The mechanism of endothelium-independent relaxation induced by the wine polyphenol resveratrol in human internal mammary artery

Resveratrol, a stilbene polyphenol found in grapes and red wine, produces vasorelaxation in both endothelium-dependent and endothelium-independent manners. The mechanisms by which resveratrol causes vasodilatation are uncertain. The aim of this study was to investigate the mechanism(s) of endothelium-independent resveratrol-induced vasorelaxation in human internal mammary artery (HIMA) obtained from male patients undergoing coronary artery bypass surgery and to clarify the contribution of different K+ channel subtypes in resveratrol action in this blood vessel. HIMA rings without endothelium were precontracted with phenylephrine. Resveratrol induced a concentration-dependent relaxation of the HIMA. A highly selective blocker of ATP-sensitive K+ channels, glibenclamide, as well as nonselective blockers of Ca2+-sensitive K+ channels, tetraethylammonium and charybdotoxin, did not block resveratrol induced relaxation of HIMA rings. 4-Aminopyridine (4-AP), non selective blocker of voltage gated K+ (KV) channels, and margatoxin that inhibits KV1.2, KV1.3, and KV1.6 channels abolished relaxation of HIMA rings induced by resveratrol. In conclusion, we have shown that resveratrol potently relaxed HIMA rings with denuded endothelium. It seems that 4-AP- and margatoxin-sensitive K+ channels located in smooth muscle of HIMA mediated this relaxation.     

Testosterone relaxes human internal mammary artery in vitro

Preliminary clinical studies of testosterone therapy in male patients with coronary artery disease raised promising results. However, there is no study on in vitro effects of testosterone in human isolated arteries. We investigated the effect of testosterone on contractile tone of human isolated internal mammary artery. The responses in human internal mammary artery (IMA) were recorded isometrically by a force-displacement transducer in isolated organ baths. Testosterone (10 nM to 100 microM) was added cumulatively to organ baths either at rest or after precontraction with KCl (68 mM) and PGF2alpha (10 microM). Testosterone-induced relaxations were tested in the presence of cyclooxygenase inhibitor indomethacin (10 microM), nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME, 1 microM), nonselective large-conductance Ca2+-activated and voltage-sensitive K+ channel inhibitor tetraethylammonium (TEA, 1 mM), ATP-sensitive K+ channel inhibitor glibenclamide (GLI, 100 microM), and voltage-sensitive K+ channel inhibitor 4-aminopyridine (4-AP, 1 mM). Testosterone produced relaxation in human IMA (Emax 33% and 41% of KCl- and PGF2alpha-induced contraction, respectively). Vehicle had no significant relaxant effect. Except for TEA, the relaxation at low concentrations is not affected by either K+ channel inhibitors (GLI and 4-AP) or L-NAME and indomethacin. We report for the first time that supraphysiological concentrations of testosterone induce relaxation in IMA. This response may occur in part via large-conductance Ca2+-activated K+ channel-opening action.     

Modulatory role of the vascular endothelium in the contractility of human isolated internal mammary artery

1. Endothelium-dependent relaxant responses and modulation of contractile responses were investigated in human isolated internal mammary artery (HIMA), a vessel widely used for coronary bypass surgery. 2. Acetylcholine and ionophore A23187 (both 10 nM-1 microM) elicited concentration-dependent relaxations of precontracted HIMA. These relaxations were abolished after rubbing of the endothelium, they were inhibited by methylene blue and were insensitive to indomethacin. 3. Histamine at concentrations lower than 10 microM elicited an endothelium-dependent, methylene blue-sensitive relaxation of precontracted HIMA. This effect of histamine was inhibited by the H1-receptor antagonist mepyramine. Bradykinin, noradrenaline and alpha 2-adrenoceptor agonists (in the presence of prazosin) did not relax unrubbed HIMA in which acetylcholine or A23187 were shown to be efficient. 4. Tissue levels of guanosine-3':5'-monophosphate (cyclic GMP) were found to be significantly higher in unrubbed HIMA rings than in matched rubbed rings. 5. Methylene blue evoked a slow contraction in resting HIMA, and this contraction was significantly greater in unrubbed than in rubbed preparations. Also, methylene blue enhanced the contractile response of HIMA to noradrenaline and this potentiating effect was significantly greater in unrubbed than in rubbed preparations. Indomethacin induced a slow contraction, of similar magnitude in unrubbed and rubbed HIMA rings. 6. In resting HIMA, the concentration-effect curve of noradrenaline-induced contraction was significantly shifted to the left after rubbing of the endothelium, without change in the maximal responses. In unrubbed rings the EC50 value of noradrenaline was about 2 fold that in rubbed rings. 7. Histamine also contracted resting HIMA in a concentration-dependent manner and in addition, it triggered rhythmic activity. This rhythmic activity was more prominent in unrubbed preparations and could be partially inhibited by indomethacin. The concentration-effect curve of histamine-induced contractions was displaced to the left after rubbing the endothelium, without changes in the maximal responses. The EC50 value of histamine in unrubbed rings was 4 to 9 fold that found in rubbed rings, depending on the level of tension taken into account for the concentration-effect curve during rhythmic contractions. 8. In the presence of nifedipine (3 microM), noradrenaline-induced contractions were not significantly altered, whereas histamine-induced contractions were found to be inhibited by about 70%.(ABSTRACT TRUNCATED AT 400 WORDS)     

Furosemide inhibits thromboxane A2-induced contraction in isolated human internal mammary artery and saphenous vein

Evidence suggests that, in addition to its diuretic property, furosemide also may exert direct vascular effects. Because thromboxane A2 (TXA2) has a role in the control of vascular tone, we investigated the effect of furosemide on the contraction induced by U46619 (a stable TXA2 mimetic) on isolated human internal mammary artery (IMA) and saphenous vein (SV). Concentration-response curves to U46619 were performed in the absence (vehicle) or the presence of furosemide (0.1-1 mM) on rings of IMA and SV. In addition, the relaxant effect of furosemide (0.1 microM-1 mM) also was evaluated on U46619-precontracted IMA and SV. The participation of cyclooxygenase derivatives was studied by pretreatment with indomethacin. Furosemide (0.1-1.0 mM) caused parallel rightward shifts of U46619 concentration-response curves without affecting the maximal responses in both IMA and SV. Treatment with indomethacin (1 microM) modified neither the inhibitory effect of furosemide on U46619-induced contractions, nor the relaxant effect of furosemide on U46619-induced contractions, nor the relaxant effect of furosemide on U46619-precontracted IMA and SV. In conclusion, furosemide at high concentrations inhibited U46619-induced contraction in human isolated IMA and SV and relaxed U46619-precontracted IMA and SV by mechanisms independent of the release of relaxant prostaglandins. These results suggest that blockade of TXA2 receptors by furosemide may contribute to explaining the therapeutic effects of furosemide in the treatment of severe heart failure.     

Contractile effects of 3,4-methylenedioxymethamphetamine on the human internal mammary artery

Since the late 1980s numerous reports have detailed adverse reactions to the use of 3,4-methylenedioxymethamphetamine (MDMA) associated with cardiovascular collapse and sudden death, following ventricular tachycardia and hypertension. For a better understanding of the effects of MDMA on the cardiovascular system, it is critical to determine their effects at the vasculature level, including the transporter or neurotransmitter systems that are most affected at the whole range of drug doses. With this purpose in mind, the aim of our study was to evaluate the contractile effect of MDMA in the human internal mammary artery, the contribution of SERT for this effect and the responsiveness of this artery to 5-HT in the presence of MDMA. We have also studied the possible involvement of 5-HT₂ receptors on the MDMA contractile effect in this human blood vessel using ketanserin. Our results showed that MDMA contracted the studied human's internal mammary artery in a SERT-independent form, through activation of 5-HT_2A receptors. Considering the high plasma concentrations achieved in heavy users or in situations of acute exposure to drugs, this effect is probably involved in the cardiovascular risk profile of this psychostimulant, especially in subjects with pre-existing cardiovascular disease.     

Rho-kinase inhibitors prevent agonist-induced vasospasm in human internal mammary artery

1. Vasospasm of arterial conduits used for coronary artery surgery is an important cause of graft failure and is likely to result partly from raised levels of vasoconstrictor substances such as thromboxane A(2) and endothelin-1. Our aim was to find pharmacological agents that could prevent agonist-induced vasospasm. 2. Isometric tension was recorded from discarded segments of human left internal mammary artery (LIMA). Submaximal contraction evoked by the thromboxane A(2) mimetic U46619 (10 nM) was not inhibited by a blocker of store- and receptor-operated Ca(2+) channels (30 microM SKF96365) in the presence of diltiazem. Furthermore, contractions to < or =1 nM U46619 were preserved when extracellular Ca(2+) was reduced from 2.5 mM to 60 nM. Thus, sustained U46619-evoked contraction occurred without Ca(2+) influx. 3., We hypothesized that contraction might occur via Rho-kinase-mediated Ca(2+)-sensitization of myofilaments. Inhibitors of Rho-kinase (Y27632 and HA1077) were profound relaxants. If contraction was pre-evoked by 10 nM U46619, Y27632 and HA1077 caused full relaxation with EC(50)s of 1.67+/-0.22 microM and 3.58+/-0.35 microM respectively. Y27632 was also effective if applied before U46619, but was less potent. 4. Y27632 abolished contraction evoked by endothelin-1 and significantly reduced resting tone in the absence of a vasoconstrictor. 5. Rho-kinase-mediated Ca(2+)-sensitization appears to be a major mechanism of vasoconstriction in human LIMA. Rho-kinase inhibitors may have an important role in preventing vasospasm in arterial grafts used for coronary artery surgery.     

Interaction between endothelin and vasodilators in the human internal mammary artery.

1. The internal mammary artery (IMA) is the primary choice as an arterial graft for coronary artery bypass surgery. Endothelin (ET) has been recently measured with an increased release after cardiopulmonary bypass for coronary artery bypass grafting. Threshold concentrations of ET-1 have been found to amplify specifically contractions induced by noradrenaline and serotonin. This study was designed to investigate the effect of glyceryl trinitrate (GTN) and calcium antagonists on ET-1 contraction in the human IMA. 2. Human IMA segments taken from 21 patients undergoing IMA-coronary artery bypass grafting were mounted in an organ bath under the physiological pressure determined from their own length-tension curves. Four ring segments were allocated into four groups. One served as a control and the others were treated with GTN (10, 100 nM, or 30 microM) for 5 min or nifedipine (20 or 200 nM, or 30 microM) for 25 min before concentration-contraction curves to ET-1 were established. In separate experiments, the concentration-relaxation curves to GTN or nifedipine were established in the IMA rings precontracted with ET-1 (10 nM). 3. Pretreatment of IMA with GTN for 5 min did not alter the ET-1-induced contraction. Pretreatment with 20 or 200 nM of nifedipine slightly but not significantly, altered the maximum contraction induced by ET-1. Higher concentrations (30 microM) significantly reduced the maximum contraction force (P = 0.008). On the other hand, GTN caused 76.44 +/- 6.35% relaxation in ET-1-precontracted IMA. In contrast, the nifedipine-induced relaxation was difficult to establish due to unsustained contraction to ET-1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Melatonin inhibits nitrate tolerance in isolated coronary arteries

(1) The present study was designed to test the hypothesis that melatonin inhibits nitrate tolerance in coronary arteries. (2) Rings of porcine coronary arteries were suspended in organ chambers for isometric tension recording. Nitrate tolerance was induced by incubating the tissues with nitroglycerin (10(-4) M) for 90 min, followed by repeated rinsing for 1 h. Control rings that had not been exposed previously to nitroglycerin, but were otherwise treated identically, were studied simultaneously. The rings were contracted with U46619 (1-3 x 10(-9) M) and concentration-response curves to nitroglycerin (10(-9)-10(-4) M) were obtained. (3) Nitrate tolerance was evident by a 15- to 20-fold rightward shift in the concentration-response curve to nitroglycerin in rings with and without endothelium exposed previously to the drug for 90 min. Addition of melatonin (10(-9)-10(-7) M) to the organ chamber during the 90-min incubation period with nitroglycerin partially inhibited nitrate tolerance in coronary arteries with intact endothelium; however, melatonin had no effect on nitrate tolerance in coronary arteries without endothelium. (4) The effect of melatonin on nitrate tolerance in coronary arteries with endothelium was abolished by the melatonin receptor antagonist, S20928 (10(-6) M). In contrast to melatonin, the selective MT(3)-melatonin receptor agonist, 5-MCA-NAT (10(-8)-10(-7) M), had no effect on nitrate tolerance in coronary arteries. (5) The results demonstrate that melatonin, acting via specific melatonin receptors, inhibits nitrate tolerance in coronary arteries and that this effect is dependent on the presence of the vascular endothelium.     

白藜芦醇对离体犬冠状动脉血管环的影响

目的：研究白藜芦醇和17β-雌二醇对狗冠状动脉舒张特征的影响及其机制。方法：制备狗冠状动脉血管环，固定于盛有K-H液的恒温肌槽内，并观察等长时血管张力的变化。结果：白藜芦醇和17β-雌二醇使KCI及无钙K-H液中CaCl2量效曲线明显右移，使肌条敏感性和最大收缩反应明显降低。Nω-L-硝基精氨酸、甲烯兰、正矾酸钠及去细胞内皮，可部分阻断白藜芦醇和17β-雌二醇的舒张血管作用。格列本脲组对白藜芦醇和17β-雌二醇的舒张作用没有影响。结论：白藜芦醇和17β-雌二醇舒张血管都具有内皮依赖性，与KATP仰通道无关。     

Unfractioned heparin produces vasodilatory action on human internal mammary artery by endothelium-dependent mechanisms

The aim of this study was to investigate whether unfractioned heparin produces a direct vasodilatory effect on the human internal mammary artery (IMA) and the possible underlying mechanisms. Samples of redundant IMA were obtained from 20 patients undergoing coronary artery bypass graft surgery, and concentration-response curves to unfractioned heparin were constructed. Unfractioned heparin (0.5-6 U/mL) caused a concentration-dependent relaxation in the endothelium-intact human IMA rings precontracted with phenylephrine (10(-6) M). Removal of endothelium significantly inhibited the responses of human IMA to unfractioned heparin (P < 0.05). Nomega-Nitro-L-arginine methyl ester (L-NAME, 10(-4) M), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10(-5) M) and L-NAME (10(-4) M) plus ODQ (10(-5) M) partially reduced unfractioned heparin-induced vasodilatory response in endothelium-intact rings, whereas indomethacin alone had no effect. The vasodilatory effect of unfractioned heparin was completely inhibited by 40 mM KCl in the presence of L-NAME, ODQ, and indomethacin. These results clearly demonstrated that unfractioned heparin causes a concentration-dependent vasodilatation in human internal mammary artery, and this action seems to be via endothelium-dependent mechanisms, including generation of nitric oxide and endothelium-derived hyperpolarizing factor.     

Inhibitory effects of calcium antagonists on alpha-adrenoceptor-mediated contraction in the human internal mammary artery.

1. The internal mammary artery has become a preferred coronary bypass graft. Sympathomimetic amines are spasmogens for vasospasm and calcium antagonists are frequently administered drugs perioperatively. The effect of calcium antagonists on alpha-adrenoceptor-mediated contraction depends on the subtype of alpha-adrenoceptor and the type of origin of vascular smooth muscle. This study was designed to investigate the effect of calcium antagonists on alpha-adrenoceptor-mediated contraction in the IMA. 2. Human IMA segments taken from 22 patients undergoing IMA--coronary artery bypass grafting were mounted in an organ bath under the physiological pressure determined from their own length-tension curves. 3. Three ring segments were allocated into three groups. One served as a control and the others were treated with clinically related concentrations of nifedipine (20 or 200 nM) for 25 min before concentration-contraction curves to alpha 1-adrenoceptor agonist methoxamine (MO) or full alpha-adrenoceptor agonist noradrenaline (NA) were established. 4. In separate experiments, the concentration-relaxation curves to nifedipine were established in the IMA rings precontracted with MO (30 microM) or NA (10 microM). Glyceryl trinitrate (GTN, 3 microM) was added to further relax the vessels. 5. Pretreatment with nifedipine (200 nM) only slightly inhibited the MO- (1.74 +/- 0.32 vs 2.88 +/- 0.56 g) or NA- (2.43 +/- 0.66 vs 3.60 +/- 0.82 g) induced contraction without statistical significance (P > 0.05). 6. On the other hand, nifedipine only caused 34.49% relaxation in the MO-precontracted and 24.39% relaxation in the NA-precontracted IMAs. In contrast, GTN caused 76.16% (against MO, P < 0.05) or 92.22% (against NA, P < 0.0001) relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of short-term exposure to homocysteine on vascular responsiveness of human internal mammary artery

The aim of this study was to investigate the acute direct effects of homocysteine (Hcy) on the vascular responsiveness of human internal mammary artery (IMA) and to define the possible underlying mechanisms. The contractile response to both phenylephrine (Phe) (-36%) and KCl (-18%) was significantly reduced in arteries that were incubated with Hcy (10 (-4)M, 30 minutes), compared with controls (P < 0.05). Removal of endothelium did not significantly alter the responses of human IMA to Phe. Hcy (10 (-6)M) also caused a relaxation response in human IMA rings precontracted with Phe (10 (-4) M) and this effect was not inhibited by N-nitro-L-arginine methyl ester (L-NAME, 10(-4) M), by l-NAME (10 (-4)M) + indomethacin (10 (-4)M), or by intimal rubbing. In addition, contractions induced by stepwise addition to calcium (Ca2+) to high KCl solution with no Ca(2+) were significantly inhibited by Hcy incubation as well as contractions induced by Phe in the absence of extracellular Ca (2+) (P < 0.05). On the other hand, Hcy (10 M, 30 minutes) did not significantly inhibit the relaxation responses to either acetylcholine (ACh) or sodium nitroprusside (SNP) (P > 0.05). These results demonstrated that short-term exposure to Hcy significantly decreased vascular responsiveness in human IMA without affecting endothelium-dependent and -independent vasorelaxation. This effect is not NO-, prostaglandin- or endothelium-dependent. The mechanism is uncertain but seems to depend on the interactions of Hcy with Ca(2+) influxes and/or other undefined direct effects in this tissue.     

The relationship between risk factors and testosterone-induced relaxations in human internal mammary artery

In human internal mammary artery (IMA), testosterone induces vasodilation that shows marked variability among patients. We aimed to investigate the relationship of this variability with cardiovascular risk factors. Cumulative relaxations to testosterone after precontraction with KCl were examined in IMA segments from patients with identified cardiovascular risk factors such as hypercholesterolemia, diabetes, hypertension, smoking, age, gender, body mass index (BMI), and number of occluded vessels. Testosterone responses were significantly diminished in subjects with 3 compared with 1 risk factor. Hypercholesterolemia independently influenced testosterone responses by significantly decreasing its maximum, and smoking significantly decreased the sensitivity to testosterone. Thus, the variability observed in testosterone-induced vascular relaxations may in part be related to differences in risk factors present among the individuals studied.     

Vasorelaxation induced by vascular endothelial growth factor in the human internal mammary artery and radial artery

OBJECTIVES: Due to potential therapeutic value of vascular endothelial growth factor (VEGF) in coronary artery disease, the effect and mechanism of VEGF in human arteries used as coronary bypass grafts become important but not fully understood. VEGF-mediated endothelial regulation in vasorelaxation was studied in internal mammary artery (IMA) and radial artery (RA), compared with that of the classical agent-acetylcholine (ACh). The role of nitric oxide (NO), prostacyclin (PGI2), and endothelium-derived hyperpolarizing factor (EDHF) was investigated. METHODS: VEGF- and ACh-induced responses were measured in RA and IMA with or without endothelium and in the absence or presence of inhibitors of nitric oxide synthase or prostacyclin. In addition, the VEGF-induced PGI2 was measured by enzyme immunoassay. RESULTS: VEGF induced similar relaxation in RA (59.2+/-9.3%) and IMA (56.1+/-6.4%) that was significantly inhibited by N(omega)-nitro-L-arginine (L-NNA) plus oxyhemoglobin (HbO) (IMA: 24.9+/-4.3%, P=0.03 vs. RA: 25.0+/-8.6%, P=0.01) or by indomethacin (INDO) (IMA: 21.8+/-2.5%, P=0.000 vs. RA: 30.0+/-6.6%, P=0.04) with more inhibition in IMA than RA (P<0.05). In addition, the VEGF-induced PGI2 was significantly higher in IMA than RA (11.5+/-2.1 vs. 4.9+/-1.1 pg/ml/mg, P=0.002). INDO+L-NNA+HbO reduced the VEGF-induced relaxation to 20.8+/-4.6% in RA vs. 4.8+/-1.6% in IMA (P=0.01). In contrast, the maximal relaxation induced by ACh in RA (55.9+/-6.0%) and IMA (48.5+/-5.3%) was largely inhibited by L-NNA in IMA and RA (14.7+/-3.0%, P=0.000 vs. 15.2+/-3.2%, P=0.004) but little affected by INDO. CONCLUSIONS: VEGF induces similar relaxation in IMA and RA with significantly more PGI2-mediated relaxation and higher stimulated PGI2 level in IMA but more EDHF-mediated relaxation in RA. In comparison, ACh-induced relaxation mainly depends on NO. Thus, our study reveals a significant difference in the mechanism of the endothelium-dependent relaxation induced by VEGF and ACh.     

Effect of the vascular endothelium on contractions induced by noradrenaline and phenylephrine in perforating branch of the human internal mammary artery

The effects of noradrenaline (Nor) and phenylephrine (Phe) on the isolated, non-precontracted perforating branch of the human internal mammary artery (HIMA) were investigated. Nor and Phe induced concentration-dependent contractions of intact and endothelium-denuded arterial rings with no statistically significant differences between the pEC(30) and maximal response values. The pretreatment of arterial rings with indomethacin had no effect on Nor- and Phe-induced contractions of both, intact and endothelium-denuded preparations. The pre-addition of L-NMMA did not affect contractions of perforating branch of the HIMA evoked by Nor, but provoked significant potentiation of Phe-induced contractions of perforating branch of the HIMA both intact and denuded of endothelium only at Phe concentration higher than 3 x 10(-6)M. The effects of selective alpha1-adrenoceptor antagonist, prazosin and selective alpha2-adrenoceptor antagonist, rauwolscine were concentration-dependent, and they induced a significant shift to the right (for both studied antagonists) of the concentration-response curves for Nor in both preparations with or without endothelium. The effects of prazosin and rauwolscine on the concentration-response curves for Phe were similar. In conclusion, this study has shown that Nor and Phe induce concentration-dependent contractions of the perforating branch of the HIMA. Removal of the endothelium did not modify this effect. Products of cyclooxygenase pathway had no influence on Nor and Phe action. Endothelium derived nitric oxide (NO) had no modulatory effect of Nor-induced contractions, but inhibition of NO synthesis provoked potentiation of Phe-induced contractions either in intact or endothelium-denuded preparations. The mechanism of this effect remains still unclear. On the basis of differential affinity of the antagonists and affinities of Nor and Phe themselves, we suggest that alpha1-adrenoceptor subtype is probably involved in the Nor- and Phe-induced contraction of the perforating branch of the HIMA both intact or denuded of endothelium.     

Inhibitory effects of glyceryl trinitrate on alpha-adrenoceptor mediated contraction in the human internal mammary artery.

1. Sympathomimetic amines have been considered to be related to vasospasm. Previous studies showed that the human internal mammary artery (IMA) was capable of weak beta-adrenoceptor mediated relaxation and that alpha-adrenoceptor agonists may induce contraction in the human IMA. 2. We investigated the effects of glyceryl trinitrate (GTN), a vasodilator agent often used perioperatively, on alpha-adrenoceptor mediated contraction in the human IMA. 3. Discarded human IMA segments were taken from 37 patients who underwent IMA--coronary artery bypass graft operations and equilibrated in an organ bath. 4. A specially designed technique was used to normalize the vessel segments under the pressure similar to the in vivo situation. Noradrenaline (NA), phenylephrine (PE), and methoxamine (MO) were used to contract the vessel segments. 5. GTN fully relaxed PE or MO (submaximal concentration) induced precontraction. Therapeutic plasma concentration of GTN relaxed 40-90% of the PE induced contraction (2.82 g, EC50 = 7.92 +/- 0.06 -log M) and 20-90% of the MO induced contraction (1.8 g, EC50 = 7.63 +/- 0.16 -log M). Pretreatment by the therapeutic plasma concentration of GTN inhibited the contraction induced by NA, PE in a different range. It reduced the NA induced contraction (6.9 g) by 14.8-38% (P greater than 0.05) and the PE induced contraction (4.3 g) by 7.9-39.3% (P greater than 0.05). The alpha 1-adrenoceptor antagonist prazosin, at the therapeutic plasma concentration, nearly totally abolished the NA or PE induced contraction (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Histamine receptors in the smooth muscle of human internal mammary artery and saphenous vein

The effects of histamine were characterized and compared in the vascular smooth muscle of two human isolated blood vessels, the human internal mammary artery (HIMA) and the human saphenous vein (HSV). Segments of these vessels were obtained during aortocoronary bypass surgery and their intimal surface was rubbed in order to eliminate any possible influence of the endothelium. Histamine contracted both types of vessels in a concentration-dependent manner and this effect was antagonized by the H1 receptor antagonists mepyramine and cicletanine. In the case of HIMA only this antagonism was found to be competitive (pA2 values of 9.3 and 7.7 for mepyramine and cicletanine, respectively). Histamine-induced contractions were not significantly affected by phentolamine (0.3 microM). In HSV, but not HIMA, indomethacin (5 microM) significantly depressed histamine-induced contractions (by about 30%). In the presence of the H2 receptor antagonist cimetidine (10 microM), concentration-response curves of histamine-induced contractions were significantly shifted to the left in both HIMA and HSV, suggesting the presence of H2 receptors mediating relaxation. HIMA and HSV precontracted by noradrenaline could be partially and concentration dependently relaxed by histamine, only in the presence of a H1 receptor antagonist. This relaxation was inhibited by cimetidine. The results show that in de-endothelialized HIMA and HSV histamine induced mainly contraction which is sensitive to the H1 receptor antagonists. Only in HIMA, nevertheless, was competitive antagonism established. In addition, histamine-induced relaxation, antagonized by cimetidine, could be demonstrated in both precontracted vessels, indicating the presence of H2 receptors.     

The effects of potassium channel opener P1075 on the human saphenous vein and human internal mammary artery

Because adrenergic contractions can contribute to the development of life-threatening spasm of coronary artery bypass graft, this study was performed to investigate the effect of adenosine 3-phosphate (ATP)-sensitive K channel (KATP) opener P1075 on contractions of isolated human saphenous vein (HSV) and human internal mammary artery (HIMA). Phasic contractions were evoked by electric field stimulation (20 Hz) and noradrenaline. The sustained contractions were evoked by phenylephrine. The presence of pore-forming Kir6.1 and Kir6.2 subunits of the KATP channels in the HIMA and only Kir6.2 in the HSV was confirmed immunomorphologically. P1075 inhibited in the HSV only, the electrical field stimulation contractions more strongly than noradrenaline contractions. In addition, the phenylephrine contractions of HSV were more sensitive to P1075 in comparison to those of HIMA. Glibenclamide, a KATP channel blocker antagonized the vasodilatation produced by P1075 in both grafts differently, because its effect was more prominent on the P1075-induced inhibition of contractions of HSV than of HIMA. We conclude that P1075 has a vasorelaxant effect and inhibited adrenergic contractions of the tested grafts. This effect is graft and vasoconstrictor selective and seems to be mediated by Kir6.1- and/or Kir6.2-containing KATP channels. Thus, P1075 can be considered as a potential drug in the prevention of graft spasm.     

Interaction between capsaicin and nitrate tolerance in isolated guinea-pig heart

Capsaicin-induced increases in heart rate and coronary flow were blocked by N(G)-nitro-L-Arg-methyl ester (30 mM) in Langendorff-perfused guinea-pig hearts. Neither heart rate nor coronary flow changed by capsaicin in hearts from animals made tolerant to the hypotensive effect of 30 microg/kg nitroglycerin by the administration of 50 mg/kg nitroglycerin subcutaneously 4 times a day over 3 days. We conclude that the effector function of sensory nerves may deteriorate in nitrate tolerance.     

Thermal preconditioning protects the human internal mammary artery from hypoxia/re-oxygenation-induced damage

1. Preconditioning has been demonstrated to ameliorate ischaemia/reperfusion injury in several cells and tissues. Therefore, in the present study we investigated whether preconditioning of human bypass grafts, internal mammary artery (IMA) and saphenous vein (SV) induces heat shock protein (Hsp) expression and reduces apoptosis in response to subsequent hypoxia/re-oxygenation damage in both vessels. 2. Internal mammary artery and SV rings, obtained from 30 patients (median age 66.5 years) undergoing coronary artery bypass grafting, were either incubated for 30 min at 42 degrees C (preconditioned) or kept in a standard incubator at 37 degrees C (not preconditioned). Six hours later, graft segments were exposed to 90 min hypoxia followed by a 30 min re-oxygenation period. Western blot, real-time quantative polymerase chain reaction analysis and apoptosis detection by the Terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling method were performed. 3. Heat-preconditioned IMA showed significantly increased protein expression of Hsp72 after hypoxia/re-oxygenation treatment compared with controls (median 9.1 vs 5.0 microg/mg total protein; P = 0.048). Expression of Hsp73 was weak and Hsp60 was not detectable in the IMA. 4. In the SV, neither protein nor mRNA expression of Hsp were significantly different between preconditioned and not preconditioned veins. 5. There were significantly fewer apoptotic cells in the intima of the preconditioned compared with not preconditioned IMA (P = 0.041) after hypoxia/re-oxygenation injury, whereas in the SV apoptosis was not significantly prevented by preconditioning. 6. Mild heat preconditioning before hypoxia/re-oxygenation injury is a stimulus for Hsp72 protein expression and a reduction in apoptosis in the human IMA.