Cellular calcium regulatory machinery of vasorelaxation elicited by petasin
1. The present study examined the cytosolic Ca2+ regulatory machinery involved in the vasorelaxation produced by petasin, a sesquiterpene isolated from Petasites formosanus.
2. Aortic rings isolated from Sprague-Dawley rats were exposed to petasin (0.01–100 μmol/L) to elucidate its vascular effects on isometric contraction elicited by vasoconstrictors, as well as the contribution of the endothelium and Ca2+ to the responses observed. In addition, L-type voltage-dependent Ca2+ channel (VDCC) activity and [Ca2+]i were determined in cultured vascular smooth muscle cells (VSMCs) from Sprague-Dawley rats in the presence of 1–100 μmol/L petasin using whole-cell patch-clamp recording and the fluorescent probe fura-2/AM. The effects of petasin on vascular responses were compared between aortic rings from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats.
3. Petasin reduced isometric contraction elicited by KCl or the L-type Ca2+ channel opener BayK 8644 (IC50 3.0 ± 0.4 and 4.1 ± 1.1 μmol/L, respectively) in aortic rings isolated from Sprague-Dawley rats, independent of the endothelium. In addition, petasin triggered a rightward shift in the concentration–response curve to KCl while reducing the maximal response by 82%. In Ca2+-depleted and high K+-depolarized aortic rings, 1–100 μmol/L petasin pretreatment attenuated the Ca2+-induced contraction in a concentration-dependent manner.
4. In cultured VSMCs, whole-cell patch-clamp recording revealed that petasin inhibited VDCC activity. Measurement of [Ca2+]i using fura-2/AM fluorescence indicated that petasin suppressed the KCl-induced increase in [Ca2+]i. However, receptor binding assays failed to identify any significant interaction between petasin and the dihydropyridine binding sites of the L-type VDCC.
5. In aortic rings from SHR and WKY rats, petasin inhibited Ca2+-induced contractions in Ca2+-depleted and high K+-depolarized solution with a more pronounced effect in rings from SHR.
6. Together, the results suggest that direct Ca2+ antagonism of L-type VDCC in vascular smooth muscle may account, at least in part, for petasin-induced vasorelaxation. The more pronounced effect of the sesquiterpene in blood vessels from SHR suggests its possible therapeutic potential in the mangement of hypertension.
Available from: PubMed Central
- "However, the active ingredients and their action mechanisms responsible for the effects of the extracts of Petasites hybridus have not been fully elucidated. For example, anti-allergic effect of P. hybridus extracts was previously suggested to be due to L-type Ca 2+ channel blockage by petasin and isopetasin (Bickel et al., 1994; Thomet et al., 2001; Resnati et al., 2002; Fiebich et al., 2005; Wang et al., 2010). However, neither petasin nor isopetasin inhibited COX- 2 enzyme activity in vitro (Fiebich et al., 2005). "
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ABSTRACT: To explore the anti-allergic and anti-inflammatory effects of extracts of Petasites genus, we studied the effects of s-petasin, a major sesquiterpene from Petasites formosanus (a butterbur species) on asthma and peritonitis models. In an ovalbumin-induced mouse asthma model, s-petasin significantly inhibited the accumulations of eosinophils, macrophages, and lymphocytes in bronchoalveolar fluids. S-petasin inhibited the antigen-induced degranulation of β-hexosamidase but did not inhibit intracellular Ca(2+) increase in RBL-2H3 mast cells. S-petasin inhibited the LPS induction of iNOS at the RNA and protein levels in mouse peritoneal macrophages. Furthermore, s-petasin inhibited the production of NO (the product of iNOS) in a concentration-dependent manner in the macrophages. Furthermore, in an LPS-induced mouse model of peritonitis, s-petasin significantly inhibited the accumulation of polymorpho nuclear and mononuclear leukocytes in peritoneal cavity. This study shows that s-petasin in Petasites genus has therapeutic effects on allergic and inflammatory diseases, such as, asthma and peritonitis through degranulation inhibition in mast cells, suppression of iNOS induction and production of NO in macrophages, and suppression of inflammatory cell accumulation.
Available from: Ismaila Raji
- "An average of 5 consecutive readings was recorded. Rats were trained every 3 days for BP measurement for two weeks prior to the start of the actual experiment [26-29]. "
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Tulbaghia violacea Harv. (Alliaceae) is used to treat various ailments, including hypertension (HTN) in South Africa. This study aims to evaluate the contributions of muscarinic receptors and changes in plasma aldosterone levels to its anti-hypertensive effect.
In the acute experiments, methanol leaf extracts (MLE) of T. violacea (30–120 mg/kg), muscarine (0.16 -10 μg/kg), and atropine (0.02 - 20.48 mg/kg), and/or the vehicle (dimethylsulfoxide (DMSO) and normal saline (NS)) were respectively and randomly administered intravenously in a group of spontaneously hypertensive (SHR) weighing 300 to 350 g and aged less than 5 months. Subsequently, T. violacea (60 mg/kg) or muscarine (2.5 μg/kg) was infused into eight SHRs, 20 min after atropine (5.12 mg/kg) pre-treatment. In the chronic (21 days) experiments, the SHRs were randomly divided into three groups, and given the vehicle (0.2 ml/day of DMSO and NS), T. violacea (60 mg/kg/day) and captopril (10 mg/kg/day) respectively into the peritoneum, to investigate their effects on blood pressure (BP), heart rate (HR), and plasma aldosterone levels. Systolic BP and HR were measured using tail-cuff plethysmography during the intervention. BP and HR were measured via a pressure transducer connecting the femoral artery and the Powerlab at the end of each intervention in the acute experiment; and on day 22 in the chronic experiment.
In the acute experiments, T. violacea, muscarine, and atropine significantly (p < 0.05) reduced BP dose-dependently. T. violacea and muscarine produced dose-dependent decreases in HR, while the effect of atropine on HR varied. After atropine pre-treatment, dose-dependent increases in BP and HR were observed with T. violacea; while the BP and HR effects of muscarine were nullified. In the chronic experiments, the T. violacea-treated and captropril-treated groups had signicantly lower levels of aldosterone in plasma when compared to vehicle-treated group. Compared to the vehicle-treated group, significant reduction in BP was only seen in the captopril-treated group; while no difference in HR was observed among the groups.
The results obtained in this study suggest that stimulation of the muscarinic receptors and a reduction in plasma aldosterone levels contribute to the anti-hypertesive effect of T. violacea.
Available from: Grzegorz Grześk
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ABSTRACT: Cyclosporine belongs to the group of the most commonly used immunosuppressants. Hypertension occurs in approximately 30% of patients treated with this drug. However, the pathogenesis of this occurrence has not been explained to date. The purpose of our study was to clarify the mechanisms leading to the evolution of hypertension induced by cyclosporine A (CsA). We examined the changes in transmission within receptors and around the receptors. We also aimed to elucidate the mechanisms responsible for averting arterial hyperresponsiveness induced by the drug. Experiments were performed on isolated and perfused tail arteries of Wistar rats. Tissues surrounding the artery were removed and the proximal segment (length of 2-3 cm) was used for cannulation. Cannulated arteries were placed in a 20-ml glass chamber (vertical position). The contraction force in our model was measured by an increased degree of perfusion pressure with a constant flow rate (approximately 1 ml/min). The results showed that in the presence of CsA, the concentration-response curves/phenylephrine (PHE) curve shifted to the left. Cyclosporine increased the reactivity of the arteries to PHE. This effect was directly linked to the increase in the receptor reserve. The analysis of the reactivity of vascular smooth muscle showed that CsA increased the influx of calcium ions from the extracellular to the intracellular area. No difference was found between the contraction triggered by Bay-K8644 in the presence of CsA and the control probe. The increase in perfusion pressure induced by CsA was blocked by L-type calcium channel blockers (nifidipine and diltiazem). The results from our experiments show that CsA increases the reactivity of vessels to the effect of catecholamines. CsA also enhances signal transmission between G-protein coupled receptors (GPCRs) and calcium channels. The activation of protein kinase C also plays a significant role in this process. Our results suggest that the best choice for the pharmacotherapy of hypertension induced by CsA would be calcium channel antagonists.
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