Anisotropic strain transfer through the aortic valve and its relevance to the cellular mechanical environment.

Aortic valve interstitial cells are responsible for maintaining the valve in response to their local mechanical environment. However, the complex organization of the extracellular matrix means cell strains cannot be directly derived from gross strains, and knowledge of tissue structure-function correlations is fundamental towards understanding mechanotransduction. This study investigates strain transfer through the valve, hypothesizing that organization of the valve matrix leads to non-homogenous local strains. Radial and circumferential samples were cut from aortic valve leaflets and subjected to quasi-static mechanical characterization. Further samples were imaged using confocal microscopy, to determine local strains in the matrix. Mechanical data demonstrated that the valve was significantly stronger and stiffer when loaded circumferentially, comparable with previous studies. Micromechanical studies demonstrated that strain transfer through the matrix is anisotropic and indirect, with local strains consistently smaller than applied strains in both orientations. Under radial loading, strains were transferred linearly to cells. However, under circumferential loading, strains were only one-third of applied values, with a less direct relationship between applied and local strains. This may result from matrix reorganization, and be important for preventing cellular damage during normal valve function. These findings should be taken into account when investigating interstitial cell behaviours, such as cell metabolism and mechanotransduction.

Expression of the familial cardiac valvular dystrophy gene, filamin-A, during heart morphogenesis.

Myxoid degeneration of the cardiac valves is a common feature in a heterogeneous group of disorders that includes Marfan syndrome and isolated valvular diseases. Mitral valve prolapse is the most common outcome of these and remains one of the most common indications for valvular surgery. While the etiology of the disease is unknown, recent genetic studies have demonstrated that an X-linked form of familial cardiac valvular dystrophy can be attributed to mutations in the Filamin-A gene. Since these inheritable mutations are present from conception, we hypothesize that filamin-A mutations present at the time of valve morphogenesis lead to dysfunction that progresses postnatally to clinically relevant disease. Therefore, by carefully evaluating genetic factors (such as filamin-A) that play a substantial role in MVP, we can elucidate relevant developmental pathways that contribute to its pathogenesis. In order to understand how developmental expression of a mutant protein can lead to valve disease, the spatio-temporal distribution of filamin-A during cardiac morphogenesis must first be characterized. Although previously thought of as a ubiquitously expressed gene, we demonstrate that filamin-A is robustly expressed in non-myocyte cells throughout cardiac morphogenesis including epicardial and endocardial cells, and mesenchymal cells derived by EMT from these two epithelia, as well as mesenchyme of neural crest origin. In postnatal hearts, expression of filamin-A is significantly decreased in the atrioventricular and outflow tract valve leaflets and their suspensory apparatus. Characterization of the temporal and spatial expression pattern of filamin-A during cardiac morphogenesis is a crucial first step in our understanding of how mutations in filamin-A result in clinically relevant valve disease.

5-Hydroxytryptamine mediates endothelium dependent coronary vasodilatation in the isolated rat heart by the release of nitric oxide.

STUDY OBJECTIVE: The aim was to investigate further the endothelium dependent vasodilator action of 5-hydroxytryptamine (5-HT) on the rat coronary circulation. DESIGN: Using saponin to damage the endothelium and L-NMMA (NG-monomethyl-L-arginine), the selective inhibitor of nitric oxide formation, we examined the role of endothelium and nitric oxide in causing 5-HT induced vasodilatation in the isolated rat heart. EXPERIMENTAL MATERIAL: 56 rat hearts were excised and perfused on a Langendorff preparation. MEASUREMENTS AND MAIN RESULTS: 5-HT at (10(-9) to 10(-5) M) and glyceryl trinitrate at (10(-5) to 10(-3) M) (n = 24) induced a dose dependent increase in coronary flow. Chemical removal of the endothelium by exposure to saponin (30 micrograms.ml-1) (n = 8) abolished the 5-HT induced vasodilatation but had no effect on the response to glyceryl trinitrate. Pretreatment of rats (n = 8) with L-NMMA (100 mg.kg-1) unmasked a strong vasoconstrictor effect of 5-HT but did not affect the glyceryl trinitrate induced vasodilatation. Perfusion of L-NMMA pretreated hearts with L-arginine at 10(-4) M (n = 8) restored the vasodilatation induced by 5-HT but L-arginine perfusion had no effect on the extent of 5-HT or glyceryl trinitrate induced vasodilatation in normal hearts (n = 8). CONCLUSIONS: In the coronary circulation of the isolated rat heart, 5-HT mediates its vasodilator effect via endothelium dependent release of nitric oxide.

L-arginine reverses low coronary reflow and enhances postischaemic recovery of cardiac mechanical function.

OBJECTIVE: To evaluate the effect of L-arginine, the physiological substrate of nitric oxide (NO), upon coronary flow (CF) and mechanical function during reperfusion following cardioplegic arrest. METHODS: Two groups of isolated rat hearts were subjected to cardioplegic arrest for 4 h at 4 degrees C. In group 1 (n = 10) cardioplegic arrest was followed by 4 consecutive periods of reperfusion with Krebs buffer (control), Krebs plus L-lysine (1 mmol/1), Krebs plus L-arginine (1 mmol/1) and Krebs plus L-NGmonomethylarginine (L-NMMA), a specific inhibitor of NO synthesis, (0.5 mmol/1). In group 2, hearts (n = 8) were perfused by Krebs, then L-NMMA, during both pre- and postischaemic periods. In group 3, hearts (n = 8) were perfused by Krebs, then L-arginine (1, 2 and 4 mmol/1). In group 4 (n = 5), NO released into the perfusate was measured before ischaemia and during reperfusion. RESULTS: In group 1, L-arginine enhanced the postischaemic CF (ml/min +/- s.e.m.) from 15.0 +/- 0.4 to 17.2 +/-0.4. This was reduced by L-NMMA to 11.3 +/- 0.3. Postischaemic cardiac output (% of preischaemic value +/- s.e.m.) was increased from 55.8 +/- 2.4 to 80.1 +/- 2.5 by L-arginine and dropped to 54.3 +/- 2.3 with L-NMMA. In group 2, the pre- and postischaemic loss of coronary flow (CF) by L-NMMA was 51% and 31% respectively. In group 3, L-arginine did not modify CF. In group 4 the preischaemic level of NO (in nmol/ml/min) in the coronary effluent, measured by chemiluminescence, was 14.84 +/- 0.83 and dropped significantly (P < 0.05) to levels ranging from 3.80 +/- 0.56 to 4.75 +/- 0.51 during the postischaemic period. CONCLUSION: Exogenous administration of L-arginine improves low coronary reflow and postischaemic mechanical function.

5-Hydroxytryptamine receptor profile in healthy and diseased human epicardial coronary arteries.

