Endothelial function of human gastroepiploic artery

Limited flow capacity of the right gastroepiploic artery graft: postoperative echocardiographic and angiographic evaluation

BACKGROUND

The flow capacity of the right gastroepiploic artery graft has not been clarified.

METHODS

Angiographic and echocardiographic studies were conducted in 30 patients who had undergone coronary artery bypass grafting using both the internal thoracic and right gastroepiploic arteries. The luminal diameter of the arterial grafts was measured from the postoperative angiograms. The adequacy of the myocardial blood supply from the arterial grafts was evaluated by dobutamine stress echocardiography.

RESULTS

With echocardiography, 14 patients exhibited an ischemic response in the gastroepiploic artery grafted region, whereas no patients exhibited an ischemic response in the internal thoracic artery grafted area. The luminal diameter of the gastroepiploic artery and a younger age were correlated with the ischemic response observed in the dobutamine stress echocardiography. A luminal diameter of the gastroepiploic artery of greater than 2.6 mm had the highest sensitivity and specificity for a nonischemic change.

CONCLUSIONS

To generate the maximal flow reserve, the luminal diameter of the gastroepiploic artery when used as a graft should be sufficiently large enough, nearly 3 mm at the anastomosis.

Endogenous nitric oxide and prostaglandins synergistically counteract thromboembolism in arterioles but not in venules

It has been shown that NO and prostacyclin (prostaglandin I(2)) from cultured endothelium synergistically inhibit blood platelet aggregation in vitro. However, it is unknown whether this synergism is also effective in the inhibition of thromboembolism in vivo and, if it is, whether it differs between vessel types. Therefore, the effect of endogenous NO and prostacyclin, in combination or alone, on thromboembolism was studied in an in vivo model. Thromboembolism was induced by micropipette puncture of rabbit mesenteric arterioles and venules (diameter 18 to 40 micrometer). In addition, the influence of wall shear rate was analyzed. In arterioles, the combined inhibition of NO synthase (N(G)-nitro-L-arginine [L-NA] 0.1 mmol/L; local superfusion) and of cyclooxygenase (aspirin [ASA] 100 mg/kg IV) resulted in a pronounced, significant prolongation of embolization duration (median >600 seconds) compared with control (median 153 seconds) or treatment with either L-NA (234 seconds) or ASA (314 seconds). This combined effect of L-NA+ASA was greater than the sum of the individual effects of L-NA and ASA. In contrast, in venules L-NA+ASA had no additional effect on embolization duration (209 seconds) compared with the effect of L-NA alone (230 seconds); ASA alone had no effect (122 seconds; control 72 seconds). Interestingly, only in the L-NA+ASA arterioles did embolization correlate positively with wall shear rate (r(s)=0.687; P=0.028). In conclusion, this study indicates that in arterioles, but not in venules, endogenous NO and prostaglandins synergistically counteract ongoing thromboembolism after vessel wall injury and that the combination of endogenous NO and prostaglandins appears to protect against enhancement of arteriolar thromboembolism by wall shear rate.

Atrial natriuretic peptide-induced release of cyclic guanosine monophosphate by coronary bypass grafts

BACKGROUND

Superior long-term patency rates of the internal mammary artery (IMA) versus saphenous vein (SV) after coronary artery bypass grafting are well documented. Higher production rates of vasodilating and platelet-inhibiting mediators (prostacyclin and nitric oxide) by the IMA seem to have a major impact on its long-term durability and resistance to coronary artery graft disease. For the right gastroepiploic artery (RGEA) marked release of protective mediators is reported as well. The vasodilating effect of cyclic guanosine monophosphate (cGMP) released after stimulation by atrial natriuretic peptide might serve as another graft protective system. The aim of the present study was to determine cGMP release by IMA, RGEA, and SV after atrial natriuretic peptide challenge.

METHODS

Samples of human IMA (n = 19), RGEA (n = 7), and SV (n = 18) discarded during coronary artery bypass grafting were stimulated with 10(-6) mol/L atrial natriuretic peptide after a resting phase in nutrient medium. Release of cGMP was determined by 125-iodide radioimmunoassay.

RESULTS

Basal cGMP production rates of the IMA (759.9 +/- 277.0 fmol/cm2) and RGEA (739.9 +/- 186.0 fmol/cm2) were higher than production rates of SV (281.2 +/- 64.0 fmol/cm2). Application of atrial natriuretic peptide led to a statistically significant increase of cGMP release in IMA grafts (1,939.3 +/- 778.0 fmol/cm2), whereas RGEA (618.4 +/- 141.3 fmol/cm2) and SV (221.7 +/- 64.5 fmol/cm2) remained at basal levels (p < 0.05).

CONCLUSIONS

From these data we conclude that the IMA in comparison with the RGEA and SV produces more extracellular cGMP when stimulated by atrial natriuretic peptide. This effect might support the cGMP-mediated protective properties of nitric oxide and could underline the extraordinary suitability of the IMA as a bypass conduit.

The response of blood flow between the internal thoracic and ileocecal arteries to inotropic agents in a canine model

The pharmacologic response of coronary artery bypass conduits is of great importance. This study was designed to clarify the response of blood flow between the internal thoracic artery (ITA) and the ileocecal artery (ICA) to inotropic agents. The responses of the ITA and ICA to epinephrine, dopamine, isoproterenol, and dobutamine were examined by collecting free-flowing blood from a canine model. There were no significant differences in the response to inotropic agents between the ITA and the ICA. Epinephrine and dopamine increased the graft flow, whereas isoproterenol and dobutamine decreased the graft flow percentages of the cardiac output. These results suggest that the flow response to inotropic agents is equivalent in canine ITA and ICA grafts.

Exclusive use of arterial grafts in coronary artery bypass operations for three-vessel disease: use of both thoracic arteries and the gastroepiploic artery in 256 consecutive patients

METHODS

From September 1989 to September 1994 we operated on a consecutive group of 256 patients with three-vessel disease in whom we used the right gastroepiploic artery together with both internal thoracic arteries. Vein grafts were not used in these patients. This population consisted of 233 men and 23 women whose ages ranged from 31 to 77 years (mean age 57.8 years).

RESULTS

Hospital morbidity and mortality were not directly related to the use of the gastroepiploic artery. Patency of the anastomoses in a subgroup of 56 patients (22%) a mean of 16 months after the operation was 98% for the left internal thoracic artery, 96% for the right internal thoracic artery, and 88% for the gastroepiploic artery. Five-year actuarial survival (including in-hospital deaths) was 95.9% and was related only to age. From discharge until the end of follow-up, two patients had a myocardial infarction, six patients underwent a reintervention procedure, and 18 patients had a return of angina pectoris.

CONCLUSION

We conclude that the concomitant use of the gastroepiploic artery with the both internal thoracic arteries has low morbidity and mortality in patients with three-vessel disease operated on by experienced surgeons. At this moment, we have no reason to believe graft patency will deteriorate in the future. On the basis of these results, the knowledge that arteries are to be preferred over veins for coronary bypass grafting, and the absence of a leg incision, we believe this operative technique is superior to the use of venous grafts.

Vascular reactivity of arterial coronary artery bypass grafts--implications for their performance

Specific properties of the vessel wall of arteries employed as coronary bypass grafts are thought to play an important role in the short- and long-term performance of these conduits. Heterogeneity in the endothelial and smooth muscle cell function between different arteries may provide particular vessels with properties which will favor them for use as bypass conduits. The aim of this review is to provide an insight into how the vascular reactivity of presently used arterial conduits varies and to discuss the clinical implications of these findings both in terms of flow modulation in response to physiologic and exogenous vasoactive mediators and long-term patency.

Morphometric analysis of the right gastroepiploic artery and the internal mammary artery

BACKGROUND

The internal mammary artery (IMA) and the right gastroepiploic artery (RGEA) are frequently used as conduits for coronary artery bypass grafting.

METHODS

Morphometric measurements and histologic characteristics of the RGEA and the IMA were studied in 25 patients undergoing coronary artery bypass grafting.

RESULTS

External radius was found to be more in the IMA (range, 18 to 56 microns; mean, 39.56 microns) in comparison with the RGEA (range, 24 to 51 microns; mean, 32.52 microns; p < 0.01). There was no significant difference between the vessels in intimal thickness (IMA: 0.0 to 0.25 micron; mean, 0.05 micron; RGEA: 0.0 to 0.28 micron; mean, 0.09 micron), internal radius (IMA: 5 to 47 microns; mean, 28.40 microns; RGEA: 16 to 42 microns; mean, 23.56 microns), area of media (IMA: 1,690 to 3,476 microns2; mean, 2,777.52 microns2; RGEA: 1,659 to 3,600; mean, 3,012.44 microns2), intimal thickening index (IMA: 0.0 to 0.02; mean, 0.01; RGEA: 0.0 to 0.13; mean, 0.01), and medial index (IMA: 0.14 to 0.60; mean, 0.36; RGEA: 0.18 to 0.63; mean, 0.39). Histologic examination of the RGEA showed more defects in continuity of internal elastic lamina and rich smooth muscle cells in the media.

CONCLUSIONS

There was no difference in the morphometric measurements of the IMA and the RGEA except external radius, which was greater for the IMA. The histologic differences found in the RGEA may indicate an increased propensity for atherosclerosis of the RGEA as compared with the IMA. Some concern regarding the long-term patency of the RGEA in myocardial revascularization is warranted.

Diffuse vasospasm following stenting of a free gastroepiploic artery graft: resolution with balloon angioplasty and intensive medical therapy

Vasospasm following balloon angioplasty of gastroepiploic artery bypass grafts can be prevented or reversed with vasodilators. In our patient, stent deployment for ostial stenosis of a free gastroepiploic artery graft was accompanied by severe, diffuse spasm and a change in graft configuration that required both intensive medical therapy and balloon angioplasty for resolution.

Right gastroepiploic-to-coronary artery bypass. The first decade of use

BACKGROUND

The right gastroepiploic artery was first used by us as a coronary artery bypass graft (CABG) in June 1984 and has become an accepted alternative conduit for myocardial revascularization.

METHODS AND RESULTS

We have now performed this operation in 126 patients (111 of whom were men) aged 32 to 78 years. The right gastroepiploic artery was used as a pedicle graft to the right main coronary artery in 25 patients, to its posterior descending branch in 90, to a left ventricular branch in 2, to branches of the circumflex system in 6, and to the left anterior descending artery in 1. Free (aortocoronary) gastroepiploic grafts were placed to circumflex branches in 2 patients. There were 2 hospital deaths (stroke, arrhythmia), and mean +/- SD postoperative stay was 7.5 +/- 2.0 days. All survivors were symptomatically improved and are functionally in New York Heart Association functional class I or II. There have been 3 late deaths (at 34, 50, and 84 months) in 2 to 120 months of follow-up (mean, 41.4 months). Angiography of bypass grafts and coronary arteries was performed in 44 patients at 7 days to 80 months postoperatively, providing direct evidence of gastroepiploic graft patency in 34 patients and strong indirect evidence in another 6; adequate data could not be obtained in 3 patients for technical reasons, and 1 graft was occluded.

CONCLUSIONS

These short-term, intermediate, and long-term results demonstrate the suitability of the right gastroepiploic artery as a CABG. The use of the right gastroepiploic artery as a graft to coronary arteries on the posterior wall of the heart, in conjunction with one or both internal mammary arteries, has the potential to allow complete myocardial revascularization with viable arterial grafts.

Arterial grafts for coronary artery surgery

Fifty specimens of left internal mammary artery, right gastroepiploic artery and right inferior epigastric artery were examined for length, diameter and frequency of atherosclerotic changes. Mean usable length was 132.4 mm for internal mammary arteries, 127.9 mm for gastroepiploic arteries and 128.4 mm for inferior epigastric arteries. One gastroepiploic artery was occluded. Histological examination revealed atherosclerotic plaques in seven internal mammary arteries (14%), 12 gastroepiploic arteries (24%) and 14 inferior epigastric arteries (28%). These findings emphasize the superiority of the inferior epigastric artery as the graft of choice for coronary artery bypass grafting. Gastroepiploic artery and inferior epigastric artery should only be used as additional grafts if 'all-arterial-grafting' is intended.

Late endothelial function of free and pedicled internal mammary artery grafts

The internal mammary artery has greater long-term patency than the saphenous vein when used for coronary bypass grafting. Therefore, bilateral use of the internal mammary artery for grafting with the right internal mammary artery used as a "free" graft may result in improved graft survival. The study objectives were to compare the endothelial-dependent and -independent vasodilatory response in free and pedicled internal mammary artery grafts in patients who had previously undergone coronary surgery. Free (group 1, n = 8) and pedicled (group 2, n = 7) internal mammary artery grafts were studied by comparing the response to selective infusion of the endothelial-dependent vasodilator substance P (1.4 up to 22.4 pmol/min in doubling dose increments) followed by isosorbide dinitrate (2 mg over 2 minutes), in patients undergoing coronary angiography, 1 month to 6 years after coronary surgery. Maximal dilatory response to substance P was 8.7% +/- 1.8% in pedicled grafts compared with 8.8% +/- 2.3% in free grafts (p = not significant), with the dose response for both groups being similar. Infusion of isosorbide dinitrate produced only minimal further dilatation in both groups. No significant difference was found in endothelium-dependent and -independent vasodilatory response between free and pedicled internal mammary artery grafts, suggesting that the use of the free right internal mammary artery and other arterial grafts may enhance graft survival.

Comparison among arterial grafts and coronary artery. An attempt at functional classification

Various arterial conduits have been used for coronary artery bypass grafting. However, arterial grafts are not uniform either in anatomy or in function. Some conduits are more spastic than others and there may be possible differences in long-term patency rates. The diverse biologic characteristics promote a necessity of classification of arterial grafts, which may facilitate the understanding of surgeons of biologic characteristics of various arterial grafts and provide a scientific basis for searching for new grafts. Another important issue is the comparison of reactivity between arterial grafts and coronary arteries. In this study, we aim to compare the pharmacologic reactivity among the human arteries (grafts and coronary arteries) and to classify arterial grafts. Segments of three arterial grafts (gastroepiploic, internal mammary, and inferior epigastric) taken from patients undergoing coronary artery bypass grafting and coronary arteries taken from explanted hearts were studied in organ baths for the contraction to four vasoconstrictors (endothelin-1, thromboxane A2 mimetic U46619, full adrenoceptor agonist norepinephrine, and depolarizing agent potassium) under physiologic pressure. The diameter of the four arteries at a pressure of 100 mm Hg was similar (p > 0.05). However, the gastroepiploic artery contracted to higher forces (9.41 +/- 2.0 gm for endothelin, 11.79 +/- 1.85 gm for U46619, 13.54 +/- 2.7 gm for norepinephrine, and 11.11 +/- 1.97 gm for potassium) than did the coronary artery and internal mammary artery (p < 0.05) for all the tested vasoconstrictors and higher than the inferior epigastric artery for potassium and norepinephrine (p < 0.05). There was no significant difference among the other three arteries (internal mammary artery, inferior epigastric artery, and coronary artery) regarding the maximal contraction force to any vasoconstrictor. No difference was detected in regard to the sensitivity (effective concentration causing 50% of the maximal response) to the vasoconstrictors among the four arteries. This study reveals that among the arterial grafts and the coronary artery, the gastroepiploic artery has the highest contractility to various vasoconstrictors. On the basis of our findings and physiologic and embryologic knowledge we propose a classification for arterial grafts: type I (somatic arteries), type II (splanchnic arteries), and type III (limb arteries). Types II and III are prone to spasm because of higher contractility whereas type I arteries are usually less spastic. This classification may have important clinical implications for the understanding of arterial graft spasm or patency and may be useful in the search for new grafts.

Potential use of the intercostal artery as an in situ graft: a cadaveric study

The third to eighth intercostal arteries (ICAs) were bilaterally dissected in 10 cadavers to assess their length and possible routes to coronary arteries if used as in situ grafts. The mean lengths for the intercostal arteries harvested were 27.0 +/- 2.9 cm on the left and 27.4 +/- 3.2 cm on the right. The shortest anatomic route to the coronary arteries of the in situ ICAs harvested was medial to the lung and either superior to or inferior to the hilum. By using either the superior or inferior routes in situ ICAs were long enough to reach the major coronary artery territories in all cadavers. The most suitable ICAs for grafting the coronary arteries and the shortest routes were as follows: left anterior descending--left fifth ICA by inferior route; circumflex coronary artery-left fifth ICA by inferior route; and right coronary artery-right seventh ICA by inferior route. We conclude that it is anatomically feasible to use the intercostal artery as an in situ graft in coronary artery operation.

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.

Effects of tachykinins on the splanchnic circulation: a comparison of the dog and rat

Responses to the administration of graduated doses of tachykinins were examined in various vascular beds of the dog. Among the tachykinins, all vascular beds studied demonstrated that the greatest vasodilation responses was produced by substance P. However, each tachykinin demonstrated a specific pattern of response. With substance P the greatest sensitivity was seen in the superior mesenteric artery (SMA), with neurokinin B in the celiac axis, and with neurokinin B a prolonged vasodilation response of the SMA compared to the other two vessels was seen. The response to substance P in the SMA of the rat was considerably less than that of the dog.

Mechanism underlying substance P-induced relaxation in dog isolated superficial temporal arteries

1. In helical strips of dog superficial temporal arteries with intact endothelium, substance P elicited a concentration-related relaxation with an EC50 of 2.8 (2.4-3.2) x 10(-10) M. 2. The relaxant response to the peptide in low concentrations (1-4 x 10(-10) M) sufficient to produce approximately half maximal relaxation was not inhibited by indomethacin, but was markedly suppressed by NG-nitro-L-arginine (L-NOARG), a nitric oxide (NO) synthase inhibitor, and by endothelium denudation. 3. High concentration (10(-7) M) of substance P produced marked relaxations in endothelium-intact strips. Removal of the endothelium attenuated the relaxation, and indomethacin or tranylcypromine suppressed the endothelium-independent relaxation. In indomethacin-treated strips with intact endothelium, L-NOARG attenuated but did not abolish the relaxation. The residual, L-NOARG-resistant relaxation was not significantly inhibited by ouabain, glibenclamide or tetraethylammonium. 4. Substance P (10(-7) M) increased the levels of cyclic GMP and cyclic AMP. The increase in cyclic GMP was abolished by endothelium denudation and treatment with L-NOARG, whereas the cyclic AMP increment was abolished by indomethacin. 5. Three different mechanisms may be involved in the substance P-induced relaxation: (1) an endothelium-dependent relaxation mediated by the release of NO from the endothelium, resulting in an increase of cyclic GMP (low and high concentrations of the peptide); (2) an endothelium-independent relaxation in association with cyclic AMP increment caused by prostaglandin I2 released from subendothelial tissues (high concentration), and (3) another endothelium-dependent relaxation possibly mediated by unidentified mediator(s) released from the endothelium (high concentration).

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)

Different vascular reactivity of human internal mammary and inferior epigastric arteries in vitro

Vascular responses to endogenous agonists may determine patency rates of bypass graft conduits. The effect of constrictors (noradrenaline, phenylephrine, serotonin, histamine, angiotensin II) and dilators (acetylcholine, substance P, bradykinin, nitroglycerin) were compared in human internal mammary and inferior epigastric arteries in vitro. The latter vessel type has been recently advocated as an additional conduit for coronary artery bypass grafting. Whereas the alpha-adrenoceptor- (noradrenaline, phenylephrine) and serotonin receptor-mediated contractions were similar in both vessels, histamine-induced contractions were greatly enhanced in internal mammary arteries (maximal responses in percent of 80 mmol/L KCl, 131% +/- 15% versus 59% +/- 8%). Maximal contractions in response to angiotensin II were greater in inferior epigastric arteries (50% +/- 6% versus 25% +/- 5%). The endothelium-independent relaxations in response to nitroglycerin were identical in both vessels. In contrast, the endothelium-dependent relaxations in response to acetylcholine, substance P, and bradykinin were significantly greater in the inferior epigastric than in the internal mammary arteries (maximal relaxations expressed as percent of prostaglandin F2 alpha-induced precontraction: acetylcholine, 94% +/- 5% versus 77% +/- 5%; substance P, 85% +/- 4% versus 24% +/- 5%; bradykinin, 77% +/- 5% versus 26% +/- 3%). It is concluded that the inferior epigastric artery has a high endothelial capacity to release endothelium-derived relaxing factor. It appears that the inferior epigastric artery possesses credentials to be successfully used for coronary artery bypass grafting.

Clinical experience with the right gastroepiploic artery in coronary artery bypass grafting

The excellent long-term results with the internal mammary artery for coronary artery bypass grafting have prompted the search for other conduits with similar characteristics. From December 1989 to December 1991, the right gastroepiploic artery (RGEA) has been used as an in situ graft to the posterior descending coronary artery in 51 patients at the Montreal Heart Institute. The patients' age averaged 50 +/- 11 years. Three-vessel coronary artery disease was present in 41 patients and two-vessel disease in the remaining 10 patients. In all but 1 patient, bilateral internal mammary artery grafting was performed in addition to RGEA grafting. The number of grafts per patient averaged 3.2 +/- 0.8. There was no operative mortality. Morbidity was minimal with only myocardial infarction and a pleural effusion in 1 patient. In 1 patient, a splenectomy had to be performed because of iatrogenic tear during dissection of the RGEA. The average hospital stay was 8.2 +/- 2.6 days. Enteral nutrition was resumed on average 2 days after operation. Angiographic evaluation of RGEA grafts was performed before discharge or within the first month after surgery in 31 patients. In 28 patients (28/31, 90%) the RGEA graft was patent, two grafts were occluded, and in the remaining patient, the graft could not be visualized due to technical difficulties during angiography. A second angiographic evaluation was performed in 5 patients, 1 year after operation. Four RGEAs were patent and 1 was occluded. Clinical follow-up averaged 4 months (range 1 to 15 months).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Endothelial vasomotor regulation in health and disease

The purpose of this review is to provide the anaesthetists with a comprehensive update on the endothelial-cell control of local blood flow. This single cell layer was originally thought to represent only a passive barrier. It is now evident that it plays an active role in a broad variety of biological functions. Since the discovery of the endothelial-derived relaxing factor (EDRF), it has been the subject of a considerable amount of research. It is established that EDRF is secreted continuously at a basal state and that many physical stimuli as well as vasoactive substances can modulate its secretion. Evidence presented indicates that the endogenous vasodilatation produced by EDRF is similar to that of the exogenous nitrovasodilator nitroglycerin and nitroprusside (i.e., nitric oxide). Aside from EDRF, the endothelium produces other vasodilating as well as vasoconstricting factors. A review of the physiology of the endothelium regarding the local control of blood flow is provided along with its influence upon several pathophysiological states. Also included is an overview of the influence of anaesthetic agents on endothelial function. These findings linking vasomotor control to endothelial function will help to explain pathophysiological process and may lead to new therapeutic modalities.

Effects of vasoactive neuropeptides on human saphenous vein

OBJECTIVE

To assess the role of neuropeptides in the control of vascular tone in the human saphenous vein the actions of substance P, vasoactive intestinal peptide, calcitonin gene related peptide, neuropeptide Y, and somatostatin on this blood vessel were examined.

METHODS

In vitro organ bath techniques were used with preparations of saphenous veins obtained from 29 patients (aged 41-66) who were undergoing coronary bypass surgery.

RESULTS

Substance P, vasoactive intestinal peptide, and calcitonin gene related peptide relaxed pre-constricted vessels in a dose dependent manner with a rapid onset of action, taking one to two minutes to reach a plateau at each dose. Substance P (10(-9) to 10(-6) mol/l) induced relaxation with a maximum response (mean (SEM)) 23.0 (6.6)% of the total relaxation induced by glyceryl trinitrate 1 microgram/ml and a 50% maximal effective concentration of 6.8 x 10(-9) mol/l. Vasoactive intestinal peptide (10(-10) to 10(-7) mol/l) produced a relaxation of 27.0 (5.1)% at 10(-7) mol/l. The maximum responses induced by substance P and vasoactive intestinal peptide were significantly reduced, to 3.7 (2.8)% and 4.7 (2.0)% respectively, after removal of the endothelium. Calcitonin gene related peptide (10(-10) to 10(-7) mol/l) elicited only 14.3 (2.6)% relaxation at 10(-7) mol/l, and this was not affected by removal of the endothelium. By contrast, neuropeptide Y and somatostatin exerted concentration dependent constriction on resting vessels. Neuropeptide Y (10(-10) to 10(-7) mol/l) caused prolonged contraction (roughly 20 minutes to reach a maximum plateau at each dose). At 10(-7) mol/l, the constriction amounted to 28.0 (12.0)% of the response to 90 mM KCl, in ring segments with or without endothelium. Somatostatin (10(-10) to 10(-6) mol/l) quickly caused contraction with a maximum response of 42.7 (15.0)% and a maximum response of 42.7 (15.0)% and a 50% maximal effective concentration of 6.7 x 10(-6) mol/l. The constriction was greatly increased when endothelium was removed, with a maximum response of 78.2 (16.8)% and a 50% maximal effective concentration of 4.3 x 10(-7) mol/l.

CONCLUSIONS

Vasoactive peptides have diverse effects on the vascular tone these effects are endothelium dependent. The exact physiological role and implication for performance of bypass grafts require further investigation.

Vascular reactivity of human internal mammary and gastroepiploic arteries

Patency rates of bypass graft conduits are thought to be influenced by the determinants of vascular tone. This study has comparatively examined the response of the human internal mammary and gastroepiploic arteries to potassium, noradrenaline, dopamine, 5-hydroxytryptamine, thromboxane, and histamine. The response to potassium was significantly greater in the gastroepiploic artery (Emax = 79.5 +/- 9.6 mN) than in the internal mammary artery (Emax = 27.0 +/- 6.4 mN). Dose-related constrictions were observed in both vessels to all agonists except histamine, which was ineffective in the gastroepiploic artery. Noradrenaline and dopamine produced comparable dose-related constrictions in each vessel, with similar EC50 and Emax (expressed as a percentage of potassium response) values, but 5-hydroxytryptamine (Emax, gastroepiploic = 10.8% +/- 1.9%; internal mammary = 71.8% +/- 21.2%) and thromboxane (Emax, gastroepiploic = 116.7% +/- 4.0%; internal mammary = 169.6% +/- 19.4%) were more efficacious in their constriction of the mammary artery; the potencies were similar. We conclude that there is a heterogeneity of response to some vasoconstrictors between the human internal mammary and gastroepiploic arteries. The internal mammary artery may be more predisposed to events that initiate vasospastic disorders.