Comparative study of the rat uterine smooth muscle relaxant activity of three bisbenzyltetrahydroisoquinolines with tetrandrine

Abstract— The relaxant activity of three bisbenzyltetrahydroisoquinolines—obaberine, popisonine and lindoldhamine—was examined in rat isolated uterus and their inhibitory potencies were compared with that of tetrandrine. All alkaloids tested relaxed KCl-depolarized rat uterus and totally or partially inhibited oxytocin-induced rhythmic contractions. The degree of methylation of the free phenolic hydroxy groups and the loss of one diarylether bridge influence the potency of relaxant action of these alkaloids. Only alkaloids with absolute configuration 1R,1′S or 1R1′R acted intracellularly, promoting relaxation of contractile responses induced by oxytocin or vanadate in a Ca²⁺-free medium.     

Relaxant Effect of Tetrazepam on Rat Uterine Smooth Muscle: Role of Calcium Movement

Tetrazepam is a benzodiazepine derivative clinically used as a muscle relaxant. The aim of the present work was to examine its effect on uterine smooth muscle of the rat in estrus. Tetrazepam required micromolar concentractions to relax contractile responses induced by KCl and acetylcholine in Ca²⁺ solution, but not oxytocin-induced contraction. In Ca²⁺-free solution, tetrazepam inhibited Ca²⁺-induced contractions in depolarized uterus and vanadate-induced contractions. We suggest that tetrazepam relaxes contractile responses induced by activation of voltage-sensitive calcium channels and receptor-operated calcium channels with little selectivity or that it antagonizes the effect of calcium at subsequent steps, possibly intracellular stores sensitive to vanadate but not sensitive to oxytocin. The inhibition of contraction of rat uterus is not related to high-affinity peripheral benzodiazepine binding sites.     

Pharmacology: α-Adrenoceptor Interaction of Tetrandrine and Isotetrandrine in the Rat: Functional and Binding Assays

The action of 1S,1′S-tetrandrine, a bisbenzyltetrahydroisoquinoline alkaloid, on α₁-adrenoceptors has been compared with that of its isomer 1R,1′S-isotetrandrine. The work includes binding assays to analyse the affinity of these products for the [³H]prazosin binding site of rat cerebral cortical membranes and functional studies on rat isolated aorta to examine the effects of both alkaloids on intracellular calcium processes related or not to α-adrenoceptor activation. A radioligand receptor-binding study showed that both compounds interacted with the α₁-adrenoceptors displacing [³H]prazosin from the specific binding site. The K_i values (inhibition constants) were 0.69±0.12 and 1.6±0.4 μM for tetrandrine and isotetrandrine, respectively. The functional studies showed that both alkaloids concentration-dependently inhibited noradrenaline-induced contraction in Ca²⁺-free solution (IC50 values, i.e. the concentrations needed to induce 50% inhibition, were 252.8 and 174.9 μM for tetrandrine and isotetrandrine, respectively), the spontaneous contractile response elicited by extracellular calcium after depletion of noradrenaline-sensitive intracellular stores (increase in resting tone; IC50 values 11.6 and 19.6 μM for tetrandrine and isotetrandrine, respectively) and the refilling of intracellular Ca²⁺ stores sensitive to noradrenaline (IC50 values 7.4 and 14.9 μM for tetrandrine and isotetrandrine, respectively). The results show that tetrandrine and isotetrandrine interact with α₁-adrenoceptors by displacing the [³H]prazosin binding site and that both compounds inhibit mainly the Ca²⁺-dependent process and have less action on α₁-adrenoceptors. Tetrandrine is more potent than isotetrandrine.     

Facilitation of the vasorelaxant action of calcium antagonists by basal nitric oxide in depolarized artery

We investigated the effect of NO/cyclic GMP pathway on the action of calcium antagonists (isradipine, nisoldipine, lacidipine, verapamil, diltiazem) in rat aorta exposed to 100 mM KCl. For this purpose constitutive NO synthase was blocked by using 100 M N-nitro-l-arginine (l-NNA).The steady-state contractile response evoked by 100 mM KCl was enhanced when the basal NO release had been blocked. The combined effects of basal NO release and calcium antagonists resulted in an inhibition greater than additive. Concentrations of calcium antagonists producing 50% inhibition of contraction were about 3-fold lower in the presence of the basal NO release than in its absence (P < 0.01). ⁴⁵Ca^2– influx stimulated by 100 mM KCl was not affected by the basal NO release, but was inhibited by isradipine and verapamil regardless of NO blockade. Thus, the facilitation of the action of calcium antagonists by NO/cyclic GMP pathway seemed not to be accompanied by a modification of their action on L-type calcium channels. To confirm this, we measured the contractile tension and the calcium signal in fura-2 loaded rings, pretreated with either verapamil or verapamil plus 8-bromo cyclic GMP (BrcGMP), and further exposed to increasing concentrations of extracellular Ca^2– ([Ca²⁺]_o) in 100 mM KCl solution. The increase in cytosolic Ca²⁺ ([Ca²⁺]_cyt) evoked by increasing ([Ca²⁺]_o) in rings pretreated with verapamil alone was not different from rings pretreated with verapamil plus BrcGMP. In contrast, the [Ca²⁺]_o-contraction curve was significantly shifted to the right in rings pretreated with verapamil plus BrcGMP.These results show that the NO/cyclic GMP pathway facilitates the inhibitory effect of calcium antagonists on 100 mM KCl-evoked contraction. This phenomenon is not related to a modification of calcium channel blockade, but could result from the reduction of the sensitivity of contractile machinery to Ca²⁺ by cyclic GMP.     

Relaxant Activity of Three Aporphine Alkaloids from Annona cherimolia on Isolated Aorta of Rat

In the present study we tested the relaxant effect of three aporphine alkaloids—roemerine, anonaine and dehydroroemerine—isolated from the roots of Annona cherimolia, on isolated strips of rat thoracic aorta. All compounds completely relaxed KCl- and noradrenaline-induced contractions with different potencies depending on their structural characteristics. The experiments, carried out in Ca²⁺-free medium using two different agonists (noradrenaline and caffeine) which mobilize calcium intracellularly by different mechanisms of action, showed that the alkaloids made no contribution to intracellular calcium processes. The present study provides evidence that the relaxant effects produced by aporphine alkaloids may be due to the blockade of calcium movements across the cell membrane, mainly through voltage-operated channels, and to the disruption of α₁-adrenoceptors connected to receptor-operated channels.     

Ca2+ influx in spontaneously hypertensive rats is sensitive to calcium antagonists

Upon perfusion with a solution containing Ca²⁺, after Ca²⁺-free perfusion, aortic rings from spontaneously hypertensive rats (SHR) responded with a contraction. The contraction was usually transient. When verapamil or nifedipine were added prior to and during Ca²⁺ repletion, the force developed was reduced to 25% of that of uninhibited contraction. Aortas from normotensive rats did not show comparable properties. These findings demonstrate strate that calcium influx in aortic smooth muscle of SHR occurs mainly via voltage-dependent calcium channels.     

Differential effects of nifedipine,verapamil, and diltiazem on noradrenaline-induced contractions,adrenergic transmitter release,and alpha-adrenoceptor binding in the female rabbit urethra

Summary In order to study differences in action between Ca²⁺-entry blockers on smooth muscle and peripheral nerves, the effects of nifedipine, verapamil, and diltiazem on noradrenaline (NA)-induced contractions and electrically evoked release of ³H-NA were investigated in the female rabbit urethra. In addition, possible influences of Ca²⁺-entry blockers on alpha-adrenoceptors were studied with radioligand binding technique. Exposure to Ca²⁺-free medium completely abolished the contractile response to 1 M NA in the rabbit urethra, indicating that the contraction was entirely dependent on influx of extracellular Ca²⁺. The Ca²⁺-entry blockers inhibited the NA-induced contractions in the following order of potency: nifedipine>verapamildiltiazem. In contrast to nifedipine and diltiazem, which produced a maximum inhibition of between 50 and 60%, verapamil was able to abolish the contractile responses to NA. The electrically evoked efflux of ³H-NA was decreased by diltiazem and increased by verapamil, whereas nifedipine failed to alter the ³H-NA efflux. Only verapamil was effective in inhibiting specific ³H-DHE binding to a crude membrane preparation of the rabbit bladder base and urethra, and the inhibition appeared to be of the competitive type. It is suggested that the effects of verapamil on electrically evoked efflux of ³H-NA and on NA-induced contractions can be partly explained by blockade of pre- and post-junctional alpha-adrenoceptors. The failure of nifedipine and diltiazem to abolish the NA-induced contraction might indicate the existence of different Ca²⁺-entry pathways in urethral smooth muscle.     

In vitro vasodilator mechanisms of the indole alkaloids rhynchophylline and isorhynchophylline,isolated from the hook of<Emphasis Type="Italic"> Uncaria rhynchophylla</Emphasis> (Miquel)

Rhynchophylline (Rhy) and isorhynchophylline (Isorhy), indole alkaloids from Uncaria hooks, reportedly exert hypotensive and vasodilatory effects, but the mechanism of action is unclear. We therefore investigated the relaxant effects of these two isomeric alkaloids in rat arteries in vitro, in particular in respect of the various functional Ca²⁺ pathways. Both Rhy and Isorhy relaxed aortic rings precontracted with phenylephrine (PE, 1 µM) in a dose-dependent manner (3–300 µM). Removal of endothelium and preincubation with L-NAME (300 µM) slightly inhibited but did not prevent the relaxant response. These results indicate that Rhy and Isorhy act largely in an endothelium-independent manner. Unlike nicardipine, both alkaloids not only inhibited the contraction induced by 60 mM KCl (IC₅₀ 20–30 µM), but also that induced by PE and U46619, albeit to a lesser extent (IC₅₀ 100 and 200 µM, respectively). These results suggest that Rhy and Isorhy may act via multiple Ca²⁺ pathways. In contrast to their inhibitory effects on KCl-induced and receptor-mediated contractions, where both isomers were comparably potent, Rhy was more potent than Isorhy at higher concentrations (>100 µM) in inhibiting both caffeine (25 mM)- and cyclopiazonic acid (CPA, 30 µM)-induced contractions. Similar results observed with caffeine in Ca²⁺-containing medium were also observed in Ca²⁺-free medium. However, 0.1–0.3 µM nicardipine (which completely inhibited KCl-induced contraction) had no significant inhibitory effect on CPA-induced contractions. Taken together, these results indicate discrimination between these two isomers with respect to Ca²⁺-induced Ca²⁺ release and non-L-type Ca²⁺ channel, but not for IP₃-induced Ca²⁺ release and L-type Ca²⁺ channels. Similar relaxant responses to KCl- and caffeine-induced contractions were seen when these two alkaloids were tested on the smaller mesenteric and renal arteries. In conclusion, the vasodilatory effects of Rhy and Isorhy are largely endothelium independent and are mediated by L-type Ca²⁺ channels. At higher concentrations, they also affect other Ca²⁺-handling pathways, although to a lesser extent. While there is no discrimination between the two isomers with respect to the contraction induced by KCl or agonists (PE and U46619), differential effects between Rhy and Isorhy were seen on caffeine- and CPA-induced contractions.     

Relaxant effect induced by wogonin from Scutellaria baicalensis on rat isolated uterine smooth muscle

Context: Wogonin is a flavone derivative isolated from Scutellaria baicalensis Georgi (Labiatae) root, which is a traditional Chinese drug used as an anti-inflammatory and for management of dysmenorrhea.

Objective: The effect of wogonin on the uterus has not yet been examined. We investigated the relaxant effects of wogonin on contractile activity of isolated uterine strips of rats.

Materials and methods: The effect of wogonin on spontaneous uterine contraction, and uterine contraction induced by agonists, K⁺-depolarization and oxytocin in Ca²⁺-free solution was observed. To clarify the type of potassium channel, we tested the effects of 4-aminopyridine, tetraethylammonium and glibenclamide.

Results: Wogonin reduced the contractile amplitude of uterine strip smooth muscle of rats in a dose-dependent manner. The concentration of wogonin for reducing the contraction amplitude by 50% (IC₅₀) on spontaneous contractions was 60.5 μM. Wogonin also inhibited the contraction induced by three agonists (oxytocin, prostaglandin F_2α and acetylcholine). For the uterine strips pretreated with oxytocin in Ca²⁺-free solution or K⁺-depolarization, wogonin showed relaxant effect on the induced uterine contractions. In addition, whereas the inhibitive effect of wogonin on the contraction of uterine smooth muscle in rats could be partly blocked by 4-aminopyridine and tetraethylammonium, it was not influenced by glibenclamide.

Discussion and conclusion: Wogonin significantly inhibited the contraction of rat uterine smooth muscle probably through the inhibition of the inflow of extracellular calcium into cells via cell membrane, and intracellular release of calcium ions. In addition, the relaxant effect induced by wogonin might be due in part to the opening of voltage-dependent and large conductance Ca²⁺-activated K⁺ channels.     

Inhibitory effects of protein kinase inhibitors and cytoskeletal inhibitors on Ca2+-free contraction of rat uterus

In rat uterine smooth muscle, sustained Ca²⁺-free contraction was observed by oxytocin in Ca²⁺-free solution. This Ca²⁺-free contraction was effectively inhibited by protein kinase inhibitors and cytoskeletal inhibitors but myosin-light chain kinase (MLCK) inhibitors were not so effective. Simultaneous addition of a protein kinase inhibitor and a cytoskeletal inhibitor caused synergestic inhibition. These results suggest that the mechanism for Ca²⁺-free contraction involves some protein kinase and cytoskeletal elements rather than MLCK.     

Selective inhibition of calcium entry induced by benzylisoquinolines in rat smooth muscle.

The mechanism of relaxant activity of six benzylisoquinolines was examined in order to determine the minimal structural requirements that enable these compounds to have either a non-specific action like papaverine or an inhibitory activity on calcium entry via potential-operated channels. All the alkaloids tested totally or partially relaxed KCl-depolarized rat uterus and inhibited oxytocin-induced rhythmic contractions. Only glaucine and laudanosine inhibited K(+)-induced uterine contractions more than oxytocin-induced uterine contractions. In Ca(+)-free medium, sustained contractions induced by oxytocin or vanadate were relaxed by the alkaloids tested except for glaucine and laudanosine indicating no inhibitory effect on intracellular calcium release. Those alkaloids containing an unsaturated heterocyclic ring (papaverine, papaverinol, papaveraldine, N-methylpapaverine and dehydropapaverine) exhibited a more specific activity than those with a tetrahydroisoquinoline ring.     

Role of extra- and intracellular calcium in the contractile action of agonists in the guinea-pig ileum

Summary The effects of Ca²⁺-channel blockers (nifedipine and verapamil), EGTA, caffeine or the removal of external Ca²⁺ on the contractile action of different agonists and transmural electrical stimulation were examined in isolated segments of the proximal and terminal part of the guinea-pig ileum. The effects of agonists and nerve stimulation on membrane potential were also studied by means of the sucrose gap method. Acetylcholine-elicited contractions in both parts and noradrenaline-as well as histamine-induced contractions in the terminal part of the ileum were composed of an initial phasic and a sustained tonic component. Single pulse transmural nerve stimulation elicited smooth muscle twitches, whereas addition of CaCl₂ to the tissue bath containing Ca²⁺-free and high-K⁺ medium elicited a sustained contraction. Both verapamil and nifedipine were more potent in inhibiting the tonic phase of the responses to the agonists or CaCl₂ than inhibiting the phasic contractions elicited by transmural nerve stimulation, acetylcholine or noradrenaline. The excitatory junction potentials (e j.p.s.) as well as smooth muscle twitches were reduced only by high nifedipine concentrations. The effects of acetylcholine on membrane potential and input membrane resistance were affected minimally by the omission of extracellular Ca²⁺, while the contractions gradually disappeared on repetitive agonist application in the absence of external Ca²⁺ and were blocked by caffeine preexposure. In Ca²⁺-free solution noradrenaline and histamine partially reduced each other's motor effect, while neither of them changed the contractile action of acetylcholine, yet the contraction induced by noradrenaline was prevented and that of histamine significantly reduced by preexposure to acetylcholine. These results suggest that the potency of acetylcholine to release Ca²⁺ from its caffeine-sensitive intracellular stores is much higher than that of histamine and noradrenaline. Send offprint requests to V. Bauer at the above address     

SELECTIVITY OF DIFFERENT CALCIUM ANTAGONISTS ON T- AND L-TYPE CALCIUM CURRENTS IN GUINEA-PIG VENTRICULAR MYOCYTES

Both L- and T-type calcium channels are present in the heart. In cardiac myocytes L-type calcium channels are blocked by the classical calcium channel blockers, while T-type calcium channels are thought to be insensitive to these drugs and to be selectively blocked by mibefradil. We aimed to compare the T/L calcium channel blocking selectivity of several calcium channel blockers by evaluating their effects on both components evoked in the same cell from a holding potential corresponding to the normal physiological value (−90 mV). Currents were recorded in single patch-clamped guinea-pig ventricular myocytes, superfused with a Na⁺- and K⁺-free solution to abolish overlapping currents. Two dihydropyridines (amlodipine and lacidipine), verapamil diltiazem and mibefradil were tested; for each compound concentrations equieffective on L-type Ca²⁺ current were used. All calcium channel blockers, at concentrations blocking less than 30% of L-type Ca²⁺ current, inhibited a significant amount of T-type Ca²⁺ current, varying from 0.8% (diltiazem) to 28% (mibefradil). We calculated for each compound the T/L ratio. As expected, mibefradil showed the highest T selectivity; lacidipine and diltiazem resulted to be L selective. Verapamil and amlodipine were not selective. Thus, the calcium channel blockers can be differentiated on the basis of their T/L selectivity.     

New 1,4-benzothiazepine derivative,K201, demonstrates cardioprotective effects against sudden cardiac cell death and intracellular calcium blocking action

In order to find drugs with suppressive effects against sudden cardiac cell death due to myofibrillar overcontraction, the cardioprotective effects of a new 1,4-benzothiazepine derivative, 4-[3-{1-(4-benzyl)piperidinyl}propionyl]-7-methoxy-2,3,4,5-tetrahydro-1,4-benzothiazepine, K201, in comparison with five other compounds, including a representative α-antagonist, β-antagonist, and Ca²⁺ channel antagonists, were investigated in an experimental myofibrillar overcontraction model of isolated rat heart. In addition, the effects of K201 on the contraction of isolated vascular smooth muscle of rat aorta and on the binding of cardiac annexin V with actin were compared with those of diltiazem and KT362. The degree of myofibrillar overcontraction was histologically scored on a four-grade scale (0, 1, 2, and 3) as myocardial injury score (MIS). Suppressive effects of myofibrillar overcontraction could not be observed with nicorandil and prazosin at 10^?5 M. Propranolol at 10^?5 M, verapamil at 10^?6 M, and diltiazem at 10^?6 M demonstrated a significant suppressive effect with MIS of 1.0 ± 0.4 (P < 0.01), 1.5 ± 0.3 (P < 0.01), and 1.5 ± 0.3 (P < 0.01), respectively. K201, even at 10^?7 M, displayed significant suppression with MIS of 1.8 ± 0.2 (P < 0.01). K201 inhibited contraction of isolated vascular muscle induced by K⁺ (40 mM) and NE (1 μM) at almost the same concentration. The lC₅₀ ratio (NE/K⁺) of K201 was 2.3. The inhibition by K201 of the response to K⁺ was less marked than that by diltiazem. Its inhibition of the response to NE was greater than that by diltiazem or KT362. K201 demonstrated an inhibitory effect on binding of cardiac annexin V with actin dependent on calcium concentration, but diltiazem and KT362 did not demonstrate any action to inhibit this reaction. These results indicate that K201 was a more effective cardioprotectant than propranolol, verapamil, and diltiazem in the experimental myofibrillar overcontraction model. K201 has intracellular Ca²⁺ blocking action in addition to weak α-1 adrenergic blocking activity and Ca²⁺ blocking activity. © 1994 Wiley-Liss, Inc.     

Selective chiral inhibition of Ca2+ entry promoted by bisbenzyltetrahydroisoquinolines in rat uterus.

The effects of diltiazem and six bisbenzyltetrahydroisoquinoline alkaloids (antioquine, 7-O-methylantioquine, dimethylantioquine, monterine, granjine and cordobimine) were studied in rat isolated uterus in order to clarify the mechanisms of their relaxant actions. All the compounds tested completely relaxed KCl-induced contractions and totally or partially inhibited oxytocin-induced rhythmic contractions. Only alkaloids with absolute configurations (1R,1'S or 1R,1'R) acted intracellularly, promoting relaxation of contractile responses induced by oxytocin in a Ca(2+)-free medium, as does papaverine. Alkaloids of the antioquine series (1S,1'R) selectively inhibited Ca2+ entry. The great rigidity of these structures and their stereoselective action make these alkaloids useful in studies of the conformational features of the Ca2+ channel.     

Effects of Vanadate on Responses of Guinea-pig Isolated Trachea to Spasmogens

Abstract— The effects of vanadate on the contractility of the guinea-pig isolated trachea was examined. Vanadate (0·1 Mm ) produced a sustained contraction that was abolished in Ca²⁺-free EGTA (0·1 Mm )-containing physiological salt solution but was resistant to verapamil (1 μm ). Vanadate (0·1 Mm ) depressed tracheal responses to CaCl₂ (in Ca²⁺-free depolarizing solution), KCl, acetylcholine, histamine and 5-hydroxytryptamine. For vanadate (10 μm ), the inhibition of spasmogenic responses only reached statistical significance for histamine and 5-hydroxytryptamine. Caffeine (1 Mm )-induced spasm (trachea at 20°C in the presence of indomethacin (2·8 μm )) was not affected by vanadate (10 μm -0·1 Mm ). Vanadate (0·1 Mm ) slightly depressed the responses to KCl (50 Mm ), acetylcholine (1 Mm ), histamine (1 Mm ) or 5-hydroxytryptamine (0·1 Mm ) observed in Ca²⁺-free EGTA (0·1 Mm )-containing physiological salt solution. Vanadate (0·5 Mm ) depressed Ca²⁺ (20 μm )-induced contraction of trachea which had been chemically skinned of its plasmalemmal membranes. The mechanism of the inhibitory effect of vanadate on tracheal responses to a variety of spasmogens remains obscure, but, under in-vitro conditions, vanadate clearly does not induce hyper-reactivity of airway smooth muscle to spasmogens.     

The effect of Mn2+, Zn2+, Ba2+ and Ca2+ on spontaneous motility in sheep duodenum in vitro

• 1.1. The effects of several ions, Mn²⁺, Zn²⁺, Ba²⁺ and Ca²⁺, on spontaneous motility were investigated in longitudinal smooth muscle strips from sheep duodenum, in vitro
• 2.2. Mn²⁺ (0.5–1.5 mM) and Zn²⁺ (0.5–5 mM) inhibited both the amplitude and frequency of motility in Krebs solution and in Ca²⁺-free medium.
• 3.3. Ba²⁺(0.5–5 mM) evoked three types of contractile responses: (i) an increase in the frequency and a reduction of the amplitude of spontaneous contractions; (ii) a slight increase in muscle tone of the phasic contractions; and (iii) a rapid initial phasic contraction followed by slowly fading contraction. Ca²⁺ induced two kinds of responses in spontaneous motility: (i) a fast phasic contraction, followed by an increase in the amplitude and frequency of phasic contractions with no changes in its tone; and (ii) an increase in the amplitude of contractions.
• 4.4. The Ba²⁺-induced contractions were inhibited by EDTA, verapamil and diltiazem, but were not modified by sodium nitroprusside. The Ca²⁺-induced contractions were reduced by verapamil and diltiazem.
• 5.5. Our results show that Mn²⁺ and Zn²⁺ behave as inhibitors of sheep duodenum motility. In contrast, Ba²⁺ and Ca²⁺ stimulate motility. It is suggested that Ba²⁺ can penetrate the cells through voltage-dependent Ca²⁺ channels and behave as a partial substitute for Ca²⁺.

     

Influence of calcium on the effects of okadaic acid and its interaction with caffeine and theophylline in rat myometrium

The effects of okadaic acid (OA), a monocarboxylic acid produced by marine dinoflagellates belonging to the genera Dinophysis and Prorocentrum, and their interactions with theophylline and caffeine were studied on the rat-isolated uterus in a calcium-containing medium and a calcium-free medium in the presence of 10^–3 M EGTA.Okadaic acid (5 × 10^–6 to 5 × 10^–5 M) induced a concentration-dependent contraction of the rat-isolated uterus corresponding, with 5 × 10^–5M, to 142.3±6.1% (n = 7) of the contraction induced by oxytocin 10^–6 M. The time to peak tension was inversely proportional to the maximum effect produced. The contraction was not sustained and was followed by a concentration-dependent decrease in tone. In a Ca²⁺-free medium containing 10^–3 M EGTA the contractile effects of OA were significantly inhibited or reduced. A 30 min pretreatment with theophylline (3 × 10^–3 M) or caffeine (2 × 10^–2 M) significantly reduced, in a Ca²⁺-containing medium, the maximum contractile effect of OA 10^–5 and/or 2 × 10^–5 M and shortened the relative time to peak tension. In a Ca²⁺-free medium containing 10^–3 M EGTA, only the second effect was observed. With a 1 min pretreatment and in a Ca²⁺-containing medium, theophylline 3 × 10^–3 M and caffeine 10^–2 M did not modify the maximum effect of OA 10^–5 M but shortened the time to peak tension. The same concentrations of the xanthines potentiated the E_max of OA 5 × 10^–6 M in the Ca²⁺-containing medium or in a Ca²⁺-free medium containing 10^–3 M EGTA. Okadaic acid 10^–6 M used as 30 min pretreatment versus OA 10^–5 M and 2 × 10^–5 M behaved like caffeine or theophylline.These results suggest that the OA-induced contraction of the rat uterine smooth muscle is partly effected by transmembrane calcium movements which can be inhibited in an O-Ca²⁺–10^–3 M EGTA solution or by theophylline or caffeine. This contraction also involves mobilization of Ca²⁺ from an intracellular pool which is also xanthine-sensitive. The latter effect seems to be important in inducing the contractile effect. This study does not exclude the possibility of other mechanisms being involved in the contraction induced by OA. Correspondence to: M. L. Candenas at the above address in Burjassot-València     

当归芍药散活性部位DSS-A-N-30对大鼠离体子宫平滑肌收缩的影响

目的观察当归芍药散提取部位DSS-A-N-30对离体子宫平滑肌收缩的影响,并探讨其可能的作用机制。方法制备离体大鼠子宫肌条,观察DSS-A-N-30对子宫平滑肌自发性收缩,子宫收缩激动剂诱发的子宫平滑肌条剧烈收缩,KCl致子宫平滑肌条强直收缩及缩宫素(催产素)在无钙平衡盐溶液中致子宫平滑肌条持续收缩的影响。结果DSS-A-N-30(141.5,283和566mg.L-1)可以显著抑制子宫平滑肌的自发性收缩;对缩宫素(10IU.L-1)、前列腺素F2α(1mg.L-1)和乙酰胆碱(10μmol.L-1)引起的子宫平滑肌剧烈收缩有抑制作用;对KCl(60mmol.L-1)引起的子宫平滑肌强直收缩无明显作用;对缩宫素(10IU.L-1)在无钙平衡盐溶液中引起的子宫平滑肌条持续收缩有显著抑制作用。结论DSS-A-N-30可能主要通过抑制细胞内钙库释放而松弛子宫平滑肌,对子宫平滑肌收缩产生直接的抑制作用。提示DSS-A-N-30是当归芍药散的活性部位之一,有可能开发为新型痛经治疗药物。     

Effect of sea nettle (Chrysaora quinquecirrha) venom on isolated rat aorta

Wan Wan Lin, C. Y. Lee and J. W. Burnett. Effect of sea nettle (Chrysaora quinquecirrha) venom on isolated rat aorta. Toxicon26, 1209–1212, 1988.—The venom from sea nettle (Chrysaora quinquecirrha) (1–10μg/ml) produced an irreversible contraction of the isolated rat aortic ring that was slow in onset, increased with time, and reached maximum in about 10–20 min. The contraction was not inhibited by pretreatment with phenoxybenzamine, atropine, indomethacin, tetrodotoxin, ouabain, low Na⁺ or Na⁺-free medium, however, it was markedly decreased by the Ca²⁺ channel blockers, nifedipine and verapamil. In Ca²⁺-free medium, no increase in tension was produced by the venom. It is concluded that sea nettle venom causes a contraction of the rat aortic ring by increasing Ca²⁺ influx through the voltage-dependent Ca²⁺ channels.