STUDY OBJECTIVE: The aim of the study was to investigate the receptor events that mediate the vascular effects of 5-hydroxytryptamine (5-HT) on human coronary arteries, since 5-HT has long been thought to play a role in coronary artery vasospasm. DESIGN: Recently available selective receptor agonists and antagonists were used to examine the 5-HT receptor subtypes present in human epicardial coronary arteries using in vitro organ baths. EXPERIMENTAL MATERIAL: 138 segments of coronary arteries were obtained from 21 patients aged 2-66 years undergoing heart transplantation. MEASUREMENTS AND MAIN RESULTS: 5-HT produced only concentration dependent contractions of coronary artery segments. No evidence was obtained for 5-HT receptors mediating either endothelium dependent or endothelium independent vasorelaxation. In tissue from patients without ischaemic heart disease, 5-HT effects were mimicked by (+/-)-alpha-methyl-5-HT (alpha-me-5-HT), a selective agonist at 5-HT2 receptors. In addition, the selective 5-HT1-like receptor agonist GR43175 produced contractions which achieved 30% of the maximum response to 5-HT. Responses to alpha-me-5-HT were surmountably antagonised by the non-selective antagonist methiothepin (0.1 mumol.litre-1) as well as the 5-HT2 receptor antagonist ketanserin (0.1 mumol.litre-1). In contrast GR43175 effects were resistant to blockade by ketanserin, but remained sensitive to methiothepin. Responses to the two agonists were not antagonised by the 5-HT3 receptor antagonist MDL72222 (1.0 mumol.litre-1). Vessel segments from ischaemic heart disease patients also contracted to alpha-me-5-HT and GR43175. Diseased arteries contracted with a decrease in the maximal response induced by both alpha-me-5-HT and by 90 mM K+ depolarisation compared to "normal" vessels, but the effect of GR43175 was preserved in the diseased arteries. Vascular rings adjacent to an atheromatous lesion were more reactive to GR43175 than serial segments taken distal to the lesion. CONCLUSIONS: These results show that both 5-HT1-like and 5-HT2 receptors mediate contraction of human epicardial coronary arteries and indicate that effects mediated by 5-HT1-like receptors but not 5-HT2 receptors are preserved in patients with ischaemic heart disease.

Comparison of cyclic GMP in human internal mammary artery and saphenous vein: implications for coronary artery bypass graft patency.

OBJECTIVE: The aim was to examine the capacity of the human saphenous vein (native and surgically prepared) and the internal mammary artery to generate cyclic GMP, the second messenger that mediates smooth muscle relaxation following production of nitric oxide. METHODS: 209 vessel segments were used from 22 patients undergoing coronary revascularisation. Isolated vessel segments were stimulated with a range of endothelium dependent and endothelium independent agonists and flash frozen for radioimmunoassay for cyclic GMP. RESULTS: Control/basal levels of cyclic GMP were significantly higher in the internal mammary artery than either native or distended saphenous vein. Endothelium dependent agonist stimulation with acetylcholine, bradykinin, or substance P induced significant increases in cyclic GMP in internal mammary artery and native saphenous vein, whereas distended veins showed non-significant changes in response to agonist stimulation. Endothelium removal abolished agonist stimulated increases in cyclic GMP. Glyceryl trinitrate and sodium nitroprusside elicited significant further increases in cyclic GMP in native vein and internal mammary artery. All values obtained were significantly greater in arterial than in venous tissue. CONCLUSION: Differences in basal and stimulated cyclic GMP activity in arteries and veins have been shown. This could represent an additional protective mechanism against constrictor influences in arterial bypass grafts, which may explain their documented better long term performance.

Induction of nitric oxide synthase in human vascular smooth muscle: interactions between proinflammatory cytokines.

OBJECTIVE: We have attempted to demonstrate the induction of inducible nitric oxide synthase in human vascular tissue and define the capacity of different cytokines to induce this enzyme. METHODS: Segments of human arteries were stimulated with lipopolysaccharide (10 micrograms/ml), interleukin-1 beta (5 U/ml), tumor necrosis factor-alpha (10 U/ml), and interferon-gamma (200 U/ml). Cytokines were either used alone or in certain combinations, as well as in the presence of L-NG-monomethyl-arginine (100 mumol/l) or cycloheximide (1 mumol/l). Induction was assessed by measurement of mRNA expression, immunocytochemical localisation of the expressed protein, nitric oxide synthase activity and levels of nitrite, a product of nitric oxide formation. RESULTS: PCR analysis showed the presence of mRNA for iNOS in stimulated samples which could be inhibited by cycloheximide. There was positive staining with an antibody against human iNOS in the media of stimulated vessel segments. Stimulated segments were also shown to contain Ca(2+)-independent nitric oxide synthase activity. The cytokines and lipopolysaccharide together gave a significant rise in levels of nitrite in the medium after 36 and 48 h, which was inhibited by L-NG-monomethyl-arginine and cycloheximide. Only interferon-gamma incubated alone was capable of increasing nitrite levels. This effect was enhanced by co-incubation with either interleukin-1 beta, tumor necrosis factor-alpha or lipopolysaccharide. CONCLUSION: We have shown that increased production of nitrite by human vascular tissue in response to cytokines is associated with induction of iNOS as shown at the molecular and protein levels, and further supported by the presence of increased Ca(2+)-independent nitric oxide synthase activity following cytokine stimulation.

