Comparison of the vasorelaxant effect of nitroprusside and nitroglycerin in the human radial artery in vitro

Relaxant effect of the prostacyclin analogue iloprost on isolated human radial artery: An approach for the reversal of graft spasm

Radial artery graft spasm in the perioperative or postoperative period of coronary bypass surgery necessitates urgent treatment due to risk of graft failure and mortality. Herein, we evaluated the effect of iloprost, a prostacyclin (PGI₂) analogue, against the contractions produced by noradrenaline and potassium chloride on isolated human radial artery. Following the determination of endothelial and vascular relaxing capacities of the arteries, iloprost (10^-9M-10^-6M) was cumulatively applied on rings precontracted submaximally with the spasmogens. In some rings, the response to iloprost was assessed following pretreatment with nitric oxide (NO) synthase inhibitor, l-NAME (3×10^-4M,30min). Iloprost produced complete relaxations on radial artery rings precontracted with noradrenaline whereas, only moderate relaxations against the contractions induced by potassium chloride. Notably, the relaxation to iloprost was remarkably blunted in radial arteries with impaired endothelial function. Moreover, the relaxation to iloprost was unchanged in rings pretreated with l-NAME. Our results demonstrated that iloprost could be a potent relaxant agent in reversing radial artery spasm, particularly initiated by noradrenaline, possibly acting via an endothelium-mediated mechanism unrelated to NO.

Examining the Use of Sodium Nitroprusside in Coronary Artery Bypass Grafting: Is the Benefit Worth the Cost?

Purpose: Sodium nitroprusside is a vasodilator frequently used in the coronary artery bypass grafting (CABG) setting. However, the price of a 50-mg vial of sodium nitroprusside increased from $5.00 in 2003 to up to $900 in 2016. The purpose of this review is to help health systems balance high-quality patient care with economic responsibility. Methods: A MEDLINE literature search was performed using the search terms "nitroprusside" and "coronary artery bypass." All English-language trials in human subjects assessing the use of sodium nitroprusside in the setting of CABG were evaluated. The references of these studies were also reviewed. Results: In the setting of CABG, sodium nitroprusside attenuates conduit vasospasm and reduces the incidence of inflammation, atrial fibrillation, and acute kidney injury after surgery. However, other vasodilators are more effective at maintaining postoperative blood pressure at goal. Conclusions: Despite its cost, sodium nitroprusside may be an appropriate agent to use during CABG operations, but other agents should be considered for treatment of postoperative hypertension.

Antispastic Management in Arterial Grafts in Coronary Artery Bypass Grafting Surgery

Arterial grafts have long-term patency superior to vein grafts but have a tendency to develop spasm that can lead to potentially life-threatening complications. A perfect antispastic protocol should include advanced surgical technique and adequate pharmacologic methods. All pharmacologic vasodilator drugs relax the vessel through specific mechanisms, and therefore, there is no perfect, single best vasodilator to prevent or treat spasm of the arterial graft against all mechanisms of contraction. One of the choices is to use a combination of pharmacologic vasodilators targeting different mechanisms of spasm to obtain the reliable and best effect.

Labetalol, nebivolol, and propranolol relax human radial artery used as coronary bypass graft

OBJECTIVE

Beta-blockers are a heterogeneous class of agents that are used in the treatment of many cardiovascular diseases, especially hypertension and atherosclerosis, and that are commonly prescribed after cardiac surgery. In the present study, the aim is to investigate the vasorelaxant effects of some common beta-adrenoceptor blockers on the human radial artery in vitro, as well as their relaxation mechanisms.

METHODS

Radial artery rings sourced from human patients were mounted in an organ bath and tested for changes in isometric tension in relaxation response to labetalol, nebivolol, and propranolol in the presence and absence of NG-nitro-L-arginine methyl ester (3 × 10(-5) mol/L) and tetraethyl ammonium (3 × 10(-4) mol/L).

RESULTS

The labetalol (10(-8) to 10(-4) mol/L), nebivolol (10(-8) to 10(-4) mol/L), and propranolol (10(-8) to 10(-4) mol/L) induced concentration-dependent relaxations on the radial artery rings, which had been precontracted with phenylephrine (10(-6) mol/L). The relaxation response induced by labetalol in the isolated radial artery rings was significantly higher when compared with the nebivolol and propranolol samples (P < .05). NG-nitro-L-arginine methyl ester significantly reduced the relaxation of nebivolol (P < .05), and tetraethyl ammonium significantly reduced the relaxation of labetalol, nebivolol, and propranolol (P < .05).

CONCLUSIONS

We speculated that the relaxant effect of labetalol, nebivolol, and propranolol was due partly to the Ca(2+)-activated K(+) channels. In addition, the relaxation induced by nebivolol was largely related with nitric oxide release. Nebivolol, and partly propranolol, may provide significant therapeutic benefit, but labetalol can be a good alternative for coronary artery bypass grafting with radial artery use.

Arterial grafts: clinical classification and pharmacological management

In comparison with standard saphenous vein grafts, use of the internal mammary artery (IMA) as a coronary artery bypass graft has achieved superior long-term results. This is related to the differences in the biological characteristics between the venous and arterial grafts. However, even arterial grafts are not uniform in their biological characteristics. The variation in the perioperative behavior of the grafts and in their long-term patency may be related to different characteristics. These factors should be taken into account in the use of arterial grafts, some of which are subjected to more active pharmacological intervention during and after the operation to obtain satisfactory results. To better understand the biological behavior of the grafts, their common features and their differences, a clinical classification may be useful for a practicing surgeon. Based on experimental studies of their vasoreactivity combined with anatomical, physiological and embryological considerations, we have proposed a functional classification for arterial grafts that may be useful clinically. Our classification suggests that there are three types of arterial grafts: Type I-somatic arteries; Type II-splanchnic arteries; and Type III-limb arteries. Type I arteries have enhanced endothelial function and release more nitric oxide and other relaxing factors. Type II arteries, such as the gastro-epiploic artery, and Type III arteries, such as the radial artery (RA), have higher pharmacological reactivity to vasoconstrictors. This classification explains why the IMA has the best long-term patency. Because Type II and III arteries are prone to spasms due to higher contractility, they require more active pharmacological interventions. Furthermore, the harvesting technique of the conduits, including the saphenous vein and IMA, are described and discussed in this article. Prevention of spasms using two cocktails of medications (verapamil + nitroglycerin and nicardipine + nitroglycerin) during harvesting of the conduits is described. These solutions have been demonstrated to be clinically effective.

Magnesium and diltiazem relaxes phenylephrine-precontracted rat aortic rings

Perioperative vasospasm during cardiovascular surgery is a challenging problem. Several vasodilator agents are frequently utilized for its prevention in surgical practice. Magnesium and diltiazem both have known potential vasorelaxant effects. We planned to compare the efficacy of diltiazem and magnesium in relieving phenylephrine-precontracted rat aortic rings. Ten young adult female Wistar albino rats weighing 230-260 g were used in this study. The aortic rings in the organ bath equilibrated and reached their baseline tension. Precontraction was induced by 0.001 mmol/l phenylephrine and cumulative concentration-relaxation curves were obtained by consecutively increasing the addition of either diltiazem (10(-6)-0.1 mmol/l) or magnesium (0.1-10 mmol/l). The mean maximal relaxation responses observed by diltiazem and magnesium on separate aortic rings were 90 ± 3 and 53 ± 2%, respectively. The calculated EC50 of diltiazem was 0.01035 mmol/l, whereas the EC50 of magnesium was 4.064 mmol/l (P < 0.05). Both magnesium and diltiazem produced vasorelaxation on phenylephrine-precontracted rat aortic rings in this study, but the potency of diltiazem regarding the EC50 value was significantly higher than that of magnesium. Magnesium could be a candidate together with diltiazem to inhibit vasospasm on arterial grafts during coronary bypass surgery.

Role of endothelin-1 receptor antagonists in vasoconstriction mediated by endothelin and other vasoconstrictors in human internal mammary artery

BACKGROUND

The action of antagonists for endothelin type A (ET(A)) and type B (ET(B)) on the vasoconstriction mediated by various vasoconstrictors in the human bypass grafts have not been well-defined. We studied the role of antagonists for both ET(A) and ET(B) receptors in vasoconstriction mediated by endothelin-1 and other vasoconstrictors in the human internal mammary artery (IMA).

METHODS

Isolated IMA rings (n = 192, taken from 49 patients) were studied in organ bath for the interaction between endothelin-1, angiotensin II, U46619, and potassium chloride and the antagonist for ET(A) (BQ-123) or ET(B) (BQ-788).

RESULTS

Significant relaxations were observed by BQ-123 (agonist: endothelin-1, 84.9 +/- 7.9%; angiotensin II, 45.5 +/- 5.1%; and U46619, 30.7 +/- 5.7%) or BQ-788 (agonist: endothelin-1, 66.5 +/- 11.3%; angiotensin II, 38.9 +/- 4.2%; and U46619, 30.8 +/- 4.0%), but not to potassium chloride-induced precontraction. Incubation of IMA with BQ-123 or BQ-123 + BQ-788 significantly shifted the concentration-contraction curve to endothelin-1 rightward (p < 0.05 vs control) with effective concentration causing 50% of maximal response (EC50) (-7.59 +/- 0.04 or -7.81 +/- 0.05 vs -8.47 +/- 0.05 log M in the control, p < 0.001), whereas BQ-788 alone did not affect the contraction curve (p = 1.0 vs control). In contrast, none of the endothelin-1 inhibitors and the combination demonstrated significant depression effects on angiotensin II, U46619, or potassium chloride-induced contraction.

CONCLUSIONS

The present study demonstrates the role of ET(A) and ET(B) antagonists in the endothelin-1-mediated contraction in the human IMA and indicates the dominant role of ET(A) receptors. Although these effects are specific to endothelin-1, cross-action between endothelin-1 and angiotensin II exists. These findings provide useful knowledge for the future development of the clinical antispastic protocol in coronary bypass surgery.

Investigation of the vasorelaxant effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) and diethylamine/nitric oxide (DEA/NO) on the human radial artery used as coronary bypass graft

The radial artery (RA) is used as a spastic coronary bypass graft. This study was designed to investigate the mechanism of vasorelaxant effects of YC-1 (3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole), a nitric oxide (NO)-independent soluble guanylate cyclase (sGC) activator, and DEA/NO (diethylamine/nitric oxide), a NO-nucleophile adduct, on the human RA. RA segments (n = 25) were obtained from coronary artery bypass grafting patients and were divided into 3-4 mm vascular rings. Using the isolated tissue bath technique, the endothelium-independent vasodilatation function was tested in vitro by the addition of cumulative concentrations of YC-1 (10-10 to 3 x 10-7 mol/L) and DEA/NO (10-8 to 3 x 10-5 mol/L) following vasocontraction by phenylephrine in the presence or absence of 10-5 mol/L ODQ (1H-(1,2,4)oxadiazole(4,3-a)quinoxalin-1-one), the selective sGC inhibitor, 10-7 mol/L iberiotoxin, a blocker of Ca2+-activated K+ channels, or 10-5 mol/L ODQ plus 10-7 mol/L iberiotoxin. We also evaluated the effect of YC-1 and DEA/NO on the cGMP levels in vascular rings obtained from human radial artery (n = 6 for each drug). YC-1 (10-10 to 3 x 10-7 mol/L) and DEA/NO (10-8 to 3 x 10-5 mol/L) caused the concentration-dependent vasorelaxation in RA rings precontracted with phenylephrine (10-5 mol/L) (n = 20 for each drug). Pre-incubation of RA rings with ODQ, iberiotoxin, or ODQ plus iberiotoxin significantly inhibited the vasorelaxant effect of YC-1, but the inhibitor effect of ODQ plus iberiotoxin was significantly more than that of ODQ and iberiotoxin alone (p < 0.05). The vasorelaxant effect of DEA/NO almost completely abolished in the presence of ODQ and iberiotoxin plus ODQ, but did not significantly change in the presence of iberiotoxin alone (p > 0.05). The pEC50 value of DEA/NO was significantly lower than those for YC-1 (p < 0.01), with no change Emax values in RA rings. In addition, YC-1-stimulated RA rings showed more elevation in cGMP than that of DEA/NO (p < 0.05). These findings indicate that YC-1 is a more potent relaxant than DEA/NO in the human RA. The relaxant effects of YC-1 could be due to the stimulation of the sGC and Ca2+-sensitive K+channels, whereas the relaxant effects of DEA/NO could be completely due to the stimulation of the sGC. YC-1 and DEA/NO may be effective as vasodilator for the short-term treatment of perioperative spasm of coronary bypass grafts.

Direct comparison of relaxation and cGMP production in human coronary by-pass grafts in response to stimulation with natriuretic peptides and a nitric oxide donor

In the present study, we investigated the vasodilator properties of A-type, B-type and C-type natriuretic peptides (ANP, BNP and CNP respectively) and the NO (nitric oxide) donor sin-1 (3-morpholino-sydnonimine) in human by-pass grafts. In contrast with previous studies, the same vessel was used to demonstrate a direct link between cGMP production and functional relaxation. Remnants of the IMA (internal mammary artery) and SV (saphenous vein) were obtained from 82 patients undergoing coronary artery by-pass grafting. The responses to cumulative concentrations of ANP, BNP, CNP and sin-1 in vessel rings pre-contracted with a thromboxane A2 agonist (U46619) were measured in an organ bath. Additionally, intracellular cGMP production after single submaximal dose application of these drugs to vessel rings was determined by a RIA. ANP (P=0.001) and sin-1 (P<0.001) caused significant concentration-dependent relaxation of the IMA. In the SV, only sin-1 (P<0.001) induced marked concentration-dependent relaxation. At a single submaximal concentration, significant relaxation as well as intracellular cGMP production were found in response to ANP, BNP and sin-1 in the IMA. In contrast, in the SV, only sin-1 significantly induced cGMP production and relaxation. There was a moderate, but significant, correlation between intracellular cGMP net production and net relaxation in the IMA. In conclusion, ANP, as the most powerful relaxant of all the natriuretic peptides tested on the IMA, may be a possible alternative vasorelaxant to overcome peri-operative vasospasm in this artery. In contrast with sin-1, ANP and BNP were not effective vasorelaxants of the SV. Net relaxation in response to natriuretic peptides correlated with cGMP net concentrations in the IMA.

Topical Vasodilators for Preventing Radial Artery Spasm during Harvesting for Coronary Revascularization: Comparison of 4 Agents

BACKGROUND

There is still controversy about which vasodilator solution is best for storing radial artery (RA) conduits prior to coronary artery bypass grafting. The aim of this pilot study was to investigate how 4 different topical vasodilators applied during RA harvesting affect blood flow with the vessel in situ.

MATERIALS AND METHODS

The subjects were 85 patients who underwent RA harvesting in preparation for coronary artery bypass grafting. Each case was assigned to 1 of 5 groups (17 RAs each) that were treated with different solutions: normal saline (control), nitroglycerin, diltiazem, papaverine, and adenosine. Standard clinical concentrations were used. The RA was partially harvested (pedicle attached proximally) and flow rates and hemodynamic parameters (mean arterial pressure, heart rate, central venous pressure) were recorded at 2 time points: (1) pretreatment and (2) after 5 minutes of immersion in 60 mL of treatment solution. Results were compared within and between groups, and post-treatment-to-pretreatment ratios were calculated for each variable.

RESULTS

There were no significant differences among the groups' mean pretreatment flow rates (P = .979) or mean posttreatment flow rates (P = .069). All except the diltiazem group showed a significant rise in mean flow rate from pretreatment to posttreatment. The mean posttreatment-to-pretreatment ratios for RA flow rate were 1.28 +/- 0.39 in the saline group, 1.85 +/- 0.72 in the nitroglycerin group, 1.31 +/- 0.48 in the diltiazem group, 1.37 +/- 0.64 in the papaverine group, and 1.23 +/- 0.42 in the adenosine group. Only the mean flow ratio in the nitroglycerin group was significantly higher than that in the saline group (P = .003). The mean flow ratios in the other vasodilator groups were not statistically different from the flow ratio in the saline group.

CONCLUSIONS

These preliminary results indicate that topical application of nitroglycerin solution effectively prevents perioperative spasm of the RA in patients undergoing coronary artery bypass surgery. The authors recommend this solution for preparation and storage of RA grafts. Randomized controlled trials with power analysis will give more definitive information.

Comparative Effects of Tolazoline and Nitroprusside on Human Isolated Radial Artery

BACKGROUND

The radial artery is increasingly being used in coronary revascularization as an alternative conduit to a saphenous vein graft. Its perfect endothelial capacity provides a high patency rate comparable with the internal mammary artery (IMA). However, its spastic characteristics cause difficulties during its intraoperative preparation and may lead to early postoperative graft failure. Thus, treatment and/or prevention of radial artery spasm with an effective vasodilator agent is essential for its longevity. Endogenous vasoconstrictors, including noradrenaline, endothelin-1, and thromboxane A2, are likely to play a role in the pathogenesis of graft spasm. In the present study, we evaluated the vasorelaxant effect of tolazoline, a nonselective alpha-adrenoceptor blocker, against the contractions induced by various spasmogenic agents in an isolated human radial artery.

METHODS

Tolazoline (10(-9)-10(-4) M) or sodium nitroprusside (SNP, 10(-9)-10(-4) M) were cumulatively applied on radial artery rings precontracted submaximally with noradrenaline, endothelin-1, thromboxane analogue, U46619, or potassium chloride. In addition, some rings were pretreated with tolazoline (4 x 10(-6) M) for 30 minutes and the contractile response curve to noradrenaline was assessed in its presence.

RESULTS

Tolazoline effectively reversed noradrenaline-induced contractions in the radial artery, whereas it failed to produce remarkable relaxations on rings contracted with other spasmogenic agents, while SNP overcame the contractions induced by all spasmogens to a similar extent. In addition, brief pretreatment of radial artery rings with tolazoline significantly inhibited the contractions to noradrenaline.

CONCLUSIONS

Tolazoline is not as broadly effective as SNP against all spasmogens investigated; however, it may be effective in counteracting alpha-adrenoceptor-mediated vasospasm in human radial arteries.

Sharp dissection versus electrocautery for radial artery harvesting

Radial arteries have been increasingly used during the last decade as conduits for coronary artery revascularization. Although various harvesting techniques have been described, there has been little comparative study of arterial damage and patency. A radial artery graft was used in 44 consecutive patients, who were randomly divided into 2 groups. In the 1st group, the radial artery was harvested by sharp dissection and in the 2nd, by electrocautery. These groups were compared with regard to radial artery free flow, harvest time, number of clips used, complications, and endothelial damage. Radial artery free flow before and after intraluminal administration of papaverine was significantly greater in the electrocautery group (84.3 +/- 50.7 mL/min and 109.7 +/- 68.5 mL/min) than in the sharp-dissection group (52.9 +/- 18.3 mL/min and 69.6 +/- 28.2 mL/ min) (P=0.003). Harvesting time by electrocautery was significantly shorter (25.4 +/- 4.3 min vs 34.4 +/- 5.9 min) (P=0.0001). Electrocautery consumed an average of 9.76 clips, versus 22.45 clips consumed by sharp dissection. The 2 groups were not different regarding postoperative complications, except for 3 cases of temporary paresthesia of the thumb in the electrocautery group; histopathologic examination found no endothelial damage. We conclude that radial artery harvesting by electrocautery is faster and more economical than harvesting by sharp dissection and is associated with better intraoperative flow and good preservation of endothelial integrity.

Pharmacological assessment of composite arterial conduits using angiography early in the postoperative period

OBJECTIVES

Muscular arteries are vulnerable to vasospasm unlike elastic arteries. Having developed experimental models of composite arterial grafts, we assessed and compared the responses of the grafts with different pharmacological agents using angiography early in the postoperative period.

SUBJECTS AND METHODS

We harvested the internal thoracic artery (ITA) and brachial-median artery (BMA) from 10 sheep. BMA was used as an alternative to the radial artery. Each vessel was assessed histologically and morphologically. Then, a serial composite graft was constructed so that BMA was interposed. On postoperative day one or two, angiography was performed on the composite graft to measure the diameter of each vessel in response to phenylephrine (alpha-adrenergic receptor agonist), nitroglycerin+phenylephrine, and milrinone+phenylephrine.

RESULTS

The BMA had a wide media layer which consisted of abundant smooth muscle cells. The combined intima and media were thicker in BMA than in ITA (p<0.01). After injection of phenylephrine, the BMA diameter decreased (2.5+/-0.4 mm to 1.9+/-0.3 mm, p<0.01), while the ITA diameter remained unchanged (3.7+/-0.2 mm to 3.6+/-0.2 mm). Continuous infusion of nitroglycerin or milrinone prevented phenylephrine-induced vasoconstriction of the BMA (p<0.05).

CONCLUSIONS

These results suggest that muscular arteries have a more pronounced vasoconstrictive response to alpha-adrenergic receptor agonists than the elastic arteries. To avoid potential decrease in graft flow of muscular artery, it is advisable to use a vasodilator nitroglycerin or milrinone early in the postoperative period.

Comparative study of functional responses and morphometric state of distal radial arteries in male and female

BACKGROUND

Differences can exist in terms of physiology and morphology of blood vessels on the basis of gender. Radial artery is now considered to be the second choice for coronary artery bypass grafting. However, there is a lack of comparative studies on the function and morphometery of radial arteries in female and male patients.

METHODS

Radial arteries from 9 female and 9 male patients undergoing coronary artery bypass grafting were used to compare the effects of vasoconstrictors, noradrenaline and 5-hydroxytryptamine, as well as the influence of endothelium-dependent (with methacholine) and endothelium-independent (with sodium nitroprusside) relaxations. Furthermore, morphomteric measurements of smooth muscle thickness, lumen perimeter, lumen area, and intima area (including plaque) of distal radial arteries from female and male patients were also made.

RESULTS

Radial arteries from female patients when compared to male patients were significantly more sensitive to the actions of noradrenaline, and somewhat more sensitive towards the actions of 5-hydroxytryptamine. However, no significant differences were found between the relaxant effects of methacholine in radial arteries of female and male patients. In contrast, radial arteries from female patients when compared to male patients were significantly less sensitive to the relaxant effects of sodium nitroprusside. Morphometric measurements of blood vessels from female and male patients revealed that vessels obtained from female patients had a smaller lumen area and perimeter than vessels from male patients. In contrast, there were no significant differences between tunica intima area (including plaque area) or smooth muscle thickness in radial arteries of female patients when compared to male patients. However, the radial arteries from female patients had a significantly greater ratio of tunica intima area (including plaque) to lumen area when compared with radial arteries from male patients.

CONCLUSIONS

Differences exist between the functional behavior and morphometery of radial arteries of female and male patients. It is possible that postbypass, radial artery graft may show different characteristics in female versus male patients.

Prevention of radial artery graft vasospasm after coronary bypass

BACKGROUND

Pharmacologic prophylaxis for prevention of notorious radial artery (RA) spasm is critical because of the increasingly routine use of the RA conduit during coronary bypass. Therefore, we investigated the vasodilatory effect of calcium antagonist in combination with nitroglycerin (NTG) RA segments.

METHODS

We evaluated the vasodilatory effect of nifedipine alone, verapamil alone, diltiazem alone, NTG alone, and calcium antagonist in combination with in endothelin-1 (ET-1)-, angiotensin II (AII)-, 5-hydroxytryptamine (5-HT)-, and norepinephrine (NE)-precontracted human RA rings mounted in organ baths.

RESULTS

Nifedipine (10(-5) M) alone, diltiazem (10(-5) M) alone, verapamil (10(-5) M) alone, and NTG (10(-5) M) alone showed maximum vasodilatory effect in either 10(-7) M ET-1-, 10(-7) M AII-, 10(-5) M NE-, or 10(-4) M 5-HT-precontracted RA segments. The 10(-5) M NTG alone-induced vasodilation (88.5% +/- 7.7%) in ET-1-precontracted segments was the highest vasodilation (ANOVA, p = 0.0008) among NTG alone-induced vasodilatory effects in RA. The relaxing effect of any of the calcium antagonists alone varied from 32.7% +/- 13.2% to 76.5% +/- 20.5% in RA precontracted with different vasoconstrictors. Nearly 200% vasodilation was observed with calcium antagonist in combination with NTG in AII-precontracted vessels. Nonetheless, the vasodilatory effect of calcium antagonist in combination with NTG in RA segments precontracted with different vasoconstrictors other than AII was nearly 100%.

CONCLUSIONS

A calcium antagonist in combination with NTG is more potent than calcium antagonist alone or NTG alone in prevention of human RA vasospasm after coronary bypass.

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.