenol on myocardial performance and energetics was investigated in normal guinea pig myocardium and in patients with normal left ventricular function. The in vitro experiments were performed by simultaneous isometric force and heat measurements using sensitive antimony-bismuth thermopiles. Following the application of isoproterenol (10(-8) M) isometric peak twitch tension and tension-time integral increased significantly by 185% and 142%, respectively. Tension-independent heat which reflects high energy phosphate hydrolysis of excitation-contraction coupling increased by 183%. Tension-dependent heat reflecting the high energy phosphate hydrolysis of the crossbridges increased by 417%. The ratio of tension-dependent heat to tension-time integral increased by 131%. The recovery/initial heat ratio, reflecting the efficiency of the recovery metabolism, and the resting metabolism did not significantly change. In the patients the effect of isoproterenol on myocardial energetics was evaluated in terms of myocardial efficiency. Following isoproterenol administration, left ventricular systolic stress-time integral decreased by 49% due to reductions in end-diastolic pressure, end-diastolic volume and duration of systole. Pressure-volume work remained unchanged. Myocardial oxygen consumption per minute increased in proportion to heart rate. The ratio of myocardial oxygen consumption per beat to left ventricular systolic stress-time integral increased significantly by 95%. External myocardial efficiency was unaltered. Thus, isoproterenol increases the energy turnover of excitation-contraction coupling and increases the energy consumption of the crossbridges disproportionately to developed tension-time integral in the guinea pig heart.

Influence of propranolol on high energy phosphate and tissue acidosis in regional ischemic myocardium of pigs: assessment with arterial pressure and respiration gated in vivo 31-phosphorus magnetic resonance spectroscopy

In an attempt to define the metabolic abnormalities of the ischemic myocardium, the changes in high energy phosphates, inorganic phosphate and intracellular pH were serially and quantitatively evaluated in ischemic porcine hearts having no collateral circulation, using arterial pressure and respiration gated in vivo 31P magnetic resonance spectroscopy. The protocol was also modified for propranolol pretreatment (0.6 mg/kg intravenously) to define its effect on the metabolism of ischemic myocardium. In the non-treated group, creatine phosphate was rapidly depleted by 10 minutes after ischemia; by 40 minutes, ATP and intracellular pH gradually decreased to 10 ± 11% of control and to 5.90 ± 0.26, respectively, and inorganic phosphate rose to 303 ± 43% of control. In the propranolol treated group, the concentrations of creatine phosphate and ATP were higher, and those of inorganic phosphate and tissue pH were similar compared with controls during 40 minutes of ischemia. This suggests that the beneficial effect of propranolol on the ischemic myocardium is due to the preservation of ATP, an essential energy resource for numerous enzymatic reactions in viable myocardium.

Platelet-activating factor: lack of direct action on guinea pig myocardium and possible transmitter release from cardiac sympathetic nerve endings at high concentrations

Microelectrode and mechanical studies were performed with isolated guinea pig myocardium (right ventricular free walls and papillary muscles) to examine the effects of platelet-activating factor (PAF) and lysophosphatidylcholine (LPC). Low concentrations of PAF (10(-8) to 10(-6) M, a range equivalent to the blood concentrations that produce marked hypotension in vivo) had no effects on action potential configuration and contractile force. High concentrations (10(-5) to 10(-4)M) of PAF and LPC per se elicited slow response action potentials with concomitant contraction (restored contraction) in the myocardium depolarized with elevated K+ (25 mM); they also augmented slow responses and restored contractions produced by a low concentration of isoproterenol (10(-8) M). Although these results suggested there was an increase in slow Ca current, the slow responses and restored contractions thus produced were greatly suppressed or abolished by the addition of a beta-adrenoceptor blocking agent, sotalol (10(-5) M), and by pretreatment with reserpine (5 mg/kg i.p., 24 h prior). In accordance with our previous conclusions, the present results suggest that direct cardiac action is not involved in the mechanisms of hypotension produced by PAF. It was also shown that high concentrations of PAF and LPC may act nonspecifically as amphiphilic compounds to induce transmitter release from sympathetic nerve endings, which may in turn augment the Ca current channels in the myocardial cell membrane.

