摘要:

Since the expression of genes for platelet-derived growth factor (PDGF)-A and PDGF β-receptor are reciprocally regulated in vascular wall cells after balloon injury, we have investigated the ability of specific vasoactive molecules or growth factors to reproduce the injury pattern of gene expression in cultured rat smooth muscle cells (SMCs) and assessed the effect of inactivating α-thrombin on injury-induced expression of PDGF-A mRNA by vascular wall cells in vivo. The molecules investigated, to which vascular SMCs may be locally exposed after mechanical injury, included vasoactive factors (α- and β-adrenergic agonists, serotonin, histamine, angiotensin II, and endothelin) and growth factors (PDGF-AA, PDGF-BB, basic fibroblast growth factor, insulin-like growth factor, epidermal growth factor, and α-thrombin). In cultured rat SMCs, only α-thrombin (0.1–100 nM), among these compounds, produced the pattern of transiently increased PDGF-A and decreased PDGF β-receptor mRNA. PDGF-B chain mRNA levels remained undetectable in these cultured SMCs. The dependence of these changes in gene expression on the proteolytic activity of α-thrombin was shown by the interruption of altered gene expression or DNA synthesis after incubating the cultured SMCs with covalently inactivated α-thrombin using d-Phe-Pro-Arg chloromethyl ketone, a synthetic direct active-site irreversible inhibitor of α-thrombin. Continuous intravenous infusion of this synthetic antithrombin into baboons for 6 hours (100 nmol/kg per minute maintaining constant plasma levels of 3.0±0.5 μg/ml) after inducing balloon-catheter arterial injury also prevented the threefold increase in expression of PDGF-A mRNA characteristically exhibited by untreated mechanically injured vessels. We conclude that α-thrombin initiates an injury pattern of PDGF ligand and receptor gene expression both in vitro and in vivo. The importance of α-thrombin in the development of vascular lesion formation induced by mechanical injury and the possible usefulness of interrupting α-thrombin activity in the prevention of restenosis remain to be determined.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Serotonin (5-HT) and other contractile agonists stimulate Na+-H+exchange in vascular smooth muscle. Since intracellular alkalinization, per se, stimulates contraction, we tested whether 5-HT-induced contraction was associated with an increased pHi. In HCO3-free buffer (pH. 7.4), 5-HT (10−5M) increased pHi, as measured by 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein fluorescence, from 7.10±0.03 to 7.34±0.03 (p<0.01) in primary cultures of canine femoral artery vascular smooth muscle cells grown to confluence in the presence of 10% fetal calf serum. In HCO3- buffer (24 mM, pHo7.4), resting pHiwas 7.26±0.04 (p<0.01 versus HCO3-free buffer) but was not altered by 5-HT. In both types of buffer, 5-HT stimulated 5-(N-ethyl-N-isopropyl)amiloride-sensitive22Na+uptake (Na+-H+exchange). In HCO3- buffer and in Na+- and HCO3-free buffer, 5-HT increased 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive36Cl−uptake, suggesting that 5-HT stimulated Na+-independent Cl-HCO3−and Cl−-Cl−exchange activities, respectively. Individual vascular smooth muscle cells were then cultured on rat tail tendon collagen gels in the presence of 0.5% fetal calf serum, and cell length and pHiwere measured by video and epifluorescence microscopy. 5–HT contracted cells in a dose-dependent, reversible, and ketanserin-inhibitable manner. These cells, like cells grown in 10% fetal calf serum, exhibited Na+-H+and Na+-independent Cl−-HCO3- exchange. In HCO3−buffer, 5-HT contracted cells without an associated change in pHi. We concluded the following: 1) 5-HT stimulated both Na+-H+and Na+-independent Cl−-HCO3exchange activities in cultured vascular smooth muscle cells in parallel. 2) As a result of enhanced H+and HCO3−efflux, pH;was not altered. 3) In the presence of HCO3-, 5-HT-induced contraction was not associated with a change in pHi.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

This study investigates the vasomotor activities of prostaglandin (PG) D2in bovine coronary arteries in relation to endothelial function. Isolated segments of bovine coronary arteries with intact endothelium were concentration-dependently relaxed by PGD2(0.01–1 μM), a reaction that was blocked by a selective PGD receptor antagonist (BW A868C). There was a tight correlation between PGD2- and acetylcholine-induced relaxations (r=0.894,n=96,p<0.001). Removal of endothelium abolished the PGD2-induced relaxation and unmasked a contractile activity of the compound. Inhibition of endogenous PGI2formation by indomethacin did not modify these responses, whereas inhibition of endogenous nitric oxide generation byNG-nitro-L-arginine andNG-monomethyl l-arginine (10 or 100 μM) or scavenging of released nitric oxide by oxyhemoglobin (3 μM) considerably (>50%) antagonized the PGD2-induced relaxation. The vessel relaxation by PGD2was associated with a threefold to fourfold increase in vascular cGMP. A considerable reduction in vascular cGMP was measured after removal of the endothelium (by 53%) and inhibition of endogenous nitric oxide generation byNG-nitro-l-arginine (by 70%o). This also resulted in a complete inhibition of PGD2-induced cGMP accumulation. Similar results were obtained with the stable PGD2mimetic ZK 110.841, suggesting that these biological activities of PGD2were due to the compound itself and not caused by any PGD2metabolite. A slight but significant increase in cAMP was observed in arteries with intact endothelium as well as after removal of endothelium. Because the relaxing effect of PGD2was strictly endothelium dependent, the observed relaxation cannot be explained by cAMP. These data demonstrate a receptor-mediated, endothelium-dependent, nitric oxide-mediated, and cGMP-mediated vessel relaxation by PGD2.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

This study investigated developmental changes in Na+-H+ exchange and HCO3−-Cl−exchange activities in newborn and adult rabbit hearts. pHiwas measured using the fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein in isolated myocytes. Myocardial mechanical function was measured in the isolated ventricular preparation. Intracellular acidosis with normal pH. was induced by an NH4Cl (10 mM) prepulse technique. Upon removal of NH4Cl, pHifell transiently and then recovered toward the control level. In the HCO3-/CO2-buffered solution, the rate of recovery of pH;in the newborn was greater than in the adult. In the HCO3-/CO2-buffered solution, 5-(N-ethyl-N-isopropyl)amiloride (EIPA), an inhibitor of Na+-H+ exchange, inhibited the recovery of pHicompletely in the adult. In the newborn, however, significant recovery of pHiwas observed in the presence of EIPA. In the presence of both EIPA and 4-acetamido-4'-isothiocyanatostilbene-2',2'-disulfonic acid (SITS), an inhibitor of HCO3-Cl exchange, the recovery of pHiwas not observed in the two age groups. In the HEPES-buffered solution that did not contain HCO3-/CO2, the rate of recovery of pHiafter NH4Cl removal was similar in the two age groups. In the HEPES-buffered solution, the recovery of pHiwas completely inhibited by EIPA in the two age groups. In the presence of EIPA in the HCO3/CO2-buffered solution, contractile function decreased during acidosis after NH4Cl removal and did not recover in the adult. In the newborn, significant recovery of contractile function was observed after NH4Cl removal in the presence of EIPA. The recovery of mechanical function observed in the presence of EIPA in the newborn was inhibited by SITS. These data suggest that, although there is no developmental change in the Na+-H+ exchange activity, HCO3-Cl exchange is more active in the premature myocardium. The presence of the HCO3−-Cl- exchanger is important in maintaining myocardial contractile function during acidosis, especially when Na+-H+ exchange is inhibited and may partly explain the greater resistance of the premature myocardium to acidosis.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Pharmacological modulation of [K+]oaccumulation and action potential changes during acute myocardial ischemia is under evaluation as a promising new antiarrhythmic and cardioprotective strategy during myocardial ischemia and reperfusion. We studied the effects of cromakalim, a K+channel opener that activates ATP-sensitive K+channels, in isolated arterially perfused rabbit interventricular septa subjected to ischemia and reperfusion and, through use of the patch clamp technique, in inside-out membrane patches excised from guinea pig ventricular myocytes. During aerobic perfusion, 5 μM cromakalim shortened action potential duration (APD) from 217±7 to 201±10 msec, had no effect on [K+]o, and reduced tension by 17±3% (n=11). During ischemia, pretreatment with 5 μM cromakalim resulted in 1) more rapid APD shortening (71±9 versus 166±7 msec at 10 minutes and 63±12 versus 122±8 msec at 30 minutes), 2) similar [K+]oaccumulation after 10 minutes (8.9±0.3 versus 9.6±0.5 mM) but a trend toward increased [K+]oaccumulation after 30 minutes (11.0±1.7 versus 9.6±1.0 mM), and 3) similar times for tension to decline to 50o of control (2.14±0.16 versus 2.14±0.19 minutes) but shorter time to fall to 20% of control (4.34±0.33 versus 4.90±0.22 minutes;p=0.003). After 60 minutes of reperfusion following 30 minutes of ischemia, recovery of function was similar, with a trend toward better recovery of developed tension (to 58±9%o versus 39±10% of control; p=0.18) and tissue ATP levels in cromakalim-treated hearts but no differences in APD or rest tension. Thus, 5 μM cromakalim had mild effects in normal heart but greatly accelerated APD shortening during ischemia without markedly increasing [K+] accumulation, possibly because the more rapid APD shortening reduced the time-averaged driving force for K+efflux through ATP-sensitive K+channels. A significant cardioprotective effect during 30 minutes of ischemia plus 60 minutes of reperfusion could not be demonstrated in this model. In excised membrane patches studied at room temperature, the ability of cromakalim to activate ATP-sensitive K+channels was significantly potentiated by 100 μM but not 15 μM cytosolic ADP, suggesting that in addition to the modest fall in cytosolic ATP during early ischemia, the rapid increases in cytosolic ADP may further sensitize cardiac ATP-sensitive K+channels to activation by cromakalim. This factor may contribute to the marked acceleration of APD shortening during ischemia produced by concentrations of cromakalim that have minimal effects on APD in aerobic perfused tissue. Activation of ATP-sensitive K+channels by cromakalim was not significantly affected by other ischemic factors such as lactate (20 mM), Pi(10 mM), or acidosis (pH 6.5).

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The purpose of this study was to test the hypothesis that abnormal intracellular calcium handling characterizes myocardial stunning. Isolated, isovolumic, buffer-perfused ferret hearts were loaded with the bioluminescent calcium indicator aequorin for simultaneous measurement of individual calcium transients and left ventricular pressure. After 15 minutes of global ischemia and 20 minutes of reperfusion, left ventricular developed pressure was significantly reduced (75±7 versus 93±6 mm Hg,p<0.05). During ischemia, [Ca2+], levels were significantly elevated compared with preischemic levels, both during systole (1.38±0.31 versus 0.88±0.2 μM,p<0.05) and end diastole (0.85±0.16 versus 0.38±0.13 μM,p<0.05). Early during reperfusion, [Ca2+]iwas also significantly elevated during systole (1.63±0.44 versus 0.88±0.20 μM,p<0.05) and end diastole (0.75±0.15 versus 0.38±0.13 μM,p<0.05). After 20 minutes of reperfusion, myocardial stunning occurred, but [Ca2+]iwas not significantly different from preischemic levels. Thus, myocardial stunning does not result from decreased levels of activator calcium. The force-pCa relation generated by the stunned hearts was shifted downward compared with that generated by the control hearts, consistent with a decrease in maximum calcium-activated force (Fmax). At steady state during tetanus, the decrease in Fmaxwas confirmed, but there was no significant difference in the slope of the force-pCa relation of the stunned hearts versus controls. Thus, we conclude that stunned myocardium is characterized by decreased Fmaxwithout desensitization of the myofilaments to [Ca2+]i. Elevations of [Ca2+]iduring ischemia and reperfusion precede myocardial stunning and may relate to its pathogenesis.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The effects of age and blood pressure on fibronectin expression in the rat heart were studied in the normotensive Wistar and Wistar-Kyoto (WKY) strains and in the spontaneously hypertensive rat (SHR). Fibronectin mRNA expression decreased threefold between 10 and 40 weeks of age in Wistar hearts, with changes of similar magnitude occurring between 6 and 24 weeks in WKY rats. In contrast, no decrease in fibronectin mRNA was observed in SHR hearts during this time span. These results are in contrast to changes observed previously in the aorta, where an increase in fibronectin mRNA occurred with age in all three rat strains. Ribonuclease protection analysis showed a small age-specific increase in the relative content of EIIIA+ fibronectin mRNA isoforms in hearts from Wistar rats, whereas no change was found in the relative amount of either EIIIA or EIIIB isoforms in SHR hearts. Changes similar to those observed for fibronectin mRNA, although of different magnitudes, were observed in mRNA levels for collagen α1(III) and β1 integrin. In Wistar hearts, collagen α1(III) mRNA levels decreased fivefold to sixfold between 10 and 40 weeks of age, whereas a twofold to threefold decrease in β1 integrin was observed in WKY hearts between 6 and 24 weeks of age. Western blot analysis revealed a positive correlation between fibronectin mRNA and protein for age-dependent changes in ventricular tissue but not in the atria, suggesting that the regulation of fibronectin expression during the changes common to both aging and hypertrophy could involve both transcriptional and posttranscriptional mechanisms.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The molecular basis of myocardial adaptation to ischemia and reperfusion is poorly understood. It is thought that nuclear proto-oncogenes act as third messengers, converting cytoplasmic signal transduction into long-term changes of gene expression. We studied the expression of six nuclear proto-oncogenes (Egr-1, c-fos, fosB, c-jun, junB, and c-myc) in myocardium subjected to ischemia and reperfusion in anesthetized pigs. Stunning was achieved by two 10-minute left anterior descending coronary artery occlusions separated by 30 minutes of reperfusion. Hearts were excised after the first occlusion, after the first reperfusion, and at 30, 120, 150, and 210 minutes of reperfusion after the second occlusion. Total RNA was prepared from stunned as well as normally perfused myocardial tissue and subjected to Northern blotting. The response of the six nuclear proto-oncogenes varied.fosBgene expression was never detected. The c-mycgene was expressed, but its level was unchanged by ischemia. c-junexpression was slightly increased by ischemia (3.1±0.6-fold). The c-fos, Egr-1, andjunBgenes were highly induced, being fivefold to sevenfold higher in experimental than in control tissue. In three animals pretreated with the β,-antagonist metoprolol and then subjected to the above experimental protocol, the induction of proto-oncogenes was similar to that in nonblocked controls. Our results show that the myocardial adaptive response to ischemic stress includes the induction of at least four transcription factors that may be further operative in repair processes and angiogenesis.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

To improve electrocardiographic localization of the site of origin of ectopic left ventricular (LV) impulse formation in the heart with prior myocardial infarction, 62-lead body surface QRS integral maps were studied during LV pacing at a total of 221 endocardial sites in 14 patients with previous anterior (AMI), inferior (IMI), lateral (LMI), or anterior and inferior (AMI/IMI) myocardial infarction. The anatomic location of each pacing site was computed using digitized biplane fluoroscopic images and plotted on standardized LV endocardial polar projections. A data base of characteristic AMI and IMI mean QRS integral maps was developed after visually selecting subgroups with nearly identical QRS integral morphology from the ectopic activation sequences produced at 110 sites in eight patients with AMI and at 66 sites in four patients with IMI. Intrasubgroup pattern uniformity and intersubgroup pattern variability were statistically verified. The endocardial pacing site locations belonging to each AMI and IMI subgroup were depicted as segments on the respective LV polar projections. In patients with AMI, a total of 18 typical mean QRS integral patterns were obtained, whereas 22 different mean total QRS integral patterns showing more substantial intersubgroup variation were acquired in patients with IMI. Postero-lateral regions exhibited a relatively low electrocardiographic sensitivity (six AMI and five IMI patterns) as compared with anteroseptal regions (12 AMI and 17 IMI patterns). Total QRS integral patterns obtained at 24 sites in one patient with LMI were largely compatible with the IMI mean total QRS integral patterns, whereas the majority of total QRS integral patterns acquired at 21 sites in one patient with AMI/IMI corresponded with the AMI mean total QRS integral patterns. The results show that total body surface QRS integral maps generated during LV pacing in patients with prior myocardial infarction cluster by pattern and that each QRS integral pattern is related to a circumscribed endocardial segment of ectopic impulse formation. The relation between a given QRS integral pattern and the position and size of the corresponding paced segment is dependent on infarct location. The present infarct-specific data base of characteristic total body surface QRS integral patterns provides a clinical tool to obtain detailed electrocardiographic localization of ventricular arrhythmias in patients with previous myocardial infarction.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

To determine whether the overload associated with myocardial infarction and ventricular failure in rats is coupled with activation of DNA synthesis in the remaining left and right ventricular myocytes, flow cytometric analysis was performed on myocyte nuclei prepared from both ventricles 7 and 30 days after coronary occlusion. In addition, oral captopril was administered in separate groups of control and experimental rats to establish whether a relation existed between attenuation of ventricular loading and magnitude of DNA synthesis in myocytes. Results demonstrated that left ventricular failure and right ventricular dysfunction at 7 days after infarction were biventricularly associated with marked increases in the number of myocyte nuclei in the G2M phase of the cell cycle. In contrast, the fraction of nuclei in the G0+G1phase decreased. In compaiison with the earlier time point, the 30-day interval was characterized by a significant magnitude of cardiac hypertrophy, a moderate amelioration of ventricular pump fumction, and a decrease in the percentage of myocyte nuclei in the G2M phase in both ventricles. However, 30 days after infarction, the number of right ventricular myocyte nuclei in the S and G2M phases remained elevated with respect to control animals. Captopril therapy reduced the extent of ventricular loading and the population of myocyte nuclei in the cell cycle at 7 days. In conclusion, DNA synthesis in myocyte nuclei may represent an important adaptive component of the myocardial response to infarction.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID