Biomedical subjects

Chiu-Yin Kwan

Publications and source records attributed to Chiu-Yin Kwan.

At least 19 recordsLinked to original sources

PubMed2006

Ca2+-mediated ascorbate release from coronary artery endothelial cells.

1.--The addition of Ca(2+) ionophore A23187 or ATP to freshly isolated or cultured pig coronary artery endothelial cells (PCEC) potentiated the release of ascorbate (Asc). Cultured PCEC were used to characterize the Ca(2+)-mediated release. An increase in Ca(2+)-mediated Asc release was observed from PCEC preincubated with Asc, Asc-2-phosphate or dehydroascorbic acid (DHAA). 2.--The effects of various ATP analogs and inhibition by suramin were consistent with the ATP-induced release being mediated by P2Y2-like receptors. 3.--ATP-stimulated Asc release was Ca(2+)-mediated because (a) ATP analogs that increased Asc release also elevated cytosolic [Ca(2+)], (b) Ca(2+) ionophore A23187 and cyclopiazonic acid stimulated the Asc release, (c) removing extracellular Ca(2+) and chelating intracellular Ca(2+)inhibited the ATP-induced release, and (d) inositol-selective phospholipase C inhibitor U73122 also inhibited this release. 4.--Accumulation of Asc by PCEC was examined at Asc concentrations of 10 microM (Na(+)-Asc symporter not saturated) and 5 mM (Na(+)-Asc symporter saturated). At 10 microM Asc, A23187 and ATP caused an inhibition of Asc accumulation but at 5 mM Asc, both the agents caused a stimulation. Substituting gluconate for chloride did not affect the basal Asc uptake but it abolished the effects of A23187. 5.--PCEC but not pig coronary artery smooth muscle cells show a Ca(2+)- mediated Asc release pathway that may be activated by agents such as ATP.

Adenosine Triphosphate↗

PubMed2005

A novel in vitro endothelium-dependent vascular relaxant effect of Apocynum venetum leaf extract.

1. In the present study, a novel in vitro vascular relaxant effect of Apocynum venetum leaf extract (AVLE; also called 'Luobuma'), obtained from a traditional Chinese medicinal herb with known antihypertensive effects, is reported in isometric contraction studies of rat aorta and superior mesenteric artery. At low concentrations (0.3-10 microg/mL), AVLE had no effect on the resting tension of either blood vessel and caused relaxation in agonist-precontracted vessels with functionally intact endothelium. 2. We demonstrated pharmacologically that the AVLE-induced vasorelaxation was mediated selectively by the endothelial cells in both blood vessels. Using NG-nitro-L-arginine methyl ester (L-NAME) and a low concentration of KCl (15 mmol/L), we also demonstrated that AVLE acted by releasing endothelium-derived relaxation factors; nitric oxide (NO) in the rat aorta and NO plus endothelium-derived hyperpolarizing factor in the rat mesenteric artery. 3. The vascular relaxation following brief exposure to AVLE appeared to persist even after subsequent prolonged washout; this was manifested as an attenuated contraction to subsequent application of phenylephrine (PE) compared with the PE-induced contraction after exposure to carbachol (CCh) and subsequent similar washout. The addition of L-NAME at this point in the absence of AVLE totally restored the contraction to PE, suggesting that enzymatic generation of endothelial NO persisted even after brief exposure to AVLE. 4. Unlike the endothelium-dependent NO-mediated relaxation induced by CCh, which is mediated by endothelial muscarinic receptors (and inhibited by atropine), the relaxation induced by AVLE was not inhibited by atropine and, thus, was not mediated by muscarinic receptors. However, similar to CCh-induced relaxation, AVLE-induced relaxation was associated with the activation of K+ channels. 5. These results provide a strong scientific basis for the folk use of AVLE decoction for antihypertensive therapy in traditional Chinese medicine.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed2005

Exploratory thoughts concerning educational reform with problem-based learning in China.

The author, a novice problem-based learning (PBL) advocate in China and a young faculty member of the School of Stomatology at Wuhan University, joined a PBL tutorial group as an observer during his two-month visit at McMaster University. He describes his observations and thoughts as they relate to the current reform of health sciences education in China.

China↗

PubMed2004

Vascular effects of Siberian ginseng (Eleutherococcus senticosus): endothelium-dependent NO- and EDHF-mediated relaxation depending on vessel size.

Siberian ginseng (SG) has been widely and historically consumed as a health food product for the improvement of self well-being, but whether vascular relaxation may contribute to such a therapeutic health effect has not been studied. We therefore investigated the vasorelaxant effect of the aqueous extract of the roots of SG (Eleutherococcus senticosus Maxim) using several in vitro vascular rings prepared from dog carotid artery, rat aorta and rat mesenteric artery. SG extract (0.04-0.8 mg/ml) caused concentration-dependent relaxation in dog carotid arterial rings pre-contracted with 100 microM phenylephrine (PE), and the relaxation was primarily endothelium-dependent. Treatment with 100 microM L-NOARG (a nitric oxide synthase inhibitor) either prevented or totally reverted SG-induced relaxation, suggesting that the endothelium-dependent relaxation was mediated by NO. Similar endothelium-dependent vascular relaxant responses were also obtained with rat aortic and mesenteric arterial rings, except that it occurred over a relatively higher concentration range of SG (0.5-2.0 mg/ml). When tested in the presence of 300 microM L-NAME, the vasorelaxant effect of SG was inhibited totally in rat aorta but only partially in rat mesenteric artery. The relaxation to SG that was insensitive to L-NAME in rat mesenteric arterial rings was eliminated when the rings (both proximal and distal ends) were pre-treated with a combination of 300 microM L-NAME and 15 mM KCl indicating the involvement of endothelium-derived hyperpolarizing factor (EDHF). This vasorelaxant response of the SG extract was inhibited partially by atropine (1 microM), completely by TEA (5 mM), but not by indomethacin (1 microM) or propranolol (10 microM). SG up to 2 mg/ml had no effect on KCl-induced contraction in any of the vascular rings studied. When compared with carbachol-induced (CCh) relaxation, SG resembles CCh in that the sensitivity to L-NAME inhibition is dependent on vascular size, i.e. aorta >proximal end of mesenteric artery >distal end of mesenteric artery. However, SG exhibited different potencies to relaxation while CCh showed similar potency (EC(50) of about 0.2 microM) in all three vascular segments. In conclusion, we have demonstrated that the vascular effect of SG is endothelium-dependent and mediated by NO and/or EDHF depending on the vessel size. Other vasorelaxation pathways, such as inhibition of K(+)-channels and activation of muscarinic receptors, may also be involved.

Animals↗

PubMed2004

Peroxynitrite resistance of sarco/endoplasmic reticulum Ca2+ pump in pig coronary artery endothelium and smooth muscle.

We examined the effects of peroxynitrite pre-treatment on sarco/endoplasmic reticulum Ca(2+) (SERCA) pump in pig coronary artery smooth muscle and endothelium. In saponin-permeabilized cells, smooth muscle showed much greater rates of the SERCA Ca(2+) pump-dependent (45)Ca(2+) uptake/mg protein than did the endothelial cells. Peroxynitrite treatment of cells inhibited the SERCA pump more severely in smooth muscle cells than in endothelial cells. To determine implications of this observation, we next examined the effect of the SERCA pump inhibitor cyclopiazonic acid (CPA) on intracellular Ca(2+) concentration of intact cultured cells. CPA produced cytosolic Ca(2+) transients in cultured endothelial and smooth muscle cells. Pre-treatment with peroxynitrite (200 microM) inhibited the Ca(2+) transients in the smooth muscle but not in the endothelial cells. CPA contracts de-endothelialized artery rings and relaxes precontracted arteries with intact endothelium. Peroxynitrite (250 microM) pre-treatment inhibited contraction in the de-endothelialized artery rings, but not the endothelium-dependent relaxation. Thus, endothelial cells appear to be more resistant than smooth muscle to the effects of peroxynitrite at the levels of SERCA pump activity, CPA-induced Ca(2+) transients in cultured cells, and the effects of CPA on contractility. The greater resistance of endothelium to peroxynitrite may play a protective role in pathological conditions such as ischemia-reperfusion when excess free radicals are produced.

Animals↗

PubMed2004

Learning of medical pharmacology via innovation: a personal experience at McMaster and in Asia.

Pharmacology, a discrete preclinical discipline of the traditional medical curriculum, identifies itself distinctly different from the other preclinical or clinical subjects in knowledge base as well as learning/teaching instructions. It exists in series with other pre-clinical courses (e.g., anatomy, biochemistry and physiology), and in parallel with other paraclinical courses such as pathology, microbiology and community medicine. Such arrangement makes learning of pharmacology rather difficult and deficient with regard to its therapeutic relevance and clinical application. In recent years, medical curricula based on clinical cases have emerged as a platform in which pharmacology is one integrated component in a holistic approach to medical education. In this problem-based learning (PBL) model, students learn, with teachers' facilitation, in a student-centered environment, based on self-directed, clinically relevant and case-oriented approach, usually in a small-group tutorial format. In PBL, pharmacology is learned in concert with other subject issues relevant to the case-problem in question, such as anatomy, physiology, pathology, microbiology, population health, behavior science, etc. Students learn via problem-evoked curiosity and motivation, in an environment which encourages free inquiries and intensive discussions in a cooperative rather than competitive atmosphere. Teachers facilitate students' learning objectives rather than deliver pre-packed knowledge and dictate what they think students should learn. A change towards PBL curriculum appears to be beneficial in better preparing the medical students as life-long learners capable of coping with changes in knowledge and skills associated with the progressive and dynamic social/economic transformation in the Asia-Pacific regions. Evidence is presented that this is indeed happening.

Asia↗

PubMed2003

Endothelium-dependent vascular relaxation induced by Eucommia ulmoides Oliv. bark extract is mediated by NO and EDHF in small vessels.

The vasorelaxant effects of the aqueous extract prepared from the bark of the Chinese medicinal herb, Eucommia ulmoides Oliv. (also referred to as Tu-Chung or Du-Zhong), which is a common active ingredient in traditional antihypertensive herbal prescriptions in China, have recently been characterized in rat aorta and dog carotid artery. The vasorelaxant effect of eucommia bark extract on these large elastic arteries was found to be entirely endothelium-dependent and nitric oxide (NO)-mediated. Since smaller muscular arteries play a more dominant role in the change of peripheral resistance and thus the regulation of blood pressure, we have now compared the relaxant effects of eucommia bark extract using aorta and the proximal as well as the distal ends of the superior mesenteric arteries from the rat, with a specific objective to investigate whether smaller muscular arteries also elicit endothelium-dependent vascular relaxation (EDVR) in response to eucommia bark extract. We have also determined whether the EDVR, if indeed occurring in the mesenteric arteries, is mediated entirely by NO, or whether it also involves endothelium-derived hyperpolarizing factor (EDHF). We found that all three types of vessel preparations elicit EDVR in response to the eucommia bark extract concentration-dependently in a similar manner to the relaxant responses to carbachol (CCh). Although the NO synthase inhibitor L-NAME totally abolished the EDVR in aorta, it only partial abolished EDVR in mesenteric arteries isolated from each end, the distal end being more resistant to L-NAME. However, the residual L-NAME-resistant relaxation of the rat mesenteric arteries could be further inhibited by preincubation of the vessels with the combination of L-NAME and 15-20 mM KCl (KCl itself at this low concentration caused little or no contraction). Therefore, the EDVR induced by the eucommia extract and CCh in aorta is mediated entirely by NO, and that in mesenteric arteries by NO as well as EDHF, with the EDHF component (inhibited by KCl) larger in the smaller distal end of the rat mesenteric artery. Results of our study offer a plausible mechanistic basis for the vasorelaxing action of Eucommia ulmoides Oliv., which may account for its well-documented antihypertensive action.

Animals↗

PubMed2003

In vitro vasodilator mechanisms of the indole alkaloids rhynchophylline and isorhynchophylline, isolated from the hook of Uncaria rhynchophylla (Miquel).

Rhynchophylline (Rhy) and isorhynchophylline (Isorhy), indole alkaloids from Uncaria hooks, reportedly exert hypotensive and vasodilatory effects, but the mechanism of action is unclear. We therefore investigated the relaxant effects of these two isomeric alkaloids in rat arteries in vitro, in particular in respect of the various functional Ca2+ pathways. Both Rhy and Isorhy relaxed aortic rings precontracted with phenylephrine (PE, 1 microM) in a dose-dependent manner (3-300 microM). Removal of endothelium and preincubation with L-NAME (300 microM) slightly inhibited but did not prevent the relaxant response. These results indicate that Rhy and Isorhy act largely in an endothelium-independent manner. Unlike nicardipine, both alkaloids not only inhibited the contraction induced by 60 mM KCl (IC50 20-30 microM), but also that induced by PE and U46619, albeit to a lesser extent (IC50 100 and 200 microM, respectively). These results suggest that Rhy and Isorhy may act via multiple Ca2+ pathways. In contrast to their inhibitory effects on KCl-induced and receptor-mediated contractions, where both isomers were comparably potent, Rhy was more potent than Isorhy at higher concentrations (>100 microM) in inhibiting both caffeine (25 mM)- and cyclopiazonic acid (CPA, 30 microM)-induced contractions. Similar results observed with caffeine in Ca2+-containing medium were also observed in Ca2+-free medium. However, 0.1-0.3 microM nicardipine (which completely inhibited KCl-induced contraction) had no significant inhibitory effect on CPA-induced contractions. Taken together, these results indicate discrimination between these two isomers with respect to Ca2+-induced Ca2+ release and non-L-type Ca2+ channel, but not for IP3-induced Ca2+ release and L-type Ca2+ channels. Similar relaxant responses to KCl- and caffeine-induced contractions were seen when these two alkaloids were tested on the smaller mesenteric and renal arteries. In conclusion, the vasodilatory effects of Rhy and Isorhy are largely endothelium independent and are mediated by L-type Ca2+ channels. At higher concentrations, they also affect other Ca2+-handling pathways, although to a lesser extent. While there is no discrimination between the two isomers with respect to the contraction induced by KCl or agonists (PE and U46619), differential effects between Rhy and Isorhy were seen on caffeine- and CPA-induced contractions.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed2003

A new view of K+ -induced contraction in rat aorta: the role of Ca2+ binding.

Strong, K+ -induced contractions of rat aorta in Ca-free, Mg-free media were not accompanied by increased intracellular calcium concentration, [Ca2+](i), whereas such contractions in the presence of the divalent cations were correlated with rising [Ca2+](i) as assessed by fura-2. At the same time, calcium channel blockers, a modulator of Ca2+-binding proteins, and a modulator of actin polymerization, inhibited all types of K+ -induced contractions. Increasing the K+ in isotonic medium evoked a rise of (45)Ca2+ binding to the plasma membrane of freshly isolated aortic cells. Although Ca2+ -dependent events underlie the mechanism of K+ -induced vascular contractions in both the presence and absence of Ca2+, in contrast to the view that [Ca2+](i) is a key regulator of excitation-contraction coupling in smooth muscle, we suggest that the modulation of Mg2+ -dependent Ca2+ binding, probably within/at the L-type calcium channel by K+, is a trigger for aortic contraction. This Ca2+ binding may then activate actin-myosin interaction.

Actins↗

PubMed2003

In vitro relaxation of vascular smooth muscle by atropine: involvement of K+ channels and endothelium.

