Effects of hispidulin, a flavone isolated from Inula viscosa, on isolated guinea-pig smooth muscle

1. In small concentrations (10(-7)-3 X 10(-6) M), hispidulin caused concentration-dependent contraction of isolated guinea-pig ileum and only mild relaxation of guinea-pig tracheal rings. 2. Larger concentrations (up to 3 X 10(-4) M) caused concentration-dependent relaxation of the ileum and the trachea. All the effects on the ileum and the trachea are reversible upon removal of the compound. 3. In concentrations from 10(-7) to 3 X 10(-4) M, hispidulin had no effect on the tone of the epinephrine-contracted rings of the guinea-pig main pulmonary artery. 4. Hispidulin caused a shift to the right of the acetylcholine concentration-effect curves on ileum and trachea and significantly inhibited the maximum contractions induced by acetylcholine. 5. In Ca2+-free, depolarizing solution, hispidulin caused both a shift to the right, and an inhibition of the maximum contractions, of the CaCl2 concentration-effect curves on ileum, trachea and pulmonary artery. 6. In Ca2+-free, EGTA-containing solution, hispidulin caused concentration-dependent inhibition of the contractions induced in the pulmonary artery by epinephrine and in the ileum by histamine. 7. These observations suggest that hispidulin may interfere with Ca2+ binding to the Ca2+-receptor protein(s) in the smooth muscle cell and/or with the agonist-induced Ca2+-release from intracellular stores. Less likely, hispidulin may interfere with Ca2+ influx through smooth muscle cell membrane.     

Control of the phasic and tonic contractions of guinea pig stomach by a ryanodine-sensitive Ca2+ store

In some smooth muscle cells, the rise in intracellular Ca2+ as a result of a Ca2+ influx via plasma membrane Ca2+ channels can activate a further increase in intracellular Ca2+ as a result of Ca2+ release from intracellular stores. This study examined the role of the Ca2+-induced Ca2+ release from the ryanodine-sensitive intracellular Ca2+ stores in shaping the smooth muscle contractions of guinea pig stomach. The contractile activity of isolated muscle strips of the fundus, corpus and antrum region of the stomach was recorded under isometric conditions. Ryanodine, an activator of Ca2+-induced Ca2+ release, concentration dependently (10(-7)-3x10(-5) M) increased the tone of fundus and corpus strips. Ryanodine had a dual action on the phasic contractions of the antrum and corpus: increase by the low concentrations (up to 10(-6) M) and inhibition by the high concentrations (10(-6)-3x10(-5) M). Nifedipine (10(-5) M) completely inhibited the ryanodine (10(-6) M)-induced phasic contractions and only partly the ryanodine (3x10(-5) M)-induced tonic contractions. In the presence of 10(-5) M cyclopiazonic acid, a specific inhibitor of sarcoplasmic reticulum Ca2+-ATPase, ryanodine (3x10(-5) M) further increased the tone of the corpus and fundus strips. Ryanodine (3x10(-5) M) induced tonic contractions in the fundus and corpus precontracted by acetylcholine (10(-5) M), and inhibited the acetylcholine (10(-6) M)-induced phasic contractions in the antrum and corpus. Ruthenium red, an inhibitor of Ca2+-induced Ca2+ release, concentration dependently (10(-6)-10(-4) M) decreased the tone and amplitude of the phasic contractions. The data obtained provide evidence for the participation of a sarcoplasmic reticulum Ca2+-induced Ca2+ release mechanism in shaping the tonic and phasic contractions of guinea pig stomach, and highlight important tissue differences.     

Effects of dapiprazole on contractile responses of guinea pig isolated ileum

The effects of dapiprazole, a relatively new alpha 1-adrenolytic agent, on contractile responses and on spontaneous mechanical activity were studied in guinea pig isolated ileum. Dapiprazole (10(-10) to 10(-4) M) produced a concentration-dependent inhibition of high K+ (80 mM) -induced contractions. These inhibitory effects were observed with dapiprazole added either before or after the induced contractions. The Ca2+-induced contractions of K+-depolarized ileum were also inhibited by dapiprazole. Dapiprazole inhibited in a non competitive manner the responses of the ileum to: carbachol, histamine, 5-hydroxytryptamine, pentagastrin, angiotensin II and cholecystokinin. In order to analize whether dapiprazole exerts an intracellular effect on Ca2+-store, skinned preparations were used. The results suggest that dapiprazole might inhibit Ca2+ entry through both voltage-and receptor-operated channels of the smooth muscle membrane.     

Effects of khellin on contractile responses and 45Ca2+ movements in rat isolated aorta.

The effects of khellin on contractile responses and 45Ca2+ flux have been studied in rat isolated aortae. Khellin (10(-5)-3.2 x 10(-4) M) produced a concentration-dependent inhibition of noradrenaline (10(-6) M) and high K+ (80 mM)-induced contractions. At 3.2 x 10(-4) M, khellin increased cAMP levels and reduced 45Ca2+ influx in resting tissues and in tissues stimulated by noradrenaline (10(-5) M) and high K+ without affecting basal 45Ca2+ efflux or noradrenaline induced 45Ca2+ efflux. It is concluded that in rat isolated aorta, khellin caused a non-specific inhibition of Ca2+ influx but may also exhibit intracellular actions, thus decreasing the availability of Ca2+ required for activation. One or more of these mechanisms may be related to an increase in intracellular cAMP levels.     

Effects of oxodipine on isolated rabbit aorta and mesenteric resistance vessels.

The inhibitory effects of the dihydropyridine Ca2+ antagonist, oxodipine, on contractions and 45Ca2+ influx stimulated by noradrenaline (NA) and high K+ in rabbit aorta were compared to the same parameters measured in mesenteric resistance arteries. In aortic rings oxodipine, 10(-11)-10(-6) M, inhibited in a concentration-dependent manner the contractions induced by high K+ (IC50 = 9.0 +/- 4.0 x 10(-10) M) or by Ca2+ in high K+ solution (IC50 = 6.2 +/- 2.4 x 10(-9) M), while responses to NA were only slightly affected (IC50 greater than 10(-6) M). In mesenteric resistance vessels oxodipine inhibited the contractions induced by high K+ and NA but was more effective against NA- than high K(+)-induced contractions (IC50 = 5.2 +/- 3.1 x 10(-10) and 1.2 +/- 1.8 x 10(-8) M, respectively). The concentration-inhibition curves for high K(+)-induced contraction and 45Ca2+ influx in aorta were almost superimposable (I50 = 2.2 +/- 2.0 x 10(-9) M), whereas NA-induced contractions were inhibited less than 45Ca2+ influx (I50 = 8.2 +/- 2.6 x 10(-8) M). In mesenteric resistance vessels the curves for contraction and 45Ca2+ influx stimulated by high K+ and NA were also superimposable, but 45Ca2+ influx stimulated by NA was more sensitive to oxodipine than that stimulated by high K+ (I50 = 3.9 +/- 2.0 x 10(-10) and 2.2 +/- 1.2 x 10(-8) M, respectively). It is concluded that the effects of oxodipine can be attributed to its ability to inhibit Ca2+ entry through both potential- and receptor-operated pathways.(ABSTRACT TRUNCATED AT 250 WORDS)     

Different pathways for Ca2+ influx and intracellular release of Ca2+ mediated by muscarinic receptors in ileal longitudinal smooth muscle.

Muscarinic receptor-mediated elevations in intracellular Ca2+ concentration ([Ca2+]i) in the longitudinal smooth muscle of guinea pig ileum were studied by the use of fura-2 fluorescence. Dose-response analysis indicated a difference in the potencies of carbachol (CCh) to increase [Ca2+]i in the presence and absence of extracellular Ca2+. For the increase in [Ca2+]i due to Ca2+ release from intracellular stores in the absence of extracellular Ca2+, the ED50 value of CCh was 3 x 10(-5) M. On the other hand, in the presence of Ca2+, the ED50 value was 2.5 x 10(-7) M, indicating that a low concentration of CCh (less than 10(-7) M) caused influx of extracellular Ca2+ without Ca2+ release. Oxotremorine and pilocarpine induced Ca2+ influx, but were less potent inducers of Ca2+ release. CCh also stimulated the formation of inositol trisphosphates (IP3) with an ED50 value of (4.5 x 10(-5) M), which was similar to that for Ca2+ release from intracellular stores. Treatment of the smooth muscle with neomycin (1 mM), a phospholipase C inhibitor, abolished both CCh-induced IP3 formation and Ca2+ release from intracellular stores, but did not affect CCh-induced Ca2+ influx. These results suggest that the pathway for muscarinic stimulation of Ca2+ influx through plasma membranes is different from that for Ca2+ release from intracellular stores, which seems to be coupled with IP3 formation.     

The inhibitory effect of the flavonoid galangin on urinary bladder smooth muscle contractility is mediated in part by modulation of Ca2+ release from intracellular stores

The present study was designed to examine the effect of the flavonoid galangin on the muscarinic receptor mediating a carbachol-induced contraction and to investigate the effect of the flavonoid on Ca (2+) release from intracellular stores in the urinary bladder of the pig. Galangin (10(-7) -10(-4)M) produced a concentration-dependent inhibition of the contractile responses to electrical field stimulation (EFS) and carbachol (10(-5)M). Galangin (3 x 10(-5)M) reduced muscle contractions evoked by carbachol (10(-5)M) in calcium-containing solution as well as contractions evoked by carbachol and caffeine (2 x 10(-2)M) in Ca(2+)-free solutions significantly. The flavonoid had a stronger effect on the maximal force of the contractions induced by caffeine, compared to contractions induced by carbachol. These results suggest that galangin has an important effect on the intracellular calcium mobilization, which might be attributed predominantly to its influence on ryanodine-receptors.     

Mechanism involved in the spasmolytic effect of a mixture of two triterpenes, cycloartenol and cycloeucalenol, isolated from Herissanthia tiubae in the guinea-pig ileum

The smooth muscle relaxant properties of a mixture of the two triterpenoids cycloeuclalenol and cycloartenol (CC) isolated from Herissanthia tiubae (Malvaceae) were studied in several smooth muscle preparations. CC inhibited contractions induced by carbachol, histamine and KCl in the guinea-pig ileum, but no spasmolytic activity was found in guinea-pig trachea or rat aorta. In guinea-pig ileum, concentration-response curves to carbachol and CaCl (2) in high K(+) were shifted to the right by CC in a concentration-dependent manner with slopes of the Schild plot differing from the unity. IC(50) values were 3.4 +/- 0.8 x 10 (-5) M and 8.44 +/- 1.87 x 10 (-5) M for carbachol and CaCl(2), respectively. The phorbol ester TPA, which activates protein kinase C (PKC), potentiated contractions induced by submaximal concentrations of carbachol. This potentiation was inhibited by CC. Desensitization of PKC by TPA completely abolished the inhibition produced by CC on carbachol-induced contractions. Together, our results indicate that inhibition of PKC is involved in the spasmolytic effect of CC in the guinea-pig ileum.     

Effect of nifedipine in arterial vasculature of human placenta

1. Nifedipine induced concentration-dependent relaxations in segments of human placental arteries precontracted with 40 mM K+. 2. Preincubation of segments with nifedipine induced concentration-dependent inhibition of contractions elicited by 40 mM K+ (IC50, 2.5 x 10(-9) M) and 10(-7) M 5-HT (5.9 x 10(-8) M). 3. The time-course of contractions elicited by K+ and 5-HT (responses not sustained) in the absence and in the presence of nifedipine was different. 4. Nifedipine inhibited Ca addition-evoked contractions in Ca-free medium containing 40 mM K+ or 10(-7) M 5-HT, mainly those obtained in depolarized segments. 5. These results indicate that these arteries are very sensitive to nifedipine and that the voltage-operated Ca channels are more affected by the Ca antagonist than receptor-operated ones.     

The inhibitory effect of tiamulin on high K(+)-induced contraction in guinea pig intestinal smooth muscle.

Tiamulin with an IC50 of 1.7 x 10(-6) M inhibited both the rapid and sustained contractions induced by hyperosmotically added 60 mM K+ (Hyper 60 K+) without changing the membrane potential in the intestinal muscle. Tiamulin inhibition (2 x 10(-6)-2 x 10(-5) M) of the Ca(2+)-induced contraction in depolarized muscle was competitively antagonized by raising external Ca2+. Tiamulin (2 x 10(-5) M) slightly affected the Hyper 60 K(+)-induced phasic contraction under hypoxia and the carbachol-induced phasic contraction. Moreover, tiamulin (2 x 10(-5) M) inhibited the Hyper 60 K(+)-induced contraction with decreasing [Ca2+]cyt level. Although the inhibitory effect of 10(-7)-10(-5) M monesin, an inhibitor of mitochondrial respiration, on the Hyper 60 K(+)-induced contraction was reduced under hypoxia, the effect of tiamulin (2 x 10(-7)-2 x 10(-4) M) was not modified. Tiamulin changed neither the intracellular Na+ and K+ content of the depolarized muscle nor the Ca(2+)-induced contraction in the chemically skinned preparations. These results suggest that the inhibitory action of tiamulin on the Hyper 60 K(+)-induced tonic contraction is possibly due to the competitive inhibition of Ca2+ entry through the voltage-dependent Ca2+ channel of the intestinal smooth muscle cell.     

Endothelium-independent vasorelaxant effect of dioclein, a new flavonoid isolated from Dioclea grandiflora, in the rat aorta

We have investigated the endothelium-independent vasorelaxant effect of the new flavonoid dioclein (5,2',5'-trihydroxy-6-7-dimethoxyflavanone) in the rat aorta. In endothelium-denuded vessels, dioclein induced a concentration-dependent relaxation of aortic rings precontracted with noradrenaline (IC50 = 3.5+/-0.89 x 10(-4) M and KCl (IC50 = 5.2+/-1.2 x 10(-4) M). In the absence of extracellular calcium, dioclein reduced the contraction induced by noradrenaline (maximal reduction approximately 33%) but not that induced by caffeine. Dioclein also produced a concentration-dependent inhibition of the sustained contractions induced by the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate in normal (IC50 = 4.0+/-0.2 x 10(-4) M) and Ca2+-free solution (IC50 = 4.0+/-0.3 x 10(-4) M). The results indicate that the endothelium-independent vasorelaxant effect of dioclein may be explained by inhibition of contractions dependent on activation of protein kinase C, voltage-dependent Ca2+ influx and on the release of intracellular Ca2+ stores sensitive to noradrenaline.     

Effects of ryanodine on tension development in rat aorta and mesenteric resistance vessels.

1. The effect of ryanodine on contractile responses dependent either on intracellular Ca2+ release or on extracellular Ca2+ influx were studied in aorta and mesenteric resistance vessels of the rat. 2. In aorta, in the presence of extracellular Ca2+, pretreatment with ryanodine (10(-5)M) did not modify contractile responses to noradrenaline (NA) (10(-6)M) whereas in the absence of Ca2+, pretreatment with ryanodine reduced to about 25% the contractile response to NA (10(-6)M) and totally abolished the transient contraction elicited by caffeine (5 x 10(-2)M). 3. In mesenteric resistance vessels, ryanodine (10(-5)M) had no effects on NA (10(-5)M)-induced tension in the presence of extracellular Ca2+ but totally abolished contractile responses to caffeine (10(-2)M) in the absence of Ca2+. 4. In K+ -depolarized mesenteric resistance vessels, pretreatment with ryanodine (10(-5)M) significantly enhanced contractile responses to Ca2+ concentrations higher than 10(-4)M and 10(-3)M for arteries depolarized with 30 mM and 40 mM K+ respectively. Concentrations of either diltiazem (6 x 10(-7)M) or nifedipine (10(-8)M) that abolished contractile responses to Ca2+ in depolarized arteries (K+, 40 mM) did not totally inhibit the enhancement of Ca2+ -induced contractions obtained in the presence of ryanodine. 5. Ryanodine did not modify the Ca2+ concentration-effect relationships in mesenteric resistance vessels exposed to NA or arginine vasopressin. 6. These data are consistent with the hypothesis that ryanodine induces a release of Ca2+ from intracellular stores, resulting in a subsequent reduction of the amplitude of contractions dependent upon intracellular Ca2+ liberation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mediators involved in the rat uterus contraction in calcium-free solution.

1. The effect of (Na+ + K+)-ATPase inhibitor ouabain (10(-5)-3 x 10(-4) M), and the (Ca2+ + Mg2+)-ATPase inhibitors vanadate (6 x 10(-6)-6 x 10(-4) M), oxytocin (2 x 10(-9)-4 x 10(-8) M, and prostaglandin F2 alpha (PGF2 alpha, 10(-7)-6 x 10(-6) M) were assayed on rat uterus incubated in Ca-free medium. 2. Vanadate, oxytocin and PGF2 alpha, but not ouabain, induced contractions in a dose-dependent way (ED50: 7.5 +/- 0.03 x 10(-5) M; 6.5 +/- 0.064 x 10(-9) M and 3.8 +/- 0.085 x 10(-7) M). 3. Vanadate (3 x 10(-4) M) and oxytocin (OT, 10 mU/ml = 2 x 10(-8) M)-induced tonic contraction were not modified by nifedipine (10(-10)-10(-6) M), monensin (10(-5)-3 x 10(-4) M) or amiloride (10(-5)-10(-3) M). 4. The intracellular calcium release inhibitors TMB-8 (10(-6)-10(-4) M) and dantrolene (3 x 10(-6)-10(-4) M), and the prostaglandin release inhibitor indomethacin (3 x 10(-8)-6 x 10(-5) M) relaxed the vanadate and OT-induced tonic contractions. 5. The calmodulin inhibitors trifluoperazine (3 x 10(-5)-3 x 10(-4) M), bepridil (10(-8)-3 x 10(-4) M), calmidazolium (10(-7)-10(-4) M) and W-7 (10(-7)-10(-5) M) also relaxed the vanadate and OT-induced tonic contractions. 6. Our results suggest that oxytocin and vanadate-induced contractions on rat uterus in Ca-free medium could be produced by release of prostaglandins and intracellular calcium, and mediated by calmodulin.     

MCI-826 is a potent and selective antagonist of peptide leukotrienes (p-LTs) and has characteristics distinctive from those of FPL 55712.

Antagonistic effects of a newly synthesized compound, (E)-2,2-diethyl-3'-[2-[2-(4-isopropyl)thiazolyl]ethenyl]succinanilic+ ++ acid sodium salt (MCI-826) on the contraction of the isolated guinea pig trachea and human bronchus induced by various agonists including peptide leukotrienes (p-LTs), histamine, acetylcholine (ACh), prostaglandin (PG) D2 and others were investigated and compared with the effects of a p-LT antagonist, FPL 55712, in some experiments. MCI-826 potently antagonized LTD4- and LTE4-induced contractions at extremely low concentrations in the isolated guinea pig trachea with pA2 values of 8.3 and 8.9, respectively, on a molar basis. These values indicated that MCI-826 is over 100 times stronger than FPL 55712. Similarly, MCI-826 at 10(-8) g/ml (2.4 x 10(-8) M) markedly antagonized LTD4-induced contractions of the isolated human bronchus. Although FPL 55712 fairly inhibited the 10(-9) g/ml LTC4-induced contraction of the isolated guinea pig trachea, MCI-826 had little effect on the contraction at high concentrations like 3 x 10(-6) g/ml (7.1 x 10(-6) M). MCI-826 modestly affected the other agonist-induced contractions and the resting tonus of the isolated guinea pig trachea at 10(-6) g/ml (2.4 x 10(-6) M) or higher concentrations, but FPL 55712 caused fair inhibition of some of those contractions and gradually lowered the resting tonus with time. These results indicate that MCI-826 is a highly potent and selective antagonist of LTD4 and LTE4 and can be a useful tool for biological and pharmacological experiments on p-LTs.     

Effects of Bay K 8644 on contraction of the human isolated bronchus and guinea-pig isolated trachea.

The effects of Bay K 8644, a dihydropyridine which increases calcium flux through the potential-operated channels were studied on the contractions induced by histamine, acetylcholine, KCl and Ca2+ on human isolated bronchial strips and the results were compared to those obtained on guinea-pig isolated tracheal spirals. Subsequently the contractant effects of Bay K 8644 in K+-enriched medium and in the presence of Ca2+ 0.03 mM were investigated. In Krebs normal calcium medium, Bay K 8644 did not significantly modify the EC50 of acetylcholine or histamine on the human bronchus, but in concentrations of 10(-7)-10(-6)M it potentiated the effects of KCl on that preparation. It did not modify the EC50 of acetylcholine, histamine or KCl on the guinea-pig trachea. In Ca2+-free Krebs medium with additional K+ (30 mM), Ca2+ concentration-response curves were displaced to the left by Bay K 8644 in the two preparations. Shifts were 0.52 +/- 0.11 and 0.72 +/- 0.16 log units respectively with Bay K 8644 10(-8) and 10(-7) M on human bronchus (n = 4) and 0.67 +/- 0.16 and 1.06 +/- 0.19 log units respectively with Bay K 8644 10(-7) and 10(-6) M on the guinea-pig trachea (n = 5). In Krebs medium with Ca2+ 0.03 mM and K+ 30 mM, Bay K 8644 (10(-8) to 10(-6) M) contracted both the human bronchus and the guinea-pig isolated trachea. This effect was competitively antagonized by nicardipine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Maintained contractions of rat uterine smooth muscle incubated in a Ca2+-free solution

The effects of acetylcholine (10(-4) M), prostaglandin E2 (10(-6) M), vanadate (5 X 10(-4) M) and fluoride (10(-2) M) have been studied on the mechanical and electrical activities of rat myometrial strips perfused in Ca2+-free EGTA-containing solutions. All four substances produced maintained contractions which could be initiated repeatedly after exposure to Ca2+-free solution for more than 1 h, without a significant decrease. The largest contractions were obtained with vanadate and the smallest ones with acetylcholine. The tension was usually 7-30% of the control contraction triggered by an action potential in Ca2+ containing solution. Maintained contractions induced by fluoride were unaffected by isoprenaline while those induced by acetylcholine, prostaglandin E2 and vanadate were completely relaxed. Prostaglandin E2- and vanadate-induced contractions were slightly reduced by Na+ removal or by adding Ca2+ antagonists. In contrast, contractions induced by acetylcholine were suppressed in Na+-free solution and largely inhibited in the presence of Ca2+ antagonists. The depolarization induced by acetylcholine in Ca2+-free solution was strongly dependent on the external Na+ concentration. The relationship between the size of the acetylcholine-induced depolarization and the membrane potential (shifted by constant currents) was linear, giving an apparent reversal potential for acetylcholine close to zero potential. In Ca-free solutions and in the presence of atropine, Na+ action potentials of long duration can be evoked which produced contractions of the same order of magnitude as those initiated by acetylcholine-induced depolarizations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ouabain distinguishes between nicotinic and muscarinic receptor-mediated catecholamine secretions in perfused adrenal glands of cat.

1. The effect of ouabain on catecholamine (adrenaline and noradrenaline) secretion induced by agents acting on cholinoceptors was studied in perfused cat adrenal glands. Acetylcholine (ACh) (5 x 10(-7) to 10(-3) M), pilocarpine (10(-5) to 10(-3) M) and nicotine (10(-6) to 5 x 10(-5) M) caused dose-dependent increases in catecholamine secretion. Both ACh and nicotine released more noradrenaline than adrenaline and the reverse was the case for pilocarpine. 2. Ouabain (10(-5) M) enhanced catecholamine secretion induced by ACh (10(-5) M), pilocarpine (10(-3) M) and nicotine (3 x 10(-6) M) during perfusion with Locke solution. The ratio of adrenaline to noradrenaline was not affected by ouabain. 3. In the absence of extracellular Ca2+, ACh and pilocarpine, but not nicotine, still caused a small increase in catecholamine secretions, which were enhanced by treatment with ouabain (10(-5) M) plus Ca2+ (2.2 mM) for 25 min. The effect of ouabain was much more significant on noradrenaline secretion than on adrenaline secretion. The enhanced response was blocked by atropine (10(-6) M) but not by hexamethonium (5 x 10(-4) M). 4. Nifedipine (2 x 10(-6) M) inhibited the responses to pilocarpine and nicotine. The treatment with ouabain (10(-5) M) reversed only the response to pilocarpine and resulted in a significant increase in the proportion of noradrenaline released. 5. It is suggested that ouabain enhances evoked catecholamine secretions by facilitating Ca2+ entry through nicotinic receptor-linked Ca2+ channels and by increasing the intracellular Ca2+ pool linked to muscarinic receptors.     

Depressant action of oxybutynin on the contractility of intestinal and urinary tract smooth muscle

Experiments were carried out in-vitro using segments of guinea-pig ileum, taenia caeci, ureter and detrusor. In the ileum, oxybutynin (30, 100 nM) competitively antagonized acetylcholine-induced contractions but did not alter those induced by histamine. Higher concentrations of oxybutynin (up to 10 microM) induced a non-competitive depression of responses to both agonists and caused a parallel shift to the right of the Ca2+-induced contractions in taenia caeci strips bathed in a Ca2+-free, high-K+ medium. In the ureter, oxybutynin (1-10 microM) impaired rhythmic muscular contractions in normal medium and after CaCl2 addition in Ca2+-free medium. Similarly to verapamil (10, 30 microM), oxybutynin (10, 30 microM) depressed both the cholinergic and non-adrenergic, non-cholinergic components of the electrically-induced contractions of detrusor strips. It is concluded that oxybutynin has anticholinergic properties and, at higher concentrations, exerts a direct spasmolytic activity possibly mediated by blockade of the transmembrane Ca2+ fluxes responsible for smooth muscle contraction.     

Antiallergic effects of mequitazine. 1. In vitro experiments

The antiallergic effects of 10-(3-quinuclidinylmethyl)phenothiazine (mequitazine) were investigated in vitro. The results obtained were as follows: 1) In the isolated trachea and lung parenchyma of guinea pigs, mequitazine showed a fairly potent antagonistic action against contractions induced by both histamine (Hi) and acetylcholine (ACh). Mequitazine was much less potent in antihistaminic action and slightly more potent in anticholinergic action than ketotifen. The contractions of the preparation by leukotriene (LT) D4 were antagonized by mequitazine, although the potency was moderate, showing an IC50 value of 2.3 x 10(-5) g/ml in the trachea and 5.1 x 10(-5)g/ml in the lung parenchyma. Mequitazine had no effect on the contraction of the trachea by PGF2 alpha, but inhibited that of the lung parenchyma with pA2 = 7.0. 2) Mequitazine (10(-6) g/ml) slightly inhibited the Schultz-Dale reaction of the isolated guinea pig trachea, while ketotifen at the same concentration did not show any effect. 3) The contraction of the isolated guinea pig trachea by Ca2+ influx was slightly inhibited by mequitazine (10(-5) g/ml). 4) Mequitazine competitively inhibited the cyclic AMP-dependent phosphodiesterase activity from the rat lung with a potency of 10 times and 5 times more than those of ketotifen and theophylline, respectively. 5) Mequitazine (10(-6) to 10(-5) M) suppressed both the anaphylactic and phospholipase A2-induced histamine release from the peritoneal cells of rats. 6) Mequitazine (10(-5) g/ml) also inhibited the anaphylactic and Ca ionophore-induced histamine release from the leukocytes of the atopic patients and normal subjects. 7) The anaphylactic releases of histamine, LTB4 and peptide LT from the human lung fragments were dose-dependently inhibited by mequitazine (10(-7) approximately 10(-5) g/ml).     

Influence of cadmium ions on the reactivity of isolated human uterine arteries

The isometric contractions were recorded for pieces of uterine arteries as well as ascending branches of uterine artery (1-2 mm diameter) obtained from 36 nonpregnant, premenopausal women undergoing hysterectomy. Contractile responses to K(+)-depolarization, noradrenaline, and Ca+2 ions were studied. Cadmium at concentrations 10(-9)-10(-3) M produced no changes of tension in the investigated arteries. Incubation (15 min) with low concentration of cadmium (10(-9)-10(-7) M) evoked an increase of amplitude of K(+)-induced contractions in 50% of investigated vessels. Cadmium at concentrations of 10(-6)-10(-3) M gradually inhibited contractions. The influence of cadmium on contractions evoked by noradrenaline was similar to those on K(+)-induced contractions. In a Ca(2+)-free medium, 10(-5) M cadmium induced tonic contractions and pretreatment with 10(-7) and 10(-5) M cadmium slightly enhanced Ca(2+)-induced contractions. Cadmium concentration of 10(-4) M caused substantial inhibition of Ca(2+)-induced contractions. The results suggest that in the human uterine vessels cadmium is not only a Ca(2+)-channels blocker but also interferes with intracellular mechanisms involved in excitation-contraction coupling.