Endothelin-1 stimulates proliferation of human coronary smooth muscle cells via the ET(A) receptor and is co-mitogenic with growth factors.

We investigated the effects of endothelin-1 (ET-1) on growth of cultured human coronary artery smooth muscle cells (cSMC). ET-1 alone stimulated DNA synthesis in growth-arrested cSMC as measured by [3H]thymidine incorporation, with a maximum 63 +/- 23% increase above control by 10(-7) M (P < 0.05). ET-1 (10(-7) M) also stimulated increases in cyclin D1 protein levels after 24 h, and in absolute cell number after 4 days. Furthermore, ET-1 stimulated protein synthesis (maximum 73 +/- 32% increase in [3H]leucine incorporation by 10(-7) M (P < 0.05)), as well as triggering intracellular calcium transients in human cSMC, as visualised under fura-2 fluorescence microscopy. The selective ET(A) receptor antagonist BQ123 inhibited the increases in DNA synthesis, cell number, protein synthesis and intracellular calcium concentration in response to ET-1, whereas the ET(B) receptor antagonist BQ788 had no such effects. Furthermore, the ET(B) agonist sarafotoxin 6c had no effect on cSMC DNA synthesis. In addition, co-incubation of ET-1 with threshold concentrations of the growth factors, platelet-derived growth factor-BB (PDGF-BB), basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF), resulted in pronounced synergistic increases in DNA synthesis over that observed with the factors alone. In conclusion, we have shown that ET-1 stimulates proliferation of human cSMC via the ET(A) receptor and is also a co-mitogen with the growth factors tested. These findings indicate a role for ET-1 in the development of coronary intimal hyperplasia in man.

Action of vasoactive intestinal peptide and distribution of its binding sites in vessels used for coronary artery bypass grafts.

In an attempt to establish the possible role of vasoactive intestinal peptide (VIP) in the regulation of vasomotor tone of coronary artery bypass grafts, this study examined the action of this peptide and the distribution of [125I]VIP binding sites in isolated human gastroepiploic artery (GEA), internal mammary artery (IMA) and saphenous vein. VIP (10(-10)-3 x 10(-7) M) elicited concentration-dependent relaxations in ring segments that were preconstricted with the thromboxane analog U46619. The maximal response was mean +/- SEM 79 +/- 4%, 52 +/- 8% and 23 +/- 3% of glyceryl trinitrate (3 x 10(-5) M)-induced maximal smooth muscle relaxation in the GEA, IMA and saphenous vein, respectively. Both receptor-binding and competition studies indicated that there was a higher density of [125I]VIP binding to smooth muscle cells of the GEA and IMA than to the saphenous vein. Total binding, at 50pM [125I]VIP, was 604 +/- 89, 381 +/- 64 and 87 +/- 12 amol/mg wet weight in the GEA, IMA and saphenous vein, respectively. Dense binding of [125I]VIP was associated with the tunica media in all the vessels studied. There was also binding to perivascular regions with no obvious binding to endothelial cells. These data demonstrate that arterial grafts, particularly the GEA, are more sensitive to the relaxant effect of VIP and this may possibly be due to a higher receptor density.

Influence of endothelin on human coronary arteries and localization of its binding sites.

