摘要:

The purpose of this study was to determine the heart rate and arterial blood pressure changes to isometric skeletal muscle contraction and muscle stretch before and after microinjecting an antagonist to substance P (SP) or somatostatin (SOM) into the L-7 dorsal horn region of the spinal cord of anesthetized cats. Anesthesia was induced by administering an anesthetic gas mixture and was subsequently maintained with α-chloralose. Triceps surae contraction was induced by electrically stimulating the L-7 ventral root. Three muscle manipulations (all 1 minute in duration) were performed: 1) continuous tetanic contraction, 2) intermittent tetanic contractions (1 second of contraction, 1 second of relaxation), and 3) passive muscle stretch. Saline microinjections had no effect on the cardiovascular responses to these muscle manipulations. However, both peptide antagonists blunted the pressor response to a continuous tetanic contraction as mean arterial pressure increased 47±4 and 44±4 mm Hg before and 28±3 and 28±4 mm Hg after microinjecting the SP or SOM antagonist, respectively. In contrast, neither antagonist influenced the increase in mean arterial pressure produced by passive stretch; values were 43±6 versus 41±6 mm Hg (SP antagonist) and 39±7 versus 42±7 mm Hg (SOM antagonist) before and after injections, respectively. Microinjecting the SOM antagonist attenuated the pressor response to intermittent tetanic contractions (44±4 mm Hg before SOM antagonist versus 26±4 mm Hg after SOM antagonist), whereas the SP antagonist had no effect (35±3 mm Hg before SP antagonist versus 32±4 mm Hg after SP antagonist). These data suggest that the spinal release of SP and SOM plays a role in eliciting the cardiovascular responses to isometric muscle contraction. Furthermore, the release of these peptides appears to be the result of activation of contraction, not mechanically sensitive muscle afferents.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Single or multiple brief periods of ischemia (preconditioning) have been shown to protect the myocardium from infarction after a subsequent more prolonged ischemic insult. To test the hypothesis that preconditioning is the result of opening ATP-sensitive potassium (KATP) channels, a selective KATPchannel antagonist, glibenclamide, was administered before or immediately after preconditioning in barbital-anesthetized open-chest dogs subjected to 60 minutes of left circumflex coronary artery (LCX) occlusion followed by 5 hours of reperfusion. Preconditioning was elicited by 5 minutes of LCX occlusion followed by 10 minutes of reperfusion before the 60-minute occlusion period. Glibenclamide (0.3 mg/kg i.v.) or vehicle was given 10 minutes before the initial ischemic insult in each of four groups. In a fifth group, glibenclamide was administered immediately after preconditioning. In a final series (group 6), a selective potassium channel opener, RP 52891 (10 μ/kg bolus and 0.1 μg/mg/min i.v.) was started 10 minutes before occlusion and continued throughout reperfusion. Transmural myocardial blood flow was measured at 30 minutes of occlusion, and infarct size was determined by triphenyltetrazolium staining and expressed as a percent of the area at risk. There were no significant differences in hemodynamics, collateral blood flow, or area at risk between groups. The ratio of infarct size to area at risk in the control group (28±6%) was not different from the group pretreated with glibenclamide in the absence of preconditioning (31±6%). Preconditioning produced a marked reduction (p<0.002) in infarct size (28±6% to 6±2%), whereas glibenclamide administered before or immediately after preconditioning completely abolished the protective effect (28±6% and 30±8%, respectively). RP 52891 also produced a significant (p<0.03) reduction (28±6% to 13±3%) in infarct size. These results suggest that myocardial preconditioning in the canine heart is mediated by activation of KATPchannels and that these channels may serve an endogenous myocardial protective role.