Antiulcerogenic activity of Lippia alba (Mill.) N. E. Brown (Verbenaceae)

Lippia alba (Mill.) N. E. Brown Verbenaceae, known popularly as 'Juanilama' or 'Salvia Sija', is prized widely in folk medicine in Guatemala. Its leaves are employed as an infusion and decoction as a remedy for stomach problems, dysentery, colds and cough, febrifuge, as well as a sedative and in spasmolitic remedies. The present study reports the effects of the infusion of L. alba on the rat gastric mucosa. The following behavioural parameters were evaluated: (a) gastric irritancy test in Wistar rats; (b) antiulcer activity, short term and long term; (c) acid secretion; (d) measurement of total proteins; (e) estimation of total protein bound and nonprotein sulfhydryl groups. Ranitidine (100 mg/kg, p.o.) was used as the reference antiulcer drug. Oral treatment with the infusion (12.5 g dry plant/kg) did not cause gastric irritancy in the rats treated during five consecutive days. In addition, the oral administration of L. alba was found to be effective at preventing gastric ulceration induced by indomethacin (50 mg/kg, p.o.) in rats in the short term (1 day) and long term (5 days).     

Anticonvulsant activity of essential oils and active principles from chemotypes of Lippia alba (Mill.) N.E. Brown

In the present work we studied the anticonvulsive effects of the essential oils (EOs) from three chemotypes of Lippia alba (Mill.) N.E.Brown (Verbenaceae). Animals (female Swiss mice, 25 g) were treated with the EO and, 30 or 60 min after intraperitoneal (i.p.) or oral (p.o.) administration, respectively, injected with pentylenetetrazole (80 mg/kg, i.p.) and observed for 30 min. The results showed that EO I (200 and 400 mg/kg), EO II (100, 200 and 400 mg/kg), and EO III (400 mg/kg), i.p., produced an increased latency time for the first convulsion as related to controls. Death latency was greater in the groups receiving EO I (50 and 100 mg/kg), EO II (100 and 200 mg/kg), and EO III (200 mg/kg), i.p. Orally, while no effect was demonstrated with EOs at doses of 200 or 400 mg/kg, significant increases in the latency of convulsion and latency of death were observed with EO I at the highest dose (800 mg/kg). Similarly, EO III at this dose was also effective as far as latency of convulsion is concerned. Animals treated with citral (100 mg/kg, i.p.), beta-myrcene or limonene (200 mg/kg, i.p.), EOs chemical constituents, presented significant increases in the latency of convulsion and percentage of survival as compared to controls. After oral administration these effects were observed only with a higher dose (400 mg/kg). The association of EOs with diazepam significantly potentiated their effects, suggesting a similar mechanism of action and indicating that citral, beta-myrcene, and limonene are probably the EOs active compounds.     

Chemical constituents of the essential oil of Lippia laxibracteata (Verbenaceae)

The oil from the aerial parts of Lippia laxibracteata Herzog (Verbenaceae) was obtained by hydrodistillation and analyzed by GC and GC/MS. The major component of the oil was thymol (67%) with minor amounts of p-cymene (10%), cis-beta-ocimene (7%) and carvacrol (4.5%).     

The role of polar phytocomplexes on anticonvulsant effects of leaf extracts of Lippia alba (Mill.) N.E. Brown chemotypes

Objectives The purpose of the present work was to characterize the pharmacological profile of different L. alba chemotypes and to correlate the obtained data to the presence of chemical constituents detected by phytochemical analysis. Methods Essential oils from each L. alba chemotype (LP1—LP7) were characterized by gas chromatography–mass spectrometry (GC‐MS) and extracted non‐volatile compounds were analysed by HPLC and GC‐MS. The anticonvulsant actions of the extracted compounds were studied in pentylenetetrazole‐induced clonic seizures in mice and their effect on motor coordination was studied using the rota‐rod test in rats. The synaptosomes and synaptic membranes of the rats were examined for the influence of LP3 chemotype extract on GABA uptake and binding experiments. Key findings Behavioural parameters encompassed by the pentylenetetrazole test indicated that 80% ethanolic extracts of LP1, LP3 and LP6 L. alba chemotypes were more effective as anticonvulsant agents. Neurochemical assays using synaptosomes and synaptic membranes showed that L. alba LP3 chemotype 80% ethanolic extract inhibited GABA uptake and GABA binding in a dose‐dependent manner. HPLC analysis showed that LP1, LP3 and LP6 80% ethanolic extracts presented a similar profile of constituents, differing from those seen in LP2, LP4, LP5 and LP7 80% ethanolic extracts, which exhibited no anticonvulsant effect. GC‐MS analysis indicated the occurrence of phenylpropanoids in methanolic fractions obtained from LP1, LP3 and LP6 80% ethanolic extracts and also the accumulation of inositol and flavonoids in hydroalcoholic fractions. Conclusions Our results suggest that the anticonvulsant properties shown by L. alba might be correlated to the presence of a complex of non‐volatile substances (phenylpropanoids, flavonoids and/or inositols), and also to the volatile terpenoids (β‐myrcene, citral, limonene and carvone), which have been previously validated as anticonvulsants.     

Chemical composition and protective effect of Juniperus sabina L. essential oil against CCl4 induced hepatotoxicity

The hepatoprotective activity of the total extract of Juniperus sabina L. against CCl₄ induced toxicity in experimental animals was previously reported and indicated promising results. Essential oil of J. Sabina was prepared by hydrodistillation method. Components of the oil were identified by comparison of GC-MS and retention indexes with reported data. The hepatoprotective effect of the essential oil against CCl₄ induced toxicity was studied using male Wistar rats and silymarin at 10 mg/kg p.o as standard drug. The protective effect was evaluated via serum biochemical parameters such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), gamma glutamyltranspeptidase (GGT), and total bilirubin as well as tissue parameters including non-protein sulfhydryl groups (NP-SH), malonaldehyde (MDA) and total protein (TP). Histopathological study was applied on the liver tissues using Mayer’s hematoxylin stain, Periodic Acid Schiff – Hematoxylin (PAS-H) and Masson trichrome technique on light microscope. Electron microscope images were also obtained for more detailed study.     

Mechanisms involved in the vasodilator effect induced by diosgenin in rat superior mesenteric artery

The aim of this study was to investigate the vasorelaxant effect induced by diosgenin in superior mesenteric rings. In rings pre-contracted with phenylephrine (10 microM), diosgenin caused concentration-dependent relaxations [EC(50) = (3.3 +/- 1.2) x 10(- 4)M, E(max) = 94.2 +/- 2.6 %]. Vascular relaxation induced by diosgenin was significantly inhibited after removal of the endothelium (E(max) = 46 +/- 8.8%, p < 0.001) or after pre-treatment of the rings with N-nitro-L-arginine methyl esther (l-NAME) 100 or 300 microM (E(max) = 35.3 +/- 4%; 28.1 +/- 3.3%, respectively, p < 0.001), atropine 1 microM (E(max) = 24.6 +/- 3.4%, p < 0.001), hydroxocobalamin 30 microM (E(max) = 54.0 +/- 9.6%, p < 0.001), 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) 10 microM (E(max) = 46.0 +/- 8.0%, p < 0.001) or indomethacin 1 microM (E(max) = 22.6 +/- 11.8%, p < 0.001). Vasorelaxation evoked by diosgenin was significantly inhibited after pre-treatment of preparations with both selective and non-selective inhibitors of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels, iberiotoxin 100 nM or tetraethylammonium (TEA) 1mM, respectively (E(max) = 62.5 +/- 9.1%; 65.7 +/- 1.1%, p < 0.001). Conversely, in endothelium-denuded vessels, none of BK(Ca) channel blockers modified the relaxant effect induced by diosgenin. In mesenteric endothelial cells loaded with FURA-2 diosgenin was able to increase intracellular calcium concentrations, which were significantly decreased by atropine 1 microM. In addition, in isolated mesenteric rings, diosgenin induced marked increase in nitric oxide (NO) levels, which was completely abolished after functional endothelium removal. The results obtained here demonstrated that diosgenin-induced relaxation appears to involve endothelial muscarinic receptor activation with increase in intracellular calcium concentrations and consequent release of endothelium-derived relaxing factors (EDRFs), mainly NO and cyclooxygenase derivatives, which activate BK(Ca) channels. Nevertheless, further studies are necessary to clearly elucidate residual endothelium-independent relaxation induced by diosgenin.     

Endothelium-dependent contraction and direct relaxation induced by baicalein in rat mesenteric artery.

The vascular effect of purified baicalein from Scutellaria baicalensis Georgi (Huangqin) was examined in rat isolated mesenteric arteries. Baicalein exerts both contractile and relaxant effects on the U46619-, phenylephrine- or high K+-contracted endothelium-intact arteries. In endothelium-denuded arteries, the contractile response to baicalein (0.3-10 microM) was absent while the relaxant response to baicalein (30-300 microM) remained. Pretreatment with 100 microM N(G)-nitro-L-arginine (L-NNA) or 3 microM methylene blue abolished the baicalein-induced contraction while 10 microM indomethacin or 100 nM BQ610 had no effect. Pretreatment with baicalein (3-10 microM) significantly attenuated the relaxation induced by acetylcholine or by A23187. In contrast, baicalein did not affect the sodium nitroprusside-induced relaxation in endothelium-denuded arteries. Baicalein also concentration dependently inhibited the contractile response to 1 microM phorbol 12,13-diacetate (PDA) in Ca2+-free solution. Baicalein had little effect on the contractile response to 60 mM K+ or to 10 mM caffeine in endothelium-denuded arteries. The baicalein-induced relaxation was unaffected by 1 microM glibenclamide or by 3 mM tetraethylammonium ions in endothelium-denuded arteries. These results indicate that baicalein at low concentrations caused a contractile response and inhibited the endothelium-dependent relaxation, probably through inhibition of endothelial nitric oxide (NO) formation/release. At higher concentrations, baicalein relaxed the arterial smooth muscle partially through inhibition of the protein kinase C-mediated contractile mechanism.     

Chemical composition of the essential oil of creeping thyme (Thymus serpyllum s.l.) growing wild in Lithuania

The results on the chemical composition of the essential oils hydrodistilled from three forms of T. serpyllum growing wild in the Curonian Spit (west of Lithuania) are presented in this study. GC and GC/MS results of volatile oils show that the analysed plants can be defined as a specific chemotype within the Serpyllum section, which can be characterised by a high content of 1,8-cineole (16.3-19.0%) in the essential oil. In addition, one form of the plants with white-coloured blossoms was exceptionally rich in E-carvyl acetate (18.7%). Phenolic compounds, thymol and carvacol, were not detected in the T. serpyllum plants analysed, which is a characteristic feature of the Serpyllum species growing in the Northern European countries.     

Mechanism of noradrenaline potentiation by prostaglandin E2 in rat mesenteric artery.

1 Effects of prostaglandins E2 and F2 alpha (PGE2 and PGF2 alpha) on vasoconstrictor responses to noradrenaline (NA) and methoxamine in isolated mesenteric arteries of the rat were investigated. 2 PGE2 and to a lesser extent PGF2 alpha potentiated vasoconstrictor responses to NA and methoxamine. 3 Prior treatment with reserpine increased, and bretylium reduced, the extent of potentiation significantly. 4 NA vasoconstriction persisted for 1 h after Ca2+ was removed from the perfusing Krebs solution. Prostaglandin-induced potentiation was absent in Ca2+-free Krebs, but increased proportionately with increase in external Ca2+ concentration. 5 Vasoconstriction induced by high potassium, was not potentiated by PGE2. 6 It is concluded the PGE2 potentiates NA vasoconstriction by facilitating Ca2+ influx.     

Endothelium-dependent mesenteric vasorelaxant effects and systemic actions of endothelin (16-21) and other endothelin-related peptides in the rat.