Inhibition of Na-K pump current in guinea pig ventricular myocytes by dihydroouabain occurs at high- and low-affinity sites.

Binding of cardiac glycosides to the Na+,K+-dependent ATPase has been shown to occur at both high- and low-affinity sites. However, recent reports suggest that glycoside-induced inhibition of electrogenic Na-K pump current occurs with simple first-order binding kinetics at relatively low-affinity sites. This implies that high-affinity binding sites have little to do with Na-K pump inhibition during exposure to cardiac glycosides. To better understand the role of the high-affinity site, we investigated the concentration dependence of Ipump inhibition by dihydroouabain (DHO) in guinea pig ventricular myocytes through use of wide-pore patch pipettes to "fix" internal Na+ activity at approximately 30 mM and to voltage clamp at -40 mV (T = 34 degrees C). DHO was found to have no effect on membrane conductance at a holding potential of -40 mV. Holding current was monitored and the difference between steady-state holding current before and during external exposure to nine concentrations (range, 0.01-1,000 microM) of DHO was measured and normalized to cellular membrane capacitance. The concentration dependence of the inhibition of Na-K pump current was biphasic and well fitted to a two-binding site model with inhibitory KD values of 0.05 microM and 64.5 microM. This is consistent with previously reported 3H-ouabain binding studies in guinea pig myocardium. These findings indicate that the electrogenic properties of the Na-K pump can be inhibited by glycoside binding to both high- and low-affinity sites.

Распределение лейцил-тРНК синтетазной активности в безрибосомных экстрактах печени кролика и миокарда свиньи

Распределение лейцил-тРНК синтетазной активности в безрибосомных экстрактах печени кролика и миокарда свиньи

Rest- and stimulation-dependent changes in exchangeable calcium content in rabbit ventricular myocardium.

Ca2+ shifts in the isolated, perfused ventricular muscle of rabbit hearts were investigated with the aid of 45Ca under the conditions of complete equilibration of preparations with 45Ca containing solution. The "cellular" 45Ca content was calculated by subtraction of 45Ca2+ dissolved in the free water of extracellular space from the total tissue 45Ca2+ content. The "cellular" content of 45Ca in stimulated (60 per min) preparation was 0.887 +/- 0.067 mmol/kg wet weight (w.w.). Six minutes of rest resulted in the drop of this content to 0.503 +/- 0.054 mmol/kg w.w. despite continued perfusion with 45Ca containing solution. Contractile force (CF) decreased at that time to 23% of control. The first post-rest contraction (RSC) resulted in a gain of 0.073 mmol45Ca/kg w.w. Both the content of 45Ca and CF returned to the pre-rest values when stimulation was resumed. The difference between the 45Ca content of post-rest stimulated and rested preparations (0.384 mmol/kg w.w.) is equivalent to Ca2 fraction (Ca2), previously described in guinea pig ventricular myocardium (17, 12). However, the volume of rabbit Ca2 is only about 42% of that in guinea pig. Caffeine in concentration 12.5 mM, which did not displace Ca2 from guinea pig ventricular muscle, decreased Ca2 in the rabbit ventricle by 44%. CCCP, a protonofore destroying the mitochondrial protone gradient essential for Ca2+ uptake and maintainability, displaced Ca2 completely from rabbit ventricles. These results, although far from conclusive, do suggest that both the mitochondria and sarcoplasmic reticulum might be the site of the rate-dependent Ca2 fraction. The physiological meaning of differences in Ca2 content between rabbit, guinea pig, and rat ventricular myocardium is discussed.