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Endothelial cells, either in vivo or freshly isolated, respond when exposed to muscarinic agonists with an increase in cytosolic free calcium concentration ([Ca2+]i) and release of endothelium-derived relaxing factor (EDRF). When placed in culture, however, endothelial cells rapidly lose these responses, which may be related to changes in muscarinic receptor expression. Northern blot analysis of poly(A) + RNA from freshly isolated or cultured bovine aortic endothelial cells was used to address this problem. Through the use of specific cDNA probes complementary to the nonconserved regions of the ml, m2, m3, m4, and m5 muscarinic receptors, mRNA transcripts for the ml (3.9 kb), m2 (3.8 kb), and m3 (3.1 kb) receptor subtypes were identified in freshly isolated endothelial cells, whereas ml and m3 transcripts were identified in aortic smooth muscle. In contrast, cultured endothelial cells contained mRNA for only the m2 receptor subtype. Transcripts for the m4 or m5 receptors were not detected in either freshly isolated or cultured endothelial cells. Since ml and m3 receptor subtypes are coupled to phospholipase C, activation of which is required for EDRF release, these observations may explain the failure of muscarinic agonists to elicit a rise in [Ca2+]iand EDRF release from cultured endothelial cells.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We have recently shown that the porcine aorta releases immunoreactive endothelin-1 in a time-dependent way. Here, we examined the inhibition by atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) of endothelin-1 secretion after stimulation with angiotensin II (Ang II) by using porcine aorta. Ang II dose-dependently stimulated immunoreactive endothelin-1 secretion. Porcine ANP-(1–28) and porcine BNP-26 both inhibited such secretion in a dose-dependent way. The addition of a cyclic guanosine 5'-monophosphate (cGMP) analogue, 8-bromo-cGMP, reduced the immunoreactive endothelin-1 secretion after stimulation with Ang II. In cultured porcine endothelial cells the inhibition by porcine ANP-(1–28) and porcine BNP-26 of immunoreactive endothelin-1 secretion after stimulation with Ang II was paralleled by an increase in the cellular cGMP level. Rat ANP-(5–25) was weaker than porcine ANP-(1–28) in inhibiting immunoreactive endothelin-1 secretion and increasing cGMP in cultured cells. There was negative correlation between the percent decrease in immunoreactive endothelin-1 and the percent increase in cGMP. Neither porcine ANP-(1–28) nor BNP-26 affected the number or sensitivity of Ang II binding sites in cultured porcine endothelial cells. These results suggest that ANP and BNP inhibit endothelin-1 secretion after stimulation with Ang II, probably through a cGMP-dependent process.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Endothelium-dependent relaxations are inhibited during chronic vasospasm after subarachnoid hemorrhage in the canine basilar artery, although the luminal release of endothelium-derived relaxing factor (EDRF) is maintained. The present study investigated the mechanisms underlying the impaired vascular reactivity and in particular whether the loss of responsiveness of the smooth muscle to EDRF is due to an impaired production of cGMP. Bradykinin and nitric oxide evoked concentration-dependent relaxations in isolated canine basilar arteries with and without endothelium, respectively, which were reduced in the subarachnoid hemorrhage group. Relaxations evoked by M&B22,948 (an inhibitor of cGMP phosphodiesterases) were smaller, but those evoked by the lipophilic cGMP analogue 8-bromo-cGMP were potentiated slightly in the subarachnoid hemorrhage group. The resting levels of cGMP in rings with endothelium (reflecting the effect of spontaneous release of EDRF) and those evoked by bradykinin in rings with endothelium and by nitric oxide in rings without endothelium were diminished in the subarachnoid hemorrhage group. These data indicate that the altered endothelium-mediated relaxations of the smooth muscle after subarachnoid hemorrhage is due, at least in part, to an impaired activation of soluble guanylate cyclase leading to a reduced production of cGMP in the smooth muscle.