Endothelin, a 21 amino acid peptide synthesized by cultured porcine aortic endothelial cells, has recently been identified and shown to produce a potent and prolonged constriction of mammalian blood vessels in vitro. Using tissue obtained from explanted hearts at the time of cardiac transplantation, the response of isolated human epicardial coronary arteries to endothelin was studied. The presence of endothelin binding sites was demonstrated in these vessels using an autoradiographic technique. Endothelin produced a dose-dependent increase of tension in the isolated coronary vessels with a maximal tension achieved equal to 135% of that induced by 90 mM of potassium. The maximal response was slow to develop and had a prolonged duration of 15 to 20 minutes. Nicardipine (4 microM) failed to affect the contraction induced by low doses of endothelin, but decreased the tension obtained at high doses. However, adenosine, substance P and glyceryl trinitrate were all effective in reversing the contraction induced by endothelin, while indomethacin and acetylcholine were ineffective. These features differ from those of other endogenous constrictor agents and make endothelin a potential candidate for long-term modulation of vascular tone.

Role of vasoactive mediators in primary and secondary pulmonary hypertension.

The role of vasoactive mediators, such as endothelin-1, nitric oxide, prostacyclin, and thromboxane, in pulmonary hypertension remains undefined. This study investigated the circulating levels and transpulmonary gradients of these vasoactive mediators in patients with primary and secondary pulmonary hypertension to define whether there is increased production or decreased clearance of these substances in the lung vasculature.

A redox-based mechanism for nitric oxide-induced inhibition of DNA synthesis in human vascular smooth muscle cells.

1. The current study explored potential redox mechanisms of nitric oxide (NO)-induced inhibition of DNA synthesis in cultured human and rat aortic smooth muscle cells. 2. Exposure to S-nitrosothiols, DETA-NONOate and NO itself inhibited ongoing DNA synthesis and S phase progression in a concentration-dependent manner, as measured by thymidine incorporation and flow cytometry. Inhibition by NO donors occurred by release of NO, as detected by chemiluminescence and judged by the effects of NO scavengers, haemoglobin and cPTIO. 3. Co-incubation with redox compounds, N-acetyl-L-cysteine, glutathione and L-ascorbic acid prevented NO inhibition of DNA synthesis. These observations suggest that redox agents may alternatively attenuate NO bioactivity extracellularly, interfere with intracellular actions of NO on the DNA synthesis machinery or restore DNA synthesis after established inhibition by NO. 4. Recovery of DNA synthesis after inhibition by NO was similar with and without redox agents suggesting that augmented restoration of DNA synthesis is an unlikely mechanism to explain redox regulation. 5. Study of extracellula interactions revealed that all redox agents potentiated S-nitrosothiol decomposition and NO release. 6. Examination of intracellular NO bioactivity showed that as opposed to attenuation of NO inhibition of DNA synthesis by redox agents, there was no inhibition (potentiation in the presence of ascorbic acid) of soluble guanylate cyclase (sGC) activation judged by cyclic GMP accumulation in rat cells. 7. These data provide evidence that NO-induced inhibition of ongoing DNA synthesis is sensitive to redox environment. Redox processes might protect the DNA synthesis machinery from inhibition by NO, in the setting of augmented liberation of biologically active NO from NO donors.

Alternative pathways of angiotensin II production in the human saphenous vein.

1. The aim of our study was to demonstrate the existence, location and functional importance of an alternative angiotensin II-forming pathway other than angiotensin converting enzyme (ACE) in the human saphenous vein (SV). 2. Vascular reactivity studies using an in vitro organ bath technique showed that the SV (n=20) produced similar maximum contractions in response to angiotensin I (41.5+/-5.4 mN) compared to those observed to angiotensin II (46.7+/-10.9 mN). The response to angiotensin I could be significantly inhibited (P<0.05) by incubation with the AT1 receptor antagonist losartan (1 microM). 3. Prior incubation of segments of SV with either captopril (1 microM) (n=6), quinaprilat (1 microM) (n=7), or the chymase inhibitor soya bean trypsin inhibitor (SBTI) (10 microM) (n=7) singularly failed to have any inhibitory effect on the response to angiotensin I. However when vessel segments (n=7) were co-incubated with quinaprilat (1 microM) and SBTI (10 microM), the SV exhibited a rightward shift in curve profile to angiotensin I and a markedly reduced maximum response 12.5+/-2.4 mN, when compared to control (30.4+/-7.6 mN), quinaprilat (24.5+/-9.4 mN), and SBTI (31.6+/-10.7 mN) on their own. 4. An immunohistochemical technique employing streptavidin biotin peroxidase localised ACE to both endothelial cells and smooth muscle cells while chymase was confined to mast cells in the adventitia of the vessel wall. 5. In conclusion, our results demonstrate the existence of an alternative angiotensin I converting pathway to that of ACE, involving chymase. Therefore, there is the capacity for a continuation of angiotensin II formation, in the presence of ACE inhibition.