1. The rat isolated superior mesenteric bed, perfused with Krebs-Henseleit solution containing 10 microM indomethacin and precontracted with 100 microM methoxamine, was used to study the vasorelaxation produced by some fragments of endothelin-1, by two alanyl-substituted analogues, and by human and porcine proendothelins. The systemic cardiovascular effects of some of these peptides were also studied in anaesthetized rats. 2. Endothelin (16-21) was an endothelium-dependent vasodilator about 10 times less potent than acetylcholine and its amide was about 500 times less potent than the free acid. Human proendothelin-1 and porcine proendothelin-1 also caused endothelium-dependent relaxations but neither [Ala3,11]endothelin-1 nor [Ala1,3,11,15]endothelin-1 produced significant reductions in the methoxamine-induced tone. Sodium nitroprusside was approximately 200 times less potent than acetylcholine in the presence of the endothelium and was the only vasorelaxant to be active after destruction of the endothelium by perfusion with 0.3% CHAPS; in the absence of the endothelium it was 3.7 times more potent as a vasodilator than in its presence. 3. Porcine proendothelin-1 had weak contractile activity in the isolated mesenteric bed but porcine endothelin (22-39), endothelin (16-21) and endothelin (16-21) amide did not have vasoconstrictor actions. 4. Endothelin-3, [Ala3,11]endothelin-1, [Ala1,3,11,15]endothelin-1 and endothelin (16-21) all had systemic blood pressure effects in the anaesthetized rat. Although endothelin (16-21) did not cause vasoconstriction in vitro, it increased mean arterial pressure in vivo but was at least 100 times less potent than endothelin-3. Despite causing no vasorelaxation in vitro, [Ala1,3,11,15]endothelin-1 and [Ala3,11]endothelin-1 induced short-lived systemic depressor responses which were followed by pressor responses. Endothelin-3 was more potent as a systemic depressor agent than as a pressor agonist and, as a vasodepressor agent, it was 3-4 times more potent than either of the alanyl-substituted analogues. Endothelin-3, [Ala3,11]endothelin-1 and [Ala1,3,11,15]endothelin-1 were equipotent vasopressor agents. Porcine endothelin (22-39) had no systemic blood pressure effects. 5. This study shows directly that the presence of both disulphide bonds is required in the endothelins for them to be able to cause endothelium-dependent relaxation in the mesenteric vascular bed and that this response is mediated by different receptors from those causing contraction of the vascular smooth muscle in the mesentery. Vasorelaxation caused by endothelin (16-21) and its amide suggests that there is a receptor on the endothelium similar to one reported in the guinea-pig trachea.(ABSTRACT TRUNCATED AT 400 WORDS)     

Somatostatin inhibits the release of noradrenaline induced by electrical stimulation of the rat mesenteric artery.

Somatostatin, a peptide with antisecretory and antiproliferative effects, coexists with noradrenaline in sympathetic neurons. Octreotide, a stable somatostatin analogue, prevents hypertension and cardiovascular structural changes induced by prolonged infusion of DPSPX (1,3-dipropyl-8-sulfophenylxanthine, a non-selective adenosine receptor antagonist) in rats. In the present work we investigated the effect of somatostatin and its analogue octreotide on the release of [(3)H]noradrenaline from sympathetic nerves in the rat mesenteric artery. Rat mesenteric arteries were incubated for 60 min with [(3)H]noradrenaline (0.2 microm), mounted in perifusion chambers, washed out for 90 min and electrically stimulated (2 Hz, 5 min, 50 mA). Radioactivity was measured in the tissue and in the perifusion fluid before, during and after stimulation. Both somatostatin and octreotide inhibited tritium release evoked by electrical stimulation of in vitro preparations of rat mesenteric arteries preloaded with [(3)H]noradrenaline. The maximal effects produced by octreotide and somatostatin were a 56 and 70% inhibition of noradrenaline release, respectively. For somatostatin an EC(50)=0. 18 n m (0.01 n m-2.2 n m;n =16) was calculated. When used alone, the somatostatin receptor antagonist, cyclo(7-aminoheptanoyl-Phe- d -Trp-Lys-Thr[BZL]) (CYCAM; 1 microm), had no effect on noradrenaline release induced by electrical stimulation. However, it was able to significantly antagonize the inhibitory effects of octreotide and somatostatin. These results are compatible with a negative modulatory role of somatostatin on sympathetic neurotransmission.     

Chemical composition of essential oil and oleoresins of Zingiber officinale and toxicity of extracts/essential oil against diamondback moth (Plutella xylostella)

Abstract

Essential oil (EO) of ginger and oleoresins isolated from extraction solvents by GC–MS. Zingiberene was the major constituent in all the samples, and ethanol could extract the maximum quantity (21.2%) from the dried de-oiled cake (EDD) followed by EO (20.3%) as compared to oleoresins. Hydro-distilled EO contains higher oxygenated monoterpenes (22.4%) than oleoresins. EDD showed more toxicity to larvae of Plutella xylostella (LC₅₀?=?4957.9?mg L^?1) after 96?h and was followed by EDW (LC₅₀?=?5067.6?mg L^?1) and EF (LC₅₀?=?6631.2?mg L^?1). EO also showed promising efficacy (LC₅₀?=?5875.9?mg L^?1) and repellency (97.1%) against P. xylostella.     

Chemical composition, antimicrobial, antioxidant and cytotoxic activity of the essential oil from the leaves of Acanthopanax leucorrhizus (Oliv.) Harms

The leaf essential oil of Acanthopanax leucorrhizus, a widely used medicinal plant, was obtained by hydrodistillation and analyzed by using combination of capillary GC-FID, GC-MS and RI. Fifty-nine components, representing 93.1% of the total oil, were identified in the essential oil and the main components of the oil were β-pinene (7.3%), linalool (6.5%), p-cymene (6.3%), β-elemene (3.8%), γ-terpinene (3.7%), spathulenol (3.2%) and cis-sabinene hydrate (3.1%). Furthermore, the in vitro antimicrobial, antioxidant and cytotoxic activities of the essential oil were examined. The test results showed that the essential oil exhibited a broad spectrum of anti-microbial activity against all microorganisms tested. Gram-positive bacteria were more sensitive to the oil than gram-negative bacteria and yeasts. The oil possessed moderate cytotoxicity on human tumor cells with lower IC(50) values of 25.65μg/ml (Hep G2), 28.71μg/ml (Hela), 30.15μg/ml (Bel-7402) and 37.55μg/ml (A-549). The moderate antioxidant activity of the oil was also evaluated by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical method.     

Mechanisms underlying the vasorelaxant effect induced by proanthocyanidin-rich fraction from Croton celtidifolius in rat small resistance arteries

Proanthocyanidins are condensed tannins present in fruits, vegetables, and flowers, consumed in the human diet. These compounds are believed to decrease coronary heart disease. The present study was designed to investigate the relaxing effects of a proanthocyanidin-rich fraction (PRF) obtained from Croton celtidifolius BAILL (Euphorbiaceae) barks in rat mesenteric arterial bed (MAB) and isolated mesenteric artery (MA). In the MAB pre-contracted with phenylephrine (Phe), PRF (0.1 - 100 microg) induced a concentration-dependent relaxation of 73% (compared to the control). This effect was significantly reduced by the nitric oxide (NO) synthase inhibitor N(omega)-nitro-L-arginine (L-NOARG) or high K(+) solution and completely abolished in vessels perfused with KCl plus L-NOARG. However, the vasorelaxant effect was not altered by indomethacin, atropine, yohimbine, pyrilamine, or K(+)-channel blockers: BaCl(2), glibenclamide, ouabain, and 4-aminopyridine. In isolated MA pre-contracted with Phe, PRF also induced a concentration-dependent relaxation (0.1 - 30 microg/mL), which was in turn inhibited by endothelial removal, guanylyl cyclase inhibitor 1H[1,2,3]oxadiazolo[4,3-alpha]quinoxalin, charybdotoxin (ChTx), and ChTx plus apamin. Moreover, the relaxant effect was not altered by HOE140 and apamin given alone. The present study demonstrates that the vasorelaxing effect of PRF is dependent upon the NO-cGMP pathway in combination with hyperpolarization due to activation of Ca(2+)-dependent K(+) channels.     

