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T M Cocks

Publications and source records attributed to T M Cocks.

At least 55 records · Page 3Linked to original sources
PubMed1990

Comparison of relaxation responses of vascular and non-vascular smooth muscle to endothelium-derived relaxing factor (EDRF), acidified sodium nitrite (NO) and sodium nitroprusside.

Smooth muscle relaxant activity of endothelium-derived relaxing factor (EDRF) released from columns of cultured bovine endothelial cells by bradykinin (0.1-3 nmol/l) was measured in four non-vascular preparations: guinea-pig taenia caeci, guinea-pig trachea, rat stomach (fundus) and rat anococcygeus. Each preparation was contracted to a steady level of force with a variety of agonists such that they relaxed optimally to sodium nitroprusside (SNP). The EDRF-induced relaxations in each preparation were compared with those obtained in de-endothelialized ring preparations of greyhound coronary artery by means of paired bioassays run in parallel. EDRF released from the endothelial cell columns caused 80-100% relaxation of the coronary artery, 40-80% in the guinea-pig taenia caeci, 50-70% in the rat anococcygeus, 5-8% in the guinea-pig trachea and was undetectable in the rat stomach strip. By comparison, SNP caused maximal relaxation in all tissues compared with the coronary artery. In separate organ bath experiments the sensitivity to nitric oxide (NO: generated by adding acidified solutions of NaNO2) and SNP was compared in each preparation. SNP caused maximal relaxation in all tissues with the following order of potency: dog coronary artery greater than guinea-pig trachea greater than guinea-pig taenia = rat anococcygeus greater than rat stomach strip. In contrast, the concentration of acidified NaNO2 (NO, 300 nmol/l) that caused 96 +/- 4% relaxation in the dog coronary artery caused 84 +/- 7% and 48 +/- 1% relaxation in the taenia and anococcygeus respectively. No response attributable to NO was detected in either the trachea or rat stomach strip.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Glibenclamide is a competitive antagonist of the thromboxane A2 receptor in dog coronary artery in vitro.

1. Glibenclamide, a sulphonylurea oral hypoglycaemic agent is a widely used antagonist of cromakalim-activated K+ channels in smooth muscle. 2. In isolated ring segments of the large circumflex coronary artery from the dog, glibenclamide (1-30 microM) caused a concentration-dependent reduction in both spontaneous isometric force and contractions induced by U46619, a thromboxane A2-mimetic. 3. Glibenclamide behaved as a competitive antagonist of U46619 with an estimated pKB (-log KB) value of 6.2 by Schild regression analysis (slope 1.07). 4. Glibenclamide (30 microM) was apparently selective since it had no effect on the concentration-contraction curves to endothelin-1, noradrenaline or KCl. 5. We suggest that this additional property of glibenclamide should be considered in any smooth muscle study where active force is raised by either the exogenous application or endogenous generation of thromboxane A2.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1989

Reactivity of endothelin-1 on human and canine large veins compared with large arteries in vitro.

In comparison with snake venom sarafotoxins S6, the novel, 21-amino acid peptide, endothelin may have selective coronary artery vasoconstrictor actions. We examined endothelin-1 (ET-1) in vitro in five pairs of large arteries and veins from the greyhound dog; (coronary, internal mammary, mesenteric, renal and femoral) as well as the human forearm vein and internal mammary artery and vein. ET-1 caused concentration-dependent, tonic contractions in each pair of vessels, with EC50s significantly lower (5-10 times more sensitive) in each vein compared with the corresponding artery. The coronary artery did not show selective sensitivity to ET-1. For all veins the maximal contraction to ET-1 was approximately 100% that of the maximal contraction (Fmax) achieved with K+ depolarization. In the arteries, however, the Fmax for ET-1 ranged from only 25 to 80% of K+. The contraction responses to ET-1 in all arteries and veins were well maintained after repeated washing with ET-1-free medium. In the dog coronary artery the contraction curve to ET-1 (0.1-30 nM) was endothelium-independent. At the higher concentrations (10-100 nM), however, the peptide often induced transient, endothelium-dependent relaxations prior to the development of the tonic contractions. These results demonstrate that ET-1 is a more potent and efficacious constrictor of large veins than arteries and at high concentrations can release endothelium-derived relaxing factor-like activity from large arteries.

Animals↗
PubMed1989

Endothelin is blood vessel selective: studies on a variety of human and dog vessels in vitro and on regional blood flow in the conscious rabbit.

1. Endothelin (Et), a vasoconstrictor peptide, was 5-10-fold more potent (lower EC50) on isolated ring segments of large veins than on large arteries removed from dog coronary, mesenteric, femoral, renal and internal mammary vasculature and from the human internal mammary pedicle. 2. In the dog large coronary artery, Et (10-30 nmol/L) caused transient relaxations partway through the generation of a concentration-contraction curve. These relaxations were endothelium dependent. 3. In conscious rabbits treated with mecamylamine, Et (0.025-0.4 nmol/kg) caused a marked rise in renal vascular resistance but hindquarter vasodilation. Under the same conditions angiotensin II constricted both beds. 4. These studies suggest that Et is vascular bed and large vein selective in activity. It did not appear to be selective for large or small coronary arteries in vitro.

Animals↗
PubMed1988

Amiloride analogues cause endothelium-dependent relaxation in the canine coronary artery in vitro: possible role of Na+/Ca2+ exchange.

1. A number of amiloride analogues were used to test the proposal that Na+/Ca2+ exchange may play a role in the secretion of endothelium-derived relaxing factor (EDRF). The analogues used were those substituted on either the 5-amino group or the terminal guanidino nitrogen atom. The former block both Na+/Ca2+ and Na+/H+ exchange whilst the latter block the Na+ channel and the Na+/Ca2+ exchange. 2. Both series of compounds caused relaxation in isolated rings of dog coronary artery (EC50 values, 1-10 microM) presumably due to release of EDRF since removal of endothelium greatly attenuated the response. 3. Amiloride (1-100 microM) had little effect on either endothelium-intact or denuded arteries. 4. The guanidino substituted analogues also appeared to block selectively the relaxation response to acetylcholine in the coronary artery, independently of their EDRF-releasing activity. 5. It is proposed that endothelial cells have an active Na+/Ca2+ exchange operating in the forward mode to extrude Ca2+. This mechanism may be important in the control of EDRF release.

Amiloride↗
PubMed1987

Vasodilatation and the discovery of endothelium-derived relaxing factor.

Whether endothelium-derived relaxing factor (EDRF) is important in the physiology and pathology of vascular reactivity must await the discovery of the nature of the factor and an appropriate antagonist substance. Nevertheless the demonstration that EDRF is powerful, short-lived and can be released by a wide variety of stimuli adds a new dimension to our knowledge of the control of the circulation. The macroenvironment of the vessel wall is influenced by nerves, blood-borne factors and the architecture of the wall. The discovery of a role of the endothelial cell has for the first time forced pharmacologists to consider cell-cell interactions in the micro-environment of the blood-vessel wall. This is a potentially important target for new therapy.

Acetylcholine↗
PubMed1987

The half-life of endothelium-derived relaxing factor released from bovine aortic endothelial cells in culture.

1. The half-life of endothelium-derived relaxing factor (EDRF) in Krebs solution was determined by bioassay in vitro. 2. A column of bovine aortic endothelial cells grown on microcarrier beads in suspension culture was perfused with Krebs solution. EDRF was released from these cells by sequential treatment with increasing concentrations of bradykinin (0.01-100 nM). EDRF was detected by the relaxation of an endothelium-denuded ring segment of dog coronary artery. 3. Complete bradykinin concentration-relaxation curves were determined in the absence or presence of coils of tubing that increased the transit time (delay) between the cell column and the assay tissue. An estimate of the falls in concentration, and hence of the half-life of EDRF, was obtained from the shift of the bradykinin concentration-relaxation curves. 4. Mass-action equations were used to model the relationship between the indirectly acting agonist bradykinin and the relaxation via EDRF. The modelling adequately predicted the consequences of different transit delay times (0-4 half-lives). 5. This new analysis of half-life of an active intermediate emphasizes the measurement of changes in concentration with increasing transit time rather than a fall in tissue response. 6. The half-life of EDRF in Krebs solution is 41 s.

Animals↗
PubMed1987

Development of a large fibromuscular intimal thickening does not impair endothelium-dependent relaxation in the rabbit carotid artery.

The release of endothelium-derived relaxing factor (EDRF) was examined in the rabbit carotid artery 6 weeks after denudation with an inflated balloon catheter in vivo. A concentric, fibromuscular intimal thickening of variable width developed in all areas lined with either regenerated endothelium or modified luminal smooth muscle cells. In vitro studies showed that in vessels precontracted with serotonin, only the re-endothelialized areas could relax to the endothelium-dependent dilators methacholine, substance P and the Ca2+ ionophore A23187. Re-endothelialized areas with large concentric, fibromuscular intimal thickening (between 10 and 20 cells thick) relaxed with a similar sensitivity and maximum to methacholine compared with control areas. It is concluded that newly generated endothelial cells release EDRF whilst the specialized lining smooth muscle cells present 6 weeks after injury do not, and that the presence of a large fibromuscular intima does not prevent EDRF from reaching the media to cause relaxation.

Animals↗
PubMed1986

Endothelium-dependent relaxation is unaltered by hypertension, cholesterol or intimal thickening.

The effect of cellophane wrap hypertension (WRAP) and hypercholesterolemia (1% cholesterol diet, CHOL) for 4 weeks was assessed on the endothelium-dependent vasodilator response to acetylcholine in conscious rabbits after pharmacological autonomic blockade. Dose-response curves for the hindlimb vascular resistance (ear artery pressure/lower aortic blood flow; Doppler flowmeter) and acetylcholine infusion (i.v.) doses were unaltered in sensitivity (ED50) for any of the treatment groups. The range and slope of the curves were significantly altered by WRAP, CHOL or WRAP plus CHOL for acetylcholine and adenosine infusions consistent with medial hypertrophy in resistance vessels and raised serum viscosity. The effect of intimal thickening on the response to endothelium derived relaxing factor (EDRF) was tested in dog carotid artery ring segments in vitro 4 weeks after endothelium removal. The relaxation responses to acetylcholine (EDRF-dependent) and adenosine or nitroglycerin were not significantly altered by the neo-intima. Therefore the response to EDRF released by acetylcholine in resistance vessels was unaltered by hypertension, hypercholesterolemia or both together. Neo-intimal thickening in response to initial endothelium loss does not appear to alter EDRF responses in the carotid artery.

Animals↗
PubMed1986

Alpha 2-adrenoceptors and endothelium-dependent relaxation in canine large arteries.

Ring preparations from the carotid, coronary, renal, mesenteric and femoral arteries of the dog were precontracted with the thromboxane mimetic U46619, after ensuring that the resting conditions were comparable from the Laplace relationship. In the presence of prazosin (1 microM) and propranolol (3 microM), noradrenaline (NA) relaxed the arteries in the order coronary greater than carotid greater than femoral greater than renal = mesenteric. When maximum relaxation to nitroglycerin (10 microM) was taken to be 100% the maximum relaxation to noradrenaline in each artery was: coronary 70%; carotid 34%; femoral 19%; renal 7% and mesenteric 2%. In endothelium-intact arteries UK14304 mimicked the relaxation responses to NA and idazoxan shifted the curves to both agonists to the right, consistent with an alpha 2-adrenoceptor classification. Substance P relaxed the arteries in the same order as for NA but showed higher efficacy i.e.: coronary 100%; carotid 80%; femoral 71% renal 49%; and mesenteric 41%. Removal of the endothelium abolished the relaxation to NA. We conclude that endothelium-dependent relaxation to NA and substance P varies greatly across 5 large arteries of the dog. This may indicate that endothelium-derived relaxing factor (EDRF) release is site-dependent or that the efficacy of EDRF on smooth muscle varies; being greatest in the coronary and weakest in the renal and mesenteric arteries.

Animals↗
PubMed1986

The alpha adrenoceptors on endothelial cells.

Endothelial cells release a powerful factor (endothelium-derived relaxing factor [EDRF]) that relaxes smooth muscle cells in response to some vasodilating agents such as acetylcholine. Contraction curves to norepinephrine (NE) in greyhound, mongrel dog, and pig coronary artery rings were studied in vitro in the presence of propranolol. Removal of endothelium increased the sensitivity and maximum contraction in response to NE. In other experiments pig coronary rings were precontracted with a thromboxane mimetic U 46619 in the presence of propranolol. NE relaxed these arteries only if endothelium was present. Methoxamine was without effect but the relaxation response to NE was antagonized by phentolamine, idazoxan, and yohimbine, which suggests that there are alpha 2 adrenoceptors on endothelial cells that mediate the release of EDRF. Greyhound and mongrel dog large coronary arteries relaxed to NE only if prazosin was present, which suggests that alpha 1-adrenoceptor stimulation on the vascular smooth muscle can override the relaxation response to EDRF. Comparison of NE responses in carotid, mesenteric, renal, and femoral large arteries of the pig, greyhound, and mongrel dog indicate the nonuniformity of distribution of alpha 2 adrenoceptors on endothelium and alpha 1 and alpha 2 adrenoceptors on vascular smooth muscle. The integrity of the endothelium must now be considered in interpreting the vascular responses to alpha-adrenoceptor agonists.

Animals↗
PubMed1985

Release and properties of endothelium-derived relaxing factor (EDRF) from endothelial cells in culture.

Cultured bovine endothelial cells were seeded onto the intimal surface of endothelium-denuded rings of canine coronary artery. These rings did not previously relax to acetylcholine, substance P, bradykinin, and A23187. After seeding, the same rings relaxed to bradykinin and A23187, but not to acetycholine or substance P. Indomethacin pretreatment did not affect these responses. Cells from the same source were then grown to confluence on microcarrier beads, poured into small columns, and perfused with Krebs' solution. The perfusate from the columns was bioassayed on endothelium-denuded rings of coronary artery from either the dog or pig. Challenge of the column in the presence of indomethacin with either bradykinin or A23187 as well as acetylcholine or substance P caused release of a substance that relaxed both types of artery. Its activity half-life was 6.4 +/- 0.4 sec at 37 degrees C and it was hydrophilic and negatively charged. Prostacyclin (PGI2) as a candidate for EDRF was ruled out because 1) indomethacin failed to block its release and 2) the pig coronary artery, although insensitive to PGI2, relaxed to the endothelium-derived substance. These results show that, in response to a number of dilator drugs, cultured endothelial cells release a vascular relaxing substance (EDRF) that has characteristics similar to the EDRF of normal endothelium. The chemical nature of EDRF awaits clarification.

Animals↗
PubMed1984

Interactions between receptors that increase cytosolic calcium and cyclic AMP in guinea-pig liver cells.

The action of agonists which increase the K+ permeability of liver cells was studied by using a K+-sensitive electrode to record the net movement of K+ between guinea-pig isolated hepatocytes and their suspension medium. Two types of agonist were examined. Type 1 comprised angiotensin II, ATP, noradrenaline and amidephrine, all of which are thought to raise cytosolic Ca2+ in hepatocytes. The Type 2 agonists were isoprenaline and glucagon, which activate adenylate cyclase. Each type of agonist initiated K+ loss from the hepatocytes though the response to Type 2 agonists was more variable than that to Type 1, and sometimes absent. Simultaneous application of a small concentration of an agonist from each class caused a loss of K+ which was much larger than the sum of that seen with each agonist alone, i.e. potentiation occurred. The alpha-adrenoceptor antagonist, WB 4101, abolished potentiation if applied after an alpha-agonist, and before a Type 2 agonist, showing that both receptors have to be active for potentiation to occur. Simultaneous application of a maximal concentration of each type of agonist caused a larger loss of K+ (approximately 17% of the cell total within 45 s) than did a maximal concentration of a Type 1 agonist alone (approximately 10%). Since the K+ loss caused by these agonists is thought to be a consequence of a rise in cytosolic Ca2+, the influence of both types of agonist on 45Ca and 42K efflux from guinea-pig liver slices was studied. The effect of isoprenaline on 45Ca and 42K efflux became much greater following a previous application of the alpha-adrenoceptor agonist, amidephrine. In the presence of apamin, the potentiated effect of isoprenaline on 42K efflux was greatly reduced whereas that on 45Ca efflux was little affected. The effects of Type 1 and Type 2 agonists separately and together on the cyclic AMP content of isolated hepatocytes were examined. Type 2 agonists increased cyclic AMP in the expected way. The increase became slightly smaller, if anything, when a Type 1 agonist was applied at the same time. Hence potentiation could not be ascribed to changes in cyclic AMP formation. Possible mechanisms for potentiation are discussed. Our evidence suggests, albeit indirectly, that it is a consequence of an interaction between the effects of the two types of agonist on cytosolic Ca2+.

Adenosine Triphosphate↗
PubMed1983

Vasodilatation by acetylcholine is endothelium-dependent: a study by sonomicrometry in canine femoral artery in vivo.

External diameter of the femoral artery was measured by sonomicrometry in the anaesthetized dog. Intra-arterial acetylcholine lowered arterial pressure and thereby passively lowered diameter. When blood flow and distal resistance were controlled by roller pump and Starling resistor respectively, acetylcholine (0.1-10 microM) and substance P (0.1-1 nM) both caused up to 10% increase in diameter. Removal of endothelium by mechanically rubbing the artery lumen abolished the dilator response to acetylcholine and substance P but did not affect the response to nitroprusside. Constrictor responses to noradrenaline were unaltered by endothelium removal. Topical application of acetylcholine and substance P onto the adventitial surface of the artery also caused an increase in diameter but both agents were 50-100 times less potent by this route compared with intra-arterial infusion. These dilator responses were abolished by endothelium removal. In these circumstances acetylcholine caused constriction. We conclude that acetylcholine and substance P require an intact endothelium to elicit vasodilatation in vivo, at least for the large femoral artery. The results from the topical application experiments suggest that local neural release of vasoactive substances such as acetylcholine and substance P depend on an intact endothelium to cause vasodilatation.

Acetylcholine↗
PubMed1979

Apamin blocks certain neurotransmitter-induced increases in potassium permeability.

Apamin is a neurotoxic polypeptide of known structure isolated from bee venom. Shuba and coworkers have recently shown that it abolishes the hyperpolarising action of externally-applied ATP on visceral smooth muscle (guinea pig stomach and taenia coli) as well as the hyperpolarisation (inhibitory junction potential) that follows stimulation of the non-adrenergic inhibitory nerve supply to these tissues. As it has been proposed that ATP is the neurotransmitter involved in the latter response, Vladimirova and Shuba tentatively concluded that apamin is a specific postsynaptic blocking agent of this non-adrenergic, possibly 'purinergic', inhibition. We have confirmed the important observation that nanomolar concentrations of apamin reduce inhibition by ATP and by non-adrenergic nerve stimulation, but further experiments suggest that, rather than acting as a specific blocker of ATP receptors, apamin inhibits the increase in potassium permeability caused by a number of agents, including ATP.

Adenosine Triphosphate↗