Alteration of endothelium-dependent hyperpolarizations in porcine coronary arteries with regenerated endothelium.
(17/8105)
The present study was designed to test the ability of regenerated endothelium to evoke endothelium-dependent hyperpolarizations. Hyperpolarizations induced by serotonin and bradykinin were compared in isolated porcine coronary arteries with native or regenerated endothelium, 4 weeks after balloon endothelial denudation. The experiments were performed in the presence of inhibitors of nitric oxide synthase (Nomega-nitro-L-arginine) and cyclooxygenase (indomethacin). The transmembrane potential was measured using conventional glass microelectrodes. Smooth muscle cells from coronary arteries with regenerated endothelium were depolarized in comparison with control coronary arteries from the same hearts. Spontaneous membrane potential oscillations of small amplitude or spikes were observed in some of these arteries but never in arteries with native endothelium. In coronary arteries from control pigs, both serotonin and bradykinin induced concentration-dependent hyperpolarizations. In the presence of ketanserin, 10 micromol/L serotonin induced a transient hyperpolarization in control coronary arteries. Four weeks after balloon denudation, the response to serotonin was normal in arteries with native endothelium, but the hyperpolarization was significantly lower in coronary arteries with regenerated endothelium. In control arteries, the endothelium-dependent hyperpolarization obtained with bradykinin (30 nmol/L) was reproducible. Four weeks after balloon denudation, comparable hyperpolarizations were obtained in coronary arteries with native endothelium. By contrast, in arteries with regenerated endothelium, the hyperpolarization to bradykinin became voltage-dependent. In the most depolarized cells, the hyperpolarization to bradykinin was augmented. The changes in resting membrane potential and the alteration in endothelium-dependent hyperpolarizations observed in the coronary arteries with regenerated endothelium may contribute to the reduced response to serotonin and the unchanged relaxation to bradykinin described previously. (+info)
5-HT2B-receptor antagonist LY-272015 is antihypertensive in DOCA-salt-hypertensive rats.
(18/8105)
We previously demonstrated a change in the receptors mediating 5-hydroxytryptamine (5-HT)-induced contraction in arteries of deoxycorticosterone acetate (DOCA)-salt-hypertensive rats. Specifically, contraction to 5-HT is mediated primarily by 5-HT2A receptors in arteries from normotensive sham rats and by both 5-HT2A and 5-HT2B receptors in arteries from hypertensive rats. We hypothesized that the 5-HT2B receptor may play a role in maintaining the high blood pressure of DOCA-salt-hypertensive rats, and herein we provide data connecting in vitro and in vivo findings. The endothelium-denuded isolated superior mesenteric artery of DOCA-salt rats displayed a marked increase in maximum contraction to the newly available 5-HT2B-receptor agonist BW-723C86 compared with that of arteries from sham rats, confirming that the 5-HT2B receptor plays a greater role in 5-HT-induced contraction in arteries from DOCA-salt rats. In chronically instrumented rats, the 5-HT2B-receptor antagonist LY-272015 (0.3, 1.0, and 3.0 mg/kg iv at 30-min intervals) was given cumulatively 1 time/wk during 4 wk of continued DOCA-salt treatment. LY-272015 did not reduce blood pressure of the sham-treated rats at any time or dose. However, LY-272015 (1.0 and 3. 0 mg/kg) significantly reduced mean blood pressure in a subgroup of week 3 (-20 mmHg) and week 4 DOCA-salt (-40 mmHg) rats that had extremely high blood pressure (mean arterial blood pressure approximately 200 mmHg). Blockade of 5-HT2B receptors by in vivo administration of LY-272015 (3.0 mg/kg) was verified by observing reduced 5-HT-induced contraction in rat stomach fundus, the tissue from which the 5-HT2B receptor was originally cloned. These data support the novel hypothesis that 5-HT2B-receptor expression is induced during the development of DOCA-salt hypertension and contributes to the maintenance of severe blood pressure elevations. (+info)
Mediators of anaphylaxis but not activated neutrophils augment cholinergic responses of equine small airways.
(19/8105)
Neutrophilic inflammation in small airways (SA) and bronchospasm mediated via muscarinic receptors are features of chronic obstructive pulmonary disease in horses (COPD). Histamine, serotonin, and leukotrienes (LTs) are reported to be involved in the exacerbation of COPD, and currently, histamine has been shown to increase tension response to electrical field simulation (EFS) in equine SA. We tested the effects of these mediators and the effects of activated neutrophils on the cholinergic responses in SA. Histamine, serotonin, and LTD4 had a synergistic effect on EFS responses and only an additive effect on the tension response to exogenous ACh or methacholine. Atropine and TTX entirely eliminated the EFS-induced tension response in the presence of all three inflammatory mediators, indicating that augmentation of the EFS response applies only to the endogenous cholinergic response. Neutrophils isolated from control and COPD-affected horses were activated by zymosan, producing 18.1 +/- 2.3 and 25.0 +/- 2.3 nmol superoxide. 10(6) cells-1. 30 min-1, respectively. However, in contrast to the profound effect of mediators, incubation of SA for over 1 h in a suspension of up to 30 x 10(6) zymosan-treated neutrophils/ml did not significantly affect EFS responses of SA isolated from either control or COPD-affected horses. We conclude that in equine SA 1) the endogenous cholinergic responses are subject to strong facilitation by inflammatory mediators; 2) activated neutrophils do not affect cholinergic responses in SA; and 3) in acute bouts of equine COPD, histamine, LTD4, and serotonin (mediators primarily associated with type I allergic reaction) rather than mediators derived from neutrophils most likely contribute to increased cholinergic airway tone. (+info)
Heat shock protein expression in umbilical artery smooth muscle.
(20/8105)
Postpartum vasospasm in the umbilical arteries may be due to impaired vasorelaxation secondary to alterations in the expression of heat shock proteins. The contractile responses of pre- and full-term bovine umbilical artery smooth muscles were determined in a muscle bath. Heat shock protein expression was determined in bovine and human arterial tissues using western blotting with specific antisera. Full-term bovine and human umbilical artery smooth muscle was refractory to relaxation induced by the nitric oxide donor, sodium nitroprusside. This impaired vasorelaxation was associated with the expression of the inducible form of the heat shock protein, HSP70i, and increases in the expression of the small heat shock protein, HSP27. Small heat shock proteins have been implicated in modulating contraction and relaxation responses in vascular smooth muscles. Thus, alterations in heat shock protein expression may play a role in umbilical artery vasospasm. (+info)
Inhibitory effects of copper-aspirin complex on platelet aggregation.
(21/8105)
AIM: To study the inhibitory effects of copper-aspirin complex (CuAsp) on platelet aggregation. METHODS: With adenosine diphosphate the effects of CuAsp on platelet aggregation in vitro or in vivo were investigated. Radioimmunoassay and fluorophotometry were used to measure thromboxane B2 (TXB2) generation from platelets, the levels of TXB2 and of 6-keto-PGF1 alpha in plasma and the platelet serotonin release reaction. RESULTS: In vitro, CuAsp inhibited arachidonic acid (AA)-induced aggregation (IC50 = 17 mumol.L-1, 95% confidence limits: 9-33 mumol.L-1), the release of 5-HT (IC50 = 19 mumol.L-1, 95% confidence limits: 10-30 mumol.L-1), and TXB2 generation from platelets (P < 0.05). CuAsp 10 mg.kg-1 i.g. selectively inhibited AA-induced aggregation, and increased the 6-keto-PGF1 alpha concentration in plasma while decreased that of TXB2. CONCLUSION: CuAsp, in vitro or in vivo, shows more potent inhibitory effects on AA-induced aggregation than aspirin (Asp), related to the inhibition of platelet cyclooxygenase and the release of active substances from platelets. (+info)
Nongenomic steroidal modulation of high-affinity serotonin transport.
(22/8105)
The ability of steroids to modulate high-affinity 5-HT transport was investigated using cell-based models which stably manifest all known properties of this transport system. beta-Estradiol (E2) exhibited noncompetitive, and possibly allosteric, inhibition of both radiolabeled serotonin ([3H]5-HT) transport by, and radiolabeled cocaine congener ([3H]CFT) binding to, this system. Such inhibitory effects were observed within short time courses and unlikely to result from genomic effects normally ascribed to estrogen action. Rather, such nongenomic effects on 5-HT uptake were more akin to modulatory effects of select steroid metabolites on other plasma membrane systems such as neurotransmitter receptors and ionic channels. Beyond E2, preliminary examination of other steroid metabolites and synthetic steroid receptor agonists/antagonists revealed that inhibition of 5-HT transport is additionally attributable only to estriol (E3, an E2 metabolite) and tamoxifen (a nonsteroidal, E2 receptor antagonist). These findings indicate that the present form of transport modulation is only rendered by select compounds and not a general property of steroidal and related agents. Assessments of covalent conjugates of E2 suggested that E2 interacts with the transporter protein at allosteric site(s) inaccessible from the extracellular domain. These findings collectively suggest that steroid-mediated regulation of 5-HT transport may be a physiologically relevant mechanism, and that antidepressant as well as psychostimulant effects in vivo may contain a steroidal component. (+info)
High concentration of glucose decreases glucose transporter-1 expression in mouse placenta in vitro and in vivo.
(23/8105)
Facilitative glucose transporter-1 (GLUT1) is expressed abundantly and has an important role in glucose transfer in placentas. However, little is known about the regulation of GLUT1 expression in placental cells. We studied the changes in placental GLUT1 levels in relation to changes in glucose concentration in vitro and in vivo. In in vitro experiments, dispersed mouse placental cells were incubated under control (5.5 mM) and moderately high (22 mM) glucose concentrations, and 2-deoxyglucose uptake into cells was studied on days 1-5 of culture. After 4 days of incubation under both conditions, GLUT1 mRNA and proten levels were examined by Northern and immunoblot analyses. Treatment of cells with 22 mM glucose resulted in a significant decrease in 2-deoxyglucose uptake compared with control, from day 2 to day 5 of culture. Moreover, GLUT1 mRNA and protein levels on day 4 of culture were significantly reduced in cells incubated with 22 mM glucose compared with control. Next, we rendered mice diabetic by administering 200 micrograms/g body weight streptozotocin (STZ) on day 8 of pregnancy. Animals were killed on day 12 of pregnancy and placental tissues were obtained. [3H]Cytochalasin B binding study was carried out to assess total GLUTs, and GLUT1 mRNA and protein were measured as above. [3H]Cytochalasin B binding sites in placentas from STZ-treated mice were significantly less than those in control mice. Northern and immunoblot analyses revealed a significant decrease in GLUT1 mRNA and protein levels in diabetic mice compared with the controls. These findings suggest that the glucose concentration may regulate the expression of placental GLUT1. (+info)
Endothelin receptor expression and pharmacology in human saphenous vein graft.
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1. We have investigated the expression and pharmacology of endothelin (ET) receptors in human aortocoronary saphenous vein grafts. 2. Subtype-selective ligands were used to autoradiographically identify ET(A) ([125I]-PD151242) and ET(B)([125I]-BQ3020) receptors. In graft saphenous vein ETA receptors predominated in the media, with few ET(B) receptors identified. Neither subtype was detected in the thickened neointima. 3. The ratio of medial ET(A):ET(B) receptors was 75%: 25% in both graft and control saphenous vein. 4. ET-1 contracted control (EC50 2.9 nM) and graft (EC50 4.5 nM) saphenous vein more potently than diseased coronary artery (EC50 25.5 nM). 5. In all three blood vessels ET-1 was 100 times more potent than ET-3 and three times more potent than sarafotoxin 6b (S6b). Little or no response was obtained in any vessel with the ET(B) agonist sarafotoxin 6c (S6c). 6. The ET(A) antagonist PD156707 (100 nM) blocked ET-1 responses in all three vessels with pKb values of approximately 8.0. 7. For individual graft veins the EC50 value for ET-1 and 'age' of graft in years showed a significant negative correlation. 8. In conclusion there is no alteration in ET receptor expression in the media of saphenous veins grafted into the coronary circulation compared to control veins. ETA receptors predominantly mediate the vasoconstrictor response to ET-1 in graft vein, with no apparent up-regulation of ET(B) receptors. The sensitivity of the graft vein to ET-1 increased with graft 'age', suggesting that these vessels may be particularly vulnerable to the increased plasma ET levels that are detected in patients with cardiovascular disease. (+info)