Difference in the mechanical response to a cardioplegic solution observed between the neonatal and the adult guinea pig myocardium

We attempted in two types of preparations to delinate the difference in responses to St. Thomas' Hospital cardioplegic solution between the neonatal and the adult guinea pig myocardium. Isolated guinea pig hearts were perfused with Langendorff's method and the tension of the papillary muscle of the right ventricle was recorded. Continuous infusion of St. Thomas' Hospital cardioplegic solution (37 degrees C) for 30 minutes resulted in a significantly higher elevation of the resting tension (development of contracture) in the neonatal myocardium than in the adult. The recovery of normal contractile tension after the resumption of perfusion with normal Krebs-Ringer bicarbonate solution was smaller in the neonate with increases in the myocardial water and calcium contents. The membrane potential of the papillary muscle preparation was recorded by means of conventional glass microelectrodes. There was no significant difference in the control values of the resting membrane potential and in the degree of depolarization during exposure to St. Thomas' Hospital cardioplegic solution between the neonate and the adult. Thus the greater elevation of the resting tension produced in the neonatal myocardium by St. Thomas' Hospital cardioplegic solution was not due to a greater depolarization of the surface membrane.

Biochemical aspects of inhibition of cardiovascular low (K m) cyclic adenosine monophosphate phosphodiesterase

Multiple isozymes of cyclic nucleotide phosphodiesterase (PDE) exist in mammalian cells. At least 5 major types of PDE isozymes have been identified; they differ by substrate affinity, maximal activity, intracellular regulation or mechanism of pharmacologic inhibition. A low Michaelis constant (K m) cyclic adenosine monophosphate (cAMP) PDE, whose activity is inhibited by submicromolar concentrations of cyclic guanosine monophosphate and stimulated by cAMP-mediated phosphorylation, is present in both cardiac muscle and vascular smooth muscle. This PDE isozyme (referred to as peak III c PDE) is sensitive to selective inhibition by amrinone, milrinone, imazodan, CI-930, piroximone, and numerous other PDE inhibitors. The subcellular distribution of cardiac PDE III c varies according to species; it is found in the soluble fraction of guinea pig myocardium, in the particulate fraction of canine myocardium, and in both fractions of primate (simian and human) myocardium. Another PDE isozyme, which is sensitive to inhibition by rolipram and is less sensitive to inhibition by PDE III c inhibitors, is found in cardiac muscle of some species (i.e., soluble fractions of rat and canine myocardium) and is apparently not related to direct regulation of positive inotropy. Both positive inotropy and vasorelaxation by milrinone and other PDE III c inhibitors can be linked to inhibition of PDE III c and activation of the cAMP system. These significant relations are similar to those obtained for other cAMP-related positive inotrope/vasodilators (such as β-adrenoreceptor agonists). Moreover, an increased rate of ventricular relaxation (lusitropy), which is apparent with PDE III c inhibitors, may also be attributable to activation of the cAMP system. The potency of milrinone and other PDE III c inhibitors as positive motropes and vasodilators parallels their potency as cardiac and vascular PDE III c inhibitors. Moreover, the potency of milrinone as a competitive PDE III c inhibitor in various species (K i = 0.3 to 0.4 μM) is similar to therapeutic plasma concentrations (100 to 400 ng/ml, equivalent to 0.5 to 2.0 μM). These data support the concept that a single mechanism of action, selective inhibition of cardiovascular low K m cAMP peak III PDE, may be responsible for the major cardiovascular beneficial actions (positive inotropy/lusitropy, afterload reduction and coronary vasodilation) of milrinone and other PDE III c inhibitors for the treatment of congestive heart failure.

Insulin responsiveness of neonatal pig myocardium.

The transition from preferential use of carbohydrates to fatty acids for energy production by neonatal mammalian myocardium might be hormonally influenced. In neonatal pigs (between 1 and 4 days of age), plasma glucose, lactate, and glucagon concentrations remained constant at adult levels, while plasma triglycerides and insulin content remained stable at substantially lower levels. Insulin, whether administered in vivo or during perfusion, increased myocardial glucose utilization [GU] and lactate production [LP]. Stimulation of GU and LP by insulin exposure in vivo persisted for at least 1 h during perfusions after insulin was removed. Exogenous lactate (0.5 mM) diminished insulin-stimulated GU and LP; and was used as a substrate at 1.25 mM. Thus, insulin augmented glycolytic activity of neonatal piglet myocardium; however, exogenous lactate, within the physiological range, altered the nature of the myocardium's response by, as yet, undetermined mechanisms. Therefore, the transition from carbohydrate to fatty acid utilization for energy production by the neonatal myocardium does not appear to result from decreased carbohydrate metabolism or reduced myocardial responsiveness to insulin.

O-064 - The existence of ATP pyrophosphohydrolasc in the guinea pig myocardium and its elation to adenosine formation.

O-064 - The existence of ATP pyrophosphohydrolasc in the guinea pig myocardium and its elation to adenosine formation.

Membrane systems of guinea pig myocardium: Ultrastructure and morphometric studies

The structure and quantitative contribution of membrane systems (transverse-axial tubular system [TATS] and sarcoplasmic reticulum [SR]) have been investigated in the heart of the adult guinea pig. Although previous quantitative studies have been made of guinea pig myocardium, this is the first such study that has utilized tissue in which membrane system elements were clearly identified by selective staining (in this case by the osmium-ferrocyanide [OsFeCN] postfixation method). Both membrane systems are highly developed in ventricular cells, but a TATS is essentially absent from atrial myocytes. The ventricular TATS consists principally of large-bore elements which may be oriented transversely, axially, or obliquely, making numerous anastomoses with one another to form a highly interconnected system of extracellular spaces that penetrate to all myoplasmic depths of the ventricular cell. The cell coat that lines the lumina of these tubules is structured, containing fibrillar structures that run along the length of the tubule. The volume fraction (VV) of the ventricular TATS is low (2.5-3.2%), in consideration of the qualitative prominence of the TATS in these cells. The relative total population of sarcoplasmic reticulum is higher in the atria (VV of 10-11%) than in the ventricles (VV of ca. 8%). In all guinea pig myocytes, several major structural divisions of SR can be discerned, which include network SR, junctional SR, corbular SR, and cisternal SR. Junctional SR (J-SR) in the atrial cells is limited almost exclusively to peripheral saccules of junctional SR (PJSR), whereas both interior J-SR and PJSR are present in the ventricle. Two distinct morphological types of PJSR appear in atrial cells, including both flattened and distended saccules, the latter resembling PJSR of lower vertebrate heart. Spheroidal bodies of SR with opaque contents (corbular SR) are prominent at or near Z-line levels of the sarcomeres of atrial and ventricular cells. Cisternal SR is likely a subset of network SR, but some examples appear related to rough endoplasmic reticulum. An overall impression obtained from this study is that guinea pig atria are composed of structurally primitive cells, whereas the ventricular cardiac muscle cells are more highly developed entities.

Alcohol induced upregulation of Na, K-pump concentration in guinea pig myocardium

Alcohol induced upregulation of Na, K-pump concentration in guinea pig myocardium

Effect of diltiazem and tetrodotoxin on development of anoxic contracture of the guinea pig myocardium

In the isolated electrically stimulated right ventricular papillary muscles the onset of hypoxic contracture occurred 7 +/- 1.2 min and reached maximum 29.2 +/- 4.6 min after the onset of hypoxia. Switching off of the stimulation and diltiazem (10(-6) M) or tetrodotoxin (3 X 10(-6) M) administration delayed the development of the hypoxic contracture and decreased its maximum level. The protective action of diltiazem was noted only in the presence of rhythmical stimulation. It was concluded that, in addition to the influx of Ca ions through calcium channels, the influx of Na ions through sodium channels was important in the development of hypoxic contracture.

Studies directed toward ascertaining the active conformation of 1,4-dihydropyridine calcium entry blockers.

A series of unsymmetrically substituted 4-phenyl-1,4-dihydropyridine calcium entry blockers were investigated for their ability to relax potassium-contracted rabbit aortic smooth muscle and to competitively displace [3H]nitrendipine from its specific binding sites on guinea pig myocardial membranes in order to delineate the pharmacologically active conformer with respect to the position of the aromatic substituent (synperiplanar or antiperiplanar). The data show that the 1,4-dihydropyridine receptor distinguishes between 2',3'-disubstituted phenyldihydropyridines and 2',5'-disubstituted analogues as measured by changes of vasodilation and receptor affinity in vitro. The IC50 values for vasorelaxation by the analogues presented here correlate best with the Kd values for binding to the predominant receptor of two coexisting dihydropyridine binding sites in the guinea pig myocardium. We report the first observation of an antiperiplanar orientation of an o-phenyl substituent in the X-ray structure of 2-chlorophenyl analogue 3. Using nuclear Overhauser enhancement, we have developed a method that also demonstrates that an ortho (chloro or nitro) substituent on the phenyl ring does not preclude the presence of either synperiplanar or antiperiplanar phenyl rotamer in solution. These experimental findings contrast with the accepted belief that o-phenyl substituents essentially force these 1,4-dihydropyridines into the synperiplanar conformation exclusively.

Ｂｕｎａｚｏｓｉｎのモルモット心室筋Ｎａ ｃｈａｎｎｅｌに対す抑制作用

Ｂｕｎａｚｏｓｉｎのモルモット心室筋Ｎａ ｃｈａｎｎｅｌに対す抑制作用

Volume density and distribution of mitochondria in myocardial growth and hypertrophy

The volume density and distribution of mitochondria relative to capillaries have been measured using the technique of point counting in concentric rings, on normal and hypertrophied guinea pig myocardium. Right ventricular hypertrophy was produced by hypobaric hypoxia. In control guinea pigs right ventricular weight increased linearly with body weight. In control and hypoxic guinea pigs fiber cross sectional area (FCSA) and ventricular weight were related by a single straight line. Capillary density decreased hyperbolically with FCSA in both control and hypoxic animals. Capillary density was significantly higher ( P < 0.001) in the right ventricles of the hypoxic animals than in controls when the fibers were small but this difference disappeared as the fibers hypertrophied beyond FCSA values of 260 μm 2. Volume density of mitochondria reached a peak (29–35%) close to the capillary but then decreased significantly in the spaces farthest from the capillary (mean 25.2%). There was no significant difference in peak mitochondrial volume density in controls versus hypoxic animals. There was thus an increase in the total volume of mitochondria in these myofibers that was in direct proportion to the increases in FCSA and heart volume. The highest volume density of mitochondria was found at a distance that is approximately 15% of the total distance over which O 2 must diffuse in myocardial tissue and the peak volume density of mitochondria was thus a function of capillary density. The speculation is presented that the distribution of mitochondria may be related both to oxygen supply to the mitochondria and to the movement of high energy phosphate compounds out of mitochondria for use by myofibrils.

Congener derivatives and conjugates of histamine: synthesis and tissue and receptor selectivity of the derivatives.

A series of 19 congener derivatives and conjugates of histamine was synthesized and tested to determine whether the ligands would alter the conventional histamine activity in various tissues. The derivatives, which contained either branched or unbranched aliphatic groups, aromatic amide groups, or dipeptides, exhibited affinities for histamine type 1 and/or type 2 receptors that were widely different from the progenitor. The p-trifluoromethyl derivative of histamine with an intermediate chain length of four methylenes (compound 13) was the most potent lymphocytes H2 receptor agonist but was inactive on guinea pig myocardium H2 receptors. The deletion of a single methylene chain (compound 12) from this compound resulted in total loss of its H2 activity on lymphocytes and its H1 activity on aorta. Compound 12 became an exclusive H1 agonist on lymphocytes H1 receptors. The dipeptide conjugate (compound 17) and the aliphatic congener derivative (compound 18), both with four methylenes, retained some of the activity on guinea pig myocardium H2 receptors, but lost their activity on lymphocytes H2 receptors. Therefore, histamine can be modified at sites that are at a distance from the imidazole moiety, resulting in tissue selective histamine receptor agonists.

Ischemia- and agonist-induced changes in alpha- and beta-adrenergic receptor traffic in guinea pig hearts.

We have used radioligand binding techniques and subcellular fractionation to assess whether changes in expression of myocardial alpha 1- and beta-adrenergic receptors are mediated by a redistribution of receptors between various membrane fractions. Three fractions were prepared from the left ventricles of guinea pigs that underwent either 1 h of ischemia or injection of epinephrine (0.25 mg/kg ip): a crude membrane, a purified sarcolemma, and a light vesicle fraction. In control animals alpha 1-adrenergic receptors ([3H]prazosin binding) in light vesicles was only 25% of the total alpha 1-receptor density found in sarcolemmal and light vesicle fractions as compared with 50% for beta-adrenergic receptors ([125I]iodocyanopindolol binding sites). Although ischemia was associated with a 53% decrease in the number of light vesicle beta-adrenergic receptors and a 42% increase in the number of sarcolemma beta-receptors (P less than 0.05), there was no change in the number of light vesicle alpha 1-receptors, even though the number of sarcolemmal alpha 1-receptors increased 34%. Epinephrine treatment promoted internalization of beta-adrenergic receptors; sarcolemma beta-receptors decreased 37% and light vesicle beta-receptors increased 28% (P less than 0.025). For alpha 1-receptors, epinephrine treatment decreased the number of sarcolemmal receptors 41% (P less than 0.025) but failed to increase the number of receptors in the light vesicle fraction. The changes in receptor binding to beta-adrenergic receptors in sarcolemmal fractions were mirrored by parallel changes in isoproterenol-stimulated adenylate cyclase activity. These results indicate that alpha 1- and beta-adrenergic receptors may undergo a different cellular itinerary in guinea pig myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias and infarction in the ischemic pig heart are not mediated by xanthine oxidase-derived free oxygen radicals.

Xanthine oxidase activities of pig myocardium and blood during and following myocardial ischemia were measured using HPLC, and electrochemical detection of hypoxanthine, xanthine and uric acid. Myocardial ischemia was produced by occluding the anterior descending coronary artery two-thirds of the way from its origin. There was no accumulation of either xanthine or urate in the ischemic pig myocardium during occlusion periods of 90 min, but there was a substantial accumulation of hypoxanthine. Similarly, there was no increase in myocardial xanthine or urate during the 30 min reperfusion following coronary artery occlusion periods of 15, 30, 60 or 90 min. Following in vitro incubation at pH 8 of myocardial homogenates or blood with either hypoxanthine or xanthine and NAD, no urate production was detectable. In contrast, significant amounts of xanthine and/or urate were produced, following addition of xanthine oxidase to the reaction mixtures. Additional in vitro experiments showed that the following pig tissues were lacking xanthine oxidase activity: left and right atrial appendage, left and right ventricle, interventricular septum, anterior descending and circumflex coronary arteries, ascending aorta, lung, and blood. Large amounts of xanthine oxidase (9.3 +/- 1.8 SEM mU/g wet weight, n = 7) were found in pig liver. In the ischemic pig heart, transmural infarction developed within 60 min of ischemia. Ventricular arrhythmias and fibrillation occurred most frequently within 45 min of ischemia and within seconds after reperfusion. These results showed that the pig heart and blood were xanthine oxidase deficient, suggesting that xanthine oxidase-derived free oxygen radicals were not involved in the cytotoxic and arrhythmogenic effects brought about by myocardial ischemia and/or reperfusion in the pig.