Effects of Ca antagonists on the norepinephrine release and contractile responses of isolated canine saphenous veins to high KCl

Effects of verapamil, diltiazem and nicardipine on tritium overflow and contraction evoked by 40 mM KCl were evaluated using canine saphenous vein strips preloaded with [3H]norepinephrine. Phentolamine, 10(-6) M, almost completely inhibited the contraction induced by KCl, while it significantly enhanced the evoked tritium overflow. These responses to KCl were dependent on external Ca2+. All Ca antagonists tested significantly increased the spontaneous tritium overflow in a concentration-dependent manner without any changes in basal tension. Verapamil at 10(-6) M significantly inhibited the contraction with no significant effect on the evoked overflow; and at concentrations above 10(-5) M, it inhibited the contraction much more strongly than the evoked tritium overflow. Diltiazem and nicardipine at concentrations above 3 X 10(-6) M significantly inhibited both tritium overflow and contraction evoked by KCl. A significant correlation between inhibitions of both responses to KCl by the three Ca antagonists was observed, although the y-intercept and slope of the regression line for verapamil obtained by plotting the inhibition of the KCl-evoked contraction as a function of the inhibition of the evoked tritium overflow were greater than those for the other two antagonists. The inhibitory effects of verapamil and diltiazem on the tritium overflow and contraction evoked by KCl were not related to their local anesthetic activities. Neither the increase in the spontaneous tritium overflow nor inhibitions of the evoked tritium overflow and contraction by nicardipine were related to its phosphodiesterase inhibiting activity. These results suggest that diltiazem and nicardipine may inhibit the KCl-evoked contraction mainly by inhibiting Ca2+-dependent transmitter release from the nerve endings, while verapamil may inhibit it by acting on the postsynaptic sites and at the relatively higher concentrations used, by further inhibition of transmitter release.     

Effects of Bay K 8644 on the electrically evoked and KCl-evoked norepinephrine release and the corresponding contraction in isolated canine saphenous veins

Bay K 8644 caused no significant effects on the 3H overflow and contraction evoked by electrical stimulation in the canine saphenous vein preloaded with [3H]norepinephrine. Bay K 8644 significantly enhanced the 3H overflow evoked by 40 mM KCl in a concentration-dependent manner, which was antagonized by nisoldipine. Bay K 8644 failed to significantly augment the KCl-evoked contraction. These results suggest that there is a difference between the modes of action of Bay K 8644 on norepinephrine releases evoked by electrical stimulation and KCl.     

Effects of S14001 on adrenergic neuroeffector interaction in isolated canine saphenous veins.

1. The effects of (S) fluoro-6 (morpholinyl-2 methoxy)-8-tetrahydro-1,2,3,4 quinoleine (S14001) on adrenergic neurotransmission in isolated canine saphenous veins were investigated in experiments which measured the accumulation, overflow and metabolism of 3H-norepinephrine. 2. S14001 inhibited the accumulation of total tritium (3H-norepinephrine and 3H-metabolites of norepinephrine) in a concentration-dependent manner. 3. Under basal conditions, S14001 increased tension and basal effiux of total tritium; the latter consisted predominantly of 3H-DOPEG. The increases in these parameters were not inhibited by desmethylimipramine (DMI). 4. During electrical stimulation, S14001 increased the contraction and overflow of total tritium; the latter consisted predominantly of 3H-DOPEG. The increases in these parameters were inhibited by DMI. 5. These experiments suggest that S14001 has dual effects on adrenergic neurotransmission in the canine saphenous vein: (a) an inhibitory action on the neuronal accumulation; and (b) a pharmacological displacement of the transmitter from adrenergic nerve terminals.     

Flunarizine and alpha-adrenergic responses in isolated canine saphenous veins

Experiments were designed to determine how flunarizine affects contractions of cutaneous veins to alpha-adrenergic activation. Rings of canine saphenous vein were mounted at optimal length for isometric tension recording in organ chambers filled with physiological salt solution. At concentrations higher than those needed to inhibit KCl-induced contractions, flunarizine inhibited the contractile responses evoked by alpha 2-adrenergic agonists (B-HT 920, xylazine), partial (St-587) and full (cirazoline, phenylephrine) alpha 1-adrenergic agonists and the combined alpha 1-/alpha 2-adrenergic agonist, norepinephrine. The inhibitory effect of flunarizine against alpha 2-adrenergic responses was similar to that produced by other calcium-antagonists and results presumably from inhibition of the influx of extracellular calcium. The inhibitory effect of flunarizine against alpha 1-adrenergic responses was greater than expected and appears to result from competitive antagonism of alpha 1-adrenoceptors (pA2 = 5.79). Therefore, flunarizine can decrease adrenergic contractile responses by depressing the influx of extracellular calcium and by blocking postjunctional alpha 1-adrenoceptors.     

Effects of nicardipine and diltiazem on alpha-adrenoceptor responses in canine saphenous veins

The effects of calcium antagonists, diltiazem and nicardipine (-6.0 to -4.0 log mol/l), on the contractile responses to noradrenaline, methoxamine and BHT-920 in isolated canine saphenous vein rings, were studied with isometric tension recordings. Concentration-effect curves to the alpha-agonists were obtained in the control state and in the presence of diltiazem or nicardipine. Propranolol (-6.0 log mol/l) was present in the bath throughout. Diltiazem had no significant inhibitory effect on the responses mediated by all three agonists. Nicardipine (-5.0 and -4.0 log mol/l) produced a small but significant inhibitory effect on the responses to noradrenaline and methoxamine while it had no effect on the response to BHT-920. The effects of nicardipine were greatest on the responses to methoxamine. These calcium antagonists appeared to have only small post-synaptic inhibitory effects on the contractile responses to alpha-agonists in the canine saphenous vein with nicardipine exerting a greater inhibitory influence than diltiazem.     

A selective effect of protein kinase C activators on noradrenaline release compared with subsequent contraction in canine isolated saphenous veins.

1. Effects of protein kinase C (PKC) activators and inhibitors on both tritium overflow and subsequent contraction evoked by transmural nerve stimulation (TNS) were investigated in canine saphenous veins prelabelled with [3H]-noradrenaline. 2. Activation of PKC by stepwise increasing concentrations (0.01 nM-1 microM) of 12-O-tetradecanoylphorbol 13-acetate (TPA), phorbol 12,13-dibutyrate (PDBu) or mezerein caused a significant and concentration-dependent enhancement of the tritium overflow evoked by TNS, while the activators failed to affect the corresponding contraction except with the highest concentration of PDBu when the contraction was significantly reduced. Phorbol, which is inactive on PKC, had no effects on the tritium overflow and contraction induced by TNS. 3. PKC inhibitors, polymyxin B (1 and 10 microM) and the isoquinolinesulphonamide, H-7 (1 microM), inhibited significantly the phorbol ester-potentiated tritium overflow evoked by TNS with no effects on the contraction. H-7 and the related inhibitor H-8 at 10 microM reduced significantly both responses to TNS in the presence of TPA, while they suppressed only the TNS-induced contraction in the absence of TPA. 4. None of the PKC activators or inhibitors affected the spontaneous tritium overflow. 5. PDBu (0.01 and 0.1 microM) elevated resting tension of the veins more effectively than TPA and mezerein. 6. These results suggest that PKC may modulate electrically stimulated noradrenaline release from adrenergic nerve endings of the canine saphenous veins and the PKC activators may act more selectively on presynaptic than postsynaptic sites, but have no apparent effect on postjunctional noradrenergic mechanisms.     

Effects of leukotrienes C4 and D4 on human isolated saphenous veins.

1. Vascular injury during the intra-operative procedures of bypass surgery may be the initiating event in the gradual deterioration in the patency of the graft. Adhesion of leukocytes to the vascular endothelium frequently accompanies preparation and insertion of the graft. However, little is known about the effects of vasoactive substances released from leukocytes on vein graft performance. 2. To determine whether leukotrienes are capable of affecting the tone of blood vessels used as coronary artery bypass grafts we studied the human saphenous vein as intact rings using an isolated organ bath technique. 3. LTC4 and LTD4 caused weak endothelium-dependent relaxations at lower concentrations (1 pM to 1 nM) and powerful endothelium-independent contractions at higher concentrations (3 nM to 0.1 microM). The maximum responses to LTC4 and LTD4 for relaxations were 21.1 +/- 4.8% and 28.6 +/- 3.4% (% of noradrenaline induced tone) respectively and 64.6 +/- 9.9% and 59.1 +/- 7.9% (% response to KCl) respectively for contractions. 4. The inhibitor of nitric oxide formation, L-NG-monomethyl L-arginine, prevented the relaxations to LTD4, but not LTC4 and unmasked endothelium-dependent contractions to LTD4 (32.9 +/- 11.3%). NG-monomethyl L-arginine had no effect on the contractions produced by LTC4 or LTD4. 5. Indomethacin augmented relaxations and contractions of saphenous vein to LTC4 from 22.5 +/- 5.6 to 40.02 +/- 8.7 (P < 0.05) and 48.8 +/- 5.5% to 74.7 +/- 7.6% (P < 0.01) respectively. LTD4 responses were not affected by indomethacin treatment. 6. In conclusion, leukotrienes mediate biphasic responses in the human saphenous vein.(ABSTRACT TRUNCATED AT 250 WORDS)     

内皮素-3对犬肺动静脉的作用

阐明内皮素 3(ET 3)对肺动静脉的作用机理 .利用犬离体肺动静脉条 ,观察其张力改变 .结果可见 :①ET 3(1～ 30 μmol·L- 1)引起肺动脉舒张 (低浓度 )和收缩 (高浓度 )双向反应 ,ETB 受体激动剂IRL162 0 (1～ 30 μmol·L- 1)只引起舒张反应 ;去内皮 ,ETB 受体阻断剂IRL10 38(1μmol·L- 1)或左旋硝基精氨酸 (L NA ,10 μmol·L- 1)均使ET 3或IRL162 0所致舒张反应减弱或消失 ,ETA 受体阻断剂BQ12 3(10 μmol·L- 1)则使ET 3所致收缩反应翻转为舒张反应 ;②同浓度的ET 3和IRL162 0只引起肺静脉浓度依赖性收缩反应 ;BQ12 3可使ET 3所致收缩反应减弱 ,IRL10 38可使IRL162 0所致收缩反应减弱 ;③在BQ12 3预处理条件下给予第二剂ET 3(30 μmol·L- 1) ,肺静脉表现为舒张反应 ,吲哚美辛 (1μmol·L- 1)可使其舒张反应减弱 .本研究表明 :①存在于肺动脉平滑肌上的ETA 受体参与血管的收缩反应 ,肺动脉内皮上的ETB 受体通过释放NO参与舒张反应 ;②肺静脉平滑肌上的ETA 和ETB 受体均参与收缩反应 ,但ETB 受体所致收缩反应易脱敏 ;③在肺静脉平滑肌上可能还存在非ETA/非ETB 受体 ,通过释放舒张性PG物质参与舒张反应 .     

Differential effects of verapamil, nicardipine and diltiazem on Ca2+-dependent and Ca2+-independent noradrenaline release and contraction in isolated canine saphenous veins

We reported that verapamil, nicardipine and diltiazem inhibited both 3H overflow and contraction induced by transmural nerve stimulation (TNS) in the canine saphenous vein preloaded with 3H-noradrenaline. In the present study, the effects of these Ca channel antagonists in the presence of tetraethylammonium (TEA) were investigated to evaluate whether the antagonists act by inhibiting Ca2+ influx into the nerve endings. The effects of the drugs on both responses to tyramine were also studied. In the 1 mmol/l-TEA-pretreated veins, verapamil and nicardipine inhibited only the contraction. Diltiazem inhibited the two parameters, the effects being nearly equipotent to those in the absence of TEA. The L-cis isomer of diltiazem inhibited the TNS-evoked responses to a similar degree as diltiazem, which was unaffected by 1 mmol/l TEA. Verapamil, nicardipine and diltiazem inhibited the TNS-evoked 3H overflow in 0.25 mmol/l Ca2+ and 20 mmol/l TEA medium, the inhibitions by the two former antagonists being greater than those seen in normal Krebs solution. TEA (1 mmol/l) added after the Ca channel antagonists, overcame the inhibition of the evoked overflow by diltiazem more poorly than that by verapamil or nicardipine. Only verapamil inhibited both responses to tyramine. These data together with previous results suggest that unlike verapamil and nicardipine, diltiazem may inhibit the TNS-evoked neurotransmitter release via a mechanism being unrelated to its Ca2+ influx-inhibiting action, resulting in an inhibition of the contraction, and that only verapamil inhibits the tyramine-evoked neurotransmitter release.     

Heterogeneity of beta-adrenoceptor in canine veins: comparison among the facial, portal and saphenous veins

A study was made on the characteristics of beta-adrenoceptors in the isolated canine facial, portal and saphenous veins. Ring segments of the facial and saphenous veins and longitudinal strips of the portal vein were suspended in tissue baths containing Krebs solution oxygenated and maintained at 37 degrees C. They were moderately contracted with prostaglandin F2 alpha before examining their relaxation responses. The facial and saphenous veins fully relaxed to isoproterenol, while the portal vein relaxed to a small extent (20% of maximum relaxation) even in the presence of an alpha-adrenoceptor blockade. In contrast, both forskolin, a direct activator of adenylate cyclase, and membrane-permeable dibutyryl cyclic AMP similarly relaxed all the veins studied. Thus, the reduction of coupling between beta-adrenoceptors and the adenylate cyclase system may be involved in the decreased responsiveness of the portal vein to beta-adrenoceptor agonists. In addition, analyses of beta-adrenoceptor agonism and antagonism, using selective (beta 1: T-1583, beta 2: procaterol) and non-selective (isoproterenol) agonists as well as selective (beta 1: atenolol, beta 2: ICI 118,551) and non-selective (propranolol) antagonists, confirmed that beta-adrenoceptors in the canine facial vein are not homogeneous, with the beta 1-subtype predominating over the beta 2-subtype, and that the canine saphenous vein has a homogeneous population of the beta 2-subtype, as reported in the other species.     

Action of dopamine on isolated human saphenous veins

We have investigated the subtype of alpha-adrenoceptor responsible for the contractile effect of dopamine using isolated human saphenous vein. Lengths of saphenous vein were obtained surplus to coronary artery bypass graft operations and studied as intact rings using a conventional organ bath technique. Contractile responses to dopamine (10(-7)-10(-3) M) in the presence of propranolol, cocaine, and 17 beta oestradiol were competitively antagonised by the alpha 2-selective adrenoceptor antagonist yohimbine (10(-8)-10(-6) M) but unaffected by the alpha 1 selective adrenoceptor antagonist doxazosin (10(-8)-10(-6) M), whereas the response to norepinephrine (NE) (10(-8)-10(-3) M) was antagonised by doxazosin (10(-8)-10(-6) M), thus demonstrating the presence of alpha 1-adrenoceptors in this preparation. We conclude that the contractile effects of dopamine in isolated human saphenous vein are mediated predominantly by an action on alpha 2-adrenoceptors.     

Pharmacological studies on frozen stored canine saphenous veins and basilar arteries

Summary Canine saphenous veins were either placed in Krebs-Henseleit solution and stored for 24 h at +4°C, or immersed in FCS (fetal calf serum) containing 1.8 mol/l DMSO (dimethyl sulfoxide), slowly frozen to-70°C and stored for 4 weeks at-70°C or-190°C. Canine basilar arteries were either stored in Krebs-Henseleit solution for 24 h at +4°C or slowly frozen and stored for 3 months in FCS plus 1.8 mol/l DMSO at-70°C. Subsequent pharmacological investigations revealed a considerable attenuation of the contractile force of frozen-stored vessels but the evidence suggests that there may be a very good preservation of the main biochemical properties, such as monoamine oxidase activity, endogenous prostaglandin synthesis and uptake₁ mechanisms in veins stored at-190°C and there is an excellent correlation of thepD₂ values for various tryptamine derivatives on canine basilar arteries stored for 3 months at-70°C with those calculated on fresh preparations. It is concluded that freezing isolated blood vessels may be considered an effective means of preserving and storing vascular tissues for pharmacological investigations.     

Effects of calcium channel blockade in canine saphenous veins after storage at -190 degrees C.

1. Canine saphenous veins were investigated in vitro either within 24 h after removal or after storage at -190 degrees C for 4-5 weeks of foetal calf serum containing 1.8 M dimethyl sulphoxide. 2. Contractions and 45Ca2+ uptake in response to both depolarization and guanfacine were studied in the absence and presence of the calcium channel antagonists diltiazem, verapamil, nifedipine and the two stereoisomers of a 1,4-dihydropyridine derivative, namely the (+)-(S) enantiomer and the (-)-(R) enantiomer of 202-791 (isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-nitro-3- pyridinecarboxylate). 3. Comparison of the data obtained on unfrozen and frozen/thawed veins revealed a good preservation of both contractile responsiveness and 45Ca2+ uptake mechanisms after storage at -190 degrees C. 4. It is suggested that cryopreservation is a useful technique for storing venous smooth muscle for pharmacological studies.     

Effects of nitroglycerin on release, synthesis and metabolism of norepinephrine and activation of tyrosine hydroxylase in guinea-pigs.

Nitroglycerin produced concentration-dependent increases in outflow of norepinephrine (NE) in perfused guinea-pig hearts. These effects of nitroglycerin were inhibited by guanethidine, but were not blocked by desmethylimipramine or rauwolscine. Nitroglycerin-induced increases in NE outflow correlated with its positive chronotropic responses. Higher concentrations of nitroglycerin also increased outflow of 3,4-dihydroxyphenylglycol (DOPEG) which were inhibited by desmethylimipramine. Nitroglycerin-induced maximal outflow of NE occurred during the first 2 min, but maximal outflow of DOPEG was 2-4 min. In addition, the 3,4-dihydroxyphenylalanine formation in atrial and striatal slices were enhanced by nitroglycerin in the presence of m-hydroxybenzylhydrazine dihydrochloride (an inhibitor of aromatic L-amino acid decarboxylase). The results suggest that nitroglycerin increases release of NE which correlates with cardiac stimulation by the drug. The drug also stimulates tyrosine hydroxylase activity resulting in increased synthesis of NE.     

The effects of soman on norepinephrine uptake, release, and metabolism

The effects of 7-day administration of 5 micrograms/kg/day of soman sc on norepinephrine (NE) content, and catechol-O-methyl-transferase (COMT) and monoamine oxidase (MAO) activities of three rabbit tissues were examined. Effects on NE uptake by, and electrically stimulated release from, rabbit aorta were also determined, both in the 7-day study and with acutely applied soman. Tissues examined were the thoracic aorta, mesenteric artery, and brain stem. Significant (p less than 0.05) increases following 7 days of soman were observed in NE content: thoracic aorta, 20%; mesenteric artery, 48%; and brain stem, 121%. MAO activity decreased by 29% in the thoracic aorta, 20% in the mesenteric artery, and 48% in the brain stem. COMT activity also significantly decreased in two tissues, the thoracic aorta by 18% and brain stem by 23%. Acutely applied soman reduced electrically released NE from the thoracic aorta, but 7-day soman administration increased it. Seven-day soman administration, but not acutely applied soman increased NE uptake by the thoracic aorta. Thus, 7-day soman administration increased sympathetic capability by increasing NE content, nerve stimulation evoked NE release, and NE uptake, and by decreasing MAO and COMT activity. Therefore, repeated low-dose exposure to soman might exaggerate the response to any given level of sympathetic nerve stimulation and to NE-releasing agents.     

Dominant vasodilator action of norepinephrine in isolated, non-preconstricted simian facial veins

Using the cannula inserting method, we investigated the vascular responses to norepinephrine (NE), phenylephrine and isoprenaline (Isp) in isolated, perfused simian facial veins. NE usually induced only a vasodilation in non-preconstricted veins. Phenylephrine consistently induced only a slight vasoconstriction, and Isp produced only a vasodilation. NE-induced vasodilations were reversed to vasoconstrictions after treatment with a relatively larger dose of propranolol. It is concluded that simian facial veins have a spontaneous intrinsic tone and dominant abundant beta-adrenoceptors but sparse alpha 1-adrenoceptors.     

Pharmacology of pentoxifylline in isolated canine arteries and veins

Pentoxifylline possesses vasodilator properties, but little information is available on the mechanism of action explaining this vasodilator effect. The present experiments were designed to determine the effects of the compound on vascular smooth muscle, endothelium, and adrenergic nerves in rings of isolated canine blood vessels. Pentoxifylline did not affect basal tension in coronary and femoral arteries or in saphenous and mesenteric veins; it did not alter the rhythmic activity of the latter, but did cause endothelium-independent relaxations of unstimulated basilar arteries. In coronary arteries and saphenous veins, but not femoral arteries contracted with prostaglandin F2 alpha, the compound caused relaxations which were not affected by propranolol or by removal of the endothelium. Pentoxifylline inhibited the endothelium-dependent contractions to the Ca2(+)-ionophore A23187 in the basilar artery. In saphenous veins (with endothelium), pentoxifylline did not inhibit responses to high K+, electrical stimulation of the adrenergic nerves, or exogenous norepinephrine (NE); it reduced contractions evoked by xylazine and hypoxia. In the basilar artery and the saphenous vein, the inhibitory effect of pentoxifylline was prevented by inhibitors of cyclooxygenase and thromboxane synthetase. These experiments suggest that the dilator properties of pentoxifylline in isolated canine blood vessels are primarily at the level of the vascular smooth muscle and may involve decreased production of, or reduced responsiveness to, endogenous thromboxanes.     

Mechanisms of action of eperisone on isolated dog saphenous arteries and veins

Effects of eperisone, an antispasmodic in skeletal muscle, were investigated in helical strips of dog saphenous artery and vein. Eperisone relaxed saphenous arteries and veins previously contracted with norepinephrine, serotonin, acetylcholine, K+, or Ba2+; but in contrast, it produced contractions in the blood vessels contracted with prostaglandin (PG) F2 alpha. Treatment with eperisone attenuated the contractions induced by norepinephrine and serotonin in the arteries and those by clonidine and phenylephrine in the veins. Eperisone inhibited angiotensin II-induced relaxations, mediated possibly by endogenous PGI2, but did not alter relaxations caused by exogenous PGI2. Treatment with eperisone (10(-5) M) potentiated the contractile response to electrical stimulation of adrenergic nerves; the potentiating effect was suppressed by yohimbine. The eperisone-induced contraction in PGF2 alpha-contracted arteries was inhibited by treatment with indomethacin or aspirin, although cyclooxygenase activity was not inhibited by eperisone. These results may indicate that eperisone blocks postjunctional alpha 1- and alpha 2-adrenergic, muscarinic, serotonergic receptors and prejunctional alpha 2 adrenoceptors and reduces PGI2 synthesis via a mechanism other than cyclooxygenase inhibition.