Expression and function of angiotensin converting enzyme, chymase, and angiotensin II in the human radial artery and internal thoracic artery.

BACKGROUND: The potential role of the local renin-angiotensin system to differentially affect radial artery and internal thoracic artery graft performance has not been examined. METHODS: Contractile responses to angiotensin I and II in the radial artery and the internal thoracic artery were examined in vitro. The expression function, and localization of angiotensin receptors, angiotensin converting enzyme, and chymase were studied in radial artery and internal thoracic artery segments. RESULTS: Angiotensin I and II contractions were significantly greater (p < 0.05) in the radial artery compared to the internal thoracic artery. In both arteries, angiotensin II responses were mediated via the AT1 receptor. Messenger RNA transcripts for angiotensin-converting enzyme and chymase were detected in both arteries. Angiotensin-converting enzyme was localized to luminal and vaso vasorum endothelial cells and smooth muscle cells in both vessels, while chymase was colocalized with mast cells in adventitial and medial layers. An angiotensin converting enzyme or a chymase inhibitor singularly had no effect on angiotensin I contractions, however, when combined, a marked inhibition of the angiotensin I response was observed in both vessels. CONCLUSIONS: Our results illustrate the complexities which exist within the local renin angiotensin system and suggest that clinical trials which may modulate the system are warranted.

The renin angiotensin system in bypass graft surgery.

The renin angiotensin system is implicated in the development of vein graft disease after coronary artery bypass surgery. Components of this system have been shown to play important roles in determining the short-term and long-term performance of coronary artery bypass grafts. Significant differences exist in the commonly used arterial and venous grafts in angiotensin converting enzyme activity and angiotensin responses. The existence of a dual enzyme pathway in angiotensin II formation has also been demonstrated. Such findings have implications for the use of AT1-receptor antagonists over enzyme inhibitors to improve graft performance and prevent the development of coronary artery bypass graft disease.

Vascular biology of the radial artery.

In recent years, the use of the radial artery as a coronary artery bypass graft has enjoyed a revival. This follows the initial disappointing results with the use of this blood vessel experienced by Carpentier and colleagues in the early 1970s. The improvement in the performance of the radial artery is believed to be caused by improved harvesting techniques and the use of vasodilator drugs. However, compared with the other blood vessels used as bypass grafts, little is known about the vascular biology of this artery. The reactivity of the smooth muscle and protection offered by the vascular endothelium are known to be important factors that may determine the suitability of different arteries and veins to act as bypass conduits. The aim of this review is to examine how the properties of the vessel wall may contribute to the performance of the radial artery when used as a coronary artery bypass graft.

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.

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.

Reactivity of small intramyocardial arteries from atherosclerotic and non-atherosclerotic human hearts.

Little is known about how the vascular reactivity of the coronary microcirculation is affected by upstream atherosclerotic disease. We have examined, with a wire myograph, the responses of intramyocardial arteries from hearts in which the epicardial vessels were either free of atherosclerotic lesions (non-diseased group) or were affected by atherosclerosis (diseased group). Vasodilator responses of preconstricted vessels to substance P (84.1 +/- 12.6 compared to 42.0 +/- 19.7%) were less in vessels from the diseased group (p < 0.05). In contrast, the relaxation to bradykinin (70.2 +/- 21.2 compared to 100.6 +/- 7.9%) was increased in vessels from the diseased group (p < 0.05). The dilator responses to acetylcholine, adenosine diphosphate, histamine and sodium nitroprusside showed no significant differences between arteries from each group. 5-Hydroxytryptamine was without any significant vasodilator effect in arteries from either group. Assessment of contractile function revealed that the responses to 5-hydroxytryptamine, acetylcholine, U46619, endothelin-1 and L-N(G)-monomethylarginine in each group were not significantly different. Histamine, noradrenaline and dopamine were without any significant contractile response. These results demonstrate that upstream atherosclerosis does not confer any global impairment of endothelium-dependent vasorelaxant responses or smooth muscle hyperreactivity to vasoconstrictors in the arteries that penetrate the myocardium.

Structural, biochemical and functional effects of distending pressure in the human saphenous vein: implications for bypass grafting.

BACKGROUND: Distension of the saphenous vein before and after coronary artery bypass grafting results in damage to mechanisms that regulate vascular tone. We have investigated the relationship between the magnitude of distending pressure and the degree of structural, biochemical and functional damage to the vessel wall. METHODS: Vessel segments that had been distended to either 100 or 300 mmHg were set up in isolated organ baths and the function of the smooth muscle and endothelial cells examined. All segments examined were then fixed for assessment of structural damage by scanning electron microscopy and for immunocytochemical localisation of endothelial nitric oxide synthase. RESULTS: Segments of saphenous vein distended to 100 mmHg retained their responsiveness to KCl (90 mmol/l) and phenylephrine (10(-6) mol/l), but those pressurised to 300 mmHg had significantly reduced responses to both agents. There was also a significant reduction in response to the endothelium-dependent dilators, acetylcholine (10(-10)-10(-6) mol/l) and bradykinin (10(-10)-10(-6) mol/l) in those segments distended to 300 mmHg. Quantitative studies of structural endothelial damage showed a significant loss of endothelium at 300 mmHg distension pressure. Remaining endothelial cells retained strong positive staining for endothelial nitric oxide synthase. By electron microscopic examination, those vessels distended to 100 mmHg showed lifting and rounding of individual cells, whereas segments distended to 300 mmHg revealed major areas of denuded endothelium. CONCLUSIONS: Distension of saphenous veins to pressures equivalent to those in the systemic circulation result in structural and biochemical changes in the endothelium that are not paralleled by immediate functional vasomotor changes.

