Biomedical subjects

R Busse

Publications and source records attributed to R Busse.

At least 235 records · Page 13Linked to original sources

PubMed1988

Fendiline and calmidazolium enhance the release of endothelium-derived relaxant factor and of prostacyclin from cultured endothelial cells.

We investigated the effects of fendiline, calmidazolium and trifluoperazine, compounds described as calmodulin antagonists, on the release of the endothelial autacoids prostacyclin (PGI2) and endothelium-derived relaxant factor (EDRF). Cultured bovine aortic endothelial cells were grown on microcarrier beads and continuously superfused with Tyrode's solution. Samples collected from the superfusate were assayed for PGI2 concentration (6-keto PGF1 alpha radioimmunoassay) and for EDRF activity (stimulation of soluble guanylate cyclase in vitro). Stimulation of endothelial cells by ATP (3 microM) resulted in a 6.9 +/- 1.4-fold increase of PGI2 concentration in the superfusate (p less than 0.01) and an 8.6 +/- 3.4-fold enhanced guanylate cyclase activity (p less than 0.01). In the presence of calmidazolium (10 microM), the basal values of PGI2 concentration increased 28-fold (p less than 0.01) and the guanylate cyclase activity 10-fold (p less than 0.01). Further enhancement of both was observed after additional administration of ATP. Fendiline (30 microM) did not affect autacoid release by non-stimulated cells. However, the ATP-induced release of PGI2 and EDRF was more than doubled (p less than 0.01) in the presence of this drug compared to ATP-stimulation alone. Trifluoperazine (10 microM) had no enhancing effect on EDRF release, and the ATP-induced release of PGI2 was even significantly attenuated by 84 +/- 12% (p less than 0.01). Calmidazolium and fendiline were also applied to endothelial cells loaded with the fluorescent indicator of free calcium concentration (Ca2i+), indo-1. However, effects of calmidazolium on Ca2i+ could not be quantified since calmidazolium caused some leakage of indo-1 out of the cells. A smaller leakage was observed during the combined application of fendiline and ATP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1988

Endothelium-dependent hyperpolarization of smooth muscle cells in rabbit femoral arteries is not mediated by EDRF (nitric oxide).

Acetylcholine elicits an endothelium-dependent hyperpolarization of vascular smooth muscle cells. The experiments reported here tested the hypothesis that this hyperpolarization is mediated by the endothelium-derived relaxant factor (EDRF) identified as nitric oxide. Membrane potential was recorded with standard glass microelectrodes in smooth muscle cells in segments of rabbit femoral arteries. In endothelium-intact vessels, smooth muscle cells (resting potential: -67.0 +/- 1.3 mV) hyperpolarized significantly (P less than 0.001) by 5.7 +/- 0.9 mV in response to acetylcholine (1 microM). Inhibition of EDRF, either in the presence of hemoglobin or by pretreatment with gossypol, attenuated the relaxation elicited by acetylcholine in endothelium-intact segments precontracted with 0.1 microM noradrenaline but had no significant effect on either the control membrane potential (-62.2 +/- 1.9 mV and -68.5 +/- 2.1 mV, respectively) or the hyperpolarization in response to acetylcholine (5.0 +/- 1.6 mV and 5.8 +/- 1.6 mV, respectively). In contrast, in vessel segments with the endothelium removed, the hyperpolarization in response to acetylcholine was abolished although the control membrane potential (-68.0 +/- 5.1 mV) was not significantly different from that in endothelium-intact vessels. Sodium nitroprusside, an endothelium-dependent vasodilator and exogenous analog of EDRF, also had no significant effect on membrane potential. The lack of response to acetylcholine was not merely the result of nonspecific damage to the smooth muscle cells: vessel segments without endothelium were still able to hyperpolarize in response to various other vasodilators. These results suggest that the endothelium-dependent hyperpolarization of vascular smooth muscle cells in response to acetylcholine is not mediated by EDRF.

Acetylcholine↗

PubMed1988

Desensitization of the bradykinin-induced rise in intracellular free calcium in cultured endothelial cells.

We studied the cellular mechanism involved in the desensitization of cultured endothelial cells to bradykinin. Bradykinin (10 nmol/l) evoked a rise in the intracellular free calcium concentration [( Cai2+]), measured with the fluorescent probe indo-1, from 137 +/- 30 (+/- SEM) to 623 +/- 101 nmol/l. Cells were desensitized to bradykinin by repetitive stimulation with the peptide over 10 min, after which they no longer responded to bradykinin. However, purinergic stimulation with ATP (10 mumol/l) elicited the same increase in [Cai2+] in endothelial cells desensitized to bradykinin as in cells never exposed to bradykinin. The initial peak of [Cai2+] after stimulation with bradykinin or ATP was not affected by removal of extracellular calcium ions, indicating mobilization of Ca2+ from intracellular stores. Since GTP-binding proteins (G-proteins) are probably involved in the receptor-mediated stimulation of endothelial cells, we also tested the effects of sodium fluoride (NaF), a reported direct stimulator of G-proteins, on endothelial [Cai2+]. NaF (5 mmol/l) increased [Cai2+] to 412 +/- 88 nmol/l in control cells and was equally effective in cells desensitized to bradykinin. We conclude that the homologous desensitization to bradykinin does not occur at the level of intracellular signal transduction but at the level of membrane receptors.

Adenosine Triphosphate↗

PubMed1988

Differential role of extra- and intracellular calcium in the release of EDRF and prostacyclin from cultured endothelial cells.

1. The effects of extracellular Ca2+ on the release of endothelium-derived relaxing factor (EDRF) and prostacyclin (PGI2), and on the intracellular free calcium concentration [( Ca2+]i), were studied in cultured bovine aortic endothelial cells. 2. Receptor-mediated stimulation of endothelial cells with bradykinin (10 nM) elicited a transient release of EDRF (assayed by its stimulant effect on purified soluble guanylate cyclase) and of PGI2 (measured by radioimmunoassay for 6-keto prostaglandin F1 alpha). 3. Bradykinin (10 nM) also increased [Ca2+]i (measured with the fluorescent probe indo-1) from 125 +/- 11 nM to 631 +/- 59 nM, with the same time course as for autacoid release. 4. In Ca2+-free medium, [Ca2+]i was still increased by bradykinin but declined faster (within 1 min) to resting levels than in the presence of extracellular Ca2+. 5. PGI2 release was almost completely abolished in Ca2+-free medium. The intracellular calcium antagonist TMB-8 evoked a similar inhibition of PGI2 release. 6. In contrast, bradykinin-induced EDRF release was not significantly affected by TMB-8 but was completely abolished in Ca2+-free medium. 7. When endothelial cells were stimulated with the receptor-independent drug thimerosal (an inhibitor of the enzyme acyl-CoA-lysolecithin-acyl-transferase; 5 microM), a long-lasting release of EDRF (greater than 90 min) and PGI2 (greater than 20 min) was observed. 8. In contrast to bradykinin stimulation, thimerosal-induced autacoid release was associated with only a slight increase of [Ca2+]i to 201 +/- 13 nM after 40 min. 9. After removal of extracellular Ca2 + from thimerosal-stimulated endothelial cells, [Ca2+] was little affected during the observation time of 90s. EDRF release was completely abolished within 90s whereas PGI2 release was unchanged. 10. We conclude that EDRF production is directly controlled by extracellular Ca2+ during both receptor-dependent and independent stimulation. This effect of extracellular Ca2 + is not mediated by changes in [Ca2+]i. In contrast, PGI2 release is closely correlated to [Ca2+]i in bradykininstimulated endothelial cells. However, the results obtained during thimerosal stimulation indicate that there is not necessarily a tight coupling between the absolute level of [Ca2+]i and the amount of PGI2 released. 9. After removal of extracellular Ca2 + from thimerosal-stimulated endothelial cells, [Ca2+] was little affected during the observation time of 90s. EDRF release was completely abolished within 90s whereas PGI2 release was unchanged. 10. We conclude that EDRF production is directly controlled by extracellular Ca2+ during both receptor-dependent and independent stimulation. This effect of extracellular Ca2 + is not mediated by changes in [Ca2+]i. In contrast, PGI2 release is closely correlated to [Ca2+]i in bradykininstimulated endothelial cells. However, the results obtained during thimerosal stimulation indicate that there is not necessarily a tight coupling between the absolute level of [Ca2+]i and the amount of PGI2 released. 9. After removal of extracellular Ca2 + from thimerosal-stimulated endothelial cells, [Ca2+] was little affected during the observation time of 90s. EDRF release was completely abolished within 90s whereas PGI2 release was unchanged. 10. We conclude that EDRF production is directly controlled by extracellular Ca2+ during both receptor-dependent and independent stimulation. This effect of extracellular Ca2 + is not mediated by changes in [Ca2+]i. In contrast, PGI2 release is closely correlated to [Ca2+]i in bradykininstimulated endothelial cells. However, the results obtained during thimerosal stimulation indicate that there is not necessarily a tight coupling between the absolute level of [Ca2+]i and the amount of PGI2 released.

Animals↗

PubMed1988

Vasomotor activity of diadenosine triphosphate and diadenosine tetraphosphate in isolated arteries.

Dinucleotides diadenosine triphosphate (AP3A) and diadenosine tetraphosphate (AP4A) are released from platelet-dense granules upon agonist-induced platelet aggregation. Since most platelet-derived compounds simultaneously affect aggregation and vascular tone, we investigated whether AP3A and AP4A have vasoactive properties. Experiments were performed in isolated, saline-perfused segments of rabbit mesenteric arteries precontracted with norepinephrine. In segments with intact endothelium, both dinucleotides (1-10 microM) induced vasodilation, with AP3A responses significantly greater. Vasodilator responses to AP3A in endothelium-denuded segments were not significantly different from those in segments with intact endothelium but those to AP4A in endothelium-intact segments were reversed to a pronounced contraction after endothelium removal. Likewise, pretreatment of endothelium-intact segments with gossypol (3 microM) reversed dilator responses to acetylcholine and to AP4A into contractions, whereas AP3A-induced dilation was not affected. In segments with intact endothelium but pretreated with reactive blue (10 microM), AP4A also induced a contraction. Dilator response to AP3A was not affected. High-performance liquid chromatographic analysis of effluent from vascular segments showed that neither AP3A nor AP4A was degraded during passage through segments. These results indicate that in rabbit mesenteric arteries both nucleotides act directly, and not through their hydrolysis products, on endothelial (AP4A) and/or smooth muscle receptors. The endothelium-dependent dilator effect of AP4A, is probably mediated by endothelial P2y-purinoceptors.

Acetylcholine↗

PubMed1988

Hyperpolarization and increased free calcium in acetylcholine-stimulated endothelial cells.

In freshly harvested aortic endothelial cells from rabbits, some cellular events associated with stimulation by acetylcholine (ACh) were analyzed. ACh (3 microM) induced a transient hyperpolarization of 8.3 +/- 2.5 mV, which peaked within 3-5 s and subsequently declined with a similar time course. Hyperpolarization was caused by a transient Ca2+-dependent outward current (IoACh), which was mainly carried by K+. ACh (3 and 10 microM) also evoked transient dose-dependent increases in the intracellular free Ca2+ concentration (Ca2+i). Pretreatment with atropine (1 and 3 microM) abolished both responses to ACh, the increase in Ca2+i as well as the transient outward current. It is concluded that IoACh and the rise in Ca2+i are two manifestations of muscarinic receptor stimulation. The rise in Ca2+i might be the primary event, leading to secondary membrane hyperpolarization.

Acetylcholine↗

PubMed1988

LY 83583 interferes with the release of endothelium-derived relaxing factor and inhibits soluble guanylate cyclase.

LY 83583 (6-anilino-5,8-quinolinedione) has been reported to lower intracellular cyclic GMP by an unknown mechanism. The objective of the present study was to investigate the effect of LY 83583 on different types of vasorelaxation and to study its mechanism of action. Low concentrations of LY 83583 (less than or equal to 0.1 microM) inhibited endothelium-dependent relaxations of rabbit aortic strips induced by acetylcholine or by the calcium ionophore A23187. Higher concentrations (greater than or equal to 0.3 microM) were required to produce partial inhibition of relaxation to sodium nitroprusside and glyceryl trinitrate. Cyclic AMP-mediated relaxations, induced by isoprenaline or forskolin, were not affected by LY 83583 (10 microM). The site of interference of LY 83583 with endothelium-dependent relaxation was examined with endothelium-derived relaxing factor (EDRF) released from cultured endothelial cells that were grown on microcarrier beads and stimulated by superfusion with ATP or thimerosal. EDRF in the superfusate was detected by endothelium-denuded segments of rabbit femoral artery, which responded with dilation and, simultaneously, by purified soluble guanylate cyclase (GC) in test tubes, which was activated by EDRF. When LY 83583 was added to the glutathione-containing GC-assay or to the superfusate from cultured endothelial cells, it did not affect stimulation of soluble GC by EDRF but it slowly reversed the dilator response of the arterial detector segment. Superfusion of cultured endothelial cells with LY 83583 (1 microM), rapidly and reversibly inhibited EDRF release.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminoquinolines↗

PubMed1987

Stimulation of soluble guanylate cyclase by endothelium-derived relaxing factor from cultured endothelial cells.

Bovine endothelial cells, grown on microcarrier beads and superfused with a saline solution, were stimulated with thimerosal or bradykinin to release endothelium-derived relaxing factor (EDRF). EDRF activity in the effluent was assayed in endothelium-denuded rabbit aorta. The stimulation of purified soluble guanylate cyclase in test tubes by the EDRF-containing effluent amounted to 90-fold of basal activity and its time course correlated with that of the dilator response of the aorta. After preincubation of endothelial cells with gossypol the EDRF-induced dilator response as well as the stimulation of guanylate cyclase was suppressed.

Animals↗

PubMed1987

Photoelectric measurement of neurogenic vasoconstriction in jejunal branches of the rabbit mesenteric artery reveals the presence of presynaptic opioid delta-receptors.

The perivascular nerves of rabbit mesenteric arteries were stimulated with 15 pulses at 2 Hz, and decreases in external diameter were measured by means of a photoelectric device. Both extra- and intraluminally added [Met5]enkephalin 1 mumol/l depressed vasoconstriction, although with the second mode of application a larger inhibition occurred. Therefore, in the subsequent experiments all opioids were added into the lumen. [Met5]enkephalin 0.1 mumol/l had no effect. [D-Pen2, L-Pen5]enkephalin 3 mumol/l was less potent than [Met5]enkephalin 1 mumol/l. ICI 174864 1 mumol/l was also without effect when given alone, but antagonized the action of [Met5]enkephalin 1 mumol/l. Ethylketocyclazocine, dynorphin A(1-13), normorphine and DAGO, all 1 mumol/l, were ineffective. [Met5]enkephalin 1 mumol/l did not change the vasoconstriction evoked by the application of noradrenaline (0.1-3 mumol/l). It is concluded that in the mesenteric artery action potential-induced transmitter release, and in consequence vasoconstriction can be inhibited by the activation of presynaptic opioid delta-receptors.

Animals↗

PubMed1987

Endothelium-derived relaxant factor inhibits platelet activation.

Experiments were designed to investigate whether platelet activation is modulated by endothelium-derived relaxant factor (EDRF) which has been shown to induce vascular smooth muscle relaxation by direct stimulation of soluble guanylate cyclase. EDRF was released from cultured bovine endothelial cells, grown on microcarrier beads, by stimulation with thimerosal in the presence of indomethacin. EDRF had no effect on the intracellular free calcium concentration (Cai2+, measured with the fluorescent indicator indo-1) of resting washed human platelets but significantly attenuated the thrombin-induced rise of Cai2+ from 896 +/- 99 (SEM) to 509 +/- 48 nmol/l. EDRF significantly increased platelet cyclic GMP levels from 0.25 +/- 0.04 to 2.5 +/- 0.4 pmol/10(8) platelets and reduced the thrombin-induced aggregation to 23 +/- 3% of control. EDRF had no effect on Cai2+, cyclic GMP or aggregation after a 3 min storage interval, but superoxide dismutase (shown to increase stability of the labile factor) significantly augmented the EDRF effects on Cai2+. The antiaggregatory potency of EDRF was completely abolished in the presence of hemoglobin. The results characterize EDRF as a potent cyclic GMP-dependent antiaggregatory factor which may act synergistically in vivo with the cyclic AMP-dependent inhibitory effect of prostacyclin.

Animals↗

PubMed1987

Identification of the neuroeffector transmitter in jejunal branches of the rabbit mesenteric artery.

Vasoconstriction or excitatory junction potentials (e.j.ps) evoked by nerve stimulation (15 field pulses at 2 Hz every 3 min) were recorded in rabbit isolated jejunal arteries. The resting diameter of the arteries and its decrease in response to stimulation was measured by a photoelectric method. Vasoconstriction was insensitive to prazosin 0.1 or 1 mumol/l. Yohimbine 1 mumol/l considerably enhanced, whereas alpha,beta-methylene ATP (alpha,beta-meATP) 1 mumol/l abolished the contractile response. In order to test the effect of exogenously applied transmitter candidates, noradrenaline (0.1-1 mumol/l) and ATP (10-30 mumol/l) were added in concentrations which evoked a vasoconstriction comparable to that induced by electrical stimulation. The action of noradrenaline was prevented by prazosin 0.1 mumol/l, but was unaffected by both yohimbine 1 mumol/l and alpha,beta-meATP 1 mumol/l. Alpha,beta-meATP 1 mumol/l depressed the effect of ATP. The e.j.ps evoked by a train of 15 pulses showed facilitation up to the third response and thereafter depression; a partial summation was also observed. Prazosin 0.1 mumol/l did not change the e.j.p. amplitudes. By contrast, when yohimbine 0.1 or 1 mumol/l was added to the prazosin-containing medium, both the late e.j.ps in the train and the summation were enhanced in a concentration-dependent manner. Alpha,beta-meATP 1 mumol/l almost abolished the e.j.ps. In conclusion, in rabbit jejunal arteries, stimulation of postganglionic sympathetic nerves may release noradrenaline together with ATP which is probably the sole neuroeffector transmitter under our conditions. Transmitter release seems to be modulated by the activation of presynaptic alpha 2-adrenoceptors. Under the stimulation conditions of the present experiments the released transmitter does not activate postsynaptic alpha 1-adrenoceptors.

Adenosine Triphosphate↗

PubMed1987

Single nonselective cation channels and Ca2+-activated K+ channels in aortic endothelial cells.

In cultured bovine aortic endothelial cells, elementary K+ currents were studied in cell-attached and inside-out patches using the standard patch-clamp technique. Two different cationic channels were found, a large channel with a mean unitary conductance of 150 +/- 10 pS and a small channel with a mean unitary conductance of 12.5 +/- 1.1 pS. The 150-pS channel proved to be voltage- and Ca2+-activatable and seems to be a K+ channel. Its open probability increased on membrane depolarization and, at a given membrane potential, was greatly enhanced by elevating the Ca2+ concentration at the cytoplasmic side of the membrane from 10(-7) to 10(-4) M. 150-pS channels were not influenced by the patch configuration in that patch excision neither induced run-down nor evoked channel activity in silent cell-attached patches. However, they were only seen in two out of 55 patches. The 12-pS channel was predominant, a nonselective cationic channel with almost the same permeability for K+ and Na+ whose open probability was minimal near -60 mV but increased on membrane hyperpolarization. An increase in internal Ca2+ from 10(-7) to 10(-4) M left the open probability unchanged. Although the K+ selectivity of the 150-pS channels remains to be elucidated, it is concluded that they may be involved in controlling Ca2+-dependent cellular functions. Under physiological conditions, 12-pS nonselective channels may provide an inward cationic pathway for Na+.

Animals↗

PubMed1987

Studies on synthesis and degradation of eicosanoids by rat hepatocytes in primary culture.

The potential of hepatocytes in primary cultures to degrade the prostanoids produced by Kupffer cells and to synthesize eicosanoids, especially leukotriene B4, after treatment with D-galactosamine was studied. Hepatocytes in primary cultures showed a substantial capability to degrade all the prostanoids produced by stimulated Kupffer cells. The rate of degradation, approx. 2 pmol/min per 10(6) hepatocytes, was nearly the same for the prostaglandins D2, E2 and F2a. Lower rates were determined for thromboxane B2 (0.4 pmol/min per 10(6) cells) and for 6-ketoprostaglandin F1a (0.2 pmol/min per 10(6) cells). The degradation products of these prostanoids lacked biological activity, e.g., reactivity with specific antibodies and the ability to contract segments of rabbit femoral artery. In the presence of 30 microM arachidonic acid, hepatocytes produced only very small amounts of prostaglandins and thromboxane, ranging from less than or equal to 22 to 50 fmol/30 min per 10(6) cells. Neither untreated nor D-galactosamine-treated hepatocytes released significant amounts of leukotriene B4. Hepatocytes appear to be the site of degradation rather than synthesis of eicosanoids in the liver.

6-Ketoprostaglandin F1 alpha↗

PubMed1987

Dilation of epicardial arteries in conscious dogs induced by angiotensin-converting enzyme inhibition with enalaprilat.

Vasodilators may provoke myocardial ischemia in patients with coronary heart disease. Therefore, we analyzed in conscious dogs the effect of angiotensin-converting enzyme (ACE) inhibition by enalaprilat on parameters potentially important to provocation of myocardial ischemia, such as sympathetic activity, myocardial oxygen consumption, and vascular tone in coronary conduit and resistance vessels. Under normal sodium intake (2-4 mEq/kg/day), enalaprilat (0.03 and 0.3 mg/kg i.v. during 5-min infusion with 30-min intervals, n = 8) did not modify the norepinephrine release rate into plasma (a parameter of overall sympathetic activity). The higher dosage reduced myocardial oxygen consumption (to 87 +/- 2% of control), mean arterial pressure (MAP) (to 90 +/- 1%) and coronary conduit artery tone (normalized delta diameter: +3.2 +/- 0.7%) without dilating coronary resistance vessels. Following renin-angiotensin activation by sodium deprivation (3 X 1 mg/kg furosemide plus 7 days sodium intake less than 0.2 mEq/day), enalaprilat similarly lowered myocardial oxygen consumption and reduced vascular tone both in coronary conduit (normalized delta diameter: +4.0 +/- 0.9%) and resistance vessels (delta coronary flow: +45 +/- 12%). Although MAP declined to 76 +/- 6%, heart rate and norepinephrine release rate were not modified significantly. We propose that the dilation of epicardial arteries results from a direct intramural action. Enalaprilat seems unlikely to provoke myocardial ischemia even in states with a strongly activated renin-angiotensin system.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1987

Endothelium-derived relaxant factor inhibits effects of nitrocompounds in isolated arteries.

We investigated the influence of endothelial cells on the smooth muscle vasodilator effects to sodium nitroprusside (SNP) or Teopranitol (an organic mononitrate) in isolated segments of rabbit aorta and femoral artery. In the femoral artery, the vasodilator responses to both nitrocompounds were significantly higher in the absence of endothelial cells or after pretreatment with the endothelium-derived relaxant factor (EDRF) inhibitor nordihydroguaiaretic acid (NDGA; 10 microM). Moreover, under conditions of stimulated EDRF release (induced by acetylcholine; 30-100 nM) the vasodilator responses to SNP were further attenuated in vessels with intact endothelium. By contrast, in the rabbit aorta, the vasodilator responses to the nitrocompounds were not significantly altered by either endothelium removal or treatment with NDGA. However, in the presence of the EDRF stimulator acetylcholine, the dose-response curve to SNP was shifted to right in the aorta as well. The role of EDRF in the endothelium-mediated attenuation of the dilator potency of SNP was further investigated by using EDRF released from cultured (bovine aortic) endothelial cells. The dilator effects of SNP were compared in endothelium denuded femoral or aortic segments in the presence or absence of EDRF. The vasodilator effects of SNP in both types of arteries were significantly reduced in the presence of EDRF. We conclude that EDRF attenuates the arterial vasodilation induced by SNP and Teopranitol. The results further suggest that endothelial cells exhibit a greater basal release of EDRF in the femoral artery than in the aorta, since under unstimulated conditions an EDRF-induced attenuation was seen only in femoral and not in aortic segments.

Acetylcholine↗

PubMed1987

Selective inhibition of endothelium-dependent dilation in resistance-sized vessels in vivo.

In vivo experiments were performed in autoperfused hindlimbs of rabbits to investigate the role of endothelium-mediated vasomotion in resistance-sized vessels. The flow responses to the vasodilators acetylcholine (ACh), ATP, and substance P (SP), all of which have been shown to act in an endothelium-dependent manner in large conduit arteries, were studied before and after exposure of the hindleg vasculature to gossypol (a potent inhibitor of endothelium-mediated vasodilation in vitro). The flow responses to adenosine (ADO), nitroglycerin (GTN), and prostaglandin E2 (PGE2), which induce relaxation by a direct effect on vascular smooth muscle, were tested in the same manner. All vasodilators induced dose-dependent increases in femoral flow up to two- to threefold when administered intra-arterially. After gossypol, the flow responses to the endothelium-dependent compounds (ACh, ATP, and SP) were severely reduced (by 88 +/- 3%, P less than 0.01) or sometimes were converted to constrictions (ATP). The flow increases induced by ADO, PGE2, and GTN remained largely unaffected. Sham treatment (gossypol solute only), exposure to indomethacin (10 microM), and ganglionic blockade had no differential effect on the flow responses. The selective action of gossypol in suppressing the flow responses to the endothelium-dependent compounds ACh, ATP, and SP is consistent with a vasomotor role for endothelial cells in resistance-sized vessels in vivo.

Adrenergic beta-Antagonists↗

PubMed1987

Characterization of vascular relaxant factor released from cultured endothelial cells.

Cultured bovine endothelial cells were grown on microcarrier beads. Columns (0.2 ml) packed with microcarriers were perfused with oxygenated (20% O2) Tyrode's solution containing indomethacin (10 microM), and the effluent was passed through precontracted, endothelium-denuded detector arteries. When the endothelial cells were stimulated with bradykinin (3-100 nM), adenosine 5'-triphosphate (0.3-30 microM), or calcium ionophore A23187 (10-300 nM), they released dose-dependently a nonprostanoid compound that dilated the detector vessel. The factor, probably identical to the endothelium-derived relaxing factor of native endothelium, evoked dilations of the same magnitude in different types of detector vessels (rabbit thoracic aorta, rabbit femoral artery, canine coronary artery). However, this relaxant factor was significantly more effective in arteries precontracted by norepinephrine or serotonin than in arteries precontracted by potassium depolarization. Thus, its dilator action resembles that of the nitrovasodilators. The factor is labile, with an apparent half-life in the range of 20 to 30 seconds. Its dilator potency was inhibited by dithiothreitol (0.2 mM), metyrapone (0.2 mM), nordihydroguaiaretic acid (20 microM), and hemoglobin (1 microM), all of which apparently inactivated the factor. Synthesis or release (or both) of the relaxant factor was abolished by methylene blue (1 microM). High PO2 levels (greater than 400 mm Hg) in the perfusate markedly reduced the release of the relaxant factor from the cultured cells. This study demonstrates that a vascular relaxant factor is released from endothelial cells in monoculture by adenosine 5'-triphosphate, bradykinin, and A23187 and establishes such a culture as a useful tool for analyzing the mechanisms of endothelium-dependent vasomotion.

Adenosine Triphosphate↗

PubMed1987

Thimerosal, an inhibitor of endothelial acyl-coenzyme A: lysolecithin acyltransferase, stimulates the production of a nonprostanoid endothelium-derived vascular relaxing factor.

Thimerosal stimulates the production of a labile, smooth-muscle-relaxing substance in native and cultured endothelial cells. This substance is not prostacyclin (or any other prostaglandin) but has properties similar to the EDRF released by ACh or bradykinin. The production of EDRF in response to thimerosal is slower in onset, and may involve biochemical mechanisms different from those stimulated by other endothelium-dependent relaxants. The above results suggest that inhibition of acyl-CoA:lysophosphatide acyltransferase (by interaction with thiol groups of the enzyme) is the mechanism underlying the thimerosal-induced EDRF production.

1-Acylglycerophosphocholine O-Acyltransferase↗