PubMed Health⌕ Search

Biomedical subjects

R F Furchgott

Publications and source records attributed to R F Furchgott.

At least 37 records · Page 2Linked to original sources
PubMed1986

Phosphodiesterase inhibitors induce endothelium-dependent relaxation of rat and rabbit aorta by potentiating the effects of spontaneously released endothelium-derived relaxing factor.

The selective cyclic GMP phosphodiesterase inhibitor M&B 22948 and the less selective phosphodiesterase inhibitors papaverine and isobutylmethylxanthine (IBMX) each induced a component of relaxation of rat aortic rings that was endothelium-dependent. The most selective agent at inducing endothelium-dependent relaxation was M&B 22948, which caused little relaxation of endothelium-denuded rings at concentrations that produced almost complete relaxation of endothelium-containing rings. Although endothelium-dependent components of relaxation induced by papaverine and IBMX were clearly present, they were less well separated from the endothelium-independent components of relaxation. In the aorta of the rabbit, M&B 22948 and papaverine were less affective at inducing an endothelium-dependent component of relaxation than in the aorta of the rat, and IBMX produced no discernible endothelium-dependent component. The endothelium-dependent components of relaxation induced by M&B 22948, papaverine and IBMX on rat and rabbit aorta were probably dependent on endothelium-derived relaxing factor (EDRF), because they were associated with concomitant endothelium-dependent rises in cyclic GMP, and these components of relaxation as well as the rises in cyclic GMP were completely blocked by the EDRF-blocking agent hemoglobin. The action of hemoglobin was entirely specific, as none of the endothelium-independent components of relaxation induced by any of the phosphodiesterase inhibitors was affected by this hemoprotein. It is likely that the phosphodiesterase inhibitors induce their endothelium-dependent components of relaxation by inhibiting the hydrolysis of cyclic GMP formed in response to EDRF released spontaneously from endothelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1986

Depression of contractile responses in rat aorta by spontaneously released endothelium-derived relaxing factor.

Removal of endothelial cells on rings of rat aorta increased the sensitivity to the selective alpha-1 adrenoceptor agonist phenylephrine, to the nonselective alpha adrenoceptor agonist norepinephrine and to the selective alpha-2 adrenoceptor agonist clonidine. In the case of the first two, which are strong agonists for the alpha-1 adrenoceptor-mediating contraction, removal of endothelium increased sensitivity 4- and 6-fold at the EC30 level, but produced little or no increase in maximum. In the case of clonidine, a partial agonist for the alpha-1 adrenoceptor, which gave only about 15% of the maximum given by phenylephrine on endothelium-containing rings, removal of the endothelium not only shifted the curve to the left but also increased the maximum to about 50% of that given by phenylephrine. The depression of sensitivity to these agonists in rings with endothelium appeared to be due to the vasodepressor action of endothelium-derived relaxing factor (EDRF), as hemoglobin, a specific blocking agent of EDRF, abolished this depression. It is unlikely that the endothelium-dependent depression was due to stimulation of release of EDRF, because clonidine did not produce endothelium-dependent relaxation in precontracted rings even when its contractile action was blocked by the alpha-1 adrenoceptor antagonist prazosin. Further evidence against alpha adrenoceptor agents stimulating release of EDRF was that neither phenylephrine nor clonidine induced a rise in cyclic GMP in aortic rings, whereas acetylcholine, which does release EDRF, caused a large rise in cyclic GMP content. The possibility that the muscle cells of intact rat aortic rings were under the tonic influence of released EDRF was supported by the finding that, in the absence of any contractile agent, hemoglobin induced a fall in the basal level of cyclic GMP in endothelium-containing rings. Also consistent with EDRF being released spontaneously was the finding that contraction induced by 5-hydroxytryptamine, like that by alpha-adrenergic agonists, was also depressed in endothelium-containing rings of aorta. When the efficacy of phenylephrine as an alpha-1 agonist was reduced to about the initial efficacy of clonidine by irreversible inactivation of a very large fraction of alpha-1 adrenoceptors of the smooth muscle cells by pretreatment with dibenamine, the concentration-contraction curves for phenylephrine for both endothelium-containing rings and for endothelium-denuded rings now became very similar to the corresponding curves obtained for clonidine before receptor inactivation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1985

Interactions of endothelial cells and smooth muscle cells of arteries.

Relaxation of selected isolated arteries by acetylcholine, bradykinin, and certain other vasodilators is mediated by a factor released from endothelial cells. Relaxation by the factor (chemical identity still unknown) is accompanied by an increase of cyclic GMP. The finding that hemoglobin inhibits both endothelium-dependent relaxation and the increase in cyclic GMP may have pathophysiologic relevance.

Animals↗
PubMed1985

Blockade of endothelium-dependent and glyceryl trinitrate-induced relaxation of rabbit aorta by certain ferrous hemoproteins.

We have reported previously that hemoglobin inhibits endothelium-dependent and glyceryl trinitrate-induced relaxation in the rabbit aorta. In this study we have examined the effects of other ferrous and ferric hemoproteins on endothelium-dependent and glyceryl trinitrate-induced relaxation to determine whether they also share the inhibitory properties of hemoglobin. Of the two ferrous hemoproteins tested, myoglobin (1-10 microM) abolished the endothelium-dependent relaxation induced by acetylcholine and produced a concentration-dependent reduction in the endothelium-independent relaxation induced by glyceryl trinitrate, in a manner similar to that reported previously for hemoglobin, but reduced cytochrome C was completely ineffective. The ferric hemoproteins methemoglobin (10 microM) and metmyoglobin (40 microM) produced only a slight inhibition of acetylcholine-induced relaxation. Methemoglobin (10 microM) also blocked only slightly the endothelium-dependent relaxation induced by the ionophore A23187 and had no effect on glyceryl trinitrate-induced relaxation. The inhibitory effects of these hemoproteins were reflected in their respective effects on the stimulation of cyclic GMP levels; thus, myoglobin (10 microM) inhibited the endothelium-dependent rise in cyclic GMP content induced by acetylcholine, as was found previously for hemoglobin, but methemoglobin (10 microM) was much less effective. The effectiveness of hemoglobin and myoglobin and the ineffectiveness of reduced cytochrome C in blocking the relaxations induced by acetylcholine and glyceryl trinitrate might suggest that only ferrous hemoproteins with ligand binding sites are inhibitory.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1985

Selective blockade of endothelium-dependent and glyceryl trinitrate-induced relaxation by hemoglobin and by methylene blue in the rabbit aorta.

Hemoglobin at 1 microM reduced and at 10 microM abolished the endothelium-dependent relaxation induced by acetylcholine or by A23187 in rabbit aortic rings. Similarly, methylene blue at 10 microM reduced and at 50 microM abolished relaxation induced by acetylcholine and by A23187. Furthermore, hemoglobin (1-10 microM) and methylene blue (10-50 microM) each induced a dose-dependent inhibition of the endothelium-independent relaxation produced by glyceryl trinitrate, but neither had any effect on the relaxation produced by isoproterenol. The inhibitory effects of hemoglobin and methylene blue may be due to blockade of guanylate cyclase, as the rises in cyclic GMP content which accompany relaxation induced by acetylcholine, A23187 or glyceryl trinitrate were abolished. Isoproterenol-induced relaxation took place with no change in cyclic GMP content. Hemoglobin and methylene blue appear therefore to inhibit selectively vaso-relaxation induced by agents which increase cyclic GMP levels. Hemoglobin and methylene blue augment tone in aortic rings, particularly when endothelial cells are present, suggesting that the endothelium-derived relaxing factor (EDRF) might be released spontaneously in low concentrations. The possibility that hemoglobin inhibits endothelium-dependent and glyceryl trinitrate-induced relaxation by binding EDRF and nitric oxide, respectively, is discussed together with the proposal that methylene blue might produce its effects by oxidizing a component of guanylate cyclase, possibly a ferrous heme group linked to the enzyme molecule. Methylene blue might, in addition, interact directly with EDRF.

Acetylcholine↗
PubMed1984

Endothelial cells as mediators of vasodilation of arteries.

A brief review is first presented of findings during the past few years by the authors and by others on the nonprostaglandin endothelium-dependent relaxation of isolated arteries by a large number of vasoactive agents. Among these agents are acetylcholine (ACh); the calcium ionophore A23187; ATP and ADP; substance P; bradykinin (canine, human, and porcine arteries); histamine, acting via an H1-receptor (rat arteries); thrombin (canine arteries); serotonin (canine coronary artery); and norepinephrine, acting via an alpha2-receptor (canine coronary artery). The endothelium-derived relaxing factor (EDRF) released by ACh and other agents has not yet been identified. Our original hypothesis that arachidonic acid is the precursor of EDRF is not supported by the finding that other unsaturated fatty acids in addition to arachidonic acid, and even stearic acid, elicited nonprostaglandin endothelium-dependent relaxations. Methylene blue and hemoglobin (but not methemoglobin) rapidly inhibited relaxation of rabbit aorta by ACh or A23187, suggesting that our proposal that EDRF is a labile free radical may be correct. The endothelium-dependent relaxation by each of these agents was shown to be preceded by an endothelium-dependent increase in cyclic GMP in the smooth muscle--a finding consistent with the hypothesis that EDRF stimulates guanylate cyclase in the muscle, leading to an increase in cyclic GMP that somehow activates relaxation. Some questions relating to the potential physiological important of endothelium-dependent relaxations are discussed.

Acetylcholine↗
PubMed1983

Use of selective antagonists for determining the types of receptors mediating the actions of 5-hydroxytryptamine and tryptamine in the isolated rabbit aorta.

Competitive and noncompetitive antagonists were used to study the receptors which mediate the contraction elicited by 5-hydroxytryptamine (5-HT) and tryptamine (TRP) in the isolated rabbit aorta. The response to 5-HT was more susceptible to inhibition by competitive antagonists selective for 5-HT receptors, such as cyproheptadine, 5-methylgramine, 5-methoxygramine or 2-bromolysergic acid diethylamide, than was the response to TRP; the estimated apparent dissociation constants (KB value) for each antagonist was significantly lower when 5-HT rather than TRP was the agonist. If either of the two agonists and an antagonist were competing for the same single receptor, the KB value should be independent of the agonist. The 5-HT response was also more sensitive to the noncompetitive antagonist, dibenamine. A noncompetitive antagonist of alpha adrenergic receptors, benextramine tetrahydrochloride monohydrate (BHC), depressed the maximal TRP response 25 to 35% without affecting the 5-HT response. After blockade of alpha adrenergic receptors with BHC, KB values determined for each of the competitive antagonists using either 5-HT or TRP were no longer significantly different. Also after blockade by BHC, TRP and 5-HT responses were now equally sensitive to dibenamine. After adrenergic nerve terminals had been removed by stripping off the adventitia of the aorta, the response to TRP was still partially antagonized by BHC. It is concluded that in this preparation TRP directly activates both alpha adrenergic and 5-HT receptors and the 5-HT response is mediated by the 5-HT receptor with no involvement of alpha receptors.

Adrenergic alpha-Antagonists↗
PubMed1982

Role of endothelial cells in relaxation of isolated arteries by bradykinin.

Bradykinin elicits relaxation of isolated transverse rings of canine coronary, celiac, superior mesenteric, renal, splenic, pulmonary, gastric, and femoral arteries. After endothelial cells of the vessel wall are removed by rubbing of the intimal surface, canine arteries fail to relax upon addition of bradykinin. The endothelium-dependent relaxation of canine arteries remains intact after treatment with cyclooxygenase inhibitors (indomethacin and flurbiprofen), and this argues against mediation by prostaglandins. When they are stimulated with bradykinin, endothelial cells of canine arteries appear to release a substance mediating vascular smooth muscle relaxation. In contrast, preparations of arteries of cats (superior mesenteric) and rabbits (superior mesenteric and celiac) may be rubbed on the intimal surface without a consistent loss of sensitivity to the relaxing effects of bradykinin. In addition, relaxation of the cat and rabbit arteries is completely blocked by cyclooxygenase inhibitors. Preliminary studies indicate that bradykinin relaxes human arteries in an endothelium-dependent manner and that this effect is not mediated by prostaglandins. We have previously reported that arteries of all species tested require the presence of endothelial cells for relaxation in response to acetylcholine and we have also demonstrated, using the rabbit aorta, that this effect is mediated by the release of an uncharacterized substance from these cells that relaxes vascular smooth muscle. We conclude that bradykinin relaxes canine and human arteries via a similar mechanism but that it relaxes cat and rabbit arteries by stimulating release of prostaglandins from as yet undefined cell types.

Animals↗
PubMed1980

The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine.

Despite its very potent vasodilating action in vivo, acetylcholine (ACh) does not always produce relaxation of isolated preparations of blood vessels in vitro. For example, in the helical strip of the rabbit descending thoracic aorta, the only reported response to ACh has been graded contractions, occurring at concentrations above 0.1 muM and mediated by muscarinic receptors. Recently, we observed that in a ring preparation from the rabbit thoracic aorta, ACh produced marked relaxation at concentrations lower than those required to produce contraction (confirming an earlier report by Jelliffe). In investigating this apparent discrepancy, we discovered that the loss of relaxation of ACh in the case of the strip was the result of unintentional rubbing of its intimal surface against foreign surfaces during its preparation. If care was taken to avoid rubbing of the intimal surface during preparation, the tissue, whether ring, transverse strip or helical strip, always exhibited relaxation to ACh, and the possibility was considered that rubbing of the intimal surface had removed endothelial cells. We demonstrate here that relaxation of isolated preparations of rabbit thoracic aorta and other blood vessels by ACh requires the presence of endothelial cells, and that ACh, acting on muscarinic receptors of these cells, stimulates release of a substance(s) that causes relaxation of the vascular smooth muscle. We propose that this may be one of the principal mechanisms for ACh-induced vasodilation in vivo. Preliminary reports on some aspects of the work have been reported elsewhere.

Acetylcholine↗
PubMed1976

Dissociation constants and relative efficacies of agonists acting on alpha adrenergic receptors in rabbit aorta.

The dissociation constants (KA values) of l-norepinephrine (l-NE) and seven other agonists acting on alpha adrenergic receptors in rabbit aorta strips were determined by analysis of concentration-response data before and after fractional inactivation of receptors with Dibenamine. In experiments to determine KA values, propranolol was added to block activation of beta receptors and cocaine to block the neuronal uptake mechanism. The KA of l-NE and the KA of a second agonist, when determined on paired strips from the same aorta, were used to calculate the relative affinity and the relative efficacy (er) of the second agonist as compared to l-NE. The validity of the method used for determining KA and er values was supported by the following findings. 1) The dissociation constant (KB) of the competitive antagonist, phentolamine, determined with each of the agonists, was the same as that determined with l-NE. 2) The KA determined for l-NE was independent of the fraction of active receptors remaining (q) after pretreatment with different concentrations of Dibenamine. 3) The KB of phentolamine determined with l-NE as the agonist was the same before and after fractional inactivation of receptors. 4) After inactivation in paired strips by equal exposures to Dibenamine, the q value determined with each agonist was the same as that determined with l-NE. The mean KA value for l-NE was 3.39 +/- 0.15 X 10(-7) M. The mean relative affinities of the agonists for the alpha receptor were: l-NE, 1;L-EPINEPHRINE, 1.25; L-PHENYLEPHRINE, 0.200; L-norphenylephrine, 0.217; epinine, 0.136; dopamine, 0.0055; l-alpha-methylnorepinephrine, 0.095; dl-alpha-ethylnorepinephrine, 0.0048. The mean er of each agonist was not significantly different from that of l-NE, except for l-norphenylephrine with an e of 0.71, and dl-alpha-ethylnorepinephrine with an er of 0.41. The results are discussed from the standpoint of structure-activity relationships.

Adrenergic alpha-Agonists↗
PubMed1975

Desensitization of the adrenergic neurons of the isolated rabbit ear artery to nicotinic agonists.

At 37 degrees C the vasoconstrictor response of the isolated, perfused rabbit ear artery to an infusion of nicotine or acetylcholine (ACh) was transient--rising rapidly to a peak and then fading completely within a minute or two. After complete fade of the response during continued infusion of either nicotine or ACh (in the presence of atropine), the vasoconstrictor responses to stimulation of periarterial adrenergic neurons or to infused norepinephrine (NE) were not diminished. The fade of response was attributed to desensitization of nicotinic receptors at the adrenergic nerve terminals on which nicotine and ACh act to release NE. On washout of either nicotinic agonist after development of desensitization, recovery of sensitivity was essentially complete within several minutes, provided that neither excessively high concentrations nor excessively long periods of infusion had been used. The rate of desensitization to nicotine of ACh increased with concentration of the agonist. On infusion of high concentrations (200 mug/ml) of either, the time required for full desensitization was estimated to be less than 5 seconds. Cross-desensitization was demonstrated for nicotine, ACh and tetramethylammonium. Considerable desensitization occurred even on infusion of nicotine (1 mug/ml) slightly below that required to give a threshold vasoconstrictor response. Moreover, full desensitization without any preceding vasoconstrictor response could be obtained if the concentration of infused nicotine was gradually increased from an initial subthreshold to a final very high suprathreshold level over a 20- to 30-minute period. Both the rate and degree of desensitization to nicotine decreased as the temperature was decreased from 37 degrees to 27 degrees C. The present results are consistent with the concept that the nicotinic receptor (or receptor mechanism) at the adrenergic nerve terminal, after being activated as a result of combination with the agonist, can undergo a transformation to an inactive or desensitized state. It is proposed that under conditions where desensitization to the agonist develops in the absence of any vasoconstrictor response, the fraction of receptors in the activated state at any instant in time during the development is too small to trigger the release of NE.

Acetylcholine↗