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The characteristics of the hyperpolarization response to acetylcholine (ACh) in endothelial cells from the guinea pig coronary artery were studied by microelectrode recording technique. ACh (30 nM to 3 μM) induced membrane hyperpolarization in a dose-dependent manner. The sustenance of the response required the presence of external calcium. The hyperpolarization was not affected by nifedipine (1 μM) but was inhibited by the potassium channel blockers charybdotoxin (10 nM), tetraethylammonium (1 mM), and 4-aminopyridine (0.5 mM). Glibenclamide (10 μM) and apamin (1 μM) were not effective. The inhibitors of endothelium-derived relaxing factor/nitric oxide synthesis Nω-nitro L-arginine (50 μM) andNG-monomethyl l-arginine (30 μM) had no effect on the resting membrane potential or the ACh-induced responses. No hyperpolarization was observed with application of sodium nitroprusside (10 μM) or 8-bromo-cGMP (0.1 μM). Ouabain (10 μM) depolarized the membrane significantly by 5 mV, but the ACh hyperpolarization was not affected. Indomethacin (10 μM) was without effect on the resting membrane potential or the hyperpolarization to ACh. These results show that ACh-induced hyperpolarization is dependent on external calcium and can be inhibited by certain potassium channel blockers. The hyperpolarization response is not mediated by endothelium-derived relaxing factor/nitric oxide, cGMP, a cyclooxygenase product, or stimulation of the Na-K pump.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Extracellular superoxide dismutase type C (EC-SOD C) is a secretory SOD isoenzyme that, in vivo, is bound to heparan sulfate proteoglycans in the glycocalyx of various cell types (e.g., endothelial cells) and in the connective tissue matrix. The aim of this study was to investigate the efficacy of vascular bound EC-SOD C in protecting arterial relaxation mediated by endothelium-derived relaxing factor (EDRF) against the inhibitory effects of superoxide radicals. For comparison, the effect of CuZn SOD was also studied. This SOD isoenzyme lacks affinity toward heparan sulfate and does not bind to cell surfaces. Rings from rabbit aorta were mounted in an organ bath and acetylcholine-induced endothelium-dependent relaxation was then studied in preparations precontracted with phenylephrine. Pyrogallol (10−4M), used to generate superoxide radicals, reduced the maximal relaxant effect of acetylcholine from about 65% to 25%. When present in the buffer throughout the experiment, CuZn SOD and EC-SOD C caused a concentration-dependent prevention of the pyrogallol effect on EDRF-mediated relaxation, with a half-maximal effect at about 100 units/ml (KO2assay). In a second set of experiments, the arterial rings were preincubated with 8,000 units/ml CuZn SOD (50 μg/ml) or EC-SOD C (69 μg/ml) during 30 minutes, followed by washing, before the effect of pyrogallol on EDRF-mediated relaxation was studied in SOD-free buffer. The maximal relaxant effects of acetylcholine, expressed as the percent decrease in tension, were (mean±SEM,n=6) 61±4% (control), 22±4% (pyrogallol), 27±5% (pyrogallol+CuZn SOD), and 46±6% (pyrogallol+EC-SOD C;p<0.05 versus CuZn SOD+pyrogallol). The preincubation resulted in considerable binding of EC-SOD C to the arterial tissue, whereas negligible amounts of enzyme were present in the medium after the washing procedure. The protection by EC-SOD C was lost when the preincubation was performed in the presence of heparin (125 IU/mi), which prevents the binding of the enzyme to the arterial rings. In this case, the maximal relaxant effects of acetylcholine were (n=6) 60±4% (control), 21±4% (pyrogallol), 43±49% (pyrogallol+EC-SOD C), and 27±4% (pyrogallol+EC-SOD C+heparin;p<0.05 versus EC-SOD C+pyrogallol). It is concluded that EC-SOD C, associated with heparan sulfate proteoglycans on endothelial cell surfaces and internal structures in the aortic rings, protects against the detrimental effects of superoxide radicals on endothelium-dependent arterial relaxation.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The changes in the permeability properties of the rete capillaries of the eel in response to temperature shifts were studied during countercurrent perfusion at constant flow and pressure. Tracers and oxygen were added to the arterial perfusate. From the ratio of end concentrations of arterial to venous capillaries divided by surface area, calculated from rete weight, a value for the ratio of permeability to flow, P/F, with dimensions in centimeters−2was estimated. Because flow and surface area are constant, this provides an index of how permeability varies with time. A group of paracellular (albumin, sucrose, and sodium) and cellular (antipyrine, water, and oxygen) probes were used. When the temperature of the perfusate was raised abruptly from 25°C to 35°C, P/F values rose continuously and irreversibly from 0.042±0.009 to 0.281±0.112 cm−2(mean±SEM) for125I-albumin, from 0.082±0.006 to 1.74±0.070 cm−2for [14C]sucrose, and from 0.32±0.06 to 2.78±0.62 cm−2for22Na, whereas they were not modified for [14C]antipyrine, [3H]water, and 02. Gradual