A role of ion channels in the endothelium-independent relaxation of rat mesenteric artery induced by resveratrol

Recently it has been suggested that resveratrol relaxes different isolated arteries. The present study addressed the question whether different ion channels are involved in the endothelium-independent mechanism of vasodilatation induced by resveratrol. For that purpose, we tested the action of resveratrol on the rat mesenteric artery without endothelium. Resveratrol induced concentration-dependent relaxation of rat mesenteric artery. Among the K(+)-channel blockers, 4-amynopiridine (4-AP) moderately antagonized the resveratrol-induced relaxation, while glibenclamide, tetraethylammonium chloride, charybdotoxin, margatoxin, and barium chloride did not inhibit resveratrol-induced vasorelaxation. In rings, precontracted with 100 mM K(+), the relaxant responses to resveratrol were highly significantly shifted to the right compared to those obtained in rings precontracted with phenylephrine, but resveratrol-induced maximal relaxation was only slightly affected. In order to minimize the influence of K(+) channels and voltage-gated Ca(2+) channels (VGCCs) in vascular smooth muscle, the third contraction was made by 100 mM K(+) in the presence of nifedipine. The relaxant response to resveratrol was abolished. Thus, the mechanism of vasorelaxation induced by resveratrol probably involves activation of 4-AP-sensitive K(+) channels. Its ability to completely relax the mesenteric artery precontracted with K(+)-rich solution suggests that K(+) channel-independent mechanism(s) are involved in its vasorelaxant effect. It seems that interaction with VGCCs plays a part in this K(+) channel-independent effect of resveratrol.     

Chemical composition and in vitro cytotoxic effects of the essential oil from Nectandra leucantha leaves

Abstract

Context: Nectandra (Lauraceae) species have been used in folk medicine as an antidiarrheal, analgesic, antifungal, etc., and have many pharmacological proprieties.

Objective: Investigation of the chemical composition and cytotoxicity of essential oil from Nectandra leucantha Nees & Mart. leaves. This is the first study involving N. leucantha reported in the literature.

Material and methods: The essential oil of N. leucantha leaves was obtained by hydrodistillation. Its chemical composition was determined using a combination of GC/FID, GC/MS, and determination of Kovats index (KI). In vitro cytotoxic activity was evaluated against six cancer cell lines – murine melanoma (B16F10-Nex2), human glioblastome (U-87), human cervical carcinoma (HeLa), human colon carcinoma (HCT), human breast adenocarcinoma (MCF7), and human cervical tumor (Siha) as well as against one non-tumorigenic cell line – human foreskin fibroblast (HFF).

Results: Thirty-three compounds were identified primarily sesquiterpenes (81.41%), the main compounds being bicyclogermacrene (28.44%), germacrene A (7.34%), spathulenol (5.82%), and globulol (5.25%). Furthermore, monoterpenes were also found in the analyzed oil (12.84%), predominantly α- and β-pinenes (6.59 and 4.57%, respectively). The crude essential oil displayed significant cytotoxic activity against B16F10-Nex2 (IC₅₀ 33?±?1?μg/mL) and U87 (IC₅₀ 75.95?±?0.03?μg/mL) and HeLa (IC₅₀ 60?±?12?μg/mL) cell lines. The main identified compound, bicyclogermacrene, displayed IC₅₀ ranging from 3.1?±?0.2 to 21?±?6?μg/mL.

Discussion and conclusion: The results indicate that the crude oils from leaves of N. leucantha displayed cytotoxic activity being bicyclogermacrene, the main compound identified in the crude oil responsible, at least in part, for this potential.     

Aggregation of platelets in the mesenteric microcirculation of the rat induced by alpha-toxin (phospholipase C) of Clostridium perfringens.

We have investigated the effects of purified α-toxin (phospholipase C) of Clostridium perfringens (Yamakawa and Ohsaka, 1977) on the behavior of cellular components in the microcirculation, using cinematography on a microscopic level and electron microscopy. We demonstrated that after topical application of α-toxin to the mesentery of the rat, rolling of leucocytes along the vessel wall and sticking of leucocytes to the vessel wall occurred in venules but not in arterioles. Some of the leucocytes remained attached to the vessel wall. Thrombi were formed frequently in venules and capillaries, and at a later stage, in arterioles. With time, thrombi increased in number and size, leading eventually to stasis of the blood stream. Thrombi were also observed frequently in the mesenteric microcirculation when toxin was injected into the jugular vein of the rat. The experiments with adenosine pretreatment followed by topical application of α-toxin to the mesentery suggested that the formation of thrombi induced by this toxin does not involve the mediation of ADP. Electron-microscopic examination confirmed the formation of thrombi consisting solely of platelets. It was concluded that thrombosis must be involved as an early step in the pathogenesis of necrosis caused by α-toxin. The death of the animals injected intravenously with α-toxin may be due, at least in part, to thrombosis. It is possible that thrombosis induced by α-toxin may be one of the factors involved in the causation of toxemia often manifested in the late stage of gas gangrene.     

Modulation of vasorelaxant responses to potassium channel openers by basal nitric oxide in the rat isolated superior mesenteric arterial bed.

1. We have used the isolated buffer-perfused mesenteric arterial bed of the rat to assess the modulation of vasorelaxation to potassium channel openers (KCOs) by basal nitric oxide. 2. The dose-response curves to the KCOs, levcromakalim and pinacidil, in preconstricted preparations were significantly shifted to the left in the presence of the nitric oxide synthase inhibitor (100 microM) NG-nitro-L-arginine methyl ester (levcromakalim, ED50 = 4.47 +/- 0.70 nmol vs. 1.73 +/- 0.26 nmol, P < 0.001; pinacidil, ED50 = 16.1 +/- 4.8 nmol vs. 5.43 +/- 1.10 nmol, P < 0.001). The vasorelaxant responses to papaverine, a vasodilator which acts independently of potassium channels was unaffected by NG-nitro-L-arginine methyl ester (L-NAME). 3. Removal of the endothelium, by perfusion with the detergent CHAPS (0.3%), significantly (P < 0.001) increased the potency of levcromakalim as a vasodilator (ED50 4.47 +/- 0.70 nmol vs. 2.59 +/- 0.31 nmol). The subsequent administration of L-NAME following perfusion with CHAPS did not lead to any additional enhancement of responses to levcromakalim. 4. The presence of the non-selective adenosine antagonist, 8-phenyltheophylline (8-PT, 10 microM) significantly (P < 0.001) shifted the dose-response curve to levcromakalim to the left (ED50 4.47 +/- 0.70 nmol vs. 1.11 +/- 0.32 nmol). In the presence of both L-NAME and 8-PT, the dose-response curve to levcromakalim was also significantly (P < 0.01) shifted to the left compared with control (ED50 in the presence of both L-NAME and 8-PT was 0.42 +/- 0.08 nmol). 5. The presence of 8-bromo cyclic GMP (10 microM) reversed the increase potency of levcromakalim, observed following inhibition of nitric oxide synthase (ED50 in the presence of L-NAME was 0.59 +/- 0.01 nmol and in the presence of 8-bromo cyclic GMP plus L-NAME the ED50 was 3.17 +/- 0.80 nmol). However in the absence of L-NAME, the cell permeable analogue of cyclic GMP, 8-bromo cyclic GMP, did not affect the dose-response curve to levcromakalim compared with control (control ED50 value was 4.16 +/- 0.52 nmol vs. 3.85 +/- 1.13 nmol in the presence of 8-bromo cyclic GMP). 6. The present investigation demonstrates that both basal nitric oxide and adenosine modulate vasorelaxation to the KCOs levcromakalim and pinacidil. The modulatory effect of nitric oxide may be mediated via cyclic GMP.