摘要:

Thiadiazinones are cardiotonic agents that have potent, direct, and stereoselective actions on the myofilament response to Ca2+in intact myocardium. Their mechanism of action is unknown. We studied the effects of racemic thiadiazinone, EMD 53998 (5-[1-(3,4-dimethoxybenzoyl)-1,2,3,4-tetrahydro-6-quinolyl]-6-methyl-3,6-dihydro-2H-1,3,4-thiadiazin-2-one), and its enantiomers on Ca2+signaling in myocytes, myofilaments, and myofilament proteins. Intact canine ventricular myocytes responded to the positive enantiomer, EMD 57033, with an increase in the extent of shortening during twitch contractions without increasing the peak amplitude of the Ca2+transient. The negative enantiomer, EMD 57439, also increased the extent of shortening, but in this case there was a concentration-dependent increase in the peak amplitude of the Ca2+transient. This is predicted from in vitro data showing that this enantiomer is a relatively potent inhibitor of phosphodiesterase activity. There was no effect of EMD 57439 on the relation between pCa and actomyosin Mg-ATPase activity of canine heart myofibrils. In contrast, EMD 57033 shifted the pCa-Mg-ATPase activity relation to the left. There was no effect of either enantiomer on Ca2+binding to myofilament troponin C. Moreover EMD 57033, but not EMD 57439, stimulated actomyosin ATPase activity of myofilament preparations in which either troponin or troponin-tropomyosin had been extracted. EMD 57033 had no effect on Mg-ATPase activity of pure ventricular myosin. EMD 57033 also stimulated the velocity of actin filament sliding on myosin heads adhered to nitrocellulose-coated glass coverslips. We propose that the action of EMD 57033 is at the actin-myosin interface on a “'receptor” that may be on actin or the crossbridge. Drug binding to this domain appears to reverse the inhibition of actin-myosin interactions by troponin-tropomyosin and also to promote transition of crossbridges from weak to strong force-generating states.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

This study investigates the role of endogenous platelet-activating factor (PAF) in the production of nitric oxide (NO) by constitutive and inducible isoforms of NO synthase (NOS) in endotoxin shock. In anesthetized rats, 3 hours of endotoxemia resulted in a fall in mean arterial blood pressure (MAP) from 127±5 (control) to 61±7 mm Hg and a reduction of the pressor responses to norepinephrine (NE, 1 μg kg−1) from 33±3 (control) to 17±2 mm Hg. Endotoxemia for 3 hours also resulted in a significant reduction in the contractile effects of NE (10−8to 10−6mol/L) in thoracic aortas ex vivo. This hyporeactivity to NE was due to an enhanced formation of NO, for it was restored by the NOS inhibitorNG-nitro-l-arginine methyl ester. Animals pretreated with the PAF receptor antagonist WEB 2086 maintained higher MAP (MAP at 180 minutes, 98±6 mm Hg) and exhibited more pronounced pressor responses to NE at 180 minutes after LPS injection. Moreover, WEB 2086 attenuated by 58% the lipopolysaccharide (LPS)-induced hyporeactivity of the rat aortic rings ex vivo. At 3 hours after LPS injection, calcium-independent NOS activity was induced in the lung. The activity of inducible NOS was significantly lower (by 31%) in lungs of rats pretreated with WEB 2086. The hypothesis that WEB 2086 attenuates the induction of NOS in vivo was substantiated in vitro by the finding that pretreatment with WEB 2086 for 30 minutes inhibited the LPS-stimulated NO production in cultured murine macrophages. In anesthetized rats, PAF itself caused a biphasic (transient immediate and sustained delayed) fall in MAP, which was attenuated by the NOS inhibitorNG-methyl-l-arginine. PAF also caused induction of calcium-independent NOS activity in the lung, an effect that was prevented by WEB 2086 and dexamethasone. Thus, PAF contributes to the induction of the calcium-independent isoform of NOS by LPS administration in vitro and in vivo. In addition, PAF activated the constitutive isoform of NOS to produce NO. Thus, inhibition of NOS induction and activation may contribute to the beneficial effects of PAF antagonists in endotoxemia.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Smooth muscle myosin heavy chains (MHCs) exist in multiple isoforms. Rabbit smooth muscles contain at least three types of MHC isoforms: SM1 (204 kD), SM2 (200 kD), and SMemb (200 kD). SM1 and SM2 are specific to smooth muscles, but SMemb is a nonmuscle-type MHC abundantly expressed in the embryonic aorta. We recently reported that these three MHC isoforms are differentially expressed in rabbit during normal vascular development and in experimental arteriosclerosis and atherosclerosis. The purpose of this study was to clarify whether expression of human smooth muscle MHC isoforms is regulated in developing arteries and in atherosclerotic lesions. To accomplish this, we have isolated and characterized three cDNA clones from human smooth muscle: SMHC94 (SM1), SMHC93 (SM2), and HSME6 (SMemb). The expression of SM2 mRNA in the fetal aorta was significantly lower as compared with SM1 mRNA, but the ratio of SM2 to SM1 mRNA was increased after birth. SMemb mRNA in the aorta was decreased after birth but appeared to be increased in the aged. To further examine the MHC expression at the histological level, we have developed three antibodies against human SMI, SM2, and SMemb using the isoform-specific sequences of the carboxyl terminal end. Immunohistologically, SM1 was constitutively positive from the fetal stage to adulthood in the apparently normal media of the aorta and coronary arteries, whereas SM2 was negative in fetal arteries of the early gestational stage. In human, unlike rabbit, aorta or coronary arteries, SMemb was detected even in the adult. However, smaller-sized arteries, like the vasa vasorum of the aorta or intramyocardial coronary arterioles, were negative for SMemb. Diffuse intimal thickening in the major coronary arteries was found to be composed of smooth muscles, reacting equally to three antibodies for MHC isoforms, but reactivities with anti-SM2 antibody were reduced with aging. With progression of atherosclerosis, intimal smooth muscles diminished the expression of not only SM2 but also SM1, whereas α-smooth muscle actin was well preserved. We conclude from these results that smooth muscle MHC isoforms are important molecular markers for studying human vascular smooth muscle cell differentiation as well as the cellular mechanisms of atherosclerosis.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Peripheral vasodilator responsiveness was examined in pacing-induced heart failure (HF) in 11 conscious dogs chronically instrumented for measurement of systemic (total peripheral resistance [TPR]) and local (iliac blood flow) vascular resistance. Dose responses to isoproterenol (ISO), acetylcholine (ACh), and nitroglycerin (NTG) were examined in the same dogs before pacing (control) and after 4 to 7 weeks of rapid ventricular pacing, which induced congestive HF, characterized by increased left ventricular end-diastolic pressure (6.7±0.4 [control] versus 28 ±1.5 [HF] mm Hg) and decreased cardiac output (−30±5%) and left ventricular dP/dt (−53±3%), as well as ascites and peripheral edema. In the control state, TPR fell by 57±2% in response to ISO (100 ng/kg), by 61±3% in response to ACh (3 μg/kg), and by 55±2% in response to NTG (10 μg/kg). In HF, smaller decreases (P<.05) in TPR were observed with the same doses of ISO (−50±2%) and ACh (−49±2%) but not with NTG (−58±3%). Depressed responses to systemic ISO and ACh, but not NTG, were observed in HF in the presence of ganglionic blockade and also after local administration of smaller doses of the drugs in the absence of ganglionic blockade, but where systemic effects were not elicited. Inhibition of nitric oxide synthase increased TPR to a greater degree before HF (+154±28% [control]) than after (+80±22% [HF]) and eliminated the depressed responses to ACh but not to ISO. β-Adrenergic receptor density, as determined by125I-cyanopindolol binding in membrane preparations from mesenteric vessels was significantly decreased after HF (130±3 [control] versus 100±8 [HF] fmol/mg,P<.05) without any change in affinity. Thus, peripheral vascular β-adrenergic receptor downregulation occurs in HF, independent of altered endothelium-mediated peripheral vasodilation.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The release of substance P (SP)-like immunoreactivity (SP-LI) in the dorsal horn of the spinal cord and the cardiovascular changes to both high-tension (HT) and low-tension (LT) contractions were determined using α-chloralose-anesthetized cats. Over a 10-minute period, seven contractions (HT or LT) were induced. Each contraction was 20 seconds in duration and was followed by an 80-second quiescent period. The tension-time index (TTI) for the HT contractions was 2751±348 kgs (mean±SD), which was greater than the TTI of 813±167 kgs for the LT contractions. The HT contractions caused a greater release of SP-LI than the LT contractions: SP-LI increased from 0.18±0.02 to 0.32±0.03 fmol/100 μL and from 0.18±0.02 to 0.25±0.04 fmol/100 μL for the two types of contractions, respectively. Concomitant with this greater SP-LI release, HT contractions caused larger increases in mean arterial pressure (34 ±16 versus 11±4 mm Hg) and heart rate (18±7 versus 8±4 beats per minute) than did the LT contractions. These changes in SP-LI, mean arterial pressure, and heart rate were virtually abolished when the contractions were repeated after sectioning the L-5-S-2 dorsal and ventral roots or when the electrical stimulation of the ventral roots was repeated after muscle paralysis with gallamine triethiodide. These results demonstrate that contraction-evoked SP-LI release in the dorsal horn is related to the developed tension. Furthermore, these data provide additional support for the hypothesis that the release of SP from the central terminations of muscle afferents plays a role in mediating the cardiovascular responses to static contraction of skeletal muscle.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We have recently demonstrated an enhanced expression of inhibitory guanine nucleotide regulatory protein (Gi) in the heart and aorta from spontaneously hypertensive rats (SHR) as compared with control Wistar-Kyoto (WKY) rats; this enhanced Giexpression was associated with an increased inhibition of adenylyl cyclase by inhibitory hormones and decreased stimulation of adenylyl cyclase by stimulatory hormones. In the present studies, we have determined the levels of stimulatory and inhibitory guanine nucleotide regulatory proteins (Gsand Gi, respectively) in platelets from SHR by cholera toxin- and pertussis toxin-catalyzed ADP-ribosylations, respectively, as well as by immunoblotting techniques using specific antibodies for Gsand Gi. Cholera toxin catalyzed the ADP-ribosylation of a single protein ofMr45 000 in rat platelets from SHR and WKY rats, and the labeling of this band was not altered in SHR as compared with WKY rats. Pertussis toxin, on the other hand, catalyzed the ADP-ribosylation of a single protein band of Mr41 000 in platelets from SHR and WKY rats, and unlike the response in heart and aorta, the labeling of this band was significantly decreased in SHR as compared with WKY rats. Furthermore, immunoblotting experiments using AS/7 antibody, which is specific for Giα-1and Giα-2, showed a decrease in Giα-2in platelets from SHR as compared with WKY rats. In addition, the inhibitory effects of angiotensin II and atrial natriuretic factor on adenylyl cyclase and cAMP levels were completely abolished in SHR platelets, whereas the stimulatory effects of GTP,N-ethylcarboxamide adenosine, prostaglandin E1, and forskolin on adenylyl cyclase and cAMP levels were enhanced. These results suggest that altered responsiveness of hormones to stimulate or inhibit adenylyl cyclase and cAMP levels in platelets from SHR may partly be attributed to the decreased expression of Gilevels and not to the overexpression of Gsprotein.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Early investigators found contradictory evidence that vascular smooth muscle activation reduces the elastic modulus of the arterial wall under isotonic conditions but increases it under isometric conditions, concomitant with increased pulse-wave velocity. We examined the individual contributions of aortic constituents to the elastic modulus of the aortic wall to determine if isobaric analysis produces an accurate assessment of vascular smooth muscle activation. We used a modified Maxwell model assuming an incremental elastic modulus (Einc) composed of the elastic modulus of elastin fibers (EE), the elastic modulus of collagen fibers (EC) affected by the fraction of collagen fibers (fC) recruited to support wall stress, and the elastic modulus of the vascular smooth muscle (ESM) according to the following formula: Einc=EE+EC×fC+ESM. Eincwas assessed in eight conscious dogs using descending thoracic aortic pressure (microtransducer) and diameter (sonomicrometry) measurements. Stress-strain relations in the control state and during activation of smooth muscle by continuous administration of phenylephrine (5 μg. kg−1min−1) were obtained by transient occlusions of the descending aorta and inferior vena cava. Results were as follows: EEwas 4.99±1.58±106dynes/cm2(mean±SD), and ECwas 965.8±399.8±106dynes/cm2, assessed during the control state. Phenylephrine administration increased the theoretical pulse-wave velocity (Moens-Korteweg equation) from 5.25±+1.03 m/s during the control state to 7.57±2.53 m/s (P<.005). Active muscle exhibited a unimodal stress-strain curve with a maximum stress of 0.949±0.57±106dynes/cm2at a corresponding strain value of 1.299±0.083. The maximum value observed corresponded, on the pressure-diameter curve of the active artery, to a pressure of 234.28±46.6 mm Hg and a diameter of 17.94 ± 1.6 mm. The maximum ESMderived from the stress-strain relation of the active muscle was 8.345 ± 7.56 ± 106dynes/cm2at a strain value of 1.283±0.079. This point was located at 208.01±40.8 mm Hg and 17.73 ±1.41 mm on the active pressure-diameter curve. During activation of vascular smooth muscle, Eincdecreased (P<.05) when plotted against internal pressure but increased (P<.05) when plotted against strain, over the operative range. Our results show that (1) the analysis of the elastic behavior of active muscle is feasible in conscious dogs, (2) the isobaric analysis of elastic modulus is, in fact, a comparison of two different materials, ie, the vascular smooth muscle (with a very low elastic modulus) and the collagen fibers (whose high elastic modulus determines the mechanical properties of a largely distended artery), and (3) isometric analysis shows Eincto increase with smooth muscle activation, and therefore this type of analysis appears to be the most appropriate in functional terms.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Basic fibroblast growth factor (bFGF) has been previously shown to be mitogenic for vascular smooth muscle cells (VSMCs) in vivo, but only after vascular injury. We show in the present study that the regulation of bFGF-stimulated VSMC proliferation, by vascular cell-secreted heparin-like compounds, correlates with inhibition of bFGF binding to cell-associated heparan sulfate proteoglycans. The stimulation of cultured VSMC proliferation by bFGF was markedly reduced when these cells were cocultured with confluent endothelial cells or confluent VSMCs (100.8±8.4% and 55.6±2.3% inhibition, respectively) or with conditioned media from these two cell types. Balb/c3T3 fibroblasts had no statistically significant effect on bFGF-stimulated VSMC proliferation. Vascular cell-conditioned media also inhibited bFGF binding to heparan sulfate proteoglycans on VSMCs, and the inhibition of binding correlated linearly with the inhibition of proliferation after a critical amount of binding was inhibited (44%) (r=.952, P<.0001). Heparinase or heparitinase treatment of conditioned media removed the bFGF-inhibitory effects, presumably by degrading heparin-like compounds. Indeed, heparin itself mimicked the inhibitory effects of conditioned media on bFGF-mediated proliferation and binding to heparan sulfate proteoglycans. These results suggest a bFGF regulatory role for vascular cell-produced heparin-like compounds, linking the mitogenic effects with binding to heparan sulfate proteoglycans for this heparin-binding growth factor.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Depolarization of human atrial myocytes activates a transient outward current that rapidly inactivates, leaving a sustained outward current after continued depolarization. To evaluate the ionic mechanism underlying this sustained current (Isus), we applied whole-cell voltage-clamp techniques to single myocytes isolated from right atrial specimens obtained from patients undergoing coronary bypass surgery. The magnitude of Isuswas constant for up to 10 seconds at +30 mV and was unaffected by 40 mmol/L tetraethylammonium, 100 nmol/L dendrotoxin, 1 mmol/L Ba2+, 0.1 μmol/L atropine, or removal of Cl−in the superfusate. Isuscould be distinguished from the 4-aminopyridine (4AP)-sensitive transient outward current (Ito1) by differences in voltage-dependent inactivation (1000-millisecond prepulse to −20 mV reduced 1to1by 91.7±0.1% [mean±SEM], P<.001, versus 9.4±0.4% reduction of Isus) and 4AP sensitivity (IC50for block of Ito1, 1.96 mmol/L; for Isus, 49 μmol/L). Isusactivation had a voltage threshold near −30 mV, a half-activation voltage of −4.3 mV, and a slope factor of 8.0 mV. Isuswas not inactivated by 1000-millisecond prepulses but was reduced by 16±8% (P<.05) at a holding potential of −20 mV relative to values at a holding potential of −80 mV. Isusactivated very rapidly, with time constants (τ) at 25°C ranging from 18.2±1.8 to 2.1±0.2 milliseconds at −10 to +50 mV, two orders of magnitude faster than previously described kinetics of the rapid component of the delayed rectifier K+current. At 16°C, Isusactivation was greatly slowed (τ at +10 mV, 46.7±4.1 milliseconds; r at 25°C, 7.1±0.8 milliseconds;P<.01), and the envelope of tails test was satisfied. The reversal potential of Isus, tail currents changed linearly with log [K+]o(slope, 55.3 ±2.9 mV per decade), and the fully activated current-voltage relation showed substantial outward rectification. Selective inhibition of Isuswith 50 μmol/L 4AP increased human atrial action potential duration by 66±11% (P<.01). In conclusion, Isusin human atrial myocytes is due to a very rapidly activating delayed rectifier K+current, which shows limited slow inactivation, is insensitive to tetraethylammonium, Ba2+, and dendrotoxin, and is highly sensitive to 4AP. These properties resemble the characteristics of channels encoded by the Kv1.5 group of cardiac cDNAs and may represent a physiologically significant manifestation of such channels in human atrium.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Turkey poults fed furazolidone (Fz) in high concentrations (700 ppm) develop dilated cardiomyopathy (Fz-DCM). We tested whether five cardioactive agents were cardioprotective in this model of heart failure, ie, whether they prevented dilatation and wall thinning and improved contractile performance. We compared the effects of chronic administration of a β1-selective and a nonselective β-receptor antagonist, an β-receptor antagonist, and two Ca2+channel antagonists in the presence of Fz administration. The greatest cardioprotection was found with treatment with either propranolol or nifedipine. At the gross morphological level, the effect of propranolol (a nonselective β-adrenergic antagonist) was greater than the effect of atenolol (a selective β1-adrenergic antagonist), and the effect of nifedipine was greater than that of verapamil (Ca2+channel antagonists), with all agents more cardioprotective than phenoxybenzamine (an βl-adrenergic>β2-adrenergic antagonist). Differences in cardioprotective efficacy of each agent increased with increased concentration. These data indicate that the dose and choice of a specific type of Ca2+channel antagonist or β-receptor antagonist might be important in the treatment of dilated cardiomyopathy. All agents that were cardioprotective caused similar functional improvements at both the whole heart and isolated muscle levels. Compared with control animals, Fz-DCM animals showed a significant reduction in peak left ventricular (LV) developed pressure (92±17 versus 143±24 mm Hg, P<.05), +dP/dt (1151±219 versus 2454±549 mmHg/s), and -dP/dt (1128±291 versus 1875±396 mm Hg/s), with a significant increase in LV end-diastolic volumes (2.8±0.7 versus 0.16±00. mL for control animals,P<.05). In contradistinction, LV +dP/dt and - dP/dt values for animals receiving Fz plus a cardioactive agent that demonstrated cardioprotection were not significantly different from control values. Peak LV developed pressures were also similar for Fz animals receiving an agent that demonstrated cardioprotection and control animals not receiving any pharmacologic agent. Isolated muscles from Fz-DCM animals as well as animals receiving Fz plus cardioprotective pharmacologic agents responded normally with regard to increasing extracellular Ca2+concentrations. Peak twitch forces were greater for animals receiving cardioprotective agents plus Fz than control animals not receiving any pharmacologic agents or Fz alone. At higher stimulation rates, Fz-DCM muscles demonstrated a significantly reduced peak twitch force (4±0.5 versus 1.5±0.4 g/mm2for control muscles versus Fz-DCM muscles, respectively). The negative effect of higher stimulation rates on peak twitch force was reversed by agents demonstrating the greatest cardioprotection, eg, propranolol and nifedipine. Finally, muscles from hearts treated with agents shown to be cardioprotective in terms of mechanical performance also had a higher tissue content of certain enzymes important for maintaining normal energy (ATP) supply and normal sarcoplasmic reticulum function. These studies indicate that gross morphological changes correlate with contractile performance at the whole heart and isolated muscle level. Because of the different protection provided by drugs from a similar functional class, it is likely that these cardioactive agents act via mechanisms other than a reduction in heart rate or blood pressure. Rather, we suggest that these agents result in macromolecular remodeling in the myocyte that is conducive to preserved contractile performance.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID