Endothelium Of Internal Mammary Artery Research Articles

Expression and Function of Endothelial Nitric Oxide Synthase Messenger RNA and Protein Are Higher in Internal Mammary Than in Radial Arteries

The internal mammary artery (IMA) has a better long-term patency rate than the radial artery (RA), but the underlying molecular mechanisms are unclear. We compared endothelial nitric oxide synthase (eNOS) and related NO release in these two arteries. Real-time polymerase chain reaction was used to quantify eNOS messenger RNA (mRNA) expression level in the endothelial cells of IMAs and RAs. eNOS protein localization was determined by immunohistochemistry. NO release from the endothelium of IMAs and RAs was directly measured by an electrochemical method using a membrane-type NO-sensitive electrode. Endothelial nitric oxide synthase mRNA expression level was significantly higher in the endothelial cells of IMAs than in RAs (1.03±0.19 vs 0.53±0.09, n=7, p<0.05), but was similar in the whole vascular tissue. eNOS protein immunoreactivity was higher in the endothelial cells of IMAs than in RAs. NO release at both levels in IMAs was significantly greater than in RAs (basal: 17.5±1.9 vs 10.2±0.7 nM, n=11 each, p=0.003; stimulated with bradykinin -7 log M: 31.5±3.6 vs 14.3±5.3 nM, n=6 each, p=0.02). Endothelial cells in the IMA express higher levels of eNOS mRNA and protein than those in the RA, which is linked with higher release of NO. These findings may be related to the superior long-term patency rate of the IMA vs the RA. This study also provides some basic genetic information for grafting arteries.

The nitric oxide „eluting“ internal mammary artery bypass graft and its remodelling effect on the recipient coronary tributary

Objective: The endothelium of the internal mammary artery (IMA) produces a large amount (65–82µMOL) of nitric oxide (EDNO), which maintains continuous downstream vasodilatation in the recipient coronary vessel. NO's stable metabolite, (nitrite) can be traced in the venous drainage of the IMA recipient coronary tributary. Also, nitric oxide prevents platelet aggregation and smooth muscle cell proliferation in the tunica media, meanwhile IMA itself, seldom shows atherosclerosis. Our aim was to give details of NO metabolite collection methodology and to prove the described antiatherosclerotic effect of NO on the recipient coronary vessel by analysis of recoronarographies carried out in patients presenting de novo angina 5–15 years after initial coronary artery bypass surgery having utilized IMA bypass graft. Method: 1. Nitrite concentration measurement in the venous drainage of the LIMA recipient coronary branch by modified Takafumi Ohta method. 2. Morphological analysis of 100 recoronarographies of patients with IMA to left anterior descending (LAD) branch performed 5–12 years before, to compare quality of LAD to other coronary systems of the same individual. Results: 1.: Nitrite concentration in the described sampling site is significantly higher after LIMA-LAD anastomosis completion compared to prior state (58.6µMOL and 18.2µMOL respectively, p<0.001) 2.: Eighty four out of the 100 LAD showed no downstream atherosclerosis whatsoever, while in the right and circumflex system progressive atherosclerotic deformations could be noted. In 4 patients trivial, primordial atheromas were found distally to IMA-LAD anastomosis. Twelve IMA bypass graft were occluded. Conclusions: The long term patency rate of IMA-LAD bypass graft well may be influenced by the modulation of biochemical milieu provided by the IMA's endothelium produced nitric oxide. EDNO may also diminish arteriosclerotic progress in the IMA recipient coronary branch.

Factors Affecting Internal Mammary Artery Graft Survival: How Is Competitive Flow from a Patent Native Coronary Vessel a Risk Factor?

Recent studies have suggested that competitive flow is an important factor in early internal mammary artery (IMA) graft failure. Flow competition from minimally diseased native coronary vessels has been implicated in the failure of IMA grafts, but does not seem to affect saphenous vein grafts (SVG). The objective of this study was to determine the effects of competitive flow on SVG and IMA grafts and to compare the patterns of flow dynamics and pressure on proximal and distal grafts to the left anterior descending (LAD) artery; factors that may be involved in graft failure. Twelve mongrel dogs underwent coronary artery bypass grafting using IMAs and a SVG to an open LAD artery. The right IMA (PIMA) and the SVG were anastomosed in the proximal LAD and the left IMA (DIMA) was anastomosed at a more distal location. The procedure was performed through a left thoracotomy, using an “off pump” technique. Graft flows were measured isolated and in competition. The IMAs and SVG provided flow levels similar to the native LAD when each one was the sole inflow to the LAD. During competitive flow conditions, total and diastolic SVG flows were reduced 54.4 and 50.5%, respectively (P< 0.05). Total and diastolic PIMA and DIMA flows were reduced more drastically (68.6–73.3 and 69.5–68.1%, respectively;P< 0.05) . The DIMA had better preservation of diastolic flow compared to PIMA. A delay in the pressure wave was noted in the isolated IMAs, but not in the SVG. This pattern of flow disappeared during competition due to the large, systolic retrograde flow up the IMA grafts. In conclusion, IMAs compared to the SVG are longer and narrower conduits with lower levels of flow during competition. Low levels of flow and oscillating flow (retrograde/ antegrade) may be poorly tolerated by the IMA endothelium and may be factorial to graft failure. These data suggest that a more distal placement of the IMA graft may be protective to the arterial graft under competitive flow conditions.

Autologous neutrophil derived supernatants inhibit endothelium dependent relaxation in human coronary bypass graft

Spasm of internal mammary artery is a problem during coronary artery bypass grafting. The mechanism is unknown. The aim of this study was to determine whether supernatants derived from neutrophils affected endothelium dependent relaxation of human internal mammary artery. The studies involved use of an organ chamber, measurement of cytosolic Ca2+, electron microscopy, and chemical characterisation. Autologous neutrophils and internal mammary artery were obtained from patients undergoing the bypass grafting. Supernatants derived from the neutrophils were used to treat the patients' internal mammary artery rings. The results showed that the supernatants derived from 1 x 10(3)-5 x 10(6) cells.ml-1 neutrophils produced a potent concentration dependent inhibition of the endothelium dependent relaxation to ATP, acetylcholine, and the calcium ionophore A23187, but not the endothelium independent relaxation to sodium nitroprusside. In cultured human endothelial cells, the neutrophil derived supernatants induced an increase in cytosolic calcium ([Ca2+]i), caused calcium oscillations, and desensitised the ATP induced increase in [Ca2+]i. The increased [Ca2+]i resulted from a calcium influx. The supernatants also induced an increase in vesicle formation and possibly exocytosis in the internal mammary artery endothelium. Chemical characterisation showed that the effect of the supernatants was caused by a factor that is stable to heat, extreme pH and protease, is negatively charged and weakly hydrophobic, and has a molecular weight under 500 Dalton. Autologous neutrophils release a stable non-protein small molecule that disturbs internal mammary artery endothelial function. Since it raises [Ca2+]i and causes possible exocytosis, it may have functions beyond its inhibition of vascular relaxation. This factor could be one of the contributors to internal mammary artery spasm and late atherosclerosis.

Both ETA and ETB receptors mediate contraction to endothelin-1 in human blood vessels.

Endothelin (ET)-1 has potent vascular effects. Two endothelin receptors have been cloned, namely, the ETA receptor, which preferentially binds ET-1, and the ETB receptor, which equally binds ET-1 and ET-3 and preferentially sarafotoxin S6c. We characterized endothelin receptor subtypes on vascular smooth muscle and endothelium of isolated human internal mammary artery (IMA) and vein (IMV) and porcine coronary artery (PCA) using the ETA antagonists FR139317 and BQ-123, the ETB ligand sarafotoxin S6c, and the ETA/ETB antagonist Ro 47-0203 (bosentan). In endothelium-denuded IMA and PCA and less so in IMV, FR139317 and BQ-123 (in PCA only) shifted the concentration-contraction curves to ET-1 parallel to the right. However, even at 10(-5) mol/L, FR139317 did not inhibit a high-sensitivity portion of the concentration-contraction curve. Moreover, the ETB receptor agonist sarafotoxin S6c induced contraction in vessels preincubated with FR139317. IMV was significantly more sensitive to the contractile effect of ET-1 and sarafotoxin S6c than was IMA (P < .05). Prolonged incubation with sarafotoxin S6c (to downregulate ETB receptors) and FR139317 eliminated the contraction resistant to FR139317. The ETA/ETB receptor antagonist bosentan caused a parallel shift of the concentration-contraction curve to the right at all concentrations of endothelin. ETB receptor mRNA was detected by Northern blot analysis in IMA and aortic smooth muscle cells. In precontracted IMA and PCA with endothelium, sarafotoxin S6c did not cause endothelium-dependent relaxations, whereas transient responses occurred in IMV. Vascular smooth muscle cells of human IMA, IMV, and PCA contain both ETA and ETB receptors, whereas the endothelium of IMA and PCA does not express functional ETB receptors linked to nitric oxide and/or prostacyclin production. Hence, inhibition of endothelin-induced contraction in patients requires the use of combined ETA/ETB antagonists.

Different interactions of platelets with arterial and venous coronary bypass vessels

We studied the interaction of platelets with the wall of human internal mammary arteries and saphenous veins, suspended in organ chambers for measurement of isometric tension. Vessels were obtained during coronary bypass surgery and cut into 5 mm rings; in some the endothelium was chemically removed. Rings from several patients were randomly chosen for each experiment, and in each ring six concentrations of platelets (from healthy blood donors; 1-75 × 10 3/μl) were tested consecutively and concentration-response curves constructed; the areas under these curves were used for statistical comparisons. In rings of internal mammary artery contracted in response to noradrenaline, aggregating platelets induced endothelium-dependent relaxation which was prevented by apyrase (0·67 U/ml ADPase activity) and L-N G-monomethylarginine (1 mmol/l). By contrast, in saphenous vein rings contracted in response to noradrenaline, aggregating platelets induced only a further increase in tension. In quiescent vessels, the platelet-induced contraction did not occur in arteries with endothelium but that in veins was greater and facilitated by endothelium. Preincubation of platelets with aspirin (10 μmol/l) reduced the contraction in both vessels, but contraction was abolished only in the presence of both the thromboxane receptor antagonist SQ-30741 and the serotoninergic (5HT 2) receptor antagonist ketanserin. These findings show that platelet-derived ADP causes release of nitric oxide by the endothelium of internal mammary artery but not of saphenous vein; thromboxane A 2 and serotonin mediate contraction in vein but not artery with endothelium. These differences may contribute to differences in graft function and the clinical efficacy of antiplatelet drugs.