Cumulative addition of atropine to the organ bath containing endothelium-intact (+E) rat aorta, which was precontracted with phenylephrine (PE, 1 microM) and subsequently relaxed with carbachol (1 microM), caused biphasic changes in the vascular contractility of +E rat aortic rings. Low concentrations of atropine (10 nM-1.0 microM) caused progressive restoration of contraction to PE; whereas at higher concentrations (1-100 microM), atropine caused progressive relaxation. Atropine-induced aortic relaxation was significantly inhibited upon endothelium removal by either rubbing or saponin treatment, but considerable relaxation still persisted in the range of 30-100 microM atropine. Similar findings were also obtained when the nitric oxide (NO) generation was inhibited with 300 microM NO synthase inhibitor, L-NAME. Atropine-induced relaxation was also observed when 5-hydroxytryptamine (5-HT) was used as the agonist and the atropine-relaxation was more potent at lower concentrations of PE and 5-HT. However, atropine had no effect on the contraction elicited by KCl or prostaglandin F(2 alpha). Also, atropine-induced relaxation was not affected by indomethacin (1-10 microM), nicotine (10-100 microM) or hexamethonium (30 microM). Pretreatment of +E aorta with tetraethylammonia (TEA, 3-10 mM) or 4-aminopyridine (4-AP, 1-3 mM) showed prominent inhibitory effect on atropine-induced relaxation; on the other hand, preincubation with glibenclamide (1-10 microM), BaCl(2) (1-30 microM) or 2 microM charybdotoxin and apamin, had little effect on the relaxation induced by atropine. When added to tissues after relaxation to atropine, TEA and 4-AP concentration-dependently reversed the relaxation in -E aorta, whereas in +E aorta, TEA up to 30 mM and 4-AP up to 10 mM only partially affected atropine-induced relaxation. Although TEA and 4-AP potentiated the PE-contraction, such potentiation is unlikely to contribute to the change in sensitivity to atropine-induced relaxation, since in the presence of 15 mM KCl, which also potentiated PE-contraction to a comparable extent, the atropine-relaxation remains unchanged. Scopolamine also acts like atropine, except that the effect of scopolamine was smaller than that of atropine and is primarily endothelium-dependent. Atropine-induced relaxation also occurs in medium artery (renal artery) and small muscular artery (mesenteric artery). In conclusion, atropine-relaxation is mediated in part via voltage-dependent K(+) channels in both smooth muscle and endothelium and forms the mechanistic basis for the observed vasodilation, reduced blood pressure and facial flushing following atropine overdose.

Animals↗

PubMed2003

Endothelium-dependent vasorelaxant effects of the aqueous extracts of the Eucommia ulmoides Oliv. leaf and bark: implications on their antihypertensive action.

The vascular effects of three extract preparations from the Chinese medicinal herb, Eucommia ulmoides Oliv., which is historically an active ingredient commonly used in antihypertensive herbal prescriptions in China, were investigated with isometric contraction using isolated rat aortic and dog carotid rings. Both aqueous extracts isolated from eucommia leaf (L) and bark (B) concentration dependently caused endothelium-dependent relaxation in vessels precontracted with 1 microM phenylephrine (PE), but the methanol extract of the leaf (M) had no effect. Vessels precontracted with KCl and de-endothelialized vessels precontracted with PE were not affected by B or L. The endothelium-dependent relaxation evoked by B and L was either abolished or substantially inhibited by NG-nitro-L-arginine methyl ester (L-NAME) and methylene blue (MB), indicating the involvement of the nitric oxide (NO) synthase pathway in the vasorelaxant action of B and L. The relaxation to the aqueous extract of eucommia bark was not inhibited with 1 microM atropine, but was inhibited by 3-5 mM tetraethylammonium (TEA) and 3 mM 4-aminopyridine. This suggests that the endothelium-dependent, NO-mediated relaxation evoked by the aqueous eucommia extracts was not mediated via the activation of endothelium muscarinic receptors and may involve the activation of K+ -channels. Results in this study have provided the first evidence on the in vitro vasorelaxant action of E. ulmoides Oliv. that forms the pharmacological basis for its well-documented antihypertensive action.

Animals↗

PubMed2003

Pramanicin, an antifungal agent, raises cytosolic Ca2+ and causes cell death in vascular endothelial cells.

The effects of a newly discovered antifungal agent, pramanicin, on cytosolic Ca(2+) and cell viability of cultured bovine pulmonary artery endothelial cells and on endothelium-dependent relaxation of dog carotid arterial rings were investigated by digital dynamic fluorescence ratio imaging and morphological and contractility studies, respectively. Pramanicin 100 microM, previously shown to cause maximal endothelium-dependent and NO-mediated vascular relaxation, induced a small transient elevation of cytosolic Ca(2+) concentration in Ca(2+)-free medium; subsequent introduction of 1 mM Ca(2+) caused a steady, nonsaturating increase of Ca(2+), which could be brought down to the basal level by the addition of EGTA. At the single cell level, the elevation of cytosolic Ca(2+) initiates from the cell periphery and progresses toward the central region. When added to the plateau phase of phenylephrine-induced contraction, pramanicin induced a slow endothelium-dependent relaxation, which could be reversed with the NO synthase inhibitor, L-NOARG. When preincubated with vascular tissue, pramanicin resulted in an irreversible loss of endothelial function characterized by the lack of carbachol-induced relaxation. Pramanicin caused cell injury characterized by plasmalemmal bleb formation, leading to cell death characterized by Trypan blue staining of the nuclei in cultured vascular endothelial cells in a concentration- and time-dependent manner. Such pramanicin-induced cell death was not associated with Ca(2+)-mediated or NO-mediated mechanisms. The time course of Ca(2+) elevation corresponds with that of pramanicin-induced relaxation of precontracted arterial rings, whereas the time course of endothelial cell death corresponds to that of pramanicin-induced loss of endothelial function as assessed by carbachol-induced relaxation. The pramanicin analogue, PMC-A, a by-product of the biosynthesis of pramanicin, in which the epoxy group is replaced by a CC bond, caused little endothelial-dependent relaxation, but it was able to cause endothelial cell dysfunction, albeit to a lesser extent compared to pramanicin, suggesting a role of the epoxy group in pramanicin for its vasorelaxant effect.

Animals↗

PubMed2003

Nitric oxide, human diseases and the herbal products that affect the nitric oxide signalling pathway.

1. Nitric oxide (NO) is formed enzymatically from l-arginine in the presence of nitric oxide synthase (NOS). Nitric oxide is generated constitutively in endothelial cells via sheer stress and blood-borne substances. Nitric oxide is also generated constitutively in neuronal cells and serves as a neurotransmitter and neuromodulator in non-adrenergic, non-cholinergic nerve endings. Furthermore, NO can also be formed via enzyme induction in many tissues in the presence of cytokines. 2. The ubiquitous presence of NO in the living body suggests that NO plays an important role in the maintenance of health. Being a free radical with vasodilatory properties, NO exerts dual effects on tissues and cells in various biological systems. At low concentrations, NO can dilate the blood vessels and improve the circulation, but at high concentrations it can cause circulatory shock and induce cell death. Thus, diseases can arise in the presence of the extreme ends of the physiological concentrations of NO. 3. The NO signalling pathway has, in recent years, become a target for new drug development. The high level of flavonoids, catechins, tannins and other polyphenolic compounds present in vegetables, fruits, soy, tea and even red wine (from grapes) is believed to contribute to their beneficial health effects. Some of these compounds induce NO formation from the endothelial cells to improve circulation and some suppress the induction of inducible NOS in inflammation and infection. 4. Many botanical medicinal herbs and drugs derived from these herbs have been shown to have effects on the NO signalling pathway. For example, the saponins from ginseng, ginsenosides, have been shown to relax blood vessels (probably contributing to the antifatigue and blood pressure-lowering effects of ginseng) and corpus cavernosum (thus, for the treatment of men suffering from erectile dysfunction; however, the legendary aphrodisiac effect of ginseng may be an overstatement). Many plant extracts or purified drugs derived from Chinese medicinal herbs with proposed actions on NO pathways are also reviewed.

Animals↗

PubMed2003

Effects of peroxynitrite on sarco/endoplasmic reticulum Ca2+ pump isoforms SERCA2b and SERCA3a.

Sarco(endo)plasmic reticulum Ca2+ (SERCA) pumps are important for cell signaling. Three different genes, SERCA1, 2, and 3, encode these pumps. Most tissues, including vascular smooth muscle, express a splice variant of SERCA2 (SERCA2b), whereas SERCA3a is widely distributed in tissues such as vascular endothelium, tracheal epithelium, mast cells, and lymphoid cells. SERCA2b protein is readily inactivated by peroxynitrite that may be formed during cardiac ischemia reperfusion or during immune response after infection. Here, we compared the peroxynitrite sensitivity of SERCA2b and SERCA3a by using microsomes prepared from HEK-293T cells overexpressing the pumps. We incubated the microsomes with different concentrations of peroxynitrite and determined Ca2+ uptake, Ca2+-Mg2+-ATPase, Ca2+-dependent formation of acylphosphate intermediate, and protein mobility in Western blots. Ca2+ uptake, Ca2+-Mg2+-ATPase, and Ca2+-dependent formation of acylphosphate intermediate were inactivated for both SERCA2b and SERCA3a, but the latter was more resistant to the inactivation. Western blots showed that SERCA2b and SERCA3a proteins oligomerized after treatment with peroxynitrite, but each with a slightly different pattern. Compared with monomers, the oligomers may be less efficient in forming the acylphosphate intermediate and in conducting the remainder of the steps in the reaction cycle. We conclude that the resistance of SERCA3a to peroxynitrite may aid the cells expressing them in functioning during exposure to oxidative stress.

Animals↗

PubMed2003

The epoxy group of pramanicin is required for the optimal endothelium-dependent relaxation of rat aorta.

The vascular effects of a newly discovered anti-fungal agent, pramanicin (PMC), and its two analogues, PMC-A, in which the epoxy group is replaced by a - HC = CH - bond, and PMC-B, on which the diene is converted to the saturated (CH(2))(4)-derivative, respectively, were investigated in rat aorta. All three compounds caused an initial endothelial-dependent relaxation, which is prevented either by removal of endothelium or inclusion of the nitric oxide synthase inhibitor L-NAME. Upon prolonged incubation with the aortic rings, they also caused endothelial cell dysfunction characterized as reduced relaxation to carbachol (CCh). These effects were the strongest for PMC, being completely inhibitory at 20 microM after 30 min incubation, whereas those of PMC-A and PMC-B were smaller and comparable with each other, causing 30 - 40% inhibition at 20 micro M. PMC and its analogues had no effect on KCl-induced contraction and also had no effect on relaxation induced by sodium nitroprusside, suggesting that these compounds had no effect on the basic mechanisms of the contractile elements. Phenylephrine (PE)-induced contraction, however, was significantly reduced in the presence of these compounds, the inhibitory effect being strongest with PMC, but this inhibitory action was rapidly reversible and not of the competitive mode with respect to PE. We conclude that the epoxy group in PMC is required for the optimal vascular effects. We have discussed and speculated upon the possible mechanisms of action of PMC. The potent, selective, and irreversible inhibitory effect of PMC on the endothelial function points to its potential development into an anti-angiogenic drug.

Animals↗

PubMed2002

Tetrandrine potentiates caffeine-induced contraction but inhibits phenylephrine-induced contraction in perfused rat mesenteric artery.

Effects of tetrandrine (TET), a bisbenzylisoquinoline alkaloid, on the contractile responses of perfused rat mesenteric arteries to phenylephrine (PE) and caffeine were investigated. TET concentration-dependently (1-30 micro M) attenuated phenylephrine-induced responses but potentiated the contractile responses to caffeine (5-40 mM) in the presence and absence of Ca(2+). Berbamine (BER), a structural analogue of TET, elicited a relatively smaller inhibitory effect on the responses to PE due to Ca(2+) release or Ca(2+) influx. However, both TET and BER elicited a comparable potentiating effect on caffeine-induced contraction. Cyclopiazonic acid (CPA; 10 micro M), a selective sarcoplasmic reticulum Ca(2+)-ATPase pump inhibitor, mimicked the potentiating effect of TET when added 5 min prior to caffeine in Ca(2+)-free medium. However, CPA did not augment and might even inhibit the caffeine-induced response when it was preincubated with the tissue for 25 min prior to the addition of caffeine. We propose that TET elicits differential effects on PE- and caffeine-induced responses in perfused rat mesenteric arterial bed. The inhibitory effect of TET on PE-induced responses is probably due to its direct interactions with alpha-adrenoceptors and PE-sensitive Ca(2+)-channels. The augmentation of caffeine-induced responses by TET, particularly in Ca(2+)-free medium, is likely to be due to its partial inhibition of the sarcoplasmic reticulum Ca(2+)-ATPase pump.

Alkaloids↗

PubMed2002

Effects of papaya seed extract and benzyl isothiocyanate on vascular contraction.

To investigate their potentially toxic effects on mammalian vascular smooth muscle, pentane extracts of papaya seeds and the chief active ingredient in the extracts, benzyl isothiocyanate (BITC), were tested for their effects on the contraction of strips of dog carotid artery. BITC and the papaya seed extract caused relaxation when added to tissue strips that had been pre-contracted with phenylephrine (PE). Incubation of the tissue with papaya seed extract or BITC caused inhibition of contraction when the strips were subsequently contracted with KCl or PE. This relaxation and inhibition of contraction did not appear to be endothelium-dependent, as endothelium-denuded rings showed the same degree of relaxation or inhibition of contraction in response to the preparations/drugs as those with the endothelium intact. The effects of both BITC and the extract were irreversible, i.e., the tissue did not recover to normal contractile ability after extensive washing. Exposure of the tissue to the papaya seed extract caused slower relaxation of the tissue, compared to controls, both after contraction with PE and subsequent addition of carbachol (CCh), and after contraction with KCl and then washing. Calcium imaging studies using cultured endothelial cells showed strong influxes of Ca2+ into the cells in response to addition of the papaya seed extract. We conclude that these extracts, when present in high concentration, are cytotoxic by increasing the membrane permeability to Ca2+, and that the vascular effects of papaya seed extracts are consistent with the notion that BITC is the chief bio-active ingredient.

Animals↗

PubMed2002

Problem-based learning and teaching of medical pharmacology.

In the Faculty of Health Sciences at McMaster University, the traditional discipline-based boundaries dividing the teaching and learning of basic medical sciences, such as physiology and pharmacology, do not exist. For more than 3 decades, student-centered, self-directed problem-based learning (PBL) has been the main form of instruction for students learning pharmacology within the medical curriculum and the pharmacological issues are always embedded within a health-care problem, with consideration of many other relevant non-pharmacological issues. In PBL, pedagogic emphasis is placed on the process of learning via constructive inquiry rather than cumulative acquisition of factual knowledge. For the science students, typically in the Biology/Pharmacology cooperative courses, both student-centered learning and teacher-centered teaching approaches are being used. In this case, the PBL approach is adopted to complement the conventional lectures at the course level. For medical students, PBL continues to be the major form of instruction in a small-group tutorial setting at the curricular level. The PBL curriculum is integrated across organ systems (cardiovascular, renal, respiratory, gastrointestinal, neural, etc) and across the life cycle, spanning population- and behavior-related perspectives, rather than being recreated from discrete disciplinary areas (such as physiology, anatomy, biochemistry, pharmacology, and community medicine). Those students who lack a pharmacology background or wish to enhance their pharmacological knowledge can take a block elective or horizontal elective in pharmacology. Unlike science students, medical students need to sort out pharmacological principles from the overload of information, to integrate them into the clinically relevant situations, and to ultimately apply them to the management of patients' illness. This is most effectively achieved in a student-centered environment conducive to life-long learning.

Education, Medical, Undergraduate↗