Effects of S-11701 on accumulation, release and metabolism of norepinephrine in isolated canine saphenous veins.

1. The effects S-11701 ([morpholinyl-2)-methoxy]-8-tetrahydro-1,2,3,4 quinoline) on accumulation, overflow and metabolism of [3H]norepinephrine were investigated in isolated canine saphenous veins. 2. Saphenous veins were incubated with [3H]norepinephrine in the absence or the presence of S-11701; the drug caused a concentration-dependent inhibition of the tissue content of [3H]norepinephrine and its metabolites, except for 3-methoxy-4-hydroxymandelic acid (VMA). 3. In helical strips of canine saphenous veins previously incubated with [3H]norepinephrine and then suspended for isometric tension recording and measurement of the overflow of labelled transmitter and its metabolites, S-11701 (30 microM) significantly increased the spontaneous efflux of total 3H; this effect was almost exclusively due to an augmentation of the efflux of [3H]DOPEG. 4. During electrical stimulation (9 V, 1 Hz), S-11701 at 1 microM slightly increased the overflow of extraneuronal norepinephrine metabolites without affecting the contractile response. At the higher concentration (30 microM) the compound increased the contractive response and the overflow of 3H; the latter was due mainly to an increase in [3H]DOPEG and, to a lesser extent, in [3H]norepinephrine. 5. DMI (1 microM) did not interfere with the effects of S-11701 on DOPEG efflux. 6. These experiments indicate that in the canine saphenous vein, S-11701 causes a concentration-dependent inhibition of neuronal accumulation of [3H]norepinephrine. At higher concentrations, S-11701 enters the adrenergic nerve terminals independently of the neuronal amine carrier and displaces [3H]norepinephrine from its storage sites.     

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 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 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.     

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.     

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.     

Effects of verapamil and nitroglycerin on contractile responses to potassium and noradrenaline in isolated human peripheral veins.

Isolated ring preparations of human vein were contracted by potassium (127 mM) and noradrenaline (1.8 X 10(-5) M). The potassium-induced contracture developed more rapidly and had a higher maximum amplitude than that produced by noradrenaline. Addition of phentolamine (10(-5) M) reduced the amplitude of the potassium contracture by 22% and abolished the noradrenaline response. Verapamil and nitroglycerin relaxed preparations contracted by potassium and noradrenaline, and, when added prior to stimulation, reduced the contractile responses to these agents. Both verapamil and nitroglycerin inhibited the contractile effect of noradrenaline more strongly than that of potassium. After immersion of the preparations for 30 min. in a calcium-free medium, the responses to potassium and noradrenaline were reduced to 21.3 +/- 2.5% and 7.1 +/- 0.8%, respectively, of the control. Addition of verapamil caused a further reduction of the response to potassium, but not of that to noradrenaline. Nitroglycerin caused a further reduction of the contractions induced by both agents. When the calcium concentration in the extracellular medium was increased from 0 to 4 mM, the contractile responses to potassium and noradrenaline returned to the control level. Both verapmil and nitroglycerin inhibited the contractile responses to calcium; the inhibiting effects of verapamil were significantly more marked than those of nitroglycerin. Tachyphylaxis to nitroglycerin was demonstrated on contractions induced by potassium, but not on noradrenaline-produced responses.     

The effects of alpha-adrenoceptor antagonists on contractile responses to 5-hydroxytryptamine in dog saphenous vein.

1 5-Hydroxytryptamine (5-HT) contracted isolated saphenous vein strips of the dog, producing a biphasic concentration-effect curve. The first phase occurred with low concentrations of 5-HT (1.0 X 10(-8) TO 5.0 X 10(-6) mol/l) with a plateau between 1.0 x 10(-6) mol/l and 1.0 x 10(-5) mol/l. The second phase occurred with high concentrations of 5-HT (greater than 1.0 x 10(-5) mol/l). 2 The alpha-adrenoceptor antabonists, phentolamine (5.0 x 10(-8) to 5.0 x 10(-7) mol/l), labetalol (1.0 x 10(-6) to 1.0 x 10(-5) mol/l) and thymoxamine (1.0 x 10(-6) to 1.0 x 10(-5) mol/l), antagonized responses to high concentrations of 5-HT but responses to low concentrations of 5-HT were not antagonized. 3 The effects of high concentrations of 5-HT were antagonized by cocaine (1.0 x 10(-6) to 1.0 x 10(-5) mol/l) and were not evident in veins removed from dogs pretreated with syrosingopine. 5-HT receptors and that high concentrations of 5-HT also act indirectly on alpha-adrenoceptors by displacing noradrenaline from neuronal stores.     

L-methionine enhances the contractile responses of rat uterine smooth muscle to acetylcholine and high KCl

The contractile responses of isolated uterine smooth muscle from estradiol-treated ovariectomized rats to acetylcholine and high KCl in Ca-depleted modified Locke-Ringer (without CaCl2 and with 0.1 mM EGTA) solution on addition of CaCl2 (final concentration, 5 mM) are used as an indicator of Ca influx through the Ca channel. L-Methionine significantly enhanced these responses in the absence and presence of 3-deazaadenosine plus homocysteine thiolactone, blockers of methylation. These findings suggest that methylations of some components in isolated uterine smooth muscle seem to be important in stimulation-contraction coupling in the muscle.     

The inhibitory effect of quinacrine on contractile responses to norepinephrine in isolated rabbit aorta

1. In rabbit aorta, quinacrine, but not indomethacin nor nordihydroguaiaretic acid, inhibited contractile responses to norepinephrine and KCl. Amiloride and nifedipine did not affect the effect of quinacrine. 2. In Ca2(+)-free medium, quinacrine (3 x 10(-6)-10(-4) M) inhibited the norpinephrine response less than that to a subsequent addition of Ca2+. 3. M&B 22, 948, nitroglycerin and forskolin inhibited the Ca2+ response. The effect of quinacrine was inhibited by M&B 22,948, but not by forskolin and potentiated by nitroglycerin. 4. Quinacrine and M&B 22,948 potentiated the nitroglycerin-relaxation. The effect of quinacrine plus M&B 22,948 was not different from that of quinacrine. 5. These results indicate that the effect of quinacrine may be different from that of nifedipine but is related to cGMP.     

Effect of aging on contractile response to KCl, norepinephrine and 5-hydroxytryptamine in isolated human basilar artery.

1. We investigated the effect of aging on contractile response in human basilar artery. 2. The maximal contraction caused by KCl, norepinephrine and 5-hydroxytryptamine decreased with age. 3. ED50 value for norepinephrine or 5-hydroxytryptamine did not correlate with age. 4. These results suggest that the decrease in contractile response is due to nonspecific changes in the medial structure of the artery.     

Enhancement by L-methionine of contractile responses to acetylcholine and high KCl in uterine segment

The contractile responses of isolated uterine segments from 17 beta-estradiol-3-benzoate-treated ovariectomized rats to acetylcholine (ACh) and high KCl in Ca-depleted modified Locke-Ringer solution on addition of CaCl2 were used as indicators of Ca2+ influxes through ACh receptor- and voltage-operated Ca2+ channels, respectively. L-Methionine (L-Met) significantly enhanced these responses. The enhancement depended on the time of treatment with L-Met and concentration of L-Met. 3-Deazaadenosine (3-DAA) plus homocysteine thiolactone (HCTL), which inhibit S-adenosylmethionine-dependent methylation, caused dose-dependent inhibition of these contractile responses to ACh and high KCl. These inhibitory effects of 3-DAA plus HCTL were significantly attenuated in the presence of L-Met. Protein carboxylmethyltransferase and phospholipid methyltransferase activities were detected in the isolated uterine segment under conditions similar to those in which the contractile responses were observed. 3-DAA plus HCTL inhibited these enzyme activities. These findings suggest that S-adenosylmethionine-dependent methylations of protein and/or phospholipid in isolated uterine segment are involved in the contractile responses to ACh and high KCl in Ca-depleted modified Locke-Ringer solution on addition of CaCl2.     

Effects of Ca2+ antagonists nifedipine and diltiazem on isolated human chorionic arteries and veins.