increase of temperature was accompanied by a smaller rise in sucrose and sodium permeability and no change in albumin permeability., with decrease, the change was reversible. When the temperature was lowered abruptly from 25°C to 5°C, the P/F ratio for sucrose, sodium, and oxygen did not change, while that for [3H]water and [14C]antipyrine decreased to plateau values, from 13.0±3.2 to 9.6±2.6 and from 7.9±2.2 to 4.4±0.4 cm−2, respectively, simultaneously, P/F values for125I-albumin increased from 0.030±0.007 to 0.063±0.012 cm−2Thus, increase in rete temperature primarily increases paraceilular permeation, whereas decrease in temperature primarily decreases permeability to [14C]antipyrine and [3H]water cellular probes. Oxygen is unaffected throughout.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The effects of sea anemone toxin ATXII on single sodium channels were studied in cell-attached patches on rabbit ventricular myocytes at 20–22°C. Exposure of patches to 1,000 nM ATXII induced long-lasting bursts of openings, which were more dramatically different from control at −20 mV than at −50 mV. Mean open duration, which had a biphasic dependence on voltage in control patches, was monotonically dependent on voltage in toxin-exposed patches, being 3.5 times longer than control at −20 mV and 4.5 times longer at −10 mV. Multiple mean open durations were detected at depolarized potentials. To test whether the multiple mean open durations resulted from a mixture of modified and unmodified openings, histograms of late openings (when unmodified channels would be inactivated) were constructed. Because in most cases these fit a single exponential with a mean open duration like that of modified channels, we conclude that voltage-dependent toxin unbinding produced a mixed population of unmodified and modified openings. Consistent with this hypothesis, lower concentrations of toxin most often produced open-duration histograms best fit with two exponentials. Ensembles revealed complex decay kinetics, which could be interpreted within the context of the toxin-induced increase in mean open duration and burst duration and the summation of modified and unmodified events. Analysis of the numbers of early versus late events at −20 mV for patches exposed to 20 nM, 100 nM, and 1,000 nM ATXII predicted the ED50for ATXII block to be 285 nM at this potential. Using a five-state Markovian model, the action of ATXII could be explained as a reduction of the open-to-inactivated rate constant without effect on inactivation from closed states or other rate transitions.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

We studied changes in myofibrillar function and protein profiles after complete global ischemia with anoxia in rat hearts. Hearts were exposed to global ischemia and anoxia (CGI) for 30 or 60 minutes at 37°C, and myofibrils were prepared for measurement of Ca2+-dependent Mg2+-ATPase activity at pH 7.0 and 6.5. Hearts incubated in cold saline (1±1°C) and nonincubated hearts served as controls. Maximum ATPase activity was unchanged at pH 7.0 and pH 6.5 in myofibrils from hearts treated with 30 or 60 minutes of CGI. At pH 7.0, the Hill coefficient, which is an index of cooperative interactions among thin-filament proteins, was unchanged after 30 minutes of CGI but was significantly increased after 60 minutes of CGI. A similar trend for increased cooperativity was observed when myofibrillar ATPase activity was measured at pH 6.5 in myofibrils from rat hearts made ischemic for 30 or 60 minutes. Both 30 and 60 minutes of CGI resulted in increased pCa50values (half-maximally activating free [Ca2+]) at pH 7.0 and pH 6.5. Densitometric analysis of myofibrillar proteins separated with sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that troponin I and troponin T were degraded during 60 minutes of CGI. Two new protein bands appearing in ischemia-treated myofibrils were identified as partially degraded troponin I and troponin T with Western blots. The troponin I fragment could be phosphorylated by cAMP-dependent protein kinase. In addition, we observed phosphorylation of a protein band that corresponded to myosin light chain-2 in myofibrils from CGI-treated hearts. These results suggest that degradation of thin-filament proteins may contribute to the changes in cooperativity of Ca2+regulation of ATPase activity observed in the myofibrils from rat hearts exposed to CGI.

ISSN:0009-7330    

出版商:OVID    

年代:1992

数据来源: OVID