Biomedical subjects

T M Wong

Publications and source records attributed to T M Wong.

At least 19 recordsLinked to original sources

PubMed2001

Cardiac effects of the extract and active components of radix stephaniae tetrandrae. II. Myocardial infarct, arrhythmias, coronary arterial flow and heart rate in the isolated perfused rat heart.

The primary purpose of the present study was to compare the cardioprotective effects of the extract from radix stephaniae tetrandrae (RST) and its individual compounds, tetrandrine (Tet) and fanchinoline (Fan). Secondly, we also compared the cardiac effects of the individual compounds and the RST extract with those of verapamil, a classical Ca2+ channel blocker. The Langendorff isolated perfused rat heart preparation was used. Regional ischaemia and reperfusion was employed to induce myocardial infarct and arrhythmia. Infarct, arrhythmia, heart rate and coronary artery flow were determined in hearts treated with vehicle, RST extract, Tet, Fan, or verapamil. It was found that RST extract, of which only 9% was Tet, and Tet alone produced equally potent ameliorating effects on arrhythmia and infarct induced by ischaemia and reperfusion without further inhibiting ischaemia-reduced heart rate and coronary artery flow. Fan had no effects on arrhythmia and infarct induced by ischaemia and reperfusion; but it induced S-T segment elevation and further reduced heart rate and coronary artery flow during ischaemia. Verapamil also ameliorated the effects of ischaemia and reperfusion on arrhythmia and infarct. It should be noted that 1 microM verapamil, that produced comparable effects on infarct and arrhythmia to the RST extract and Tet, further inhibited heart rate during ischaemia. The results indicate that the RST extract produces equally potent cardioprotective and anti-arrhythmic effects as Tet alone. Both RST extract and Tet may be better choices for the treatment of arrhythmia and infarct induced by myocardial ischaemia and reperfusion than the classical Ca2+ channel blocker, verapamil as they do not further reduce heart rate during ischaemia.

Alkaloids↗

PubMed2001

Cardiac effects of the extract and active components of Radix stephaniae tetrandrae. I. Electrically-induced intracellular calcium transient and protein release during the calcium paradox.

The present study was designed to compare the cardiac actions of the extract and individual components, tetrandrine (Tet) and fangchinoline (Fan), of Radix stephaniae tetrandrae (RST). We measured the electrically induced [Ca2+]i transient in single rat ventricular myocytes and protein release following perfusion with a Ca2+ free solution (the Ca2+ paradox) from the isolated perfused rat heart, both of which are known to relate to Ca2+ influx. We found that Tet inhibited both electrically induced [Ca2+]i transient and protein release during the Ca2+ paradox, while Fan had no significant effects. The RST extract containing 9% Tet and 6% Fan by weight also affected the [Ca2+]i transient, and was only slightly, though significantly, less effective/potent than Tet alone. On the other hand, RST extract had a significantly greater inhibitory effect on protein release during the Ca2+ paradox than Tet alone. The observations suggest that the RST extract, which contains a mixture of components, may have more potent effects in the heart than its main active component.

Alkaloids↗

PubMed2001

Kappa-opioid receptor agonist inhibits the cholera toxin-sensitive G protein in the heart.

To explore the signaling mechanisms of the negative modulation of beta-adrenoceptors by kappa-Opioid receptors (kappa-OR) in the heart, the possibility of the interaction at the level of G protein and receptor was determined. Cholera toxin, an activator of the stimulatory G protein (Gs), elevated electrically induced intracellular Ca2+ ([Ca2+]i) transients and induced ribosylation of the alpha-subunit of Gs (Gsalpha) in rat ventricular myocytes. The effects were significantly attenuated by U50,488H, a specific agonist of kappa-OR, and were abolished by nor-binaltorphimine, a selective kappa-OR antagonist. The content of Gsalpha, however, was not affected by U50,488H. Receptor binding experiments showed that neither Bmax nor Kd of the binding of [3H]CGP-12177, a beta-adrenoceptor antagonist, was affected by U50,488H. The current study provides the first evidence that kappa-OR stimulation inhibits the ribosylation of the alpha-subunit of the Gs protein, thus inhibiting the action of cholera toxin on the protein.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed2001

Kappa- but not delta-opioid receptors mediate effects of ischemic preconditioning on both infarct and arrhythmia in rats.

Two series of experiments were performed in the isolated perfused rat heart to determine the role of kappa- and delta-opioid receptors (OR) in cardioprotection of ischemic preconditioning (IP). In the first series of experiments, it was found that IP with two cycles of 5-min regional ischemia followed by 5-min reperfusion each reduced infarct size induced by 30-min ischemia, and the ameliorating effect of IP on infarct was attenuated with blockade of either 5 x 10(-6) mol/l nor-binaltorphimine (nor-BNI), a selective kappa-OR antagonist, or 5 x 10(-6) mol/l naltrindole (NTD), a selective delta-OR antagonist. The second series showed that U50,488H, a selective kappa-OR agonist, or D-Ala(2)-D-leu(5)-enkephalin (DADLE), a selective delta-OR agonist, dose dependently reduced the infarct size induced by ischemia, which mimicked the effects of IP. The effect of 10(-5) mol/l U50,488H on infarct was significantly attenuated by blockade of protein kinase C (PKC) with specific PKC inhibitors, 5 x 10(-6) mol/l chelerythrine or 8 x 10(-7) mol/l calphostin C, as well as by blockade of ATP-sensitive K(+) (K(ATP)) channels with blockers of the channel, 10(-5) mol/l glibenclamide or 10(-4) mol/l 5-hydroxydecanoate. IP also reduced arrhythmia induced by ischemia. Nor-BNI, but not NTD, attenuated, while U50,488H, but not DADLE, mimicked the antiarrhythmic action of IP. In conclusion, the present study has provided first evidence that kappa-OR mediates the ameliorating effects of IP on infarct and arrhythmia induced by ischemia, whereas delta-OR mediates the effects only on infarct. Both PKC and K(ATP) channels mediate the effect of activation of kappa-OR on infarct.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed2001

Inducible HSP70 mediates delayed cardioprotection via U-50488H pretreatment in rat ventricular myocytes.

To test the hypothesis that heat-shock proteins (HSPs) mediate delayed cardioprotection of prior kappa-opioid receptor (kappa-OR) stimulation, we first correlated cellular injury and viability with the expression of HSP70s in isolated rat ventricular myocytes subjected to prior kappa-OR stimulation with the selective agonist trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide (U-50488H) and delayed lethal simulated ischemia (LSI). Cell injury and viability were indicated by lactate dehydrogenase release and trypan blue exclusion, respectively. The reduced injury and increased viability after pretreatment with U-50488H were concentration dependent and correlated directly with the expression of both stress-inducible (HSP70) and constitutive (HSC70) proteins. The effects mimic those with metabolic inhibition preconditioning (MIP). The cardioprotection against LSI by pretreatment with U-50488H and MIP was abolished and antagonized, respectively, via blockade of the kappa-OR by its selective antagonist, nor-binaltorphimine. We also found that blockade of the production of HSP70 but not HSC70 blocked the inhibitory effect of pretreatment with U-50488H on injury and viability. These observations provide evidence that stress-inducible HSP70 mediates delayed cardioprotection of prior kappa-OR stimulation.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed2001

Protein kinase C-epsilon is a trigger of delayed cardioprotection against myocardial ischemia of kappa-opioid receptor stimulation in rat ventricular myocytes.

Kappa-opioid receptor (OR) stimulation with a selective agonist, U50,488H (U50), known to mediate the delayed cardioprotection of metabolic inhibition preconditioning (MIP) against cell injury/death in rat ventricular myocytes, has been shown to act via protein kinase C (PKC). We attempted to identify the PKC isoform(s) that is activated, thus triggering delayed cardioprotection of MIP and pretreatment with 10 microM U50 (U50 pretreatment, UP). Release of lactate dehydrogenase and exclusion of trypan blue by isolated rat ventricular myocytes were used as indices of cell injury and death, respectively. Both MIP and UP induced translocation of PKC-epsilon, but not other PKC isoforms, -alpha and -delta, from cytosolic to membrane fractions. This was accompanied by reductions in cell injury/death induced by lethal simulated ischemia. The effects of MIP and UP were attenuated and abolished by 1 microM nor-binaltorphimine, a selective kappa-OR antagonist, administered before and during preconditioning/pretreatment, respectively. The effects were mimicked by 10 nM phorbol-12-myristate-13-acetate, a PKC activator, but attenuated by 5 microM chelerythrine, a PKC inhibitor. More importantly, 0.1 microM epsilonV1-2, a selective PKC-epsilon inhibitor administered before and during MIP/UP, also attenuated the effects of both treatments on cell injury/death and translocation of PKC-epsilon. On the other hand, 5 microM rottlerin, a selective PKC-delta inhibitor, did not alter the effects of either treatment on injury/death. The results indicate that both MIP and UP activate PKC-epsilon, leading to delayed cardioprotection in rat ventricular myocytes.

Acetophenones↗

PubMed2001

Signaling pathway mediated by kappa-opioid receptor is impaired in cardiac hypertrophy.

AIM: The responses of the intracellular calcium ([Ca2+]i) and the intracellular pH (pHi) to kappa-opioid receptor stimulation were determined in the single right ventricular myocytes isolated from the hearts of chronically hypoxic rats which exhibited right ventricular hypertrophy (RVH). METHODS: With the spectrofluorometric method, the electrically-induced [Ca2+]i transient and pHi were measured in myocytes loaded with fura-2 and BCECF [2',7'-bis-(2-carboxyethyl)-5-(and 6)-carboxyfluorscein], respectively. RESULTS: U50,488H, a selective kappa-opioid agonist decreased the electrically-induced [Ca2+]i transient and increased the pHi. The effect of U50,488H was mediated by protein kinase C (PKC). In the RVH, the effect of U50,488H on the [Ca2+]i transient and the pHi were significantly attenuated. In parallel, 4-phorbol 12-myristate 13-acetate (PMA), an activator of PKC, also decreased the [Ca2+]i transient and increased the pHi. In the RVH, the effects of PMA were blunted. The recovery of pHi, which was blocked by ethylisopropyl-amiloride (EIPA), following an acid loading induced by washout of 10 mmol/L NH4)Cl exposing to the cells for 10 min was the same in the RVH and control myocytes. CONCLUSION: kappa-Opioid receptor signaling was impaired in the cardiac hypertrophy due to a defect in the coupling of PKC signaling with its effector.

Animals↗

PubMed2000

kappa-Opioid receptor potentiates apoptosis via a phospholipase C pathway in the CNE2 human epithelial tumor cell line.

The mechanism by which kappa-opioid receptor (kappaor) modulated apoptosis was investigated in CNE2 human epithelial tumor cells. Induction of these cells to undergo apoptosis with staurosporine was associated with a massive increase in intracellular cAMP level. The inhibition of the increase in cAMP partially inhibited apoptosis as evidenced by a reduction of PARP and caspase-3 cleavage. Accordingly, a low but significant level of apoptosis is induced in these cells by the elevation of cAMP through the addition of forskolin and isobutylmethylxanthine. The existence of a cAMP-dependent and a cAMP-independent apoptotic pathway is therefore suggested. Receptor binding studies, RT-PCR experiments and Western blot analysis demonstrated the presence of type 1 kappaor in the CNE2 cells. Stimulation of kappaor in these cells resulted in the production of inositol (1,4,5)-trisphosphate, reduction of cAMP level and a marked enhancement of staurosporine-induced apoptosis. The potentiation of apoptosis by kappaor was prevented by inhibition of phospholipase C but was slightly enhanced by the presence of the active cAMP analogues, 8-CPT-cAMP and dibutyryl-cAMP. These data demonstrate for the first time that the phospholipase C pathway activated by type 1 kappaor expressed by cancer cells is involved in the potentiation of apoptosis.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed2000

HYAL1LUCA-1, a candidate tumor suppressor gene on chromosome 3p21.3, is inactivated in head and neck squamous cell carcinomas by aberrant splicing of pre-mRNA.

The hyaluronidase first isolated from human plasma, Hyal-1, is expressed in many somatic tissues. The Hyal-1 gene, HYAL1, also known as LUCA-1, maps to chromosome 3p21.3 within a candidate tumor suppressor gene locus defined by homozygous deletions and by functional tumor suppressor activity. Hemizygosity in this region occurs in many malignancies, including squamous cell carcinomas of the head and neck. We have investigated whether cell lines derived from such malignancies expressed Hyal-1 activity, using normal human keratinocytes as controls. Hyal-1 enzyme activity and protein were absent or markedly reduced in six of seven carcinoma cell lines examined. Comparative genomic and fluorescence in situ hybridization identified chromosomal deletions of one allele of HYAL1 in six of seven cell lines. Initial RT - PCR analyses demonstrated marked discrepancies between levels of HYAL1 mRNA and protein. Despite repeated sequence analyses, no mutations were found. However, two species of transcripts were identified when primers were used that included the 5' untranslated region. The predominant mRNA species did not correlate with protein translation and contained a retained intron. A second spliced form lacking this intron was found only in cell lines that produced Hyal-1 protein. Inactivation of HYAL1 in these tumor lines is a result of incomplete splicing of its pre-mRNA that appears to be epigenetic in nature. Oncogene (2000) 19, 870 - 877.

Alternative Splicing↗

PubMed2000

Hemorrhagic pyelitis, ureteritis, and cystitis secondary to cyclophosphamide: case report and review of the literature.

OBJECTIVE: Hemorrhagic cystitis is a well-known complication of cyclophosphamide therapy but extensive involvement of the entire urinary tract is far less common. We report here a patient who developed severe hemorrhagic pyelitis, ureteritis, and cystitis after one cycle of cyclophosphamide-containing combination chemotherapy. METHOD: A patient with synchronous carcinoma of the ovary and the uterus developed severe hemorrhagic pyelitis, ureteritis, and cystitis leading to bilateral hydronephroses and acute renal failure after one cycle of combination chemotherapy containing cyclophosphamide. The blood clots in the upper urinary tract were aspirated endoscopically and bilateral internal ureteric stents were inserted. RESULT: She underwent a prolonged diuretic phase with several episodes of hypokalemia, hypomagnesemia, and hypocalcemia and required intensive fluid and electrolytes replacement. Subsequently, she recovered fully with the ureteric stents removed 26 days later. CONCLUSION: In contrast to previous reports, where 2.8 g of cyclophosphamide was estimated to be the minimum cumulative dose required to cause hemorrhagic cystitis, this case illustrates that severe hemorrhagic complication can occur even after a low dose of cyclophosphamide (600 mg/m(2), total dose of 846 mg). Prompt diagnosis and intervention may be life-saving.

Antineoplastic Agents, Alkylating↗

PubMed2000

kappa -opioid receptor stimulation induces arrhythmia in the isolated rat heart via the protein kinase C/Na(+)-H(+)exchange pathway.

The present study attempted to determine whether the protein kinase C (PKC)/Na(+)-H(+)exchange (NHE) pathway would mediate the arrhythmogenic action of kappa -opioid receptor (OR) stimulation. We first determined the effects of U50,488H, a selective kappa -OR agonist, on PKC activity and cardiac rhythm in the isolated perfused rat heart, and intracellular pH (pH(i)), and Ca(2+)([Ca(2+)](i)) and Na(+)([Na(+)](i)) concentrations in the isolated ventricular myocyte. At 5-40 microm U50,488H concentration dependently increased the particulate PKC activity and pH(i), and induced arrhythmia. 40 microm U50,488H also increased [Na(+)](i)and [Ca(2+)](i). The arrhythmogenic effects of 40 microm U50,488H were abolished by nor-binaltorphimine, a selective kappa -OR antagonist. Blockade of PKC and NHE with respective blockers, 1 microm bisindolylmaleimide I or 0.5 microm calphostin C, and 1 microm 5-[N -methyl- N -isobutyl]amiloride or 1 microm 5-([N -ethyl- N -isopropopyl]amiloride, abolished and significantly attenuated, respectively, the effects of kappa -OR stimulation on pH(i), [Na(+)](i)and [Ca(2+)](i), and arrhythmia. To determine the role of pH(i), we observed U50,488H-induced arrhythmia at pH(i)6.8. At this pH(i), the pH(i)increased gradually both in the presence and absence of 40 microm U50,488H to a similar extent. While the increase in response to U50,488H was significantly less at pH(i)6.8 (from 0.09 to 0.10) than that at pH(i)7.1 (from 0.01 to 0.18), the arrhythmia induced by the agonist was the same at both high and low pHs. On the other hand, 5 microm monensin, a sodium ionophore, increased [Na(+)](i)and [Ca(2+)](i), and induced arrhythmia to similar extents as U50,488H. PKC and NHE inhibitors, that significantly attenuated the effects induced by U50,488H, had no effect on those induced by monensin. In conclusion, kappa -OR stimulation induces arrhythmia via PKC/NHE. [Na(+)](i)and [Ca(2+)](i), but not pH(i), may be directly responsible for arrhythmia induced by kappa -OR stimulation.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed2000

Impaired G(s)alpha and adenylyl cyclase cause beta-adrenoceptor desensitization in chronically hypoxic rat hearts.

The effects of beta-adrenoceptor stimulation with isoproterenol on electrically induced contraction and intracellular calcium ([Ca(2+)](i)) transient, and cAMP in myocytes from both hypertrophied right and nonhypertrophied left ventricles of rats exposed to 10% oxygen for 4 wk, were significantly attenuated. The increased [Ca(2+)](i) transient in response to cholera toxin was abolished, whereas increased cAMP after NaF significantly attenuated. The biologically active isoform, G(s)alpha-small (45 kDa), was reduced while the biologically inactive isoform, G(s)alpha-large (52 kDa), increased. The increased electrically induced [Ca(2+)](i) transient and cAMP with 10-100 microM forskolin were significantly attenuated in chronically hypoxic rats. The content of G(i)alpha(2), the predominant isoform of G(i) protein in the heart, was unchanged. Results indicate that impaired functions of G(s) protein and adenylyl cyclase cause beta-adrenoceptor desensitization. The impaired function of the G(s) protein may be due to reduced G(s)alpha-small and/or increased G(s)alpha-large, which does not result from changes in G(i) protein. Responses to all treatments were the same for right and left ventricles, indicating that the impaired cardiac functions are not secondary to cardiac hypertrophy.

Adenylyl Cyclases↗

PubMed2000

Impaired [Ca(2+)](i) and pH(i) responses to kappa-opioid receptor stimulation in the heart of chronically hypoxic rats.

kappa-Opioid receptor (kappa-OR) stimulation with U50,488H, a selective kappa-OR agonist, or activation of protein kinase C (PKC) with 4-phorbol 12-myristate 13-acetate (PMA), an activator of PKC, decreased the electrically induced intracellular Ca(2+) ([Ca(2+)](i)) transient and increased the intracellular pH (pH(i)) in single ventricular myocytes of rats subjected to 10% oxygen for 4 wk. The effects of U50,488H were abolished by nor-binaltorphimine, a selective kappa-OR antagonist, and calphostin C, a specific inhibitor of PKC, while the effects of PMA were abolished by calphostin C and ethylisopropylamiloride (EIPA), a potent Na(+)/H(+) exchange blocker. In both right hypertrophied and left nonhypertrophied ventricles of chronically hypoxic rats, the effects of U50,488H or PMA on [Ca(2+)](i) transient and pH(i) were significantly attenuated and completely abolished, respectively. Results are first evidence that the [Ca(2+)](i) and pH(i) responses to kappa-OR stimulation are attenuated in the chronically hypoxic rat heart, which may be due to reduced responses to PKC activation. Responses to all treatments were the same for right and left ventricles, indicating that the functional impairment is independent of hypertrophy. kappa-OR mRNA expression was the same in right and left ventricles of both normoxic and hypoxic rats, indicating no regional specificity.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed2000

The role of phosphodiesterase in mediating the effect of protein kinase C on cyclic AMP accumulation upon kappa-opioid receptor stimulation in the rat heart.

This study determined whether phosphodiesterase (PDE) was activated by protein kinase C (PKC) upon kappa-receptor stimulation, and if so, to identify the isozyme. We first studied the effects of trans-(+/-)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl] cyclohexyl) benzeneacetamide methanesulphonate (U50,488H), a selective kappa-opioid receptor (OR) agonist, and phorbol-12-myristate-13-acetate (PMA), a PKC activator, on cAMP accumulation and PDE activity in rat ventricular myocytes when PKC and PDE were inhibited by respective inhibitors. Like PMA, U50,488H decreased the forskolin-stimulated cAMP accumulation and dose-dependently stimulated the PDE activity, which were antagonized by 10(-6) M chelerythrine and bisindolylmaleimide I, selective PKC antagonists. In addition, 3-isobutyl-1-methylxanthine, a PDE inhibitor, dose-dependently attenuated the inhibition on forskolin-stimulated cAMP accumulation and abolished the stimulation on PDE activity by U50,488H and PMA. The observations suggest that PKC may enhance cAMP degradation through activating PDE upon kappa-OR stimulation. To identify the isozyme(s) mediating the effect of PKC upon kappa-OR stimulation, selective inhibitors were used. We found that 10(-5) M Ro-20-1724, a selective cAMP-specific PDE (PDE-IV) inhibitor, abolished the inhibitory effects of U50,488H and PMA, whereas 8-methoxymethyl-3-isobutyl-1-methylxanthine, erythro-9-(2-hydroxy-3-nonyl) adenine, cilostamide, and zaprinast, selective inhibitors of Ca(2+)/calmodulin-dependent PDE (PDE-I), cGMP-stimulated PDE (PDE-II), cGMP-inhibited PDE (PDE-III), and cGMP-specific PDE (PDE-V), respectively, had no effect. Moreover, rolipram, another selective PDE-IV inhibitor, also dose-dependently attenuated the inhibition on forskolin-stimulated cAMP accumulation and stimulation on PDE activity by U50,488H and PMA. In conclusion, this study has provided evidence for the first time that PKC and PDE-IV mediate the action of kappa-OR.

1-Methyl-3-isobutylxanthine↗

PubMed2000

Enhanced responses to 17beta-estradiol in rat hearts treated with isoproterenol: involvement of a cyclic AMP-dependent pathway.

We determined the effects of 17beta-estradiol, the most effective estrogen, acutely administered, on the heart/ventricular myocyte with or without treatment with isoproterenol (Iso). At 0.1 to 1 nM, 17beta-estradiol, which itself had no effect, reduced the heart rate and developed pressures in the isolated perfused heart treated with 10(-7) M Iso. One nanomolar 17beta-estradiol also inhibited the cyclic AMP (cAMP) production in Iso-treated ventricular myocytes. At 10 nM to 1 microM, 17beta-estradiol itself reduced the heart rate and incidence of ischemia/reperfusion-induced arrhythmias, with the exception of diastolic pressure. The effects of 17beta-estradiol on heart rate, systolic and mean pressures, and arrhythmias were significantly enhanced in the heart/ventricular myocyte treated with Iso. Tamoxifen, an estrogen receptor antagonist, did not antagonize the effect of 17beta-estradiol on the Ca(2+) current in ventricular myocytes treated with Iso, nor did it alter the effect of the hormone on the cAMP production augmented by Iso and forskolin. The effects of 17beta-estradiol on Ca(2+) current in the presence or absence of tamoxifen and/or Iso were similar in male rats, which do not possess the