Mechanisms underlying vasorelaxation induced in rat aorta by galetin 3,6-dimethyl ether, a flavonoid from Piptadenia stipulacea (Benth.) Ducke.

In this study, we investigated the relaxant action of galetin 3,6-dimethyl ether (FGAL) on rat aorta. The flavonoid relaxed both PMA­ and phenylephrine (Phe)-induced contractions (pD2 = 5.36 ± 0.11 and 4.17 ± 0.10, respectively), suggesting the involvement of PKC and Phe pathways or α1 adrenergic receptor blockade. FGAL inhibited and rightward shifted Phe-induced cumulative contraction­response curves, indicating a noncompetitive antagonism of α1 adrenergic receptors. The flavonoid was more potent in relaxing 30 mM KCl- than 80 mM KCl-induced contractions (pD2 = 5.50 ± 0.22 and 4.37 ± 0.12). The vasorelaxant potency of FGAL on Phe-induced contraction was reduced in the presence of 10 mM TEA+. Furthermore, in the presence of apamin, glibenclamide, BaCl2 or 4-AP, FGAL-induced relaxation was attenuated, indicating the participation of small conductance calcium-activated K+ channels (SKCa), ATP-sensitive K+ channels (KATP), inward rectifier K+ channels (Kir) and voltage-dependent K+ channels (KV), respectively. FGAL inhibited and rightward shifted CaCl2-induced cumulative contraction-response curves in both depolarizing medium (high K+) and in the presence of verapamil and phenylephrine, suggesting inhibition of Ca2+ influx through voltage-gated calcium channels (CaV) and receptor operated channels (ROCs), respectively. Likewise, FGAL inhibited Phe-induced contractions in Ca2+-free medium, indicating inhibition of Ca2+ release from the sarcoplasmic reticulum (SR). FGAL potentiated the relaxant effect of aminophylline and sildenafil but not milrinone, suggesting the involvement of phosphodiesterase V (PDE V). Thus, the FGAL vasorelaxant mechanism involves noncompetitive antagonism of α1 adrenergic receptors, the non-selective opening of K+ channels, inhibition of Ca2+ influx through CaV or ROCs and the inhibition of intracellular Ca2+ release. Additionally, there is the involvement of cyclic nucleotide pathway, particularly through PDE V inhibition.

Intensity of swimming exercise influences tracheal reactivity in rats.

Studies that evaluate the mechanisms for increased airway responsiveness are very sparse, although there are reports of exercise-induced bronchospasm. Therefore, we have evaluated the tracheal reactivity and the rate of lipid peroxidation after different intensities of swimming exercise in rats. Thus, male Wistar rats (age 8 weeks; 250-300 g) underwent a forced swimming exercise for 1h whilst carrying attached loads of 3, 4, 5, 6 and 8% of their body weight (groups G3, G4, G5, G6 and G8, respectively; n=5 each). Immediately after the test, the trachea of each rat was removed and suspended in an organ bath to evaluate contractile and relaxant responses. The rate of lipid peroxidation was estimated by measuring malondialdehyde levels. According to a one-way ANOVA, all trained groups showed a significant decrease in the relaxation induced by aminophylline (10(-12)-10(-1) M) (pD2=3.1, 3.2, 3.3, 3.3 and 3.2, respectively for G3, G4, G5, G6 and G8) compared to the control group (pD2=4.6) and the Emax values of G5, G6, G8 groups were reduced by 94.2, 88.0 and 77.0%, respectively. Additionally, all trained groups showed a significant increase in contraction induced by carbachol (10(-9)-10 (-3) M) (pD2=6.0, 6.5, 6.5, 7.2 and 7.3, respectively for G3, G4, G5, G6 and G8) compared to the control group (pD2=5.7). Lipid peroxidation levels of G3, G4 and G5 were similar in both the trachea and lung, however G6 and G8 presented an increased peroxidation in the trachea. In conclusion, a single bout of swimming exercise acutely altered tracheal responsiveness in an intensity-related manner and the elevation in lipid peroxidation indicates a degree of oxidative stress involvement.

Relaxant effect of Ent-7α-hydroxytrachyloban-18-oic acid, a trachylobane diterpene from Xylopia langsdorfiana A. St-Hil. & Tul., on tracheal smooth muscle.

Ent-7α-hydroxytrachyloban-18-oic acid, a trachylobane diterpene from Xylopia langsdorfiana, has previously been shown to relax the guinea-pig trachea in a concentration-dependent manner. In this study we aimed to elucidate the mechanisms underlying this action and so contribute to the discovery of natural products with therapeutic potential. A possible interaction between diterpene and the Ca(2+)-calmodulin complex was eliminated as chlorpromazine (10(-6) M), a calmodulin inhibitor, did not significantly alter the diterpene-induced relaxation (pD2 = 4.38 ± 0.07 and 4.25 ± 0.07; mean ± S.E.M., n=5). Trachylobane-318 showed a higher relaxant potency when the trachea was contracted by 18 mM KCl than it did with 60 mM KCl (pD2 = 4.90 ± 0.25 and 3.88 ± 0.01, n=5), suggesting the possible activation of K(+) channels. This was confirmed, as in the presence of 10 mM TEA(+) (a non-selective K(+) channel blocker), diterpene relaxation potency was significantly reduced (pD2 = 4.38 ± 0.07 to 4.01 ± 0.06, n=5). Furthermore, K(+) channel subtypes KATP, KV, SKCa and BKCa seem to be modulated positively by trachylobane-318 (pD2 = 3.91 ± 0.003, 4.00 ± 0.06, 3.45 ± 0.14 and 3.80 ± 0.05, n=5) but not the Kir subtype channel (pD2 = 4.15 ± 0.10, n=5). Cyclic nucleotides were not involved as the relaxation due to aminophylline (pD2 = 4.27 ± 0.09, n=5) was not altered in the presence of 3 × 10(-5) M trachylobane-318 (pD2 = 4.46 ± 0.08, n=5). Thus, at a functional level, trachylobane-318 seems to relax the guinea-pig trachea by positive modulation of K(+) channels, particularly the KATP, KV, SKCa and BKCa subtypes.

Spasmolytic activity of trachylobanes ent-7α-acetoxytrachyloban-18-oic acid and ent-7α-hydroxytrachyloban-18-oic acid isolated from Xylopia langsdorfiana A. St-Hil. & Tul. (Annonaceae).

We aimed to investigate the possible spasmolytic activity of ent-7α-acetoxytrachyloban-18-oic acid (1) and ent-7α-hydroxytrachyloban-18-oic acid (2) on smooth muscle models. In male rat aorta and rat uterus, both diterpenes were unable to trigger spasmolytic action. However, 2 relaxed guinea-pig trachea: Compounds 1 and 2 antagonised, significantly and concentration-dependently, carbachol- and histamine-induced phasic contractions in guinea-pig ileum. Moreover, they induced a significant and concentration-dependent relaxation in pre-contracted (KCl, carbachol or histamine) guinea-pig ileum, with 2 being 15 times more potent than 1 in histamine-contracted ileum. These dissimilar results may be due to chemical differences between them. Thus, we demonstrated that 1 and 2 seem to be promising spasmolytic agents, although further studies are required to elucidate the spasmolytic action mechanism.

Vasorelaxant action of the total alkaloid fraction obtained from Solanum paludosum Moric. (Solanaceae) involves NO/cGMP/PKG pathway and potassium channels.

ETHNOPHARMACOLOGICAL RELEVANCE: Solanum paludosum Moric. (jurubeba-roxa) is commonly used to treat hypertension as a substitute for Solanum paniculatum L. (jurubeba verdadeira). The total ethanolic extract from the root bark of Solanum paludosum have been found to cause hypotension in rats. AIM OF THE STUDY: To investigate the mechanism by which the total alkaloid fraction obtained from the root bark of Solanum paludosum (FAT-SP) acts as a vasorelaxant agent on rat thoracic aorta. MATERIALS AND METHODS: Rings of rat aorta were suspended in organ bath containing Krebs solution at 37°C, bubbled with carbogen mixture (95% O(2) and 5% CO(2)) under a resting tension of 1 g. Isometric contractions were measured using a force transducer coupled to an amplifier and a microcomputer. RESULTS: FAT-SP has been found cause relaxation of the aortic rings pre-contracted with phenylephrine (Phe) in a concentration-dependent manner, in the presence and absence of endothelium. This effect was more potent on the endothelium-intact aorta. In the presence of endothelium, neither indomethacin (non-selective cyclooxygenase inhibitor) nor atropine (non-selective muscarinic receptor antagonist), produced significant changes on the relaxation response. On the other hand, in the presence of calmidazolium (a calmodulin inhibitor), N-nitro-L-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor), hydroxocobalamin (HDX) (scavenger of free-radical nitric oxide), 1-H-[1,2,4]-oxadiazolo-[4,3a]-quinoxalin-1-one (ODQ, selective blocker of soluble guanylate cyclase), Rp-8-bromo-ß-phenyl-1,N(2)-ethenoguanosine 3':5'-cyclic monophosphorothioate sodium salt hydrate (Rp-8-Br-PET-cGMPS, competitive inhibitor of cGMP-dependent protein kinase G) or TEA(+) (tetraethylammonium, nonselective potassium channel blocker), the vasorelaxant effect was significantly reduced, suggesting the involvement of NO/sCG/PKG pathway and potassium channel opening in vasorelaxant action of the FAT-SP. CONCLUSION: The mechanism of vasorelaxant activity of the FAT-SP on rat aorta involves both NO/sCG/PKG pathway and potassium channels.

Ent-7α-acetoxytrachyloban-18-oic acid and ent-7α-hydroxytrachyloban-18-oic acid from Xylopia langsdorfiana A. St-Hil. & Tul. modulate K(+) and Ca(2+) channels to reduce cytosolic calcium concentration on guinea pig ileum.

In this study we investigated the mechanism underlying the spasmolytic action of ent-7α-acetoxytrachyloban-18-oic acid (trachylobane-360) and ent-7α-hydroxytrachyloban-18-oic acid (trachylobane-318), diterpenes obtained from Xylopia langsdorfiana, on guinea pig ileum. Both compounds inhibited histamine-induced cumulative contractions (slope=3.5±0.9 and 4.4±0.7) that suggests a noncompetitive antagonism to histaminergic receptors. CaCl(2)-induced contractions were nonparallelly and concentration-dependently reduced by both diterpenes, indicating blockade of calcium influx through voltage-dependent calcium channels (Ca(v)). The Ca(v) participation was confirmed since both trachylobanes equipotently relaxed ileum pre-contracted with S-(-)-Bay K8644 (EC(50)=3.5±0.7×10-(5) and 1.1±0.2×10-(5)M) and KCl (EC(50)=5.5±0.3×10-(5) and 1.4±0.2×10-(5)M). K(+) channels participation was confirmed since diterpene-induced relaxation curves were significantly shifted to right in the presence of 5mM tetraethylammonium (TEA(+)) (EC(50)=0.5±0.04×10-(4) and 2.0±0.5×10-(5)M). ATP-sensitive K(+) channel (K(ATP)), voltage activated K(+) channels (K(V)), small conductance calcium-activated K(+) channels (SK(Ca)) or big conductance calcium-activated K(+) channels (BK(Ca)) did not seem to participate of trachylobane-360 spasmolytic action. However trachylobane-318 modulated positively K(ATP), K(V) and SK(Ca) (EC(50)=1.1±0.3×10-(5), 0.7±0.2×10-(5) and 0.7±0.2×10-(5)M), but not BK(Ca). A fluorescence analysis technique confirmed the decrease of cytosolic calcium concentration ([Ca(2+)](c)) induced by both trachylobanes in ileal myocytes. In conclusion, trachylobane-360 and trachylobane-318 induced spasmolytic activity by K(+) channel positive modulation and Ca(2+) channel blockade, which results in [Ca(2+)](c) reduction at cellular level leading to smooth muscle relaxation.