ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

On the basis of animal models of arterial injury, smooth muscle cell proliferation has been posited as a dominant event in restenosis. Unfortunately, little is known about this proliferation in the human restenotic lesion. The purpose of this study was to determine the extent and time course of proliferation in primary and restenotic coronary atherectomy–derived tissue. Primary (n=118) and restenotic (n=100) coronary atherectomy specimens were obtained from 211 nonconsecutive patients. Immunocytochemistry for the proliferating cell nuclear antigen (PCNA) was used to gauge proliferation in the atherectomy specimens. The identity of PCNA-positive cells was then determined using immunohistochemical cell-specific markers. Eighty-two percent of primary specimens and 74% of restenotic specimens had no evidence of PCNA labeling. The majority of the remaining specimens had only a modest number of PCNA-positive cells per slide (typically < 50 cells per slide). In the restenotic specimens, PCNA labeling was detected over a wide time interval after the initial procedure (eg, 1 to 390 days), with no obvious proliferative peak. Cell-specific immunohistochemical markers identified primary and restenotic PCNA-positive cells as smooth muscle cells, macrophages, and endothelial cells. In conclusion, the findings were as follows: (1) Proliferation in primary and restenotic coronary atherectomy specimens, as indicated by PCNA labeling, occurs infrequently and at low levels. (2) The response to injury in existing animal models of angioplasty may follow a very different course of events from the clinical reality in human atherosclerotic coronary arteries and may help explain why current approaches to restenosis therapy have been ineffective.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The present study tested the hypothesis that nitric oxide production in coronary resistance vessels is an important mechanism affecting the regulation of myocardial perfusion in unanesthetized dogs. We inhibited nitric oxide synthesis with the arginine analogueNω-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg) and maintained the compressive determinants of myocardial blood flow constant by ventricular pacing. L-NAME did not affect resting coronary blood flow and reduced the receptor-mediated increase in flow to intracoronary acetylcholine (100 μg/min IC) from 143±20% (mean±SEM) under control conditions to 31±10% after L-NAME (P< .001). Coronary autoregulatory relations were determined as steady-state coronary pressure was reduced by inflating a hydraulic occluder. Initial resistance adjustments over the autoregulatory plateau were not affected by L-NAME. Closed-loop autoregulatory gain was 0.84±0.09 under control conditions versus 0.78±0.07 after L-NAME (P=NS). As coronary pressure was reduced further, however, the critical pressure at which myocardial ischemia began (lower autoregulatory break point) increased from 45±3 mm Hg under control conditions to 61±2 mm Hg (P< .001) after L-NAME. In addition, the slope of the coronary pressure-flow relation below the autoregulatory break point was reduced (1.0±0.2 versus 0.58±0.09 mL · min−1· mm Hg−1after L-NAME,P< .05), reflecting a reduction in the maximal conductance recruitable during ischemia. In concert with the effects of L-NAME on autoregulatory responses during ischemia, peak reactive hyperemic flow to a 30-second coronary occlusion was also reduced (from 200±22 to 166±24 mL/min after L-NAME,P< .01). In contrast, metabolic flow recruitment to a twofold increase in heart rate was not affected by L-NAME. These results indicate that (1) both initial autoregulatory adjustments to reductions in coronary pressure and metabolic flow recruitment are probably mediated by either myogenic and/or metabolic mechanisms and do not require nitric oxide production, and (2) during ischemia, endothelium-dependent production of nitric oxide is an important mechanism responsible for minimizing coronary vascular resistance. Thus, inhibiting nitric oxide production increases the vulnerability of the myocardium to ischemia at reduced perfusion pressure. In pathophysiological states associated with impaired endothelium-dependent vasodilation, the loss of nitric oxide–dependent resistance adjustments may contribute to the functional significance of a coronary stenosis.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The contribution of the L-arginine/nitric oxide pathway to β-adrenergic dilation of resistance coronary vessels was examined in conscious dogs instrumented for measuring coronary blood flow (CBF), left ventricular (LV) wall thickening, and LV and aortic pressures and for intracoronary injections of acetylcholine (0.003 μg/kg), nitroglycerin (0.175 μg/kg), and graded doses of isoproterenol (0.0005 to 0.004 μg/kg). Peak increases in CBF with intracoronary isoproterenol (0.001 μg/kg) averaged 105±10% from baseline. With acetylcholine, CBF increased by 158±11%, and with nitroglycerin, CBF increased by 139±10%. After the administration of intracoronaryNω-nitro-L-arginine methyl ester (L-NAME, 10 μg/kg per minute for 12 minutes) to block nitric oxide synthesis from L-arginine, baseline CBF was not altered, and CBF increased by 49±7% with isoproterenol and by 94±6% with acetylcholine; both values were smaller (P< .01) than those before the arginine analogue. With nitroglycerin, CBF was increased by 145±11%, not significantly different from the value before L-NAME. Intracoronary L-arginine (1.0 mg/kg per minute for 12 minutes), the precursor of nitric oxide synthesis, partially reversed the inhibition of L-NAME on CBF responses to acetylcholine and isoproterenol. After β1-adrenergic blockade, CBF responses to isoproterenol and acetylcholine were also reduced (P< .05) by the arginine analogue. When increases in CBF were prevented, peak changes in coronary vascular conductance with intracoronary bolus doses of acetylcholine and isoproterenol were attenuated (P< .01) by L-NAME. Thus, nitric oxide formation is an important intermediate in β-adrenergic dilation of resistance coronary vessels in conscious dogs.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

It is usually assumed that the increase in coronary blood flow observed with norepinephrine occurs through local metabolic vasodilation secondary to cardiac β-receptor activation. However, direct feedforward β-receptor-mediated coronary vasodilation is also a possibility. In dogs with α-receptor blockade, the left circumflex artery was perfused at constant pressure. The vasodilator effect of intracoronary norepinephrine injections was determined during prolonged diastoles to avoid the chronotropic and inotropic effects of norepinephrine. Norepinephrine caused a dose-dependent increase in coronary blood flow that was attenuated by both the selective β1-antagonist practolol and the selective β2-antagonist ICI 118 551. These data indicate that norepinephrine activates β1- and β2-receptors in coronary resistance vessels to cause vasodilation independent of inotropic and chronotropic effects. The physiological significance of coronary β-receptor–mediated vasodilation was investigated in the beating heart. The coronary blood flow response and coronary venous oxygen tension response were compared when myocardial oxygen consumption was increased over the same range by one of three positive inotropic interventions: (1) norepinephrine, (2) paired-pulse stimulation, or (3) norepinephrine after α-blockade. During norepinephrine infusion (intervention 1), coronary venous oxygen tension decreased, indicating that the match between myocardial oxygen consumption and oxygen delivery is not maintained when coronary blood flow is controlled by α- and β-receptors in addition to local metabolic factors. Paired-pulse stimulation (intervention 2) also resulted in a decrease in coronary venous oxygen tension, demonstrating that the balance between oxygen consumption and delivery is not maintained when blood flow is controlled by local metabolic factors alone. However, when coronary β-receptor-mediated vasodilation was unmasked by α-blockade, norepinephrine infusion (intervention 3) produced no change in coronary venous oxygen tension. Therefore, coronary β-receptor vasodilation helps maintain the balance between flow and metabolism in a feedforward manner in the beating heart.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Replication of vascular smooth muscle cells is a key event in the pathogenesis of restenosis following angioplasty. Little is known about early biochemical events involved in the proliferation of smooth muscle cells following arterial injury. In the present study, the effect of Na+-H+exchange inhibitors on neointima formation after balloon injury of the rat carotid artery was investigated. Neointima formation was quantified 14 days after injury by morphometric measurement of cross-sectional neointimal area and by fluorometric determination of DNA content. The specific Na+-H+exchange inhibitor 3-methylsulfonyl-4-piperidino-benzoyl guanidine mesylate (Hoe 694) dose-dependently reduced neointimal area and DNA content, the latter finding indicating a true antiproliferative effect. The structurally different Na+-H+exchange blocker 5-(N-ethyl-N-isopropyl)amiloride hydrochloride had comparable inhibitory effects on neointimal area and DNA content, whereas 5-methylsulfonyl-2-piperidino-benzoyl guanidine hydrochloride, a position isomer of Hoe 694 lacking Na+-H+exchange blocking properties, did not suppress neointima formation. The effect of Na+-H+exchange blockers on neointima formation depended on the duration of drug application. Maximal suppression was achieved only when Hoe 694 was applied throughout the entire experiment for 14 days. This inhibitory effect of Na+-H+exchange blocker application for the first 2 weeks following injury lasted for 2 months. In conclusion, the results of the present study reveal a potential role of Na+-H+exchange for smooth muscle cell proliferation in vascular disease.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The presence of multiple growth stimuli at the sites of vascular injury following angioplasty suggests that therapies targeted toward common growth pathways will be more effective than therapies that inhibit only a single growth factor. We tested this hypothesis using amiloride and ethyl isopropyl amiloride (EIPA), which are inhibitors of the Na+-H+exchanger, whose activity is required in many cells for proliferation and migration. In the rat carotid injury model, EIPA (100 μg/h for 15 days) significantly decreased intimal area and the ratio of intimal to medial area, whereas amiloride (25 μg/h) showed an inhibitory trend that was similar to that observed for captopril (80 mg/kg per day) and heparin (25 U/h). EIPA and amiloride inhibited rat vascular smooth muscle cell DNA synthesis, with IC50values of 8.8 and 82.2 μM, respectively. Using platelet-derived growth factor as a chemoattractant, EIPA caused a concentration-dependent inhibition of migration (IC50, ≈60 μM). Because amiloride and EIPA have nonspecific effects on cellular function (especially inhibition of tyrosine kinases), we sought to characterize the specific role of the Na+-H+exchanger in vascular smooth muscle cell proliferation and migration. We generated a Na+-H+exchanger-deficient mutant cell line [RNHE(-)]. Studies with these cells suggested that the inhibitory effects of EIPA and amiloride were mediated only in part via Na+-H+exchange because (1) RNHE(-) cells grew well at pH 6.8 to 7.5 in bicarbonate-containing medium, and (2) there was no difference in migration in response to platelet-derived growth factor in the RNHE(-) cells. In summary, these data indicate that amiloride and EIPA inhibit neointimal formation in the rat carotid after injury. However, the mechanism of inhibition is likely to involve cellular events other than Na+-H+exchange, such as an effect on tyrosine kinases.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Previous work has suggested that the primary time-dependent repolarizing current in human atrium is the transient outward current (Ito), but interventions known to alter the magnitude of the delayed rectifier current (IK) affect atrial electrophysiology and arrhythmias in humans. To explore the potential role of IKin human atrial tissue, we used the whole-cell configuration of the patch-clamp technique to record action potentials and ionic currents in isolated myocytes from human atrium. A delayed outward current was present in the majority of myocytes, activating with a time constant ranging from 348±61 msec (mean±SEM) at −20 mV to 129±25 msec at +60 mV. The reversal potential of tail currents was linearly related to log [K+]owith a slope of 55 mV per decade, and fully activated tail currents showed inward rectification. The potassium selectivity, kinetics, and voltage dependence were similar to those reported for IKin other cardiac preparations. In cells with both Itoand IK, IKgreatly exceeded both components of Ito(Ito1and Ito2) within 50 msec of a voltage step from −70 to +20 mV. Based on the relative magnitude of Itoand IK, three types of cells could be distinguished: type 1 (58% [73/126] of the cells) displayed a large Itotogether with a clear IK, type 2 (13% [17/126] of the cells) displayed only IK, and type 3 (29% [36/126] of the cells) was characterized by a prominent Itoand negligible IK. Consistent differences in action potential morphology were observed, with type 2 cells having a higher plateau and steeper phase 3 slope and type 3 cells showing a triangular action potential and lesser phase 3 slope compared with type 1 cells. We conclude that IKis present in a majority of human atrial myocytes and may play a significant role in their repolarization and that previously observed variability in human atrial action potential morphology may be partially due to differences in the relative magnitude of time-dependent outward currents.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The effects of β2- and β1-adrenoceptor (β2AR and β1AR, respectively) agonists on the cytosolic Ca2+(Cai) transient (indexed by the transient increase in indo-1 fluorescence ratio after excitation), twitch amplitude (measured via photodiode array), membrane potential, and L-type sarcolemmal Ca2+current (ICa, measured by whole-cell patch electrode) were assessed in single rat ventricular myocytes. The selective β2AR agonist Zinterol increased the amplitudes of both the Caitransient and twitch in a concentration-dependent manner. Similar results were obtained when β2ARs were stimulated with isoproterenol in the presence of the selective β1AR antagonist CGP 20712A. β1AR stimulation induced by norepinephrine increased twitch amplitude to about the same extent as did β2AR stimulation. However, several striking differences between response to β1AR and β2AR stimulation were observed. β1AR stimulation had the potent effect of abbreviating the time course of the contraction and Caitransient, and β2AR stimulation did not reduce the time course of the Caitransient and had only a minor effect on the twitch duration. For a given increase in twitch amplitude, β1AR stimulation caused a greater increase in Caitransient, suggesting a diminished Cai-myofilament interaction. β1AR, but not β2AR, stimulation evoked spontaneous Caioscillations, increased the diastolic indo fluorescence level, and caused a decline in resting cell length. β1AR and β2AR also differed in their effects on ICa. Whereas both β1AR and β2AR stimulation increased the peak ICaamplitude, β2AR stimulation markedly prolonged the ICainactivation time. Accordingly, β2AR stimulation prolonged the action potential duration to a greater extent than did β1AR stimulation. 8-(4-Chlorophenylthio)cAMP mimicked the effects of β1AR stimulation by norepinephrine but not those due to β2AR stimulation. These results clearly indicate that both β2ARs and β1ARs functionally coexist in rat ventricular myocytes but that stimulation of these receptor subtypes elicits qualitatively different cell responses at the levels of ionic channels, the myofilaments, and sarcoplasmic reticulum.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Physiological concentrations of 3,5,3′-triiodo-L-thyronine (T3) acutely increased burst-mode gating of Na+channels in rabbit ventricular myocytes. Bursting was measured as the ratio of long events to the total number of events multiplied by 100 (%LE); a long event was defined as a set of openings or a single opening with a total duration greater than or equal to five times the control mean open time (MOT) for cell-attached patches. In the cell-attached configuration, adding either 5 or 50 nM T3to the pipette increased the %LE. %LE had a biphasic voltage dependence and peaked at −50 mV, although the largest percentage change from control occurred between −30 and −40 mV. Neither unitary conductance nor the overall MOT was altered by T3-induced bursting. However, the MOT of openings within bursts increased, implying a kinetically distinct mode of channel gating during bursts. Long events sometimes were grouped into runs, but the more usual pattern suggested that modal shifts occurred in ≈1 second. Similar behavior was observed with triiodothyroacetic acid, a T3analogue that does not elicit protein synthesis. To investigate involvement of soluble second messengers, cell-attached recordings were made with and without T3in the bath. Placed outside the pipette, 50 and 100 nM T3failed to alter MOT, unitary current, or %LE. Na+channel gating also was unaffected by patch excision and by exposing the cytoplasmic face of inside-out patches to 50 nM T3. Nevertheless, excision to the inside-out configuration with 5 nM T3in the pipette dramatically increased the %LE and lengthened MOT. These results suggest that T3induced Na+channel bursting by an extranuclear mechanism that requires proximity of T3to the extracellular face of the Na+channel. Furthermore, T3was not membrane permeant on the time scale of these experiments. Na+channel bursting may contribute to the propensity for arrhythmias in hyperthyroidism and to the positive inotropic effect of acute T3administration in the stunned and ischemic myocardium.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID