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At least 487 records · Page 27Linked to original sources
PubMed1993

Endothelium-derived contracting factors.

In the past decade, the importance of endothelium in modulating vascular tone has become apparent. Endothelium can produce different vasodilators, such as prostacyclin, endothelium-derived relaxing factor (most likely nitric oxide), and endothelium-derived hyperpolarizing factor. Endothelium can also produce endothelium-derived contracting factors (EDCF) which can induce constriction of the underlying vascular smooth muscle. Constriction may be mediated by a variety of products released by the endothelium. Thus, by responding to various stimuli and releasing either relaxing or contracting factors, the endothelium can set and modulate vascular tone.

Animals↗
PubMed1995

[Effects of cyclosporine A on the reactivity of the aorta with regenerated endothelium in rats].

Cyclosporine A (CyA) affects vascular reactivity but its effect on local vascular tone following endothelial regeneration is unknown. Experiments were designed to study the effects of CyA on endothelial and smooth muscle reactivity of endothelium-regenerated arteries. Three groups of rats (n = 8) were subjected to aortic mechanical denudation. Subsequently a first group was treated 8 weeks with CyA (20 mg/kg) and a second one with an equivalent volume of CyA vehicle: olive oil (OL). A last group was submitted to a standard diet and represented the control group (CTL). After 8 weeks, aortic rings were suspended in organ chambers for assessment of endothelial and smooth muscle function. Maximal endothelial dependent relaxation to acetylcholine (CyA: 52 +/- 3%, OL: 50 +/- 4%, CTL: 48 +/- 5%; p = NS), adenosine diphosphate (CyA: 30 +/- 7%, OL: 18 +/- 2%, CTL: 24 +/- 5%; p = NS) and histamine (CyA: 38 +/- 6%, OL: 43 +/- 4%, CTL: 47 +/- 5%; p = NS) were comparable among all groups. In aortic segments studies without endothelium, increased contraction to serotonine was significantly lessened in the OL group (CyA: 259 +/- 43%, OL: 153 +/- 11%, CTL: 243 +/- 24%; p < 0.05). Maximal tension to cumulative doses of norepinephrine was increased in rings without endothelium treated with CyA (CyA: 5.8 +/- 0.6 g, OL: 4.2 +/- 0.5 g, CTL: 4.0 +/- 0.2 g; p < 0.05). All these differences were abolished in rings studied with endothelium. Endothelial independent relaxation to sodium nitroprusside were similar among all groups. In conclusion, CyA does not specifically affect endothelium-dependent relaxation of the regenerated aortic endothelium. However, our model suggests that CyA increases vascular tone mediated by increased smooth muscle sensitivity to norepinephrine and serotonine but these effects are prevented by the regenerated endothelium. This experiment demonstrates the ability of the regenerated endothelium to prevent CyA-induced vascular toxicity.

Animals↗
PubMed1995

Changes in endothelium-dependent vascular responses associated with spontaneous hypertension and age in rats.

The aim of this study was to investigate if the endothelium-dependent relaxation and the inhibitory effect of endothelium against vasoconstrictor stimuli are reduced by aging and hypertension in rat aorta. Both relaxation and isometric contraction of intact and denuded aortic rings from spontaneously hypertensive rats (SHR) of 7-9, 12-18, 28-36 and more than 70 weeks old and from age-matched Wistar-Kyoto rats (WKY) were measured in parallel. An age-related decrease of endothelium-dependent relaxation to acetylcholine was found, which was greater in arteries from SHR (p < 0.05). Indomethacin normalized the endothelium-dependent relaxations in aortic rings from either old or hypertensive rats. Relaxations elicited by nitroglycerin were slightly enhanced with age in both WKY and SHR (p < 0.05). Moreover, endothelium removal increased responsiveness to indanidine and to 5-hydroxytryptamine (5-HT). Endothelium-dependent inhibition on the contraction decreased with aging (to a greater extent in SHR). These results indicate that aging and hypertension are associated with a decrease in the endothelium-dependent responses. Endothelium-dependent relaxations of aortae from old normotensive and hypertensive rats were impaired by the production of a cyclooxygenase-derived contractile factor. However, the higher response to nitroglycerin suggests a lesser production of endogenous nitric oxide by endothelial cells.

Aging↗
PubMed1996

Effect of angiotensin receptor blockade in the rabbit aorta: influence of the endothelium.

Contractile responsiveness of the rabbit aorta (endothelium intact and denuded) to angiotensin I, II, and III was compared. The effects of converting-enzyme inhibition with enalapril, the selective AT1-receptor antagonist (losartan), and the AT2-receptor antagonist (PD 123319) on these contractile profiles were examined. In all preparations, it was found that the angiotensins produced concentration-dependent increases in tension. Differences in sensitivity were encountered; in endothelium-intact preparations, the mean EC50 values (nM with 95% confidence interval in parentheses) for angiotensin I, II, and III were 9 (95% CI 7-11), 40 (20-60), and 30 (10-40), respectively, and for denuded preparations they were 20 (11-29), 0.8 (0.7-0.9), and 30 (20-40), respectively. Enalapril decreased the maximal tension developed to angiotensin I and II, which was greater in endothelium-intact preparations. Losartan was a competitive antagonist against angiotensin I and angiotensin II in both intact and denuded preparations, with pA2 values as follows: against angiotensin I, 9.0 and 9.3 for intact and denuded, respectively; against angiotensin II, 8.3 and 8.9 for intact and denuded, respectively. Losartan antagonized angiotensin III, but the slopes of the Schild analysis were significantly less than unity. In endothelium-intact preparations, PD 123319 failed to significantly antagonize responsiveness to angiotensin I. Against angiotensin II, PD 123319 was a competitive antagonist with a pA2 of 8.3. The antagonism for PD 123319 against angiotensin III was insurmountable. In endothelium-denuded preparations, PD 123319 failed to antagonize angiotensin I and angiotensin III. Although PD 123319 appeared to inhibit the responsivenss of the rabbit aorta by angiotensin II, the slope of the Schild plot was significantly less than unity. These experiments provide evidence that angiotensin I possesses different actions from angiotensin II and III and that a functional endothelium modulates the underlying vascular response to angiotensin. In addition, the endothelium modulates the antagonism by losartan and PD 123319, supporting the notion that the endothelium possesses distinct angiotensin receptors.

Angiotensin I↗
PubMed1997

Role of endothelium and nitric oxide in the in vitro response of equine colonic venous rings to vasoconstrictor agents.

OBJECTIVE: To determine in vitro contractile responses of equine colonic veins to various vasoconstrictor agents. ANIMALS: Colonic veins collected from 8 adult horses. PROCEDURE: Veins were cut into 4-mm-wide rings, placed in organ baths at 37 C, and attached to a force-transducer interfaced with a polygraph; 2 g of tension was applied, and rings were allowed to equilibrate for 45 minutes. Bath solution was replaced, and tension was reapplied at 15-minute intervals. Cumulative concentration responses (10(-8) to 10(-4) M) were determined for each agent, using separate rings (n = 8). Three vein groups were evaluated: endothelium-intact, endothelium-denuded, and N omega-nitro-L-arginine methyl ester (L-NAME, 10(-5) M)-treated. Maximal responses by each vein to each agent were considered 100%; responses to lower concentrations were calculated as percentage of maximum. RESULTS: Considering all vein groups, comparison of the doses that caused 50% of the maximal contraction revealed relative sensitivity of colonic veins to be: angiotensin II (ANG) > thromboxane B2 analogue (TXB) > 5-hydoxytryptamine (5HT) > norepinephrine (NE) > histamine (HST) > prostaglandin F2 alpha (PGF) > vasopressin (VP). Compared with ANG, PGF, TXB, and VP, treatment with HST, 5HT, and NE evoked significantly greater responses. Endothelium-denuded and L-NAME-treated colonic veins had significantly greater maximal contractile responses than did endothelium-intact veins. CONCLUSIONS: Response of colonic veins to vasoconstrictor agents was differential; sensitivity was not altered by endothelium removal or L-NAME treatment; maximal responses of endothelium-intact veins were greater than those of endothelium-denuded and L-NAME-treated veins; and responses of endothelium-denuded and L-NAME-treated veins were not different. CLINICAL RELEVANCE: Alterations in colonic veins that mimic conditions associated with large-colon volvulus may contribute to blood flow alterations, edema formation, and vascular responses to hypovolemic and endotoxic shock.

Analysis of Variance↗
PubMed1997

Effects of calcium dobesilate on the synthesis of endothelium-dependent relaxing factors in rabbit isolated aorta.

1. Some cardiovascular disturbances which occur in diabetics are a consequence of alterations in vascular contractility as well as in endothelium-dependent relaxation. 2. Calcium dobesilate (DOBE) is a drug used in diabetic retinopathy and its mechanism of action is not yet understood. 3. The aim of this study was to investigate the effects of DOBE on synthesis and release of endothelium-dependent relaxing factor (EDRF) and endothelium-dependent hyperpolarizing factor (EDHF) in rabbit isolated aorta. 4. Endothelium-dependent relaxation induced by acetylcholine (ACh) (10(-8)-(10(-5) M) increased in the presence of DOBE 10(-5) M only when vascular endothelium was kept intact. 5. NG-nitro-L-arginine methyl ester (L-NAME; 10(-8)-10(-4) M progressively decreased the enhancing effect of DOBE on endothelium-dependent relaxation whereas it was progressively increased by L-Arg. 6. DOBE 10(-5) M increased in a non-significant manner endothelium-dependent relaxation induced by ACh when the arteries were incubated with both L-NAME 10(-4) M and indomethacin 10(-5) M. 7. DOBE (10(-6) M and 10(-5) M) was able to scavenge superoxide anion radicals generated by the hypoxanthine/xanthine oxidase reaction. 8. These results provide evidence that DOBE is able to affect the vascular disorders associated with diabetes mellitus since it enhances the synthesis of endothelium-dependent relaxing factors.

Animals↗
PubMed2001

The role of endothelium-derived hyperpolarizing factor in the regulation of the uterine circulation in pregnant rats.

OBJECTIVE: The purpose of this study was to determine whether endothelium-derived hyperpolarizing factor regulates rat uterine circulation in pregnant rats. STUDY DESIGN: Intact isolated uterine vascular beds from late pregnant rats were perfused in situ with Krebs buffer that contained dextran, indomethacin, N-nitro-L-arginine methyl ester, and phenylephrine. Endothelium-derived hyperpolarizing factor-induced decreases in perfusion pressure in response to acetylcholine were analyzed. RESULTS: The decrease in perfusion pressure induced by endothelium-derived hyperpolarizing factor was significantly attenuated by 4-aminopyridine and was abolished by a combination of 4-aminopyridine and tetraethylammonium. Endothelium-derived hyperpolarizing factor-induced decrease in perfusion pressure was abolished by potassium chloride and attenuated by miconazole, but not linoleyl hydroxamic acid. Endothelium-derived hyperpolarizing factor-induced decrease in perfusion pressure persisted after perfusion with solutions that contained 2 inhibitors of nitric oxide synthase and a scavenger of nitric oxide. Nitric oxide exerted negative feedback on the endothelium-derived hyperpolarizing factor effects. CONCLUSION: In the pregnant rat uterine vascular beds, endothelium-derived hyperpolarizing factor release is activated by a delayed rectifier type of voltage-sensitive potassium channel. Endothelium-derived hyperpolarizing factor does not seem to be related to nitric oxide or to products of lipoxygenase or cytochrome p450 mono-oxygenase pathways of arachidonic acid metabolism.

Acetylcholine↗
PubMed1987

The inhibition of release of endothelium-derived relaxant factor by manoalide, a potent inhibitor of phospholipase A2.

1 The inhibitory action of manoalide on vascular relaxation was characterized. Manoalide was a potent inhibitor of endothelium-dependent relaxations in the isolated aorta of the rabbit. Responses to acetylcholine (ACh), A23187 and substance P were reduced by manoalide in a dose-dependent manner whilst those to nitroglycerin were unaffected. 2 Repeated washing of manoalide-treated tissues did not restore the relaxant response to ACh, indicating an irreversible action of manoalide. Scanning electron microscopic studies revealed that the endothelium remained intact on manoalide-treated tissues. 3 Rabbit aortae from which the endothelium had been removed relaxed in response to perfusion with ACh when delivered via an upstream endothelium-bearing tissue, indicating release of an endothelium-derived relaxant factor (EDRF). Incubation of the tissue without endothelium with manoalide (100 nM; 30 min) or inclusion of manoalide in the superfusate at a point just distal to the endothelium bearing tissue did not reduce the relaxant potency of EDRF. 4 Contractile responses of the guinea-pig isolated ileum to ACh were not affected by manoalide and, furthermore, binding of [3H]-quinuclidinyl benzilate to striatal membranes was not reduced by manoalide except at very high concentrations. 5 Manoalide therefore appears to inhibit vascular relaxation with a selectivity directed towards that mediated by EDRF. A direct antagonism of neither cholinoceptors nor EDRF receptors occurs and it is suggested that manoalide acts at a site within the endothelium to inhibit the synthesis and/or release of EDRF. Based upon these and previous data the possibility that EDRF is lipid-like or controlled by an arachidonic acid metabolite must continue to be considered.

Animals↗
PubMed1988

Endothelium-dependent hyperpolarization of canine coronary smooth muscle.

1. Experiments were designed to determine whether endothelium-dependent relaxing factor(s) released by acetylcholine from the canine femoral artery influences the membrane potential of coronary arterial smooth muscle. 2. The membrane potential was recorded in small canine coronary arteries (internal diameter less than or equal to 500 micron; without endothelium) by means of intracellular microelectrodes. The organ bath also contained a strip of left descending coronary artery without endothelium in which isometric force was measured to bioassay relaxing factor(s) as well as segments of femoral artery with endothelium, which served as the source of endothelium-derived relaxing factor(s). 3. Acetylcholine induced endothelium-dependent, transient hyperpolarizations and relaxations that were not affected by indomethacin. 4. Inhibition of the sodium-potassium pump by ouabain or potassium-free solution did not inhibit the relaxation to acetylcholine but prevented the corresponding hyperpolarization. 5. Activation of the sodium-potassium pump of the smooth muscle cells by readmission of potassium ions after incubation in potassium-free solution caused relaxation and marked hyperpolarization. 6. These results suggest that endothelium-derived relaxing factor(s) induces hyperpolarization of vascular smooth muscle of the canine coronary artery, possibly by activation of sodium-potassium pumping, but that this effect on the cell membrane may only partially explain endothelium-dependent relaxations evoked by acetylcholine.

Acetylcholine↗
PubMed1992

Myogenic vascular regulation in skeletal muscle in vivo is not dependent of endothelium-derived nitric oxide.

The hypothesis, based on in vitro experiments on large conduit arteries, that endothelium-derived nitric oxide is a mediator of vascular myogenic reactivity was tested in cat gastrocnemius muscle in vivo. This was done by comparing, in the absence and presence of effective endothelium-derived nitric oxide blockade by the specific inhibitors NG-monomethyl-L-arginine or NG-nitro-L-arginine methyl ester, myogenic responses in defined consecutive vascular sections to dynamic vascular transmural pressure stimuli, to arterial occlusion (reactive hyperaemia), and to arterial pressure changes (autoregulation of blood flow and capillary pressure). The results demonstrated that the myogenic vascular reactivity to quick ramp transmural pressure stimuli was not attenuated by endothelium-derived nitric oxide blockade, but rather reinforced. The amplitude of the reactive hyperaemia response was unaffected by endothelium-derived nitric oxide blockade, but its duration was shortened because of faster myogenic constriction, especially of large-bore arterial resistance vessels greater than 25 microns, in the recovery phase. Both the improved myogenic responsiveness to transmural pressure stimuli and the shortening of the reactive hyperaemia by endothelium-derived nitric oxide blockade suggested that endothelium-derived nitric oxide released in vivo acts as a 'metabolic' factor which certainly does not improve, but rather depresses myogenic vascular reactivity. Autoregulation of blood flow and capillary pressure were well preserved in the presence of endothelium-derived nitric oxide blockade. It was concluded from the results of these multifaceted tests that myogenic vascular regulation in skeletal muscle in vivo seems independent of endothelium-derived nitric oxide.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Is nitric oxide the only endothelium-derived relaxing factor in canine femoral veins?

Nitric oxide may be an endothelium-derived relaxing factor in systemic arteries and pulmonary veins. The endothelium-derived relaxing factor of systemic veins has not been characterized. Experiments were designed to determine whether the endothelium-derived relaxing factor of systemic veins shared chemical properties and mechanisms of action with nitric oxide. Rings of the canine femoral vein with and without endothelium were suspended in organ chambers for the measurement of isometric force. In rings without endothelium, relaxations to nitric oxide were augmented by superoxide dismutase plus catalase and were inhibited by hemoglobin, methylene blue, and LY 83583. The endothelium-dependent relaxations to acetylcholine and A23187 were not augmented by superoxide dismutase plus catalase but were inhibited by hemoglobin and only moderately reduced by either methylene blue or LY 83583. Relaxations to sodium nitroprusside were not inhibited by methylene blue and LY 83583. Relaxations to sodium nitroprusside were inhibited by ouabain and K+-free solution; those to nitric oxide were not. These results indicate that although the endothelium-derived relaxing factor released from canine systemic veins shares some chemical properties with nitric oxide, the mechanism by which relaxations are induced by the two differ. A factor dissimilar to nitric oxide but acting like sodium nitroprusside may be released by the endothelium of canine systemic veins.

Acetylcholine↗
PubMed1991

SKF-525A does not inhibit release of endothelium-derived relaxing factor from rat thoracic aorta and dog mesenteric and femoral artery.

SKF-525A (proadifen) inhibits endothelium-dependent relaxations induced by acetylcholine, arachidonic acid and the calcium ionophore A23187. This suggests that SKF-525A is an inhibitor of endothelium-derived relaxing factor (EDRF) and that EDRF may be a product of arachidonic acid metabolism formed via a cytochrome P-450-dependent pathway or that EDRF release is dependent on cytochrome P-450. We tested this postulate using both isolated rings of rat thoracic aorta and dog mesenteric and femoral artery and the perfusion-superfusion bioassay. Rings of rat thoracic aorta and dog mesenteric and femoral artery with intact endothelium were precontracted with an EC50 concentration of norepinephrine (0.1 nmol/l) or U46619 (0.05 mumol/l) and the relaxation to acetylcholine (ACh), bradykinin, adenosine triphosphate (ATP) or nitroglycerin (GTN) were obtained before, 30 min after addition of, and 30 min after washout of SKF-525A (50 mumol/l). SKF-525A inhibited ACh-induced endothelium-dependent relaxation of rat aortic rings and endothelium-dependent relaxation of the dog mesenteric and femoral artery produced by ACh and ATP, but did not affect relaxation to bradykinin or GTN. The inhibitory effect on SKF-525A on ACh and ATP-induced relaxation was partially reversed upon its washout from the muscle chamber. Pretreatment of the blood vessels with ibuprofen (1 mumol/l) did not attenuate SKF-525A-mediated inhibition of the relaxations to any agonist. Selective exposure of dog femoral artery (donor) to SKF-525A (50 mumol/l) for 60 min did not affect the relaxation responses of endothelium-rubbed coronary artery (bioassay tissue) to basal EDRF nor to the effluent from donor tissues stimulated with ACh (10-1,000 pmol), ATP (1-100 nmol) or bradykinin (3-100 pmol). The results show that SKF-525A exhibited a reversible inhibition of endothelium-dependent relaxation by a smooth muscle mechanism unrelated to the generation of EDRF from endothelium.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1991

Role of endothelium-derived relaxing factor in regulation of vascular tone and remodeling. Update on humoral regulation of vascular tone.

In addition to preserving the permselectivity of the vascular wall and providing an antithrombogenic surface, the vascular endothelium contributes importantly to the regulation of vasomotor tone. Indeed, the endothelium participates in the conversion of angiotensin I to angiotensin II; the enzymatic inactivation of several plasma constituents such as bradykinin, norepinephrine, serotonin, and ADP; and the synthesis and release of vasodilator substances such as prostacyclin and the recently discovered endothelium-derived relaxing factor (EDRF). The diffusible EDRF released from the endothelium is nitric oxide or a substance closely related to it such as nitrosothiol. The endothelium also synthesizes and releases vasoconstrictive factors, including products derived from arachidonic acid metabolism and the recently discovered peptide endothelin. An increasing body of evidence from experimental and clinical studies indicates that EDRF and endothelium-derived contracting factors play an important role in vascular physiology and pathology. It has become apparent that the balance of these factors may be a major determinant of systemic and regional hemodynamics. Moreover, through generally opposite effects on growth-related vascular changes, contracting factors such as endothelin and relaxing factors such as EDRF also may be important determinants of the vascular response to injury in various disease states such as atherosclerosis and hypertension. It is clear that the vascular endothelium is a complex and dynamic organ. Understanding endothelium function in normal physiology and disease states is of potential clinical importance and should be the focus of future investigation.

Animals↗
PubMed1988

Response of human coronary arteries to aggregating platelets: importance of endothelium-derived relaxing factor and prostanoids.

Epicardial human coronary arteries (HCA) were obtained during heart transplantation. Strip preparations were mounted for isometric tension recording. Tension was induced with prostaglandin F2 alpha (0.3-3 microM). Aggregating human platelets (10(7)/ml and 10(8)/ml) caused marked relaxation if the endothelium of the HCA was intact, but produced modest additional constriction if the endothelium was removed. The endothelium-dependent relaxations to platelets were slightly enhanced in the presence of methysergide (1 microM) or after treatment of the platelets with the thromboxane synthase inhibitor dazmegrel (1 mM, 30 minutes). Relaxations to platelets were markedly inhibited or abolished in the presence of apyrase (1 unit/ml), after selective pretreatment of HCA with gossypol or methylene blue (both 30 microM, 30 minutes), or after addition of hemoglobin (20 microM) to the organ bath. Pretreatment of HCA (not the platelets) with aspirin (30 microM, 30 minutes) had no significant effect on platelet-induced relaxations. Adenosine 5'-diphosphate (0.1-100 microM) induced marked relaxations in endothelium-intact and much smaller relaxations in endothelium-denuded HCA. A low concentration (10 nM) of serotonin (5-HT) produced modest endothelium-dependent relaxations, higher concentrations (0.1-1 microM) led to increases in tension (also in the presence of endothelium). The thromboxane A2 mimetic U44069 (1-100 nM) was the most potent constrictor of HCA irrespective of the presence or absence of endothelium. After inhibition of thromboxane synthase, platelets produced large amounts of prostaglandins E2 and F2 alpha. Both prostaglandins constricted HCA, which can explain the limited effects of dazmegrel.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1992

Decreased endothelium-dependent hyperpolarization to acetylcholine in smooth muscle of the mesenteric artery of spontaneously hypertensive rats.

The endothelium-dependent vascular relaxation to acetylcholine (ACh) in spontaneously hypertensive rats (SHR) may be impaired because of an imbalance of endothelium-derived relaxing factor and contracting factor. However, the role of the endothelium-dependent hyperpolarization remains undetermined. We examined the ACh-induced hyperpolarization and its contribution to relaxation in arteries of SHR. Membrane potentials were recorded from the mesenteric artery trunk of 6-8-month-old male SHR and also Wistar-Kyoto (WKY) rats. Endothelium-dependent hyperpolarization to ACh was unaffected by NG-nitro-L-arginine, indomethacin, or glibenclamide; was reduced by tetraethylammonium or high K+ solution; and was enhanced by low K+ solution or methylene blue, thereby indicating that hyperpolarization is not mediated by nitric oxide (endothelium-derived relaxing factor) but is presumably mediated by a hyperpolarizing factor and is due to an opening of K+ channels that probably differ from the ATP-sensitive ones. Hyperpolarizations to ACh were markedly reduced in SHR compared with findings in WKY rats (maximum, 8 +/- 1 versus 17 +/- 1 mV). In addition, under conditions of depolarization with norepinephrine (10(-5) M), the ACh-induced hyperpolarization was even less and transient in SHR, while it was large and sustained in WKY rats (6 +/- 1 versus 29 +/- 2 mV). Endothelium-dependent relaxations to ACh in arterial rings precontracted with 10(-5) M norepinephrine were far less in SHR than in WKY rats, even in the presence of indomethacin. Furthermore, high K+ solution showed smaller inhibitory effects on the relaxations in SHR than in WKY rats. Endothelium-independent hyperpolarizations and relaxations to cromakalim, a K+ channel opener, were similar between SHR and WKY rats. It would thus appear that the endothelium-dependent hyperpolarization to ACh is reduced in SHR and this would, in part, account for the impaired relaxation to ACh in SHR mesenteric arteries.

Acetylcholine↗
PubMed2004

Effect of etomidate on endothelium-dependent relaxation induced by acetylcholine in rat aorta.

The goals of this in vitro study were to investigate effects of etomidate on endothelium-dependent relaxation induced by acetylcholine in rat aorta, and to elucidate the associated cellular mechanism. In endothelium-intact rings precontracted with phenylephrine 10(-6) M, dose-response curves for acetylcholine (10(-9) to 10(-5) M) and calcium ionophore (10(-9) to 10(-6) M) were generated in the presence and absence of etomidate (5 x10(-6) 10(-5) M). In endothelium-intact or -denuded rings precontracted with phenylephrine 10(-6) M, sodium nitroprusside (10(-9) to 10(-6) M) dose-response curves were generated in the presence and absence of etomidate (10(-5)M). Etomidate (5 x10(-6), 10(-5)M) produced a significant rightward shift in the dose-response curves induced by acetylcholine (receptor-mediated endothelium-dependent agonist) and calcium ionophore A23187 (non receptor-mediated endothelium-dependent agonist). Etomidate (10(-5)M) had no effect on sodium nitroprusside (endothelium-independent nitric oxide donor)-induced vasorelaxant response in both endothelium-intact and -denuded rings. These results indicate that etomidate at clinically relevant concentrations attenuates endothelium-dependent relaxation induced by acetylcholine by an acting at a site distal to the endothelial muscarinic receptor, but proximal to guanylate cyclase activation of vascular smooth muscle in rat aorta.

Acetylcholine↗
PubMed1993

Inhibition by sulfhydryl compounds of vascular relaxation induced by nitric oxide and endothelium-derived relaxing factor.

On rings of rabbit thoracic aorta precontracted with phenylephrine, L-cysteine (Cys) and dithiothreitol (DTT) (1-100 microM), but not glutathione (GSH), produced dose-dependent augmentation of contraction in endothelium-intact, but not in endothelium-denuded rings. The augmentation appeared to be due to inhibition of basally released endothelium-derived relaxing factor (EDRF), and was abolished by pretreatment with superoxide dismutase (SOD, 15 U/ml). At a high dose (1 mM), Cys and GSH produced transient, and DTT produced sustained endothelium-independent relaxation, not influenced by SOD. Cys and DTT (10 microM), but not GSH, produced a small but significant inhibition of acetylcholine-induced endothelium-dependent relaxation, and this inhibition was prevented by SOD. In a perfusion-bioassay system in which EDRF was released by acetylcholine from endothelium of a perfused segment of rabbit aorta, Cys and DTT (20 microM), but not GSH, infused into the perfusate between the segment and an endothelium-denuded bioassay ring, partially inhibited relaxation by the EDRF, but not when SOD was present. In organ chamber experiments, the large transient relaxation of endothelium-denuded rings produced by 75 nM nitric oxide (NO) was partially inhibited in a concentration-dependent manner by Cys, DTT and GSH (0.1-100 microM). Moderate relaxation by 15 nM NO was almost completely inhibited by each compound at 10 microM. The order of potency was Cys > DTT > GSH. Cystine, glutathione disulfide and alanine did not inhibit. Inhibition of NO-induced relaxation was largely attenuated by SOD.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1994

Cytochemical differentiation between blood and lymphatic endothelium: bovine blood and lymphatic large vessels and endothelial cells in culture.

Cytochemical differentiation between blood and lymphatic endothelium has been studied only in microvessels; 5'-nucleotidase (5'Nase) has been reported to be specific for lymphatic and alkaline phosphatase (ALPase) for blood endothelium. Adenylate and guanylate cyclase (AC and GC) have recently been proposed as lymphatic endothelial markers, but conflicting data exist. This study was designed to verify the presence of these enzymes in the endothelium of large vessels and to determine whether they are retained in endothelial cells (ECs) in culture. Segments of bovine mesenteric arteries, veins, and lymphatic collectors, and EC cultures obtained by collagenase treatment of the same vessels, were assayed for 5'Nase, ALPase, AC, and GC, and were observed by transmission electron microscopy. We found ALPase activity in blood and lymphatic vessels, and this was the only enzyme activity consistently retained under culture conditions. 5'Nase was found in lymphatic but not in blood endothelium, as previously reported for microvessels. AC and GC activity was found in blood but not in lymphatic endothelium. Hence, ALPase is not a useful marker to differentiate blood from lymphatic endothelium in large vessels, whereas 5'Nase is specific for lymphatic and AC and GC for blood endothelium. It is not clear why these enzyme activities are not expressed in culture.

5'-Nucleotidase↗