PGF2 Alpha-induced Contractions Research Articles

Inhibitory effects of ginger oil on spontaneous and PGF2alpha-induced contraction of rat myometrium.

Solvent extracts of ginger, the rhizome of Zingiber officinale Roscoe (Zingiberaceae), have been extensively studied for their pharmacological activities in smooth muscles. However, the effects of ginger essential oil on smooth muscle contractility have not been elucidated. The aims of the study were to investigate the effects of ginger oil on rat myometrial contractility. We particularly examined the effects on phasic contractions arising either spontaneously or with PGF (2) (alpha) stimulation. Ginger oil was obtained by hydrodistillation and its constituents analyzed using gas chromatography and mass spectrometry. Rats were humanely killed by asphyxiation with CO (2), and longitudinal uterine smooth muscles were isolated. Isometric force was measured and the effects of ginger oil studied. It was found that citral was the main constituent of ginger oil (24 %). Ginger oil inhibited spontaneous contractions with an IC (50) of 50 microL/100 mL (10 - 150 microL/100 mL). The PGF (2) (alpha)-induced contractions were also significantly reduced by ginger oil. Increases in external calcium concentration completely reversed the relaxant effects of ginger oil. This was the case for both spontaneous and PGF (2) (alpha)-induced contractions. The effects of ginger oil were indistinguishable from those of pure citral. In conclusion, ginger oil is a potent inhibitor of phasic activity in rat uterus, irrespective of how it was produced. Our data suggest that the effects are largely due to citral, and could be via inhibition of L-type Ca channels.

Testosterone Relaxes Human Internal Mammary Artery In Vitro

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

THG113: A novel selective FP antagonist that delays preterm labor

PGF2alpha is an important smooth muscle contractile agent that exerts significant effects on myometrium and is implicated in labor. THG113 was recently identified as a PGF2alpha receptor (FP) antagonist. We characterized the specificity and selectivity of THG113, tested its effects on PGF2alpha-induced smooth muscle contraction, and assessed its efficacy in a model of endotoxin (LPS)-induced preterm labor. [125I]THG113 bound specifically to FP-expressing but not to native (not expressing FP) HEK293 cells. In FP-expressing HEK293 cells, THG113 markedly reduced PGF2alpha-elicited phosphoinositide hydrolysis (IC50 27 nM). Similarly, PGF2alpha-evoked microvascular (retinal) contraction was noncompetitively blocked (by > 90%) by THG113. In contrast, contraction to agonists of homologous prostanoid receptors EP1 and TP (17-phenyl-trinor PGE2 and U46619) was unaffected (< 1%) by high concentrations of THG113 (100 micromol/L); THG113 (100 micromol/L) also did not affect contraction to numerous other agents including platelet activating factor, endothelin, and angiotensin II. Force and duration of PGF2alpha-evoked contractions of myometrial strips of pig (non-pregnant, luteal phase) and mouse (immediately postpartum) were markedly reduced by THG113. In an endotoxin-induced preterm mouse model, lipopolysaccharide (50 microg intraperitioneal) injection at 16 days' gestation resulted in 100% delivery within 15 h; in contrast, 70% of those treated with THG113 (1 mg/day) delivered > 24 h later (at 18 days' gestation; term: 19 days). In addition, in mice injected with lipopolysaccharide and treated 6 h later with THG113 (0.1 mg bolus followed by 1 mg/day) 40% delivered > 48 h later. Fetuses of pregnant mice treated with THG113 were born alive, had higher birth weights (1.6 +/- 0.1 v 1.4 +/- 0.05 g), and appeared healthy. This study describes an effective and selective noncompetitive FP antagonist, THG113, which significantly delays preterm delivery; this provides the basis for future investigations for its use in tocolysis.

Erythromycin inhibits prostaglandin F2alpha-induced contractions of myometrium isolated from non-pregnant rats.

The aim of this study was to investigate the effects of erythromycin on prostaglandin F2alpha (PGF2alpha)-induced contractions of isolated myometrial strips from non-pregnant rats. In vitro pharmacological study. Firat University Faculty of Medicine. Myometrium samples were taken from 55 adult Wistar rats. Myometrial strips were isolated from mature, non-pregnant Wistar rats. Isometric contractions of these strips were induced with 1 microM PGF2alpha. Effects of 0.01, 0.1, 0.2, 0.5 and 1 mM erythromycin on the frequency and amplitude of these PGF2alpha-induced contractions were recorded. The inhibition of prostaglandin F2alpha-induced contractions in vitro. Application of 0.01 mM erythromycin had no effect on either amplitude or frequency of contractions. However, 0.1, 0.2, 0.5 and 1 mM erythromycin decreased the frequency and amplitude of PGF2alpha-induced contractions. The inhibitory effect of erythromycin on amplitude was 27%, 38%, 54% and 83% (P < 0.05), and that on frequency was 10%, 16%, 32% and 61% (P < 0.05) at 0.1, 0.2, 0.5 and 1 mM concentrations, respectively. The results of this study demonstrate that erythromycin inhibits PGF2alpha-induced contractions in rat myometrium. Because PGF2alpha-induced contractions have been suggested to be involved in the pathogenesis of primary dysmenorrhoea, effects of erythromycin in this clinical entity may present a new approach for the treatment.

MaxiK channel-mediated relaxation of guinea-pig aorta following stimulation of IP receptor with beraprost via cyclic AMP-dependent and -independent mechanisms.

The present study was aimed to elucidate the cellular pathway(s) controlling vascular relaxation triggered by stimulation of prostaglandin I2 (PGI2, IP) receptor with a stable PGI2 analog, beraprost. Beraprost caused a concentration-dependent relaxation in de-endothelialized guinea-pig aorta contracted with prostaglandin F2alpha (PGF2alpha). Beraprost-induced relaxation was almost abolished in high-KCl-contracted tissue, indicating a major role of K+ conductances. In contrast to other PGI2 analogs (e.g. cicaprost and iloprost), beraprost-induced relaxation was practically abolished by a selective voltage and Ca2+-activated K+ (MaxiK, BK) channel blocker Iberiotoxin (10(-7) M) or by tetraethylammonium (2 x 10(-3) M). The relaxation induced by beraprost was not significantly affected by other K+ channel blockers glibenclamide (10(-6) M) or Ba2+ (10(-5) M), but was slightly attenuated by 4-aminopyridine (10(-4) M). Beraprost increased intracellular cyclic AMP levels, suggesting a role for cyclic AMP-dependent pathways. A selective inhibitor of cyclic AMP-specific phosphodiesterase, RO-20-1724 (10(-4) M), significantly potentiated beraprost-induced relaxation. Iberiotoxin (10(-7) M) completely counteracted this potentiation. Moreover, tension decrement due to forskolin (3 x 10(-7) M) or 8-bromo-cyclic AMP (10(-2) M) was thoroughly restored by Iberiotoxin (10(-7) M), confirming a role for a cyclic AMP-dependent mechanism. However, SQ 22,536 (10(-4) M), an adenylyl cyclase inhibitor, did not affect beraprost-induced relaxation though it almost totally inhibited the elevation of cyclic AMP contents induced by beraprost, suggesting the existence of an additional mechanism that is cyclic AMP-independent. Moreover, cholera toxin (CTX, 1 microg/ml for 6 h), which activates the stimulatory G protein of adenylyl cyclase (Gs), significantly suppressed PGF2alpha-induced contraction both in the absence and presence of SQ 22,536 (10(-4) M). Iberiotoxin (10(-7) M) was also capable of restoring the relaxation induced by CTX. These findings suggest that MaxiK channel plays a primary role in mediating smooth muscle relaxation following stimulation of IP receptor with beraprost in guinea-pig aorta. Both cyclic AMP-dependent and -independent pathways contribute to the MaxiK channel-mediated relaxation following IP receptor stimulation in this vascular tissue. Direct regulation of MaxiK channels by Gs may partly account for the cyclic AMP-independent relaxant mechanism.

Antagonistic effects of 17 beta-estradiol, progesterone, and testosterone on Ca2+ entry mechanisms of coronary vasoconstriction.

The clinical observation that coronary artery disease is more common in men and postmenopausal women than in premenopausal women has suggested cardioprotective effects of female sex hormones including hormone-mediated coronary vasodilation. The purpose of this study was to investigate whether the sex hormone-induced coronary relaxation is caused by inhibition of Ca2+ mobilization into coronary smooth muscle. The effects of 17beta-estradiol, progesterone, and testosterone on vascular reactivity and 45Ca2+ influx were tested in deendothelialized coronary artery strips isolated from castrated male pigs. Prostaglandin F2alpha (PGF2alpha) (10(-5) mol/L) caused significant, maintained contraction of coronary artery strips. Caffeine (25 mmol/L), an activator of Ca2+ release from intracellular stores, caused transient contraction in Ca2+-free solution whereas membrane depolarization by 96 mmol/L KCl, an activator of Ca2+ entry, caused maintained contraction in the presence of external Ca2+. The 3 sex hormones caused significant and concentration-dependent relaxation of PGF2alpha- and 96 mmol/L KCl-induced contractions with 17beta-estradiol being the most effective. The sex hormones did not significantly affect the transient caffeine contraction in Ca2+-free solution. In contrast, the sex hormones significantly inhibited the PGF2alpha- and KCl-induced 45Ca2+ influx. 17beta-Estradiol caused similar inhibition of PGF2alpha- and KCl-induced contractions, suggesting inhibition of the same Ca2+ entry mechanism. However, progesterone and testosterone caused greater relaxation of PGF2alpha-induced contraction than of KCl-induced contraction. We conclude that in coronary arteries of castrated male pigs, sex hormones inhibit Ca2+ entry from extracellular space but not Ca2+ release from intracellular stores. 17beta-Estradiol mainly inhibits Ca2+ entry, whereas progesterone and testosterone cause coronary relaxation by inhibiting other mechanisms in addition to Ca2+ entry.

In vitro responses to antigen stimulation: comparison between human lung parenchyma resected from asthmatic patients and non-asthmatic patients.

The airway of asthmatic patients is hyperresponsive to various stimuli in vivo. There are, however, only a few reports that compared the in vivo responsiveness of asthmatic patients and non-asthmatic subjects to those of lung parenchyma in vitro. To compare the contractile response, release of various chemical mediators, and responsiveness to drugs in samples of lung parenchyma excised from asthma patients with those of non-asthmatic subjects. Human lung parenchymal strips were subjected to passive sensitization with sera of 5+ RAST titer to mites. The strip was suspended in a magnus bath containing a buffer solution. Parenchymal contraction was induced by PGF2 alpha. After washing, the baseline concentrations of thromboxane B2 (TXB2), leukotriene (LT), and histamine were measured in each bath and then contraction was induced by the addition of a mite antigen. The concentrations of TXB2, LT, and histamine were measured after contraction. The inhibitory effects of TXA2 synthetase inhibitor (DP-1904) and TXA2 receptor antagonist (AA-2414) were also evaluated in both tissue samples. There were no significant differences between lung parenchymal tissues of asthmatic and non-asthmatic patients with regard to PGF2 alpha-induced contraction, antigen-induced contraction, release of chemical mediators, and the response to drugs. Unlike the response in vivo, there are no differences in the response to stimuli in vitro between lung parenchymal tissues of asthmatic and non-asthmatic patients.

Endothelium-dependent potentiation of prostaglandin F2alpha-induced contractions by (+/-)-[6]-gingerol is inhibited by cyclooxygenase- but not lipoxygenase-inhibitors in mouse mesenteric veins.

The mechanism of potentiation of prostaglandin (PG) F2alpha-induced contraction of mouse mesenteric veins by (+/-)-[6-gingerol was investigated in vitro. (+/-)-[6]-Gingerol (0.3mM) potentiated the maximal contraction response elicited by PGF2alpha (0.28 mm) in the presence of intact vascular endothelium, but not in its absence (de-endothelialized preparations). The potentiating effect was completely inhibited by cyclooxygenase inhibitors (0.2 mm aspirin and 0.2 mm indomethacin) and partly by calcium antagonists (2 microM verapamil, 8 nM nitrendipine and 1 microM ryanodine), but not inhibited by nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor and ONO-3708, a thromboxane (TX) A2 antagonist. The potentiation by (+/-)-[6]-gingerol is also observed in mesenteric veins of streptozotocin-diabetic mice where the enhancement of PGF2alpha-induced contraction is caused mainly by activation of lipoxygenase. The potentiation of PGF2alpha-induced contraction by (+/-)-[6]-gingerol may be caused by a cyclooxygenase-dependent release of vasoconstrictors, other than PGF2alpha and TXA2, or by inhibiting vasorelaxants released from endothelial cells of mouse mesenteric veins.

Role of mitogen-activated protein kinase pathway in prostaglandin F2alpha-induced rat puerperal uterine contraction.

In this study, prostaglandin (PG) F2alpha was found to activate mitogen-activated protein (MAP) kinase and MAP kinase kinase (MEK) in cultured rat puerperal uterine myometrial cells. PGF2alpha stimulation also led to an increase in phosphorylation of raf-1, son of sevenless (SOS), and Shc. Furthermore, we examined the mechanism by which PGF2alpha induced MAP kinase phosphorylation. Both pertussis toxin (10 ng/ml), which inactivates Gi/Go proteins, and expression of a peptide derived from the carboxyl terminus of the beta-adrenergic receptor kinase 1 (betaARK1), which specifically blocks signaling mediated by the betagamma subunits of G proteins, blocked the PGF2alpha-induced activation of MAP kinase. Ritodrine (1 microM), which is known to relax uterine muscle contraction, attenuated PGF2alpha-induced tyrosine phosphorylation of MAP kinase. Moreover, to examine the role of MAP kinase pathway in uterine contraction, an inhibitor of MEK activity, PD098059, was used. Although MEK inhibitor had no effect on PGF2alpha-induced calcium mobilization, this inhibitor partially inhibited PGF2alpha-induced uterine contraction. These results provide evidence that PGF2alpha stimulates the MAP kinase signaling pathway in cultured rat puerperal uterine myometrial cells through Gbetagamma protein, suggesting that this new pathway may play an important role in the biological action of PGF2alpha on these cells.

Chronic hypoxia inhibits postnatal maturation of porcine intrapulmonary artery relaxation.

Neonatal pulmonary hypertension is associated with increased pulmonary vascular reactivity. We studied the responses of isolated porcine intrapulmonary arteries after exposure of piglets to chronic hypobaric hypoxia (CHH) from 0 to 2.5, 3 to 6, or 14 to 17 days of age. CHH inhibited the postnatal development of endothelium-dependent vasorelaxation to acetylcholine (ACh) and the calcium ionophore A-23187. Basal accumulation of guanosine 3', 5'-cyclic monophosphate (cGMP) was unaffected, but cGMP response to ACh was inhibited. Endothelium-independent relaxation to nitric oxide (NO) and zaprinast (a phosphodiesterase inhibitor) was also inhibited, but cGMP accumulation in response to these agonists was normal. The ability of sodium nitroprusside (SNP) to cause vasorelaxation and increase cGMP accumulation was unaffected. Contractile responses to potassium chloride and prostaglandin F2 alpha (PGF2 alpha) were similar to normal after exposure from birth and 3 days and were decreased in the older group, but the ability of NG-monomethyl-L-arginine acetate to increase PGF2 alpha-induced contractions decreased. Thus exposure of newborn piglets to CHH causes 1) no increase in contractile responses and 2) impairment of endothelium-dependent and -independent relaxation by impairing signal transduction mechanisms involved in the release of NO and the effectiveness of cGMP.

Effect of Volatile Anesthetics with and without Verapamil on Intracellular Activity in Vascular Smooth Muscle

Although halothane and isoflurane inhibit receptor agonist-induced smooth muscle contraction by inhibiting Ca2+ influx via the L-type voltage-dependent Ca2+ channels, their effects on pharmacomechanical coupling remained to be clarified. The intracellular action of both anesthetics was studied during agonist-induced contractions using the Ca2+ channel blocker verapamil. Isolated spiral strips of rat thoracic aorta with endothelium removed were suspended for isometric tension recordings in physiologic salt solution. Cytosolic concentration of Ca2+ ([Ca2+]i) was measured concomitantly using fura-2-Ca2+ fluorescence. Muscle contraction was evoked by the receptor agonists with 30 nm norepinephrine or 10 microM prostaglandin F2 alpha (PGF2 alpha), followed by exposure to halothane, at 0%, 1%, 2%, and 3% or isoflurane, at 2% and 4%. The effects of the anesthetics were compared with those of 0.1-1 microM verapamil (n = 8 for each condition). To clarify the intracellular action of the volatile anesthetics on agonist-induced contractions, this procedure was repeated for the anesthetics only in the presence of 1 microM verapamil (n = 8 for each condition). The effects of both anesthetics were also examined in nonreceptor-mediated contractions evoked with a 1-microM dose of the protein kinase C activator, 12-deoxyphorbol 13-isobutylate, which increases the Ca2+ sensitivity of the contractile elements (n = 8 for each). Halothane, isoflurane, and verapamil suppressed norepinephrine-and PGF2 alpha-induced increases in muscle tension and [Ca2+]i in a concentration-dependent manner. The Ca2+-tension regression lines suggested that the volatile anesthetics reduced Ca2+ sensitivity of the contractile elements during PGF2 alpha-induced contraction. Pretreatment of the muscle strip with verapamil revealed that halothane and isoflurane released Ca2+ during norepinephrine-induced contraction and that [Ca2+]i-tension relationship was modulated during PGF2 alpha-induced contractions. Halothane at 2% and 3% and isoflurane at 4% suppressed 12-deoxyphorbol 13-isobutylate-induced increases in muscle tension, whereas they enhanced increases in [Ca2+]i, indicating that both anesthetics suppressed Ca2+ sensitivity during 12-deoxyphorbol 13-isobutylate-induced contraction. Verapamil pretreatment unmasked the intracellular action of the anesthetics. Halothane and isoflurane influenced pharmacomechanical coupling during agonist-induced contraction.

Evidence that PGF2 alpha-induced contraction of isolated guinea pig bronchi is mediated in part by release of tachykinins

To investigate whether prostaglandin F2 alpha (PGF2 alpha) stimulates the release of tachykinins and whether the tachykinins play a role in the PGF2 alpha-induced bronchial contraction, we examined the contractile response to PGF2 alpha in the presence or absence of a neutral endopeptidase (NEP) inhibitor phosphoramidon in the guinea pig main bronchus in vitro. Because NEP effectively cleaves tachykinins, we hypothesized that the inhibition of NEP would enhance a PGF2 alpha-induced bronchial contraction if PGF2 alpha stimulates the release of tachykinins. Phosphoramidon significantly enhanced the concentration-response curve to PGF2 alpha. And it also significantly enhanced 10(-5) M PGF2 alpha-induced contraction. The enhancement was significantly attenuated in tissues where the tachykinins had been depleted by treatment with capsaicin. Furthermore, the enhancement of contraction was also significantly attenuated in the presence of tachykinin antagonist FK-224 (10(-5) M). Tetrodotoxin, a sodium-channel blocker that blocks nerve conduction, did not affect the enhancement. From these results we conclude that 1) PGF2 alpha causes the release of tachykinin-like substances, 2) these substances play a role in bronchial contraction in tissues where NEP activity is inhibited, and 3) nerve conduction is not necessary for the release of these substances in the guinea pig bronchus.

Mechanisms of Ca(2+)-independent contraction in single permeabilized ferret aorta cells.

The mechanisms by which prostaglandin F2 alpha (PGF2 alpha) can cause contractions at constant intracellular Ca2+ were investigated by the direct measurement of force from single saponin-permeabilized smooth muscle cells from the ferret aorta. The size of PGF2 alpha contractions did not change between pCa 9.0 and pCa 6.6. The remainder of the experiments were carried out at pCa 7.0. At pCa 7.0, PGF2 alpha (0.1-100 microM) induced sustained force in a dose-dependent manner, reaching a maximum (2.61 +/- 0.20 microN, n = 14) in 10 minutes. Both protein kinase C pseudosubstrate inhibitor (3 microM) and staurosporine (1 microM) significantly inhibited PGF2 alpha (100 microM)-induced contractions, but staurosporine was more effective. Staurosporine caused 88.8 +/- 13.3% inhibition, whereas protein kinase C pseudosubstrate inhibitor inhibited 62.3 +/- 9.6% of the PGF2 alpha-induced contraction. An inhibitor of type-1 and type-2A protein phosphatases, microcystin-LR, at a concentration of 1 microM induced a gradual and sustained contraction (1.53 +/- 0.21 microN). A lower concentration of microcystin-LR (100 nM) also induced a small but significant contraction (0.36 +/- 0.26 microN). Pretreatment with both 1 microM and 100 nM microcystin-LR caused significant inhibition of the PGF2 alpha-induced contraction from 2.61 +/- 0.20 microN (n = 14) to 0.32 +/- 0.20 microN (n = 6) (p < 0.01) and 1.52 +/- 0.21 microN (n = 6) (p < 0.01), respectively. These results indicate that the part of the PGF2 alpha-induced contraction that occurs at a constant, low intracellular Ca2+ is the combined result of activation of protein kinase C and phosphatase inhibition.

MODULATION BY CARBON DIOXIDE AND pH OF THE CONTRACTILE RESPONSES TO POTASSIUM AND PROSTAGLANDIN F2a IN ISOLATED HUMAN PIAL ARTERIES

Variation of PCO2 with concomitant changes in extracellular pH (pHo) may modulate cerebrovascular resistance, but the direct actions of carbon dioxide and pHo on human cerebral arteries are unknown. In this study, we have evaluated the effects of different carbon dioxide tensions (2.7, 4.2 and 7.2 kPa) with either fixed (pHo = 7.44) or concomitant changes in pHo, on contractions induced by depolarization (potassium) or receptor stimulation (prostaglandin F2 alpha) in isolated human pial arteries. Isolated changes in PCO2 had no significant effect on either potency (unchanged EC50 value) or the maximum response (Emax) in potassium-contracted arteries. Hypercapnia with uncompensated pHo significantly decreased both EC50 and Emax values, whereas uncompensated hypocapnia significantly increased the EC50 value without any effect on Emax. Concentration-response curves induced by prostaglandin (PG) F2 alpha were shifted significantly to the right (increased EC50 = decreased potency) during both hypo- and hypercapnia, independent of changes in pHo. The maximal responses were enhanced significantly during hypocapnia (Emax = 110 (SEM 2)%), but this enhancement was converted into a slight attenuation when pHo was compensated (Emax = 92 (4)%). Hypercapnia, with or without compensation of pHo, decreased the Emax values to 69 (16)% and 73 (9)%, respectively. We conclude that hypocapnia increases contractility in human pial arteries--an effect which is reversed by compensation of pHo. In contrast, the hypercapnic decrease of PGF2 alpha-induced contractions appears to be independent of pHo. The results confirm a relationship between contractility and pHo, but do not exclude a direct action of carbon dioxide in receptor-stimulated arteries.

Prostaglandins and modulation of small bowel myoelectric activity.

We explored the effects of prostaglandins (PG) F2 alpha and E2 on the motor and myoelectric activity of the small intestine using closed intra-arterial injections in conscious chronically instrumented dogs. PGF2 alpha (0.125-5 micrograms) and PGE2 (1-10 micrograms) were injected via a T tube into a branch of the superior mesenteric artery perfusing a 15-cm segment of jejunum. Experiments were performed on four dogs in which the recording devices had been implanted above, below, and within the perfused segment. PGF2 alpha given during phase I of the migrating myoelectric complex cycle induced phasic contractions in the perfused segment of intestine in a dose-dependent manner. Atropine (50-100 micrograms), hexamethonium (15 mg), or TTX (10-15 micrograms) administered before the injection of PGF2 alpha failed to inhibit the effects of PGF2 alpha. In contrast pretreatment of the perfused segment with verapamil (2.5 mg) or PGE2 (1-5 micrograms) abolished the effects of PGF2 alpha. Moreover, PGE2 injected 5 min after the administration of PGF2 alpha inhibited the PGF2 alpha-induced contractions. Administration of PGE2 alone (3-10 micrograms) before the arrival of phase III activity in the perfused segment abolished phase III from this segment of intestine. Our studies indicate opposing effects of PGF2 alpha and PGE2 on small intestinal myoelectric and contractile activities. PGF2 alpha has a direct excitatory effect on the intestinal smooth muscle, which is calcium channel dependent but independent of intrinsic nerves. PGE2 has an inhibitory effect both on the spontaneous and PGF2 alpha-induced small intestinal myoelectric and contractile activity.

Reduced responses of nitrendipine in PGF2α-precontracted porcine isolated arteries after pretreatment with methylene blue

Vascular activity of nitrendipine (NTD) in different depolarized and prostaglandin F2 alpha (PGF2 alpha)-precontracted isolated porcine arteries was examined in the presence and absence of methylene blue (MB). Presence of MB potentiated the PGF2 alpha-induced contractions in all vessels studied and reduced the response of NTD in coronary and basilar arteries seven- to 23-fold. Only in ulnar arteries was the affinity of NTD slightly increased. In contrast, MB did not modify the affinity of papaverine under these conditions. Furthermore, MB had no influence on KCl-induced contractions and subsequent vasorelaxation by NTD. It is proposed that MB impaired endothelium derived relaxing factor, thereby stimulating and/or increasing the calcium influx through receptor-operated calcium channels.

Release of Endothelium-Derived Relaxing Factors from Canine Cardiac Valves

In the present study, the ability of intact cardiac valvular endothelial cells to release vasodilatory prostanoids and endothelium-derived relaxing factor was investigated. Endothelium-denuded canine coronary arteries were used for bioassay and contractile force recording. Insertion of small segments of cardiac valve (20-30 mm2) with intact endothelium into endothelium-denuded coronary arterial rings did not markedly alter the sensitivity nor magnitude of the coronary artery contractile response to KCl. In contrast, the prostaglandin F2 alpha (PGF2 alpha)-induced contraction was significantly depressed (70% decrease in magnitude and 216% increase in ED50), compared with contraction in the absence of valvular endothelium (5.52 +/- 0.49 g and ED50 of 1.18 +/- 0.02 microM, respectively). These alterations in PGF2 alpha-induced contractions were reduced to 38% decrease in magnitude and +66% in ED50 in the presence of 5 microM indomethacin. Addition of acetylcholine (0.1-30 microM) into these endothelium-denuded coronary artery/valve preparations resulted in a dose-dependent relaxation, reaching a maximum of -59.9 +/- 1.6% (mean +/- SEM of seven vessels). Preincubation of valvular endothelium with 5 microM indomethacin also reduced these acetylcholine-induced valvular endothelium-dependent relaxations to 40.4 +/- 5.5% (mean +/- SEM of 13 vessels). Addition of hemoglobin (3 microM) further attenuated relaxation to -16.0 +/- 7.7% (mean +/- SEM of 14 vessels), while superoxide dismutase (20 units/ml) potentiated the relaxant response to -81.3 +/- 9.4% (mean +/- SEM of 11 vessels) in the presence of indomethacin. These findings suggest that there is a continuous basal release of vasodilatory prostanoids and endothelium-derived relaxing factor from the valvular endothelium, which can be further stimulated with acetylcholine and superoxide dismutase, and inhibited by indomethacin and hemoglobin.

A Novel Orally Active Dopamine Prodrug TA-870. II. Evidence That TA-870 Is a Dopamine Prodrug

The mechanism of action of a new orally active dopamine (DA) prodrug, TA-870 (N-(N-acetyl-L-methionyl)-O,O-bis(ethoxycarbonyl)(DA) was studied. When TA-870 (1 mg/kg) was injected in anesthetized dogs, renal vascular resistance was decreased and renal blood flow was increased. The renal vasodilatory effect of TA-870 correlated with the plasma level of DA but not with the level of de-ethoxycarbonyl metabolite of TA-870 (i.e., N-(N-acetyl-L-methionyl)DA; DEC-TA-870). The renal vasodilatory effect of TA-870 was inhibited strongly by haloperidol and slightly by propranolol. Pretreatment with phenoxybenzamine enhanced the renal vasodilatory effect of TA-870. In the isolated rabbit splenic artery, TA-870 and DEC-TA-870 showed no effects, whereas dopamine showed a contracting effect, which was inhibited by phentolamine. In the propranolol- and phentolamine-treated splenic artery, TA-870 and DEC-TA-870 caused weak relaxant effects on PGF2 alpha-induced contraction. These effects were not antagonized by metoclopramide. On the other hand, DA showed a strong relaxant effect, which was competitively inhibited by metoclopramide. In addition, TA-870 and DEC-TA-870 further relaxed the artery that had been maximally relaxed by DA. We concluded that TA-870 and DEC-TA-870 exert weak vasodilatory effects that are different from that of DA in vitro, and that TA-870 exerts its vasodilatory effect after its conversion to free DA in vivo.

Modulation of eicosanoid-induced contraction of mouse and rat blood vessels by gingerols.

The effects of the active principles of crude ginger (a traditional Sino-Japanese medicine), the gingerols, on the contractile responses to eicosanoids were compared using isolated mouse and rat blood vessels. Leukotrienes (LT) C4 and D4, a thromboxane (TX) A2 derivative (U-46619), prostaglandins (PG) F2 alpha, PGI2-Na, PGE2, the stable PGI2 derivative TRK-100, and PGD2 induced contraction in longitudinal segments of mouse mesenteric veins in that order of potency. Exogenous arachidonic acid and PGE1 did not cause contraction. The mesenteric veins also contracted in response to noradrenaline (NA) and phenylephrine (PhE), but not to clonidine. The gingerols alone relaxed the muscle transiently and then augmented the response to PGF2 alpha, PGE2, PGI2-Na, and TRK-100, but suppressed the response to PGD2, U-46619, LTC4, LTD4, NA and PhE. (+/-)-[6]-Gingerol also potentiated the PGF2 alpha-induced contraction in longitudinal segments of rat mesenteric vein and vena cava, but inhibited it in circular segments of rat aorta and longitudinal segments of mouse mesenteric arteries. These results showed that (+/-)-[6]- and (+/-)-[8]-gingerols potentiated the contraction induced by prostanoids (except PGD2) and inhibited that produced by PGD2, TXA2, and LT, suggesting the modulation of eicosanoids-induced responses by (+/-)-[6]- or (+/-)-[8]-gingerol.

Vasodilator actions of felodipine, a new Ca2+ entry blocker

Felodipine [ethylmethyl 4-(2,3-dichlorophenyl)-1,4-dihydro-2,6-dimethyl-3,5- pyridinedicarboxylate], a new Ca2+ entry blocker, relaxed isolated canine arteries and veins precontracted with prostaglandin (PG) F2 alpha, in a concentration-dependent manner. Felodipine dilated cerebral arteries predominantly over the other arteries. Relaxations by felodipine, in low concentrations, were greater in mesenteric vein strips than in mesenteric artery strips isolated from the same dogs. The inhibitory effect of felodipine in high concentrations (10(-7)M or higher) were not reversed by repeated washing. In coronary arteries exposed to Ca2+-free media under anoxia, PGF2 alpha and Ca2+ produced persistent contractions. Reoxygenation from anoxia elicited an additional contraction. Felodipine did not affect PGF2 alpha-induced contraction in Ca2+-free media, but significantly reduced the contractions caused by Ca2+ and reoxygenation. These findings suggest that felodipine is a potent, long-acting Ca2+ entry blocker with characteristics such as a greater action on cerebral arteries and mesenteric veins than coronary and mesenteric arteries.