Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Vascular Capacitance”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46Linked to original sources

Acute effects of intravenous phosphodiesterase inhibition in chronic heart failure: simultaneous pre- and afterload reduction with a single agent.

Intravenous phosphodiesterase inhibition with milrinone is known to have a beneficial effect on haemodynamics in chronic heart failure. Its effect on lower limb capacitance vessels has not been previously investigated. We have studied the effect of intravenous milrinone in 10 patients with severe chronic heart failure. Thirty minutes after commencement of treatment mean cardiac index had risen by 26% and pulmonary artery wedge pressure, systemic vascular resistance and right atrial pressure had fallen by 51, 24 and 89%, respectively (p less than 0.05 for all changes). These changes were maintained for the 2 h observation period with no evidence of tolerance and were accompanied by a 17% increase in venous volume (p less than 0.01) and a 42% increase in ejection fraction (p less than 0.001) at 30 min; at 120 min the improvement in ejection fraction had been maintained and a further increase in venous volume to 38% above baseline was evident. The increase in venous volume was strongly correlated with the decrease in mean pulmonary artery wedge pressure and mean right atrial pressure at 30 min and 2 h (r = -0.80 and -0.69 for mean pulmonary artery wedge pressure, r = -0.88 and -0.56 for mean right atrial pressure). Milrinone therefore has clinically important venodilating properties, in addition to its known effects as an arterial vasodilator and a positive inotrope.

Aged↗

Neuropeptide Y-induced potentiation of noradrenergic vasoconstriction in the human saphenous vein: involvement of endothelium generated thromboxane.

1. We investigated the potentiating effect of low concentrations of neuropeptide Y (NPY) on the vasoconstriction induced by transmural nerve stimulation (TNS) and noradrenaline (NA) in human saphenous veins. The effects of (i) endothelium removal; (ii) the addition of the NO pathway precursor L-arginine; (iii) the ET(A)/ET(B) endothelin receptor antagonist Ro 47-0203; (iv) the cyclo-oxygenase inhibitor, indomethacin; (v) the selective thromboxane A2 (TxA2) receptor antagonists Bay u3405 and ifetroban, and (vi) the TxA2 synthase inhibitor, UK 38485, were studied in order to gain information about the mechanisms of NPY-induced potentiation. 2. Contractile response curves for TNS (0.5-8 Hz) and for exogenously administered NA (0.1-3 microM) were obtained in superfused saphenous vein rings. The contractions induced by both TNS and NA at all tested frequencies and concentrations, respectively, were significantly potentiated by 50 nM NPY in endothelium intact veins. Conversely, in endothelium-denuded vessel rings the contractile-response curves to TNS and NA overlapped both in the absence and presence of NPY, thus suggesting that a release of vasoactive substances from endothelial cells could account for the noradrenergic NPY-induced potentiation. 3. In vessels with intact endothelium, the potentiating action of NPY on TNS and NA was unaffected by the presence of high concentrations of the NO precursor L-arginine (3-10 mM) or the non-selective ET(A)/ET(B) endothelin receptor antagonist, Ro 47-0203 (10 microM). These data indicate that the NPY-induced effect does not involve either the endothelium-derived vasodilator nitric oxide or the vasoconstrictor endothelin. Conversely, in the presence of the cyclo-oxygenase inhibitor, indomethacin (30 microM), NPY failed to potentiate the vasoconstrictions produced by either nerve stimulation or by exogenous NA, thus providing evidence that arachidonic acid metabolites through the cyclo-oxygenase pathway are mainly responsible for the potentiation evoked by NPY. 4. When the TxA2 receptor antagonists, Bay u 3405 (1 microM) and ifetroban (1 microM) were added to the superfusing medium, NPY did not alter either the frequency- or the concentration-response curves for either TNS or NA. Accordingly, both TNS- and NA-induced contractions were not potentiated by NPY in the presence of the TxA2 synthase inhibitor, UK 38485 (10 microM). This clearly demonstrates the pivotal role of TxA2 in NPY-induced potentiation. 5. In superfused vein rings with endothelium, a subthreshold concentration (0.2 nM) of the TxA2 mimetic U 46619 potentiated both TNS- and NA-induced vasoconstrictions. This potentiation was higher at low stimulation frequencies and low NA concentrations, and resembled that produced by NPY. 6. Our results indicate that in the human saphenous vein NPY potentiates the contractions produced by sympathetic nerve stimulation acting at the postjunctional level, primarily on endothelial cells. In particular, the NPY-induced release of a cyclo-oxygenase metabolite, namely TxA2, may have a synergistic effect on the vasoconstriction induced by the noradrenergic mediator. Thus, such a mechanism may play a key role in the maintenance of the sympathetic tone of large human capacitance vessels.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

Implications of changes in amplitude and contour of the mercury strain gauge plethysmograph pulse tracing.

Alterations in the mercury strain gauge plethysmograph pulse tracing have been previously thought to denote changes in venous tone. This study was designed to define the implications of changes in amplitude and contour of pulse tracing. Seven normal subjects were studied. After control measurements, amyl nitrite was administered and the pulse tracing was recorded. When the haemodynamic state had returned to control levels 0.4 mg sublingual glyceryl trinitrate (GTN) was given. The amplitude of the plethysmograph pulse tracing (Y mm) and the vertical distance from the dicrotic notch to the peak of the pulse tracing (X mm) were measured. With amyl nitrite, the amplitude of the pulse tracing (Y) decreased from 10.4 +/- 1 to 4.5 +/- 0.6 mm (mean +/- SEM), while the X/Y ratio increased from 0.7 +/- 0.02 to 0.98 +/- 0.02 (P less than 0.005). After GTN Y increased from 9.3 +/- 0.8 to 31 +/- 4.8 mm (P less than 0.005) and X/Y ratio increased from 0.7 +/- 0.06 to 0.99 +/- 0.01 (P less than 0.005). Since it is known that amyl nitrite produces venoconstriction and arteriolar dilatation, and GTN causes venous and arteriolar dilatation, we conclude that an increase in Y reflects venous dilatation, and an increase in X/Y ratio, that is a fall in the dicrotic notch, denotes arteriolar dilatation. Thus, the plethysmograph pulse tracing can be used to assess the effects of drugs on the capacitance and resistance beds.

Adult↗

Compartment analysis of vascular effects of neuropeptides and capsaicin in the pig nasal mucosa.

The vascular effects of local infusion of capsaicin, substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) were monitored in an experimental model on the pig nasal mucosa. Arterial, venous and superficial mucosal blood flow (laser-Doppler flowmetry) as well as mucosal volume, reflecting changes in capacitance vessels were studied in parallel. All substances induced concentration dependent increases in the parameters studied with the exception of the decrease in the superficial mucosal flow induced by vasoactive intestinal polypeptide. This latter finding was interpreted as a stealing phenomenon and suggests that vasoactive intestinal polypeptide mainly exerts its vasodilatory effect in the deeper glandular layers of the nasal mucosa. The vasodilatory effect of capsaicin, except the laser-Doppler signal, was markedly reduced by pretreatment with a combination of the ganglionic blocking agent chlorisondamine and atropine implying that capsaicin evokes a central reflex with a final parasympathetic pathway and release of agents like vasoactive intestinal polypeptide. The remaining capsaicin response may depend on a local effect with axon reflexes and the release of sensory neuropeptides with actions on superficial mucosal blood flow.

Animals↗

Influence of cellular incorporation of n-3 eicosapentaenoic acid on intracellular Ca2+ concentration and membrane potential in vascular smooth muscle cells.

Long-term treatment with n-3 eicosapentaenoic acid (EPA) has been shown to exert hypotensive effects and have beneficial effects on atherosclerosis. To elucidate one of the underlying mechanisms of these effects, intracellular calcium concentration [Ca2+]i, and resting membrane potential were measured in rat vascular smooth muscle cells (A7r5 cell) treated with EPA, using Ca2+-sensitive dye fura-2 AM and the patch clamp technique. The alterations in fatty acid compositions of phospholipids and cell migration after treatment with EPA (30 microM) for 6 h-7 days were also examined. After treating cells with EPA, the EPA and DPA (docosapentaenoic acid) content of the phospholipid fraction (mol.%) increased in a time-dependent manner. Alternatively, arachidonic acid (AA) decreased, and then the ratio of EPA and AA (EPA/AA) increased significantly. The resting [Ca2+]i decreased from 170 +/- 46 nM (n = 16) in control cells to 123 +/- 29 nM (n = 16) in cells treated with EPA (30 microM) for 7 days. Vasopressin (100 nM), endothelin-1 (100 nM) and platelet-derived growth factor (PDGF 5 ng/ml) evoked an initial peak of [Ca2+]i, followed by a smaller sustained rise of [Ca2+]i in the presence of extracellular Ca2+. In EPA-treated cells, both the peak and the sustained rise of [Ca2+]i induced by these agonists decreased in comparison to the control cells. EPA treatment also decreased the transient [Ca2+]i rise evoked by these agonists in the absence of extracellular Ca2+. Under the current clamp condition, resting membrane potential was significantly higher in EPA-treated cells (-49.8 +/- 10.4 mV, n = 41) than in control cells (-44.6 +/- 7.4 mV, n = 41, P < 0.05), and the input resistance of the cell was lower in EPA-treated cells, while cell size and capacitance were not statistically different. In addition, long-term treatment with EPA for 7 days significantly inhibited PDGF-induced cell migration. These results suggest that cellular incorporation of n-3 eicosapentaenoic acid attenuates intracellular mechanisms related to changes of [Ca2+]i and affects membrane potential, thereby inhibiting migration of vascular smooth muscle cells. These actions of EPA may contribute to its vasorelaxant and antiatherosclerotic effects.

Animals↗

Potassium channel-mediated hyperpolarization of mesenteric vascular smooth muscle by isoflurane.

BACKGROUND: A primary source of calcium (Ca2+) necessary for excitation contraction in vascular smooth muscle (VSM) is influx via voltage-dependent Ca2+ channels. Thus, force generation in VSM is coupled closely to resting transmembrane potential, which itself is primarily a function of potassium conductance. Previously, the authors reported that volatile anesthetics hyperpolarize VSM of small mesenteric resistance arteries and capacitance veins. The current study was designed to determine whether isoflurane-mediated hyperpolarization is the result of specific effects on one or more of four types of potassium channels known to exist in VSM. METHODS: Transmembrane potentials (Em) were recorded from in situ mesenteric capacitance and resistance vessels in Sprague-Dawley rats weighing 250-300 g. In separate experiments, selective inhibitors of each of four types of potassium channels known to exist in VSM were administered in the superfusate of the vessel preparations to assess their effects on isoflurane-mediated hyperpolarization. RESULTS: Resting VSM Em ranged from -38 to -43 mV after local sympathetic denervation. Isoflurane produced a significant hyperpolarization (2.7-4.3 mV), whereas each potassium channel inhibitor significantly depolarized (2.8-8.5 mV) the VSM. Both 100 nM iberiotoxin (inhibitor of high conductance calcium-activated potassium channels) and 1 microM glybenclamide (inhibitor of adenosine triphosphatase-sensitive potassium channels) significantly inhibited VSM hyperpolarization induced by 1 MAC (minimum alveolar concentration) levels of inhaled isoflurane (0.1-0.9 mV Em change, which was not significant). In contrast, isoflurane hyperpolarized the VSM significantly despite the presence of 3 mM 4 aminopyridine (inhibitor of voltage-dependent potassium channels) or 10 microM barium chloride (an inhibitor of inward rectifier potassium channels) (3.7-8.2 mV change in VSM Em). CONCLUSIONS: These results suggest that isoflurane-mediated hyperpolarization (and associated relaxation) of VSM can be attributed in part to an enhanced (or maintained) opening of calcium-activated and adenosine triphosphate-sensitive potassium channels but not voltage-dependent or inward rectifier potassium channels.

Anesthetics, Inhalation↗

Failure of reflex venoconstriction during exercise in patients with vasovagal syncope.

BACKGROUND: In this study, we tested two hypotheses. First, we tested the hypothesis that reflex constriction of the venous capacitance beds in patients with vasovagal syncope is impaired during both subhypotensive lower-body negative pressure. Second, we proposed that splenic venoconstriction may be impaired during exercise in patients with vasovagal syncope. METHODS AND RESULTS: We evaluated 25 patients with vasovagal syncope (age, 45.0 +/- 15.9 years; 12 men, 13 women) and 24 control subjects (age, 41.3 +/- 13.7 years; 16 men, 8 women). A nuclear technique was used to assess changes in forearm venous tone during lower-body negative pressure and in splenic venous volume during cycle exercise. Changes in forearm vascular resistance (FVR) during cycle exercise were assessed with a strain-gauge plethysmography technique. The percentage reduction in unstressed forearm vascular volume during lower-body negative pressure was similar in patients and control subjects (9.0 +/- 8.0% versus 9.7 +/- 5.9%, P=NS). During exercise, splenic venous volume decreased less in patients than in control subjects (15.8 +/- 21.7% versus 42.6 +/- 12.6%, P < .0001). FVR decreased by 2 +/- 32% in patients but increased 108 +/- 90% in control subjects (P < .0001). There was no relation between percentage change in splenic volume and percentage change in FVR during exercise in either patients or control subjects (r= -.06, P=NS and r= -.18, P=NS, respectively). CONCLUSIONS: Patients with vasovagal syncope exhibit a failure of the normal increase in tone in the splenic capacitance bed and in forearm resistance vessels during dynamic exercise. Forearm venous tone increases normally during lower-body negative pressure.

Adult↗

Failure of the sulfhydryl donor N-acetylcysteine (NAC) to reverse nitrate tolerance in large epicardial arteries and the venous capacitance system of the dog.

NAC has been thought to reverse nitrate tolerance by replenishing depleted intracellular sulfhydryl groups, however data on interactions between N-acetylcysteine and nitrates in patients with stable angina are controversial and disappointing. Therefore, we studied the effect of NAC on nitrate responsiveness of epicardial arteries and of the venous system (assessed as changes in effective vascular compliance) in dogs (n = 12) during long-term nitroglycerine (GTN)-treatment (1.5 micrograms/kg/min for 5 to 6 days). In dogs with GTN-specific tolerance (shift of venous or epicardial artery dilation with 15- to 17-fold higher dosages), NAC (100 mg/kg i.v.) had no dilator effect and did not alter the dose response relations of nitroglycerin. However, in nontolerant dogs (n = 7) NAC augmented (1.5- to 2-fold) the reduction of peripheral vascular resistance induced by 0.5-1.5 microgram/kg/min GTN. In vitro, the augmentation of purified guanylate cyclase activity by GTN (100 microM) was potentiated by NAC (0.01-1.0 mM) in saline or in canine plasma, whereas NAC alone was ineffective. Therefore, NAC does not restore GTN-responsiveness in epicardial arteries or veins in vivo and a small, tolerance-independent augmentation of GTN-induced dilation may result from NAC-induced extracellular formation of a stimulant of guanylate cyclase from GTN.

Acetylcysteine↗

Sodium sensitivity in human subjects. Hemodynamic and hormonal correlates.

To investigate factors associated with sodium sensitivity, 157 subjects were studied while receiving 10 and 200 mEq sodium diets. Measurements included blood pressure (BP), forearm vascular resistance, plasma renin activity (PRA), and plasma aldosterone. Sodium repletion was associated with a greater than 5% increase in mean BP in 16% of the normotensive subjects and 29% of the borderline hypertensive subjects. Sodium-sensitive subjects were compared with sodium-resistant subjects in both the normotensive (n = 92) and borderline hypertensive (n = 65) groups. Forearm vascular resistance was significantly higher (p less than 0.05) during sodium loading in the sodium-sensitive subgroups of both the normotensive and borderline hypertensive groups (35.8 +/- 29 vs 23.8 +/- 20 [SD] and 37.5 +/- 29 vs 22.5 +/- 14 mm Hg/ml/min/100 g, respectively. Venous capacitance was lower in the sodium-sensitive than in the sodium-resistant borderline hypertensive subjects (0.8 +/- 0.21 vs 1.69 +/- 0.24 ml/100 g). During sodium restriction, PRA was significantly lower (p less than 0.01) in the sodium-sensitive subsets (2.56 +/- 1.6 vs 4.04 +/- 2.6; 2.65 +/- 2.1 vs 3.88 +/- 2.6 ng angiotensin I/ml/hr). Aldosterone was lower (p less than 0.01) during sodium depletion in the sodium-sensitive subsets (17.3 +/- 12 vs 26.3 +/- 16; 18.5 +/- 18 vs 27.9 +/- 17 ng/ml). A significant inverse correlation existed between change in BP with sodium repletion and change in PRA or level of PRA during sodium depletion (p less than 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Extracellular ATP increases [Ca2+]i in primarily cultured pig coronary smooth muscle cells via a P2Y purinoceptor subtype.

In primarily cultured pig coronary smooth muscle cells, extracellular adenosine triphosphate (ATP; 10(-9) to 10(-3) M) dose-dependently increases intracellular calcium ([Ca2+]i). The [Ca2+]i transients measured by fura-2 fluorescence consist of peak and plateau phases with [Ca2+]i values of 191.84 +/- 5.67 nM (n = 10) and 91.67 +/- 1.89 nM, respectively. In Ca(2+)-free solution, the peak phases persisted, but there was a loss of the plateau response, indicating an initial ATP-stimulated intracellular Ca2+ release and a subsequent transarcolemmal Ca2+ entry. Various agonists have been used to characterize the P2 purinoceptor subtype involved in the ATP-induced Ca2+ transients. The rank order of potency was uridine triphosphate (UTP) > ATP >> 2-meSATP > beta,gamma-meATP = alpha,beta-meATP = adenosine = 0. To examine the refilling of ATP-sensitive stores, four repetitive 60-s ATP responses were produced throughout with a 5-min recovery period in between. Now the ATP peaks gradually declined in Ca(2+)-free solution, indicating the emptying of the stores. If, however, Ca2+ entry was allowed in the "refilling period" (i.e., between the ATP pulses), the Ca2+ peaks could be maintained or restored, respectively. The data suggest that the ATP-dependent [Ca2+]i transients may be mediated via a UTP > ATP-activated P2Y purinoceptor subtype, mediating both an intracellular Ca2+ release and a transarcolemmal Ca2+ influx. The refilling of Ca2+ stores may occur through the unstimulated membrane after agonist stimulation. A putative pathway may be a "capacitative" Ca2+ entry induced on depletion of intracellular Ca2+ stores.

Adenosine↗

NO upregulation of a cyclic nucleotide-gated channel contributes to calcium elevation in endothelial cells.

We investigated whether nitric oxide (NO) upregulates a cyclic nucleotide-gated (CNG) channel and whether this contributes to sustained elevation of intracellular calcium levels ([Ca(2+)](i)) in porcine pulmonary artery endothelial cells (PAEC). Exposure of PAEC to an NO donor, NOC-18 (1 mM), for 18 h increased the protein and mRNA levels of CNGA2 40 and 50%, respectively (P < 0.05). [Ca(2+)](i) in NO-treated cells was increased 50%, and this increase was maintained for up to 12 h after removal of NOC-18 from medium. Extracellular calcium is required for the increase in [Ca(2+)](i) in NO-treated cells. Thapsigargin induced a rapid cytosolic calcium rise, whereas both a CNG and a nonselective cation channel blocker caused a faster decline in [Ca(2+)](i), suggesting that capacitive calcium entry contributes to the elevated calcium levels. Antisense inhibition of CNGA2 expression attenuated the NO-induced increases in CNGA2 expression and [Ca(2+)](i) and in capacitive calcium entry. Our results demonstrate that exogenous NO upregulates CNGA2 expression and that this is associated with elevated [Ca(2+)](i) and capacitive calcium entry in porcine PAEC.

Animals↗

Impaired NO-dependent inhibition of store- and receptor-operated calcium entry in pulmonary vascular smooth muscle after chronic hypoxia.

We have recently demonstrated that chronic hypoxia (CH) attenuates nitric oxide (NO)-mediated decreases in pulmonary vascular smooth muscle (VSM) intracellular free calcium concentration ([Ca2+]i) and promotes NO-dependent VSM Ca2+ desensitization. The objective of the current study was to identify potential mechanisms by which CH interferes with regulation of [Ca2+]i by NO. We hypothesized that CH impairs NO-mediated inhibition of store-operated (capacitative) Ca2+ entry (SOCE) or receptor-operated Ca2+ entry (ROCE) in pulmonary VSM. To test this hypothesis, we examined effects of the NO donor, spermine NONOate, on SOCE resulting from depletion of intracellular Ca2+ stores with cyclopiazonic acid, and on UTP-induced ROCE in isolated, endothelium-denuded, pressurized pulmonary arteries (213 +/- 8 microm inner diameter) from control and CH (4 wk at 0.5 atm) rats. Arteries were loaded with fura-2 AM to continuously monitor VSM [Ca2+]i. We found that the change in [Ca2+]i associated with SOCE and ROCE was significantly reduced in vessels from CH animals. Furthermore, spermine NONOate diminished SOCE and ROCE in vessels from control, but not CH animals. We conclude that NO-mediated inhibition of SOCE and ROCE is impaired after CH-induced pulmonary hypertension.

Animals↗

Mechanism for decrease in cardiac output with atrial natriuretic peptide in dogs.

To examine the mechanism by which atrial natriuretic peptide (ANP) decreases cardiac output, we studied changes in the heart, peripheral circulation, and blood flow distribution in eight dogs. ANP was given as a bolus (3.0 micrograms/kg) followed by an infusion of 0.3 microgram.kg-1.min-1. ANP did not change heart rate, total peripheral vascular resistance, and the first derivative of left ventricular pressure but decreased mean aortic pressure from 91 +/- 4 to 76 +/- 3 mmHg (P less than 0.001) and cardiac output from 153 +/- 15 to 130 +/- 9 ml.kg-1.min-1 (P less than 0.02). Right atrial pressure and left ventricular end-diastolic pressure also decreased. Mean circulatory filling pressure decreased from 7.1 +/- 0.3 to 6.0 +/- 0.3 mmHg (P less than 0.001), but venous compliance and unstressed vascular volume did not change. Resistance to venous return increased from 0.056 +/- 0.008 to 0.063 +/- 0.010 mmHg.ml-1.kg.min (P less than 0.05). Arterial compliance increased from 0.060 +/- 0.003 to 0.072 +/- 0.004 ml.mmHg-1.kg-1 (P less than 0.02). Total blood volume and central blood volume decreased from 82.2 +/- 3.1 to 76.2 +/- 4.6 and from 19.8 +/- 0.8 to 17.6 +/- 0.6 ml/kg (P less than 0.02), respectively. Blood flow increased to the kidneys. We conclude that ANP decreases cardiac output by decreasing total blood volume. This results in a lower operating pressure and volume in the venous capacitance system with no significant venodilating effects. Cardiac factors and a redistribution of flow to the splanchnic organs are not important mechanisms to explain the decrease in cardiac output with ANP.

Animals↗

Basic fibroblast growth factor regulates ionic currents and excitability of fetal rat carotid body chemoreceptors.

Basic fibroblast growth factor (bFGF) and nerve growth factor (NGF) are known mitogens and/or differentiation factors for cells of the sympathoadrenal lineage. Though carotid body (CB) chemoreceptors (type 1 cells) are considered part of this lineage, their response to bFGF is unknown and so far they appear unresponsive to NGF in vitro. In this study we use whole-cell recording to investigate whether bFGF (and NGF) can influence the development of ionic currents in these chemoreceptors, cultured from fetal (E18-19) rat pups. bFGF (10ng/ml) significantly augmented both transient inward Na+ and outward K+ currents in type 1 cells after only 2 days of treatment; after normalizing for the accompanying increase in cell size, as indicated by whole-cell capacitance, the Na+ current density was nonetheless increased by bFGF. Unlike controls, bFGF-treated type 1 cells readily fired action potentials following depolarization. These effects were not mimicked by NGF (100 ng/ml) treatment. Since the carotid body is one of the most richly vascularized organs and bFGF is a potent angiogenic factor, it is conceivable that variations in local bFGF concentrations during fetal development may contribute to the known species differences in CB chemoreceptor excitability.

Animals↗