Aging reduces postischemic recovery of coronary endothelial function.

The aging process is known to be associated with profound changes in the heart. To determine whether resistance of coronary endothelial and vascular smooth muscle function to ischemia may be related to age, four groups of rats (n = 6 in each group) of different ages (1, 5, 15, and 26 months) were subjected to cardioplegic arrest for 4 hours at 4 degrees C. The postischemic basal release of nitric oxide by endothelium, as assessed by the percentage loss of coronary flow in response to 0.5 mmol/L L-monomethylarginine, an inhibitor of nitric oxide synthase, was as follows: (mean +/- standard error of the mean): 87.1% +/- 1.7%, 81.2% +/- 2.3%, 79.6% +/- 1.9%, and 74.9% +/- 2.4% in groups 1, 2, 3, and 4, respectively. Stimulated release of nitric oxide, as assessed by percentage increase of coronary flow to 10(-5) mmol/L 5-hydroxytryptamine, an endothelium-dependent vasodilator, was as follows (mean +/- standard error of the mean): 88.3% +/- 1.5%, 83.4% +/- 2.4%, 71.1% +/- 2.7%, and 63.1% +/- 3.3% in groups 1, 2, 3, and 4, respectively. Significant differences were found between each group (p < 0.05) for both basal and stimulated release of nitric oxide. Vascular smooth muscle function, as assessed by the percentage increase in coronary flow in response to glyceryl trinitrate, an endothelium-independent vasodilator, was (mean +/- standard error of the mean): 96.7% +/- 2.1%, 92.3% +/- 5.2%, 92.9% +/- 5.0%, and 98.1% +/- 2.4% in groups 1, 2, 3, and 4 respectively. No significant difference was found between groups (p = not significant). In a protocol mimicking conditions for transplantation, the postischemic recovery of the basal and stimulated release of nitric oxide, but not vascular smooth muscle function, diminished with age.

Effect of surgical preparation and arterialization on vasomotion of human saphenous vein.

To gain an insight into venous physiologic adaptation to arterialization, this study examined the effects of thromboxane, 5-hydroxytryptamine, endothelin, leukotriene C4, and norepinephrine on isolated segments of native and distended human saphenous vein, short-term (up to 1 year) grafts, and long-term (1 to 10 year) grafts. The mean maximum constrictor responses, expressed as percentage of maximum potassium depolarization, were as follows: thromboxane analog U46619: native vein 147.0% +/- 10.5%, distended vein 251.2% +/- 29.1%, short-term graft 174.6% +/- 33.8%, long-term graft 220.9% +/- 21.7%; 5-hydroxytryptamine: native vein 115.6% +/- 6.1%, distended vein 129.9% +/- 13.3%, short-term graft 80.0% +/- 15.0%, long-term graft 95.1% +/- 12.1%; endothelin-1: native vein 126.5% +/- 22.1%, distended vein 138.1% +/- 24.7%, short-term graft 120.7% +/- 43.3%, long-term graft 171.4% +/- 26.0%; leukotriene C4: native vein 49.9% +/- 8.7%, distended vein 78.9% +/- 11.8%, short-term graft 90.8% +/- 39.1%, long-term graft 7.4% +/- 5.0%; and norepinephrine: native vein 127.0% +/- 9.3%, distended vein 155.0% +/- 17.8%, short-term graft 61.6% +/- 11.3%, long-term graft 80.1% +/- 7.7%. The vasoconstriction elicited by each agonist, in absolute terms (in millinewtons), diminished with age of graft. We conclude that surgical treatment of saphenous vein immediately renders it more responsive to U46619, norepinephrine, and leukotriene C4. An agonist-specific profile of response was evident up to 10 years after operation, which may affect myocardial blood supply when luminal bore is diminished by vein graft disease.

Endothelial function of human gastroepiploic artery. Implications for its use as a bypass graft.

The human gastroepiploic artery has been used as a coronary artery bypass conduit in a limited number of clinical studies. It has been postulated that the capacity of the endothelium to release vasoactive substances may contribute to differing patency rates observed in established bypass grafts. We have now examined endothelial function in the human gastroepiploic artery. Endothelium-dependent relaxations to substance P were observed. A maximum relaxation of 83.25% +/- 8.2% (mean +/- standard error) was attenuated to 48.5% +/- 16.4% in the presence of L-NG-monomethyl-arginine, a specific inhibitor of endogenous nitric oxide synthesis. Removal of the endothelium abolished the relaxations. With a specific radioimmunoassay, concomitant changes in levels of cyclic guanosine 3',5'-monophosphate, the second messenger that elicits smooth muscle relaxation after release of the endothelium-derived relaxing factor, were measured. It was found that the gastroepiploic artery had significantly higher resting and stimulated levels of cyclic guanosine 3',5'-monophosphate than either the internal mammary artery or the saphenous vein. In the presence of the cyclooxygenase inhibitor indomethacin, and indomethacin plus L-NG-monomethylanginine, the maximum relaxation was decreased to 70% +/- 9.5% and 59% +/- 10.8%, respectively. Our data demonstrate that endothelium-derived relaxing factor and prostacyclin may exhibit synergy in the control of vascular tone in this vessel. It is concluded that the endothelium of the gastroepiploic artery has a strong capacity to secrete vasodilators and inhibitors of platelet activity. This could have important influence on long-term patency.

Differential action of angiotensin II and activity of angiotensin-converting enzyme in human bypass grafts.

OBJECTIVE: The activity of the renin-angiotensin system may be important in determining the performance of coronary artery bypass grafts. We have examined the activity of tissue angiotensin-converting enzyme and the effects of angiotensin II in vessels used as bypass grafts. METHODS: Organ bath studies were used to determine the vasoactive effect of angiotensin II. The activity of the angiotensin-converting enzyme was assessed by metabolism of a specific synthetic substrate. RESULTS: The saphenous vein produced greater maximum responses to angiotensin II than did the internal thoracic artery. This response was not modified by inhibition of nitric oxide synthase, cyclooxygenase, or by an endothelin receptor antagonist in either vessel. Losartan, an AT1 receptor antagonist, inhibited the vasoconstrictor response in both blood vessels. Homogenates of saphenous vein and internal thoracic artery displayed tissue angiotensin-converting enzyme activity, which was inhibited by captopril. Enzyme activity was threefold greater in the vein. Both the contractile response to angiotensin II and the enzyme activity were retained in venous grafts removed up to 20 years after coronary bypass surgery. CONCLUSIONS: These data demonstrate that marked differences exist in angiotensin-converting enzyme activity and AT1 receptor responses in the saphenous vein compared with the internal thoracic artery. These findings may have important implications for the performance of the vein when used as a coronary artery bypass graft and may have clinical implications for the use of angiotensin-converting inhibitors and AT1 receptor antagonists in the prevention and treatment of vein graft disease.

Expression of vascular adhesion molecules in saphenous vein coronary bypass grafts.

BACKGROUND: Adhesion of blood elements to the endothelium is an important step in the development of vein graft disease. This study examines the expression of vascular adhesion molecules on explanted saphenous vein bypass grafts. METHODS: Immunocytochemical staining was performed using explanted saphenous vein grafts from 28 patients. Antibodies against the endothelial markers CD31, von Willebrand factor, intercellular adhesion molecule-1, vascular adhesion molecule-1, and E-selectin were used. RESULTS: Staining for CD31 and von Willebrand factor demonstrated the presence of endothelial cells in the lumen and the vasa vasorum. Expression of intercellular adhesion molecule-1 was variable between grafts, whereas vascular adhesion molecule-1 and E-selectin were almost always absent on the luminal endothelium. In contrast, the endothelium of the vasa vasorum stained positively for intercellular adhesion molecule-1 and vascular adhesion molecule-1, and was also seen on nonendothelial cells within the vessel wall. Expression of these adhesion molecules did not vary with the severity of vein graft disease. CONCLUSIONS: This study highlights the blood vessels in the adventitia as possible sites for the adhesion and migration of cells into the vessel wall.

Role of potassium concentration in cardioplegic solutions in mediating endothelial damage.

We studied the effect of potassium concentration in cardioplegic solutions on endothelial function by examining its influence on 5-hydroxytryptamine- (5-HT) and nitroglycerin-induced vasodilation in the isolated rat heart. Forty-eight rat hearts were perfused on a modified Langendorff preparation. After a baseline record of increase in coronary flow induced by 10(-7) M 5-HT and 10 micrograms/mL nitroglycerin, the hearts were perfused for 30 or 60 minutes with either St. Thomas' solution or Bretschneider solution containing 20 mmol/L of potassium or for 30 minutes with either solution containing 30 mmol/L of potassium (n = 8 in each). Initially, 5-HT and nitroglycerin caused a 39.0% +/- 3.3% and 39.7% +/- 2.8% increase in coronary flow, respectively. After 30 or 60 minutes' perfusion with St. Thomas' solution containing 20 mmol/L of potassium, there was little change in the response to 5-HT or nitroglycerin (5-HT, 43.1% +/- 4.1%; nitroglycerin, 38% +/- 3.2%). Similarly, perfusion with Bretschneider solution (20 mmol/L K+) for 30 or 60 minutes did not alter the degree of vasodilation (5-HT, 39.2% +/- 2.9%; nitroglycerin, 38.0% +/- 3.3%). However, perfusion with St. Thomas' solution containing 30 mmol/L of potassium for 30 minutes abolished the endothelial-dependent 5-HT-induced vasodilation (5-HT, -1.6% +/- 1.4%; nitroglycerin, 36.9% +/- 2.2%). Perfusion with Bretschneider solution (30 mmol/L K+) gave similar results (5-HT, -2.1% +/- 1.2%; nitroglycerin, 36.4% +/- 1.7%). We conclude that the concentration of potassium in cardioplegic solutions plays a critical role in causing functional endothelial damage.

Comparison of the morphologic and vascular reactivity of the proximal and distal radial artery.

BACKGROUND: Variations in the morphology and vascular reactivity of the proximal and distal radial artery might influence its performance as a bypass conduit. METHODS: The morphologic and functional characteristics of the proximal and distal RAs were compared with those of the left and right internal mammary arteries by using histologic and in vitro organ bath techniques. RESULTS: Proximal RA had a significantly greater medial cross-sectional area compared with that of the distal RA (2.48+/-0.27 mm2 compared with 1.86+/-0.21 mm2, p< 0.05), which were both significantly greater than the left internal mammary artery (0.54+/-0.09 mm2) or the right internal mammary artery (0.67+/-0.03 mm2). Proximal RA had a significantly greater response to 90 mmol/L potassium chloride than that of distal RA (88.4+/-7.3 compared with 60.2+/-10.3 mN, p<0.05), and both contracted more than the left internal mammary artery (30.3+/-2.9 mN) and the right internal mammary artery (32.6+/-4.1 mN). There was no difference in the response to noradrenaline and adrenaline between proximal and distal RA, both of which contracted more than the left and right internal mammary arteries. CONCLUSIONS: When choosing a segment of RA for use as a bypass conduit, regional variations in biologic properties should be considered.