5-Hydroxytryptamine (5-HT) and K+ induced contractions in human chorionic arteries and veins. 5-HT-caused responses were blocked by ketanserin (10(-7) and 10(-6) M) and prazosin (10(-5) but not 10(-6) M). K(+)-induced contractions were practically abolished in a Ca2(+)-free medium, whereas those produced by 5-HT were reduced. The efficacy (EC50 values) of diltiazem to produce relaxation in arteries and veins contracted with 40 or 75 mM K+ was similar, but normally greater than that of nifedipine. The potency of nifedipine (IC50 values) to inhibit maximal K+ contractions was greater than to inhibit maximal 5-HT contractions; diltiazem showed an inverse order of potency, which was less than that of nifedipine. The time course of 10(-6) M 5-HT and 75 mM K+ contractions was different, as much in the absence as in the presence of both Ca2+ antagonists; 5-HT contractions were transient, but sustained those elicited by K+. K+ (75 mM) and 5-HT (10(-6) M) produced increases in 45Ca2+ uptake, which were reduced by the Ca2+ antagonists. These results indicate that (a) human chorionic arteries and veins are similarly sensitive to Ca2+ antagonists, (b) 5-HT-induced contractions were largely dependent on extracellular Ca2+ and mainly mediated by 5-HT2 receptors but not by alpha 1-adrenoceptors, and (c) nifedipine was more potent than diltiazem in inhibiting Ca2+ influx through potential- and receptor-dependent Ca2+ channels.     

Effects of ouabain on contractile response to norepinephrine in isolated rat aorta.

1. Inhibition of sodium(Na+), potassium(K+)-ATPase activity was dependent on the concentration of ouabain and inverse to the concentration of potassium ([K+]) in the reaction mixture. 2. Contractility of isolated rat aorta preparation in response to norepinephrine was augmented by ouabain and low [K+]. 3. Results suggest that inhibition of Na+,K(+)-ATPase activity will be correlated with augmentation of vascular contractility maybe through activation of Na(+)-calcium exchange system.     

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 pincainide on contractile responses and 45Ca movements in rat isolated vascular smooth muscle

The effects of pincainide, a new beta-amino anilide, on contractile responses and 45Ca fluxes were studied in rat aorta and on spontaneous mechanical activity in rat portal veins. Pincainide (10(-5) to 10(-2) M) produced a dose-dependent inhibition of noradrenaline (NA) and high K+ -induced contractions. These inhibitory effects were observed with pincainide added either before or after the induced contractions. The Ca2+ -induced contractions of K+ -depolarized aorta as well as the spontaneous mechanical activity of portal veins were also inhibited by pincainide. Pincainide (5 X 10(-3) M) inhibited the 45Ca influx stimulated by 10(-6) M NA and increased 45Ca efflux. It was concluded that in isolated rat aorta, pincainide not only inhibited the influx of Ca2+ reducing the contractile responses to NA and high K+ but it also inhibited other effects related to NA-induced release of intracellular Ca2+ stores.     

Influence of temperature and extracellular pH on contractile responses in isolated human hand veins

The effects of moderate cooling and extracellular pH changes on concentration-response relationships for noradrenaline (NA), 5-hydroxytryptamine (5-HT) and prostaglandin F2 alpha (PGF2 alpha) were investigated in isolated human hand veins. pH changes were achieved by altering the NaHCO3 content of the Krebs solution. Cooling to 24 degrees reduced the maximum contractile responses to K+ (124 mM), NA and PGF2 alpha by 20-30%, whereas that to 5-HT was unchanged. The NA and 5-HT potencies were increased 8-10 times, whereas the PGF2 alpha potency was unaffected. A shift from alkalotic (pH 7.6) to acidotic (pH 6.9) conditions did not influence the contractile response to 124 mM K+, whereas the responses to NA, 5-HT and PGF2 alpha were inhibited with regard to both potency and maximum contraction. When related to neutral pH, acidosis significantly reduced only the 5-HT potency (4 times), whereas alkalosis selectively increased the NA and PGF2 alpha potencies (3 times). In the presence of prazosin (10(-7) M) cooling to 24 degrees significantly increased the NA potency, whereas no such increase was seen in the presence of rauwolscine (10(-7) M). Alkalosis significantly increased the NA potency in the presence of either antagonist. In conclusion, temperature and extracellular pH influenced the contractile responses to NA, 5-HT and PGF2 alpha in a differentiated manner. Alkalosis appeared to increase the response to both alpha 1- and alpha 2-adrenoceptor stimulation, whereas cooling preferentially increased that to alpha 2-adrenoceptor stimulation.     

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 .