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.

Assessment of human long saphenous vein function with minimally invasive harvesting with the Mayo stripper.

BACKGROUND: The use of the Mayo Stripper to harvest the long saphenous vein has been shown to improve morbidity from leg wound incisions. It has not been universally accepted because of a perceived increase in injury to the venous conduit. OBJECTIVE: To compare the function of undistended autologous long saphenous vein harvested by a Mayo stripper with the traditional 'open' technique in the same patient (n = 12) appearance. METHODS: Vascular reactivity was assessed in isolated organ baths. Contractile function was measured in response to increasing concentrations (10(-9)-10(-5) mol) of 5-hydroxytryptamine and noradrenaline. This was calculated as a percentage of the maximum contractile response to 90 mM KCl measured in millinewtons (mN) (control 41.4 +/- 12.1, (n = 11), open technique 35.8 +/- 11.1, (n = 11), Mayo stripper 33.7 +/- 15.9, (n = 11)). The endothelial dependent and independent function was assessed with acetylcholine and sodium nitroprusside, respectively. RESULTS: There was no significant difference in response to both constrictors and dilators between vein taken with the Mayo stripper compared with the traditional open technique (n = 6 for each observation; P > 0.05 by ANOVA). Histological examination by light microscopy of the vessel segments removed with the Mayo stripper was unable to show any significant damage to the vessel wall. Both functional and morphological studies were conducted by 'blinded' observers. One-year follow-up with magnetic resonance angiography (MRA) and stress thallium tomography demonstrated a patency rate with lower and upper estimates of 80 and 94%. CONCLUSIONS: We have shown that harvesting the long saphenous vein with a Mayo stripper does not compromise vascular reactivity of the long saphenous vein or long-term patency.

Vascular adhesion molecules and immunogenicity in blood vessels used as coronary artery bypass grafts.

OBJECTIVE: The performance of coronary bypass grafts can be affected by a variety of circulating cell types. The initial event in any biological effect of such cells is adherence to the vascular endothelium prior to migration into the perivascular space. We aimed to investigate the expression of molecules that regulate cell adhesion in blood vessels employed as bypass conduits. METHODS: Segments of human saphenous vein, internal mammary artery, gastroepiploic artery and inferior epigastric artery were stained using specific monoclonal antibodies against the endothelial workers EN-4, Pal-E, von Willebrand factor small (vWF), and the cell adhesion molecules platelet-endothelium cell adhesion molecule (PECAM), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), E-selectin, the leucocyte marker (CD45) and major histocompatibility complex (MHC) class I and II antigens, with visualisation by ABC immunoperoxidase method. RESULTS: All vessels had a strong expression of the endothelial specific antigens EN4, vWF, and PECAM as well as MHC class I. However, there was less expression of Pal-E, ICAM-1, E-Selectin and of the DR determinant of MHC class II. VCAM-1, DP and DQ determinants of MHC class II were expressed to a weaker extent. There were no marked differences in the expression of all the molecules examined between the four vessel types. CONCLUSION: Thus vessels used as bypass grafts are immunogenic and possess the potential to attract and interact with blood elements. Definition of the molecules responsible could offer opportunities for modulating the response to such interactions.

Oestrogen relaxes human epicardial coronary arteries through non-endothelium-dependent mechanisms.

BACKGROUND: Oestrogen-replacement therapy is associated with a reduced incidence of cardiovascular disease. The acute administration of oestrogen improves myocardial ischemia in women with coronary heart disease. In this study we investigated the relaxing effect of oestradiol-17 beta on human coronary arteries in vitro and determined the role of endothelial modulation in this relaxation by using isolated human coronary arteries. METHODS: Atherosclerosis-free epicardial arteries from men and women were removed from patients undergoing heart or combined heart and lung transplantation. The arteries were cut into ring segments and placed into organ baths containing Tyrode's solution. Changes in isometric tension were measured. The relaxing response to oestradiol-17 beta (10(-10) - 10(-5) mol/l) was investigated and the effects of endothelium, NGmonomethyl-L-arginine and indomethacin on the response of oestradiol-17 beta were assessed. RESULTS: Oestradiol-17 beta (10(-10) - 10(-5) mol/l) induced significant relaxation in coronary arteries pre-contracted with the thromboxane A2 analog (U46619; 3 x 10(-8) mol/l). Relaxation was significantly greater in coronary arteries from female patients. No significant differences were observed between arteries with or without endothelium nor after nitric oxide synthase or cyclo-oxygenase inhibition. These results indicate that oestradiol-17 beta induces human coronary artery relaxation via an endothelium-independent mechanism in vitro. The sex of the patients significantly affects sensitivity of the coronary arterial rings to oestrogen. CONCLUSION: Oestradiol-17 beta-induced coronary relaxation may play an important role in regulation of coronary tone, and may partly explain why oestrogen improves myocardial ischemia in women and why it protects postmenopausal women from the risk of developing coronary heart disease.

Endothelial function and vasodilator profile of the inferior epigastric artery.

In the inferior epigastric artery, endothelium-dependent relaxations in response to substance P, histamine, and acetylcholine were present. These were greater than reported values in saphenous veins but less than the documented responses in internal mammary and gastroepiploic arteries. Endothelium-independent stimulation with nifedipine, papaverine, sodium nitroprusside, and glyceryl trinitrate induced relaxations that also were reduced compared with established arterial conduits. These findings appear to justify the clinical use of the inferior epigastric artery as a coronary bypass graft with monitoring of its long-term results and possibly perioperative pharmacologic manipulations.

Effect of mode of application of papaverine on the contractile response of the internal mammary artery.

A study was performed to investigate the duration of action of papaverine applied either intraluminally or in a combined intraluminal and extraluminal fashion in vitro, and how the reactivity of the internal mammary artery (IMA) to a range of vasoconstrictors is affected. Segments of IMA exposed to only intraluminal papaverine (10(-4) mol/l) for 15 min recovered their contractile response to 90 mmol/l potassium chloride to pretreatment levels within 2 h. In contrast, combined intraluminal and extraluminal administration of papaverine resulted in a significant depression of the contractile response to 90 mmol/l potassium chloride (P < 0.001), which persisted for at least 5 h. Responses to 5-hydroxytryptamine, noradrenaline, the thromboxane mimetic U46619, histamine and dopamine were not significantly different between control tissues and those that had received intraluminal papaverine. The duration of action of papaverine is affected by its route of delivery and there are no significant short-term effects on the contractile mechanisms in the arterial wall after intraluminal administration.

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.

Vasoconstrictor profile of the inferior epigastric artery.

The inferior epigastric artery is a putative arterial bypass graft. The receptor mechanisms that control vascular tone are thought to play a role in the performance of bypass conduits. We have compared the vascular reactivity of the inferior epigastric artery with that of the internal mammary artery. Segments from a total of 15 inferior epigastric and 12 internal mammary arteries were examined for their response to increasing concentrations of noradrenaline, 5-hydroxytryptamine, dopamine, histamine, endothelin-1, or the thromboxane analogue U46619. The responsiveness of the smooth muscle was significantly greater in the inferior epigastric artery (p < 0.05) as judged by contractions elicited by 90 mmol/L potassium chloride. However, although the response of the inferior epigastric artery tended to be greater, this significant enhancement of smooth muscle function was not paralleled by the maximal responses of noradrenaline, 5-hydroxytryptamine, dopamine, histamine, or endothelin-1. However, the tension generated in response to U46619 did differ significantly, with maximal responses in the inferior epigastric and internal mammary arteries of 59.2 +/- 8.3 mN and 35.0 +/- 3.6 mN, respectively. When receptor function was compared by expressing the response as a percentage of that of 90 mmol/L potassium chloride, it was revealed that noradrenaline was capable of inducing significantly greater relative contractions in the internal mammary artery (114.8% +/- 20.5%) as compared with the inferior epigastric artery (49.9% +/- 19.1%); the potency of this constrictor was sixfold greater in the internal mammary artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of peri-operative storage solution on the vascular reactivity of the human saphenous vein.

The performance of the saphenous vein as a bypass conduit in myocardial revascularisation may, in part, be determined by its vascular reactivity. The present study investigates whether the choice of peri-operative storage solution influences the response of this vessel to a range of vasoconstrictors and vasodilators. Saphenous vein ring segments (210) were obtained from 24 patients undergoing coronary artery bypass surgery, and following a 1 h incubation in either (1) heparinised blood, (2) heparinised saline, (3) 199-TC solution, (4) St. Thomas' cardioplegic solution or (5) plasma-lyte solution, rings of vein were set up as organ bath preparations. The relative magnitude of control constrictor response was: noradrenaline = 5-hydroxytryptamine > or = dopamine > histamine > acetylcholine. There was a significantly different (P < 0.05) enhanced response to noradrenaline and 5-hydroxytryptamine in segments stored in heparinised saline compared to 199-TC; similarly, dopamine and noradrenaline responses were significantly potentiated (P < 0.05) following storage in heparinised saline compared to cardioplegia. Storage in plasma-lyte enhanced the response significantly storage in heparinised saline compared to cardioplegia. Storage in plasma-lyte enhanced the response significantly (P < 0.05) to acetylcholine alone. None of the solutions had a significant effect on the potency (EC50) of the constrictors. Relaxations of pre-constricted segments were recorded to acetylcholine and sodium nitroprusside, but there was no difference in efficacy or potency in these responses following storage in the different solutions. This study demonstrates that the choice of peri-operative storage solution may influence the vascular reactivity of the human saphenous vein.