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Biomedical subjects

R Busse

Publications and source records attributed to R Busse.

At least 253 records · Page 14Linked to original sources
PubMed1987

Abluminal release and asymmetrical response of the rabbit arterial wall to endothelium-derived relaxing factor.

A marked functional polarity of endothelial cells as well as an asymmetry of the vascular wall in response to vasoactive compounds is well established. Therefore, we investigated the polarity of endothelium-derived relaxant factor (EDRF) release from native endothelial cells, its diffusion characteristics, and its dilator effects on inner and outer muscle layers of the vascular wall in isolated rabbit arteries. Following exposure of rabbit aortae (with intact endothelium) to the EDRF stimulators acetylcholine, A23187, or thimerosal, a humoral dilator compound could be assayed in the adventitial superfusate of the vessels. The vasodilator effects were blocked by the EDRF inhibitors hemoglobin, dithiothreitol, and gossypol. Penetration of the dilator through the arterial wall following stimulation by acetylcholine, A23187, or thimerosal was observed only when dilator EDRF activity in the luminal perfusate was maximal. Luminally administered EDRF, released from cultured endothelial cells, did not cross the aortic wall in detectable amounts. EDRF (from cultured cells) elicited significantly smaller dilations (9 +/- 4%) when applied to the adventitial side of endothelium-denuded rabbit aortae or femoral arteries as compared with luminal application (92 +/- 7%). In contrast, sodium nitroprusside was equieffective by both routes of administration. We conclude that EDRF in native endothelial cells is released in both luminal and abluminal directions and can penetrate the entire vascular wall. However, the lengthy diffusion time and the decreasing sensitivity of outer smooth muscle layers suggest that mechanisms other than EDRF diffusion contribute significantly to the propagation of endothelium-mediated relaxation through the arterial wall.

Acetylcholine↗
PubMed1986

Increased free calcium in endothelial cells under stimulation with adenine nucleotides.

The release of vasodilating substances from the vascular endothelium has been postulated to depend on a rise in the level of intracellular free calcium (Cai++). We measured Cai++ in intact monolayers of calf endothelial cells, grown in culture, that were loaded with the fluorescent calcium indicator quin 2. Fluorescence (excitation wavelength 340 nm, emission wavelength 492 nm) was calibrated by raising Cai++ to a maximum with the calcium ionophore ionomycin (0.1 microM) and by lowering it to a minimum with ionomycin plus manganese (0.4 mM), which quenches quin 2 fluorescence completely. Loss of fluorescent dye from the cells was calculated from fluorescence at the isosbestic excitation wavelength (365 nm). Resting Cai++ was 71 +/- 3 (SEM) nM. ATP (adenosine-5'-triphosphate) raised Cai++ dose-dependently and reversibly to 458 +/- 60 nM at a concentration of 10 microM, and at 0.1 mM to values close to those that occurred under ionomycin. ADP (A-5'-PP) and AMP (A-5'-P) had smaller effects with a maximal Cai++ of 287 +/- 72 nM at 30 microM ADP and 176 +/- 17 nM at 0.1 mM AMP. At these concentrations, ADP and AMP attenuated significantly the increase of Cai++ under ATP (10 microM). Adenosine (0.1 or 0.3 mM) and acetylcholine (0.1 to 30 microM) enhanced Cai++ inconsistently, by a maximum of 50 nM. These effects were abolished by theophylline and atropine, respectively. In the absence of extracellular calcium, ATP still raised Cai++, although endothelial responsiveness declined after repetitive stimulations. We conclude that activation of purinergic receptors increases intracellular free calcium in endothelial cells, and that this increase is probably an essential trigger for synthesis of prostacyclin and the labile endothelium-derived relaxant factor.

Acetylcholine↗
PubMed1986

Pressure-diameter relationships of segments of human finger arteries.

Pressure-diameter relationships of segments of human finger arteries, aged 57-85 years, were measured in vitro. The arteries, obtained at autopsy within 48 h after death, were stored in glucose-free Tyrode at 4 degrees C. Experiments began within 40 h after autopsy. The diameter responses to various transmural pressure changes, with and without the addition of noradrenaline to the Tyrode solution in the specimen chamber, were compared with the responses of freshly excised rat tail arteries. In general, pressure-diameter relations of human finger artery segments were similar to those of rat tail artery segments, with a steep slope in the collapse region near zero pressure. Also, spontaneous rhythmic contractions and myogenic activity induced by high transmural pressures were similar to those observed in the fresh rat tail arteries. Human finger arteries, however, could contract to complete closure both spontaneously and after addition of noradrenaline, while rat tail arteries did not. The diameter changes of the arterial segments during forced 1 Hz oscillations of 20-50 mm Hg (2.7-6.7 kPa) amplitude superimposed on a mean transmural pressure were substantially smaller than those during quasi-steady inflation-deflation ramps over the same pressure range, indicating the presence of a strong viscous wall component.

Aged↗
PubMed1986

Crucial role of endothelium in the vasodilator response to increased flow in vivo.

Experiments were designed to investigate the importance of vascular endothelium in the vasomotor response to increases in flow as observed in conduit arteries (flow-dependent dilation). The diameter changes of femoral arteries (sonomicrometry) in response to increases in flow before and after endothelial damage procedures were studied in 23 dogs anesthetized with sodium pentobarbital. The functional integrity of the endothelial cells underneath the diameter sensors was tested by intra-arterial acetylcholine (local acetylcholine dilation) applied proximally to the sensors while a constant flow was maintained. Unilateral augmentation of femoral arterial flow (4.6 +/- 1.9-fold) induced by peripheral vasodilation or by arteriovenous shunt, elicited dilation (increase in diameter, 116 +/- 91 microns) in 18 of 23 dogs, whereas the diameter of the contralateral control artery was not affected. Mechanical removal of the endothelial cells by means of a balloon catheter abolished both the flow-dependent dilation and the local acetylcholine dilation, whereas the vasomotor responses to norepinephrine and nitroglycerin were not affected. Brief perfusions (1 minute) of the arteries with cell-free hydrogen peroxide solution (90 mM) also abolished the flow-dependent dilation and attenuated the local acetylcholine dilation (by 27 +/- 19%; p less than 0.02), while the responses to norepinephrine and nitroglycerin were not altered. These results suggest that endothelial cells act as mediators of flow-dependent dilation.

Acetylcholine↗
PubMed1986

Stimulation of soluble guanylate cyclase by an acetylcholine-induced endothelium-derived factor from rabbit and canine arteries.

The present study was designed to investigate the hypothesis that, during acetylcholine-induced endothelium-dependent relaxation, a factor(s) is released from endothelial cells which directly activates soluble guanylate cyclase. We attempted to determine what similarities or differences existed between this factor and endothelium-derived relaxing factor. The study was performed on segments of rabbit aorta and canine femoral artery. Purified soluble guanylate cyclase was injected into the lumen of these vascular segments, together with its substrate, for intraluminal incubation of the enzyme. In endothelium-intact vascular segments, the activity of guanylate cyclase was enhanced over control values obtained by incubation in test tubes. The stimulation was further increased by acetylcholine in concentrations which caused relaxation of the vascular segments. The stimulating principle could not be transferred from the vessel lumen to an external solution of guanylate cyclase, indicating a short life-time. Removal of the endothelium prevented formation and release of the guanylate cyclase stimulating factor(s). Atropine, mepacrine, or nordihydroguaiaretic acid, which inhibit acetylcholine-induced endothelium-dependent relaxations, also inhibited acetylcholine-induced endothelium-mediated activation of guanylate cyclase. The results support the hypothesis that acetylcholine-induced endothelium-derived relaxing factor increases cyclic guanosine monophosphate levels of vascular smooth muscle by a stimulation of soluble guanylate cyclase.

Acetylcholine↗
PubMed1986

Inhibitors of acyl-coenzyme A:lysolecithin acyltransferase activate the production of endothelium-derived vascular relaxing factor.

Considerable acyl-CoA:lysolecithin acyltransferase (LAT) activity could be demonstrated in homogenates of cultured bovine endothelial cells. This LAT activity was inhibited by thimerosal and p-hydroxymercuribenzoate in a concentration-dependent manner. Preconstricted strips of rabbit aorta were relaxed by acetylcholine or the LAT inhibitors in a concentration-dependent fashion if the endothelium was intact (maximal effect of both LAT inhibitors at 10(-5) M). In rabbit aortic strips thimerosal also induced a concentration-dependent stimulation of the formation of 6-keto-prostaglandin F1 alpha, the major cyclooxygenase metabolite of this tissue. This effect of thimerosal was more pronounced in endothelium-intact than in endothelium-denuded preparations. Inhibition of prostaglandin synthesis with indomethacin (10(-5) M) did not impair the relaxation. Thimerosal and acetylcholine-induced relaxations were abolished when the endothelium was removed or when endothelium-intact preparations were pretreated with nordihydroguaiaretic acid (3 X 10(-5) M), gossypol (5 X 10(-6) M) or dithiothreitol (3 X 10(-4) M). In contrast, mepacrine (3 X 10(-5) M), that abolished the acetylcholine response, had no effect on the thimerosal relaxation. In other experiments bovine endothelial cells were grown to confluence on microcarrier beads and packed into columns. Adding thimerosal (5 X 10(-6) M) or bradykinin (10(-10) to 10(-8) M) to the medium superfusing the columns induced the release of an unstable nonprostanoid factor (or factors) that relaxed endothelium-denuded rabbit femoral artery segments. Bradykinin induced a transient effect whereas there was a strong and long-lasting release of the factor after administration of thimerosal.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1985

The input impedance of the peripheral vascular termination in skeletal muscle.

In order to investigate the dynamic behaviour of the peripheral vessels of the arterial system, simultaneous pressure-flow measurements were made in the deep femoral artery of the rabbit at the same site. The input impedance calculated from the recorded pulses was regarded as representing the peripheral vascular termination in skeletal muscle and was expressed in terms of modulus and phase. The modulus decreases monotonously with increasing frequency while the phase angle is about -45 degrees in the low frequency range and becomes less negative with increasing frequency. This behaviour can be simulated by a model in which the inert mass of the pulsating blood, the elastic compliance of the blood vessels, and the frictional resistance to blood flow are taken into account. An essential result is that the model is provided with a considerable degree of elastic compliance, which means that the peripheral vessels as a whole possess an important compliance and do not behave like pure frictional resistances.

Animals↗
PubMed1985

Role of the endothelium in the vasomotor effects of angiotensin I in isolated arteries with or without inhibition by MK 422.

We investigated in the isolated rabbit aorta the ability of the endothelium to attenuate the vasoconstrictor effects of angiotensin (ANG) I and II. After preincubation with enalaprilat, which inhibited the conversion of ANG I to ANG II by 80%, the contractile response to ANG I (10(-8) to 10(-6) mol/l) was significantly greater in aortae which were endothelium-denuded compared with endothelium-intact segments. There was no such difference for ANG II (10(-10) to 3 x 10(-8) mol/l). We conclude that an endothelium-mediated dilatation is part of the net vasomotor action of ANG I.

Angiotensin I↗
PubMed1985

[Regulation of vascular tone by the endothelium].

In the last few years, experimental evidence has accumulated which suggests a substantial role for the endothelium in the control of vascular tone. Endothelium-dependent dilations have been demonstrated in various arteries of numerous mammalian species including man. Among the stimuli which elicit endothelium-dependent dilatation are such different stimuli as increases in blood flow and hypoxia as well as endogenous (acetylcholine, ATP, ADP, bradykinin, substance P) and pharmacological agents (calcium ionophore A 23 187, ergometrine, hydralazine, melittin). The functional importance of endothelium-dependent dilatation is emphasized by the fact that the direct vasoconstrictor effects of some of these substances (acetylcholine, histamine, norepinephrine, serotonin) on vascular smooth muscle is attenuated or even reversed by their simultaneous stimulatory effect on endothelial cells resulting in the release of a vasodilator signal. Bioassay experiments have shown that a humoral vasodilator agent with a biological half-life in the range of seconds is released from the endothelium (native or cultured) during stimulation with acetylcholine, ATP and calcium ionophore. Experimental data are presented which suggest that EDRF may act by direct stimulation of guanylate cyclase, resulting in smooth muscle relaxation due to increased smooth muscle cyclic GMP levels. The chemical nature of this nonprostaglandin endothelium-derived relaxant factor (EDRF) is still not known. The possible physiological and pathophysiological significance of endothelium-dependent dilatation in situ is discussed. Special attention is paid in this context to the potential role of EDRF activity in coronary vasomotor control.

Animals↗
PubMed1984

Species-dependent differences in the nature of endothelium-derived vascular relaxing factor.

Effluents from perfused acetylcholine-relaxed endothelium segments of rabbit aorta (or canin femoral artery) contained endothelium-derived relaxing factors (EDRF) which dilated the endothelium-free segments of rabbit femoral artery (or side branches of canine femoral artery). The half-life of EDRF was 24 +/- 3 s for the rabbit and 49 +/- 5 s for the canine system. Nordihydroguaiaretic acid was less effective against the formation of canine EDRF than of rabbit EDRF. These findings suggest species differences in the nature of EDRF.

Acetylcholine↗
PubMed1984

The role of prostaglandins in the endothelium-mediated vasodilatory response to hypoxia.

The effect of intraluminal hypoxia on vascular tone and the release of prostaglandins (PG) I2 and E2 were investigated in intact isolated segments of canine femoral and coronary arteries as well as in the rat tail artery. Perfusion with hypoxic Tyrode's solution (pO2: 20-40 mm Hg) evoked a marked vasodilation of the segments, precontracted with norepinephrine or serotonin. Simultaneously, a 2-3-fold increase in the release of 6-keto-PGF1 alpha (the stable hydrolysis product of PGI2) could be observed. In parallel to 6-keto-PGF1 alpha, smaller quantities of PGE2 were released. Removal of the endothelium as well as pretreatment with indomethacin abolished both, the dilatory response and the PG-release. After administration of verapamil as well as 3,4,5-trimethoxybenzoic acid 8-diethylaminooctylester (TMB-8) (which binds intracellular calcium) the PG-increase was abolished and hypoxic dilatation could no longer be elicited, although the vessel had still a capacity to dilate. Exogenous administration of PGI2 and PGE2 showed that in canine femoral and coronary arteries PGI2 was the most effective vasodilating prostaglandin, while in the rat tail artery PGE2 had a 10-fold higher dilating potency compared to PGI2. At very high concentrations both PGI2 and PGE2 caused vasoconstriction. Our experiments suggest that the hypoxic endothelium-dependent dilatation may be mediated by an increased PG-release. Hypoxia-induced transmembrane calcium influx into the endothelial cells seems to be the trigger reaction.

6-Ketoprostaglandin F1 alpha↗
PubMed1984

Effects of active and passive wall stress changes on the rhythmic mechanical activity of the pressurized rat tail artery.

Rhythmic mechanical activity was recorded in vitro in isolated rat tail arteries. Pressurized cylindrical segments of this artery, stretched to their in situ length, exhibit well-synchronized rhythmic contractions. Frequency and amplitude of the rhythmic activity can be modified by (1) passive stretch at a given constrictor agonist concentration, as well as by (2) active wall stress changes induced by varying doses of constrictor agonists. At a norepinephrine concentration of 0.5 microM, the frequency (f) of rhythmic contractions increases from 0.2 to 0.65 [sec-1], when the mean circumferential wall stress (sigma) is increased from 1 . 10(5) to 1 . 10(6) dyn/cm2. The relationship between f and sigma is, at a constant smooth muscle tone, virtually independent of the rate and also of the direction of the applied stress changes. Changes of the smooth muscle tone (i.e. changes of the actively developed wall stress), induced by vasoactive agents or other stimuli, lead to virtually parallel shifts of the sigma-f relationship, which is obtained by passive stretching. It is concluded that the actual stimulus for the stretch-sensing structure in the arterial smooth muscle is the change in wall stress rather than the change in strain. Since rhythmic contractions may still be observed 30-60 min after withdrawal of Ca++ from the bath solution, extracellular Ca++ seems not to be primarily involved in this rhythmicity.

Animals↗
PubMed1984

[Modulation of coronary vessel tonus: molecular and cellular mechanisms].

The cyclic interactions between myosin cross bridges and the actin filament in the presence of Ca++ with a sliding of both filaments passed each other, is considered also in vascular smooth muscle as the basic contractile mechanism. While in the striated muscle the regulation of the actin-myosin interaction occurs at the level of the actin filaments, there is a growing body of evidence that the contractile activation of the vascular smooth muscle is primarily regulated by phosphorylation of the 20,000-Dalton myosin light chain. This reaction is catalyzed by a calcium-calmodulin-dependent myosin light chain kinase. Additionally, dephosphorylated myosin cross bridges which remain attached to actin filaments over prolonged periods of time ("latch bridges") at low myoplasmic Ca2+-concentrations seem to be involved in the vascular smooth muscle in maintaining tonic active stress at a very low energy expenditure. In most arterial smooth muscle cells, the initiation of contraction (electromechanical coupling) is not associated with action potentials, but is coupled with graded membrane depolarization. During the process of excitation-contraction coupling, two mechanisms lead to increased myoplasmic calcium: a) Calcium influx through voltage-dependent channels along an electro-chemical gradient. b) Release of calcium from the sarcoplasmic reticulum or from the inside of the cell membrane, triggered either by calcium influx or directly by membrane depolarization. The pharmaco-mechanical coupling, i.e., the contractile activation by drugs without depolarization as initiating step, seems to be realized only in a few specific vessels. The stimulation of the phosphatidyl-inositol turnover (PI-cycle) in the plasma membrane by activation of alpha 1-adrenergic receptors can also be demonstrated in vascular smooth muscle cells. However, whether or not this PI-response plays a primary role in the increase of myoplasmic Ca2+ remains to be settled. The activation of alpha 2-adrenergic receptors seems to involve the action of an inhibitory guanine nucleotide-binding protein on the catalytic moiety of the adenylate cyclase. Thus, the contractile response observed may be attributed to the decrease of cyclic AMP (which is responsible for dilating effects via phosphorylation of various regulatory proteins). The decrease in the myoplasmic concentration of free-ionized calcium as a basic principle of relaxation comes about by different mechanisms, which can be classified as follows: a) Inhibition of transmembrane calcium influx into vascular smooth muscle cells by Ca-antagonists, which specifically interfere with plasmalemmal Ca2+-channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Actins↗
PubMed1984

[Contraction and relaxation mechanisms of the smooth vascular musculature].

In this short review some aspects of our current knowledge of the cellular processes which are involved in the regulation of vascular tone are discussed. We describe at first the structural components of the contractile apparatus in the vascular smooth muscle and discuss then the calcium-dependent mechanisms that regulate contractile protein activity. Phosphorylation of the 20.000-Dalton-myosin light chain is described as one of the key events in the regulation of the smooth muscle activity. However, mechanisms complementary to the primary effect of myosin phosphorylation are also considered. The differences in calcium modulation of contractile processes between striated and smooth muscle are emphasized. The activation of vascular smooth muscle through graded depolarization and/or action potential and the excitation-contraction coupling as a result of an increase of myoplasmic free calcium concentration is described. The concept of calcium channels which open by agonists acting at the membrane receptors (receptor-operated channels) without any change in membrane potential is presented. Finally, we discuss the different ways by which the level of intracellular calcium as the main factor controlling the contractility of vascular smooth muscle can be reduced. However, other mechanisms, e.g. changes in the sensitivity of the contractile proteins at a given calcium concentration must also be considered as a mechanism of relaxation.

Actins↗
PubMed1983

Endothelial cells are involved in the vasodilatory response to hypoxia.

The role of endothelial cells in the dilatory response of arteries to hypoxia was studied in vitro using perfused arterial segments of rat and dog. The pO2 of the intra- and extraluminal perfusate could be varied separately. Intraluminal hypoxia (pO2 of 40 mmHg) induced a dilation irrespective of extraluminal pO2 level. On the contrary extraluminal hypoxia could not elicit a dilation during intraluminal normoxic perfusion. Dilation during extraluminal hypoxia could only be induced if the segment was not intraluminally perfused. The dilatory response to intraluminal hypoxia was abolished after enzymatical or mechanical removal of the endothelium. While theophylline and lipoxygenase inhibitors did not influence this endothelium-induced dilation, a significant reduction of the response could be observed after incubation with indomethacin. These results support the concept that prostacyclin (PGI2) might be involved in the hypoxic endothelium-induced dilation.

Acetylcholine↗
PubMed1982

The contribution of the parallel and series elastic components to the dynamic properties of the rat tail artery under two different smooth muscle tones.

The dynamic elastic modulus (Ed) and the coefficient of wall viscosity (eta w) of the tail artery of normotensive rats were determined as functions of the circumferential wall stress under quasistatic and dynamic conditions. The experiments were performed under strong smooth muscle activation induced by norepinephrine, and during relaxation induced by papaverine. The following results were obtained. 1. Ed and eta w increase with increasing wall stress. At a given wall stress, Ed is virtually independent of frequency while eta w decreases markedly with increasing frequency. This behaviour of eta w is called thixotropy or pseudoplasticity. 2. In the wall stress range from 5--60 kPa the values of Ed, and in the wall stress range from 60--140 kPa those of eta w obtained under smooth muscle activation and during relaxation are virtually identical. 3. In the relaxed smooth muscle, the phase angles between sinusoidal pressure and radius changes area virtually independent of the mean wall stress at all frequencies. In the low stress range, the phase angles are greater at low frequencies in the activated state than in the relaxed state, decrease with increasing wall stress, and are virtually identical to the values under papaverine at high wall stresses. At high frequencies no dependence of the phase angles on the mean wall stress can be seen.

Animals↗