摘要:

There are important physiological and pathological cardiovascular consequences related to endothelial biomechanical properties. The endothelium, however, is not unique in responding to external forces; virtually all cells accommodate or respond to the mechanical environment.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We determined whether inhaling low levels of nitric oxide (NO) gas could selectively reverse hypoxic pulmonary vasoconstriction in the near-term newborn lamb and whether vasodilation would be attenuated by respiratory acidosis. To examine the mechanism of air and NO-induced pulmonary vasodilation soon after birth, we measured plasma and lung cGMP levels in the newly ventilated fetal lamb. Breathing at Fio20.10 nearly doubled the pulmonary vascular resistance index in newborn lambs and decreased pulmonary blood flow primarily by reducing left-to-right blood flow through the ductus arteriosus. Inhaling 20 ppm NO at Fio20.10 completely reversed hypoxic pulmonary vasoconstriction within minutes. Maximum pulmonary vasodilation occurred during inhalation of ≥80 ppm NO. Breathing 8% CO2at Fio20.10 elevated the pulmonary vascular resistance index to a level similar to breathing at Fio20.10 without added CO2. Respiratory acidosis did not attenuate pulmonary vasodilation by inhaled NO. In none of our studies did inhaling NO produce systemic hypotension or elevate methemoglobin levels. Four minutes after initiating ventilation with air in the fetal lamb lung, cGMP concentration nearly doubled without changing preductal plasma cGMP concentration. Ventilation with 80 ppm NO at Fio20.21 increased both lung and preductal plasma cGMP concentration threefold. Our data suggest that inhaled NO gas is a rapid and potent selective vasodilator of the newborn pulmonary circulation with an elevated vascular tone due to hypoxia and respiratory acidosis that acts by increasing lung cGMP concentration.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We evaluated transmembrane potential changes at the ends of isolated rabbit ventricular myocytes during defibrillation-strength shocks given in the cellular refractory period. The myocytes were stimulated (S1 pulse) to produce an action potential. Then a constant-field shock (S2 pulse) with an electric field of 20 or 40 V/cm was given at an S1-S2 interval of 50 msec. The cells were stained with potentiometric dye (di-4-ANEPPS), and the cell end facing the S2 anode or cathode was illuminated with a laser while the fluorescence was recorded. During S2, the cell end facing the S2 cathode became more positive intracellularly, whereas the cell end facing the S2 anode became more negative intracellularly. The S2-induced transmembrane potential change at the cell end (ΔVm) was determined relative to the amplitude of the S1-induced action potential (APA) in each recording (i.e., ΔVm/APA). In Tyrode's solution containing 4.5 mM potassium, ΔVm/APA for 40-V/cm S2 was 1.36±0.34 at the cell end facing the S2 cathode and -1.65±0.61 at the cell end facing the S2 anode (n=9). For the 20-V/cm S2, AVMAPA was 0.61±0.33 at the cell end facing the S2 cathode and -0.71±0.33 at the cell end facing the S2 anode (n=6). The ΔVm/APA was not significantly influenced by 20 mM diacetyl monoxime. These results indicate that large ΔVmvalues occurred at the ends of the cells during S2. The calculated values of ΔVm, assuming a nominal APA of 130 mV, were 177 and -214 mV for the 40-V/cm S2 and 79 and -93 mV for the 20-V/cm S2. The ΔVmwas correlated with cell size (r≥0.95) and agreed with values predicted by the S2 electric field strength multiplied by half of the cell length to within 27%. When the potassium concentration was increased to 20 mM, ΔVm/APA for 40 V/cm S2 increased 85% and 67% at the cell ends facing the S2 cathode and anode, respectively (n=9,p<0.005 versus 4.5 mM potassium), consistent with reduced APA. Thus, with normal or elevated extracellular potassium, transmembrane potential changes at the ends of cells during defibrillation-type stimulation are large enough to produce activation or recovery of voltage-dependent ion channels and may produce the effects responsible for defibrillation.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We have previously demonstrated specific insulin-like growth factor I (IGF I) mRNA transcripts in cultured endothelial and vascular smooth muscle cells and postulated an important role for IGF I in blood vessel growth responses. The purpose of this study was to characterize IGF I gene expression in a model of aortic coarctation hypertension in the rat. This high-renin model of hypertension is associated with hyperplastic vascular responses. Northern analysis of rat aorta demonstrated four specific IGF I mRNA transcripts sized 7.6, 4.6, 1.8, and 0.9-1.2 kb. Quantitation of aortic IGF I mRNA levels by solution hybridization/RNase protection assay demonstrated induction of IGF I transcripts in the hypertensive aorta; levels more than doubled at 7 days and were still significantly elevated 21 days after coarctation. In situ hybridization analysis indicated that IGF I transcripts were localized primarily to adventitial surfaces in normotensive aorta, with minimal signal detected over vascular cells. In hypertensive aortas, there was an increase in IGF I transcripts primarily over vascular smooth muscle cells. Thus, vascular IGF I gene expression is induced in this model of high-renin hypertension. IGF I may play an important role in autocrine/paracrine-mediated vessel wall remodeling in hypertension.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The gap-junctional proteins connexin43 and connexin42 have been shown to be expressed in the developing and mature avian heart, but their respective spatiotemporal distributions are unknown. In the present study, we have immunolocalized connexin42 in the conduction tissues of the adult avian heart (nonbranching bundle, bundle branches, and Purkinje fibers) and vascular endothelial cells. Connexin43 immunolabeling was confined to vascular smooth muscle. A novel microwave-based method was used to label connexin42 and connexin43 in the same tissue section. Neither connexin42 nor connexin43 was immunolocalized in working myocardium, atrioventricular node, and atrioventricular ring tissue of the bird heart. Although connexin42 first appeared in periarterial conduction myocytes and vascular endothelium at 9-10 embryonic days, the central conduction tissues, including the nonbranching bundle and proximal branches, remained immunonegative for connexin42 up until hatching (≊20 embryonic days). During the early postnatal period (1-14 days), connexin42 immunolabeling progressively spread up the bundle branches toward the nonbranching bundle. Connexin42 appeared uniformly distributed along the left bundle branch by 14 postnatal days. The distribution and spread of connexin42 immunoreactivity suggest that the emergence of specialized junctional contacts along ventricular fascicles occurs relatively late in heart development and coincides with the emergence of the chick from incubation within the egg.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Endothelium-dependent relaxation of mesenteric resistance arteries of spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto (WKY) rats was studied. Acetylcholine-induced relaxation of SHR vessels precontracted with 10 μM norepinephrine was endothelium dependent and attenuated compared with WKY vessels. The impaired response of SHR vessels was normalized by inhibition of cyclooxygenase with indomethacin. Blockade of nitric oxide synthetase withNG-nitrol-arginine methyl ester (L-NAME) or inhibition of guanylate cyclase with methylene blue attenuated acetylcholine-induced relaxation of norepinephrine-contracted SHR vessels but had no effect on WKY vessels. When vessels were precontracted with 30 nM arginine vasopressin, acetylcholine induced similar degrees of relaxation in both strains. A similar response was detected when lysine vasopressin was used to induce tone. Indomethacin had no effect on relaxation responses of SHR and WKY vessels precontracted with either form of vasopressin. L-NAME and methylene blue partially inhibited acetylcholine-induced relaxation of vasopressin-contracted vessels from both strains. Acetylcholine added at baseline did not induce contraction of vessels from either strain. It is concluded that endothelium-dependent relaxation of SHR resistance arteries is not impaired under all circumstances. Acetylcholine-induced relaxation may be suppressed in SHR resistance arteries when norepinephrine is used to induce contraction as a result of catecholamine-induced production of an endothelium-derived contracting factor. Vasopressin, on the other hand, does not elicit production of this contracting factor and may enhance the vasorelaxant action of acetylcholine in resistance arteries of both strains via actions on endothelial or vascular smooth muscle cells.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The mechanics of cardiac systole and relaxation have been studied primarily at the level of the whole heart or intact muscle. End-systolic pressure-volume relations of frog hearts have been found to be load dependent, whereas those of the mammal are relatively load independent. On the other hand, myocardial relaxation as studied at the muscle level is load independent in the frog but markedly load dependent in the mammal. Interpretation of these studies is complicated because of the unknown contribution of extracellular connective tissue, neurohumoral factors, and, in the case of the heart, the complex chamber geometry. Therefore, it is valuable to study cardiac mechanics at the level of the basic unit of contractile activity-the isolated myocyte. The goal of this study was to subject isolated frog cardiomyocytes to mechanical loading paradigms that mimic those presented to the cells within the heart. In the first part of this study, the afterload and preload of contracting cells were varied to study their effects on the end-systolic force-length relation, which was consistently found to be load independent over the range of isotonic shortening tested (typically 5%). We also investigated the force-length-time response of the cells to test the concept of the heart behaving as a time-varying elastance. Our results suggest that in this regard the frog myocyte behaves like mammalian muscle, and they are consistent with the presence of a small viscosity within the cell. We conclude that the tissue structure of the frog heart may contribute to disparity in mechanical behavior at the different structural levels. In the second part of this study, we subjected isolated frog cardiomyocytes to four different loading paradigms to test the hypothesis that myocardial relaxation in the frog is independent of load. These sequences consisted of afterloaded contractions followed by conventional isotonic-isometric relaxation (ACCR) or afterloaded contractions followed by physiologically reversed isometric-isotonic relaxation (ACPR). Relaxation was measured under isometric conditions using a variable afterload with either the ACCR or ACPR paradigms. The decay of force was independent of the cell length at which it occurred or the amount of shortening prior to it within the contractile cycle. Relaxation also was measured as relengthening of the cell under isotonic late-load conditions, using the ACPR paradigm either with a variable afterload or variable late load. Relengthening had a time course that was unaffected by changes in afterload (i.e., extents of shortening) or late load (equivalent to the filling pressure for the heart). Our results suggest that, within a 5% range of shortening from resting length, relaxation of frog cardiomyocytes (whether measured as a decay in isometric force with time or as isotonic relengthening of the cell) is independent of load and consequently may be rate-limited by Ca2+extrusion across the plasma membrane.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Although renin and angiotensinogen are known to be subject to feedback regulation, the effects of angiotensin II (Ang II) on the regulation of angiotensin converting enzyme (ACE) gene expression and enzymatic activity have not yet been studied. Therefore, the effects of exogenous Ang II infusion and ACE inhibition on ACE mRNA expression were examined. Ang II was infused intravenously in male Sprague-Dawley rats for 3 days at 100 (low dose), 300 (medium dose), or 1,000 (high dose) ng/kg per minute (n=8 for each group). Compared with control (vehicle infusion,n=8), Ang II infusion increased plasma Ang IH concentration (62,101,126 [p<0.05], and 187 [p<0.05] fmol/ml) and mean arterial blood pressure (106, 119 [p<0.05], 134 [p<0.05], and 125 mm Hg for control, low, medium, and high doses, respectively). Ang II infusion decreased ACE mRNA levels in the lung (57%, 52%, and 51%;p<0.05 for each) and testis (49%, 63%, and 53% of control for low, medium, and high doses, respectively;p< 0.05 for each), two major sites of ACE synthesis. There was, albeit less pronounced, a parallel decrease in pulmonary ACE activity (4.38, 3.92, 3.07 [p<0.05], and 3.48 [p<0.05 nM/mg per minute for control, medium, and high doses, respectively). In contrast, serum (54,50,48, and 38 [p<0.05] nM/ml per minute) and testicular (2.63, 2.08 [p<0.05], 2.24, and 2.18 nM/mg per minute for control, low, medium, and high doses, respectively) ACE activities displayed only minimal change in animals infused with Ang II. The effects of blockade of Ang II production were studied after 3 days of ACE inhibition by quinapril (10 mg/kg per day) in drinking water. Mean arterial blood pressure decreased significantly (111 versus 99 mm Hg,p<0.05). Quinapril treatment suppressed serum (43% of control,p< 0.05) and pulmonary (66% of control,p<0.001) ACE activities. However, ACE mRNA level was induced in the lung (140% of control,p<0.05). Testicular ACE activity was not significantly inhibited by quinapril (88% of control), and no significant difference was seen in the testicular mRNA levels between the two groups (98% of control). To study the effects of discontinuation of ACE inhibition on the regulation of serum ACE activity, additional rats were treated with quinapril (10 mg/kg per day for 3 days, followed by a single gavage of 10 mg/kg). Serum ACE activity was measured 6,24,48,96, and 168 hours after withdrawal of treatment. Serum ACE activity was inhibited at 6 hours after gavage. However, serum ACE activity exceeded baseline values significantly at 48 hours (193% of baseline,p< 0.05) and 96 hours (146% of baseline,p< 0.05) after discontinuation of ACE inhibition. These studies suggest that pulmonary ACE expression is subject to negative feedback by Ang II. Furthermore, our data are consistent with previous reports that ACE inhibitors do not penetrate into the testis in vivo.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Occlusion of aortocoronary venous grafts can be due to thrombosis, atherosclerosis, or vasospasm. Investigations have focused on properties of the graft itself, and little is known about the vascular reactivity and function of the native arteries proximal and distal to the vein graft, although spasm of the native artery distal to the graft site has been observed in patients. We hypothesized that the function of the endothelium of the native arteries may be altered after surgery. Autogenous venous grafts were placed in femoral arteries of rabbits to study the reactivity of the native arteries after grafting. Four weeks after graft implantation, the vein graft, ipsilateral vein, and native artery proximal and distal to the graft were removed for in vitro studies. Morphological evaluation by scanning electron microscopy and fluorescence microscopy after labeling with acetylated low density lipoprotein labeled with 1,1′-dioctadecyl-3,3,3′,3′-tetramethyl-indocarbocyanine perchlorate indicated the presence of an intact, metabolically active endothelial layer. There was no alteration in the contractile responses to phenylephrine of the arteries, vein grafts, or veins. Precontracted vein grafts, veins, and arterial segments proximal to the grafts relaxed when exposed to endothelium-dependent vasodilators (acetylcholine, arachidonic acid, and substance P), but the native arteries distal to the grafts did not. In bioassay cascade experiments, the distal artery did not release any measurable relaxing factor when exposed to acetylcholine. We conclude that the endothelium of the distal artery did not function normally. The extent and reversibility of altered endothelial function remain to be determined. This observation may help to explain the occurrence of myocardial infarction after aortocoronary bypass grafting in some patients.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Binding of urokinase-type plasminogen activator (u-PA) to specific receptors (u-PAR) on the surface of endothelial cells contributes to the regulation of plasmin-dependent processes such as fibrinolysis and angiogenesis. We studied the effect of raising intracellular levels of cyclic AMP (cAMP) and/or activating protein kinase C on the expression of u-PAR in cultured human umbilical vein endothelial cells (HUVEC). Incubation of HUVEC with forskolin stimulated a time- and concentration-dependent increase in the expression of u-PAR, measured both by an increase in the specific binding of radiolabeled single-chain u-PA (scu-PA) and by increased binding of anti-u-PAR antibodies. Maximal increase in u-PAR expression (81±11% above control,n=11) was not associated with a change in receptor affinity for scu-PA when HUVEC were incubated for 20 hours at 37°C with 50 μM forskolin. Receptor induction by forskolin was inhibited when HUVEC were preincubated with deoxyadenosine monophosphate (DAM), an inhibitor of adenylyl cyclase. A similar increase in receptor expression (128±27% above control,n=3) was induced by the cAMP analogue 8-bromoadenosine 3′:5′-cyclic monophosphate (50 mM). Forskolin induced an approximately twofold increase in the expression of a single ≊1.4-kb u-PAR messenger RNA (mRNA) transcript within 2 hours. Phorbol myristate acetate (PMA) also stimulated a time- and concentration-dependent increase in specific scu-PA binding. The maximal increase in u-PAR expression (254±27% above control,n=11) was observed when HUVEC were preincubated with 10 nM PMA for 20 hours. Induction of u-PAR by PMA was inhibited when HUVEC were preincubated with either cycloheximide or H7 but was unaffected by DAM. u-PAR induced by PMA showed a reduced affinity for scu-PA (Kd, 14±2 nM versus 3.6±0.6 nM,p<0.001;n=8). PMA stimulation for 20 hours resulted in a sixfold increase in a single: 1.4-kb u-PAR mRNA transcript, with increased levels detectable within 30 minutes. Coincubation of HUVEC with optimal concentrations of forskolin and PMA for 20 hours produced a fully additive increase in u-PAR expression at both the mRNA and protein levels. These data suggest that both cAMP-dependent and protein kinase C-dependent protein kinase pathways may independently regulate u-PAR expression in human endothelial cells.

ISSN:0009-7330    

出版商:OVID    

年代:1993

数据来源: OVID