摘要:

The effects of increased dietary cholesterol content on coronary vascular hemodynamics and endothelial cell transport function were assessed in isolated rabbit hearts during 3.5 hours of reperfusion after 30 minutes of global, no-flow ischemia. In control hearts from rabbits fed normal chow, perfusion pressure, left ventricular end-diastolic pressure, maximum + dP/dt, and the rate of intravascular clearance of radiolabelled albumin remained constant during 5 hours of continuous perfusion, while the mean transit time of radiolabelled albumin increased 1.6 ± baseline. In ischemic hearts from rabbits fed normal chow, perfusion pressure increased 59% during reperfusion while left ventricular end-diastolic pressure and maximum +dP/dt returned toward control levels. The rate of intravascular clearance of radiolabelled albumin decreased 36%, and the mean transit time of albumin increased ∼3 ± baseline. Ischemia-reperfusion injury to the cardiac vasculature and musculature was markedly increased in hearts of rabbits fed chow supplemented with 2% cholesterol for 2–3 weeks compared to rabbits fed the same diet for a longer duration (5–16 weeks) or rabbits fed normal chow. Prior to ischemia, permeation of the coronary vasculature by albumin was increased twofold in rabbits fed cholesterol for 2–3 weeks while myocyte contractile function was normal relative to chow-fed controls or the group fed cholesterol for 5–16 weeks. These effects of acute cholesterol feeding precede occlusive atherosclerotic coronary artery disease and occur at plasma cholesterol concentrations one third of those in rabbits fed cholesterol for the longer duration. These findings suggest that the altered metabolic milieu associated with an abrupt increase in cholesterol consumption and/or a rapidly increasing plasma cholesterol concentration impairs the functional integrity of the coronary vasculature and leads to increased susceptibility of the heart to ischemia-reperfusion injury.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

During an investigation of the effect of ryanodine on contractions in cardiac muscle, it was found that long rest periods removed all or most of the drug's effect. Therefore, we studied the kinetics of block development and recovery from block produced by low concentrations of ryanodine (1-100 pM) on the postrest contractions of ferret papillary muscle. At 100 pM, ryanodine depressed steady-state contraction amplitude slightly (4.2 ± 1.1% mean ± SEM,n= 10) but strongly inhibited (40–80%) the first contraction (postrest contraction) elicited on restimulation of the preparation after rest periods of 1 second to 5 minutes. Under control conditions, the nearly maximal potentiation of the twitch occurring after a standard test rest period (30 seconds of rest) was not affected by a preceding conditioning rest of up to 20 minutes. In the presence of 100 pM ryanodine, a conditioning rest increased the amplitude of the twitch elicited after a test rest, and the test rest contraction recovered toward control (drug-free) amplitude monoexponentially (time constant, 582 ± 105 seconds). Block of postrest contraction could be reinduced by stimulation and occurred faster when higher rates were used (time constants, 758 seconds at 1 Hz and 107 ± 26 seconds at 3 Hz). Since rest potentiation of twitch tension is believed to be mostly dependent on extra calcium released from the sarcoplasmic reticulum, the results suggest that the ryanodine-induced blockade of calcium release from the sarcoplasmic reticulum is use-dependent and recovers during diastole. Such use-dependence might be mediated by modulation of the drug-receptor interaction by intracellular calcium, transsarcolemmal or transsar-coplasmic reticulum membrane potential, or the state of a sarcoplasmic reticulum membrane calcium channel.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The distribution of adrenergic receptors in specific components of the heart such as vessels and myocytes cannot be determined easily with assays of membranes prepared from homogenates of whole tissue. Accordingly, we characterized the binding of the potent nonsubtype selective antagonist [125iodo]cyanopindolol to β-receptors in unfixed transmural slices of feline and canine left ventricle. Specific binding ratios >90% were achieved at radioligand concentrations near Kd and >80% at saturating ligand concentrations. Binding of radioligand to receptors in transmural slices was rapid, saturable, stereoselective, and displaceable by antagonists and agonists with the rank order of potency expected of β-adrenergic receptors. Analysis of binding isotherms indicated maximum binding capacities of 27.8 ± 6.6 and 40.6 ± 5.1 fmol/mg tissue protein and dissociation constants of 10.1 ± 1.8 and 21.3 ± 1.6 pM in feline and canine ventricular slices, respectively. The distribution of β-receptors in myocytes and selected vascular components of the heart was determined with quantitative film autoradiography and high resolution computer-based analysis and display of the density of binding sites, maximum binding capacity, and binding affinity measurements. The results of autoradiographic analysis revealed a uniform transmural distribution of receptors in regions composed primarily of ventricular myocytes but an inverse relation between the density of β-receptors and the diameter of coronary vessels. Large epicardial conductance arteries had half the receptor density of subjacent myocytes; small mural arteries had approximately 60% of the β-receptor density of nearby myocytes, and the coronary resistance arterioles had the highest receptor density of any vascular compartment, which was equivalent to that of myocytes. The methods developed should be of particular value in characterizing the distribution and function of receptor subtypes and mechanisms of regulation of adrenergic responsiveness in intact myocardium.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The normal cardiac activation sequence requires propagation of the action potential from the subendocardial Purkinje network into the underlying Ventricular muscle cells. This process occurs at specific Junctional sites distributed over the endocardial surface of both ventricles. At these Junctional sites, action potentials can be recorded from cells that appear to be interposed between the Purkinje cells and the ventricular muscle cells. The action potential upstrokes recorded from these “transitional” cells have characteristic double phases produced by electrotonic interactions with the Purkinje cells and the ventricular muscle cells. We have shown that these Junctional regions in the canine subendocardium appear to be fixed anatomic sites with locations independent of the activation sequence of the Purkinje network. In addition, the activation delay between the Purkinje cells and the ventricular muscle cells at a Junctional site and the patterns of the action potential upstrokes of transitional cells at a Junctional site are independent of the activation sequence of the Purkinje network. We have also demonstrated that at some locations there are multiple Purkinje activation signals recorded with a surface electrode and that these multiple activation signals represent discrete groups of Purkinje cells, some of which contribute to the Junctional process while others appear to be substantially uncoupled from neighboring Purkinje cell groups and the underlying transitional cells.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Using45Ca, indol, and quin2, calcium uptake was measured in isolated quiescent adult rat heart cells under different metabolic conditions. Exposure of cells in a medium containing 1 mM CaCl2 to rotenone and uncoupler resulted in adenosine triphosphatc (ATP) depletion from 17.08 ± 2.26 to 0.63 ± 0.11 nmol/mg within 8 minutes, and the cells went into contracture. In this time, the cells lost 1.65 ± 0.1 nmol Ca/mg of total rapidly exchangeable cellular calcium, and the level of free cytosolic calcium as measured by indol rose from 47.4 ± 16.3 nM to 79.8 ± 27.6 nM. The subsequent rate of rise of intracellular free calcium concentration was just 4 nM/min for at least 40 minutes. Therefore, we investigated the effect of ATP depletion on the rate of calcium entry. In cells loaded with sodium by ouabain treatment without calcium, the initial rate of calcium influx on calcium addition was inhibited by 82–84% when cellular ATP was depleted, as measured by 45Ca or indol. Quin2 also showed a strong inhibition of calcium influx by ATP depletion, but itself also caused a strong inhibition of calcium influx. The rate of calcium influx declined even further in ATP-depleted cells after the initial influx: Between 1 and 12 minutes after calcium addition, the residual 45Ca uptake rate of the first minute was inhibited by an additional 90%. We conclude that ATP depletion per se does not quickly elevate cytoplasmic free calcium and that such an elevation is prevented by a very strong inhibition of the rate of calcium entry.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Proteases from human neutrophils can generate angiotensin II directly from angiotensin I or angiotensinogen. We examined whether neutrophil protease also influences angiotensin formation by activating human prorenin (also called inactive renin). When incubated with partially purified plasma and amniotic prorenin, sonicates from 106 neutrophils resulted in 120 ± 30% and 1,240 ± 290% increase in renin activity, respectively. The pH optimum of neutrophil prorenin-activating enzyme(s) is 6.5-7.0, and the activity of the enzyme(s) is inhibited by a mixture of serine protease inhibitors but not by inhibitors of other proteases, suggesting that prorenin-activating enzyme(s) is a neutral serine protease(s). Stimulation of neutrophils by f-met-leu-phe in the presence of cytochalasin B resulted in release of prorenin-activating enzyme(s) in a dose-dependent fashion. We attempted to isolate prorenin-activating enzyme(s) from neutrophil granules using aprotinin-affinity and carboxymethyl cellulose chromatographies. Prorenin-activating enzyme(s) coeluted with cathepsin G and elastase activities. Prorenin activation was greatly inhibited by anticathepsin G antiserum. Purified cathepsin G activated prorenin in a dose-dependent fashion. Elastase probably also contributes to prorenin activation since purified elastase also activated human prorenin. We speculate that this neutrophilic angiotensin-generating system may play a role in the local generation and concentration of angiotensins by influencing multiple steps of the renin-angiotensin system.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

A calmodulin-stimulated protein phosphatase has been purified from bovine myocardium. The purification procedure involves sequential DEAE-Sephacel ion exchange chromatography, calmodulin-Sepharose affinity chromatography, and high performance liquid chromatography using a Spherogel TSK DEAE 5PW column. By SDS polyacrylamide gel electrophoresis, the purified cardiac phosphatase consists of two subunits of Mr 61,000 and 19,000, similar to the brain enzyme, calcineurin. Protein phosphatase activity of the cardiac enzyme is stimulated by Ca2+ -calmodul in and inhibited by the calmodulin antagonist drug, calmidazolium. Effects of a series of divalent cations on catalytic activity of the cardiac calmodulin-stimulated protein phosphatase are similar to those observed with calcineurin, when the two enzymes are assayed under identical conditions. Highly enriched preparations of bovine cardiac sarcolemma contain substrates of cAMP-dependent protein kinase of Mr 166 K, 133 K, 108 K, 79 K, 39 K, and 14 K, which are specifically dephosphorylated by the calmodulin-stimulated phosphatase with pseudofirst-order rate constants of 0.23, 0.46, 0.69, 0.35, 0.69, and 0.115 min-1, respectively. These substrates are not present in purified preparations of cardiac sarcoplasmic reticulum. These results support a role of the calmodulin-stimulated phosphatase in the Ca2+-regulation of specific sarcolemmal processes by protein dephosphorylation.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The antithrombogenic endothelial cell defense (ATECD) describes the properties that enable the endothelium to prevent circulating blood platelets from adhering to, or aggregating on, the vascular wall. ATECD was investigated in an experimental model in which bovine passage 0 cultured endothelial cells (EC) were incubated with aggregating platelets and autologous plasma in a computer-operated aggregometer-like device. A maximal platelet aggregation required 150 ± 10-6 M adenosine diphosphate (ADP) to be present in ECs. A 5-minute coincubation for ECs and platelets was found to be adequate in evaluating the maximal ATECD value. By increasing the EC number in the aggregation suspension, platelet aggregation was progressively inhibited through a sigmoid curve (50% inhibition of aggregation required 2 ± 104 EC). Pharmacologic modulations of ATECD by isosorbide dinitrate (ISDN) + 2-isosorbide mononitrate (2-ISMN) + 5-isosorbide mononitrate (5-ISMN) were investigated under experimental conditions reflecting either an acute nitrate effect (platelet + control ECs + drug + ADP) or a chronic effect (platelet + 5-day nitrate-treated ECs + ADP). Under acute circumstances, ISDN antiplatelet activities were profoundly magnified by ECs. Aggregation was fully arrested with 5 ± 10-5 M ISDN and an EC number of 2 ± 104, whereas the same ISDN concentration alone induced 30% inhibition of control aggregation. In contrast, there were no significant changes in platelet aggregation whether incubation was done in the presence or absence of 2-ISMN or 5-ISMN, ISDN metabolites. Long-term exposure of ECs to isosorbide nitrates (ISN) resulted in increased acquired EC changes in ATECD. 5-ISMN was a poor antiplatelet agent but was capable of counteracting ISDN effects on ATECD. Under chronic circumstances, the overall ISN effect was a stimulation of ATECD, but the final effect was lower than that expected from the summation of individual ISN effects. Such an endothelium-dependent ISDN (and perhaps 2-ISMN) antiplatelet activity is likely to explain why ISDN inhibits platelet activity in vivo, while in vitro, ISDN fails to elicit such platelet aggregation inhibition unless suprapharmacologic ISDN concentrations are used. It is suggested that pharmacologic modulation of ATECD may be a new antithrombotic therapy.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The effects of amiodarone on heart weight, production of 14C-CO2 from labelled glucose, myosin ATPase activity, and myosin isoenzyme patterns were determined by comparing control and amiodar-one-treated male Wistar rats. Since it has been suggested that amiodarone may interfere with thyroid hormone action on the heart, similar experiments were also carried out in hypothyroid and amiodar-one-plus-triiodothyronine(T3)-treated rats, and the data were compared to those obtained in amio-darone-treated rats. Amiodarone treatment for 6 weeks resulted in lower heart weight, decreased atrial production of 14C-CO2 from labelled glucose, decreased myosin Ca-ATPase activity, and preferential synthesis of V3 isomyosin. These effects were similar to those observed in hypothyroid rats but were lesser in magnitude. T3 treatment of amiodarone-treated rats reversed all the changes induced by amiodarone. Serum thyroxine (T4) was higher in amiodarone-treated than in control rats, while serum T3 was similar. Serum T3 was higher in the amiodarone-plus-T3 than in the amiodarone-treated group. These results show that 1) amiodarone-induced changes resemble hypothyroid ism with respect to cardiac myosin expression and atrial CO2 production, 2) amiodarone causes hypothyroid-like changes despite normal serum T3 and increased serum T4, and 3) T3 reverses the effects of amiodarone. These data support the hypothesis that amiodarone inhibits the action of thyroid hormone on the heart.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

It has been demonstrated by other investigators that endothelium-dependent vasodilators are more effective on arterial tissue than on venous tissue. The purpose of this study was to determine if this was due to a difference in the sensitivity of arterial and venous smooth muscle to the endothelial dilator (EDRF) or to a difference in the ability of arterial and venous endothelia to release EDRF. To differentiate between these two possibilities, an in vitro “sandwich” preparation was used in which the mechanical response to endothelium-dependent dilators of a de-endothelialized vessel was determined when “sandwiched” with an endothelialized vessel. Using dog femoral artery and saphenous vein, it was determined that acetylcholine (ACh), the ionophore A23187, and thrombin were endothelium-dependent dilators of the femoral artery, but their dilatory ability was significantly less in the saphenous vein. However, if the de-endothelialized saphenous vein was “sandwiched” with an endothelialized femoral artery, both ACh and A23187 significantly relaxed the vein. No relaxation of the de-endothelialized femoral artery occurred when it was “sandwiched” with an intact saphenous vein. Sodium nitroprusside, thought to act by a mechanism similar to EDRF, relaxed equally the saphenous vein and femoral artery. These observations suggest that the difference in responsiveness between femoral arteries and saphenous veins to endothelium-dependent dilators is due more to differences in the ability of their endothelia to release EDRF than to an inability of their smooth muscle to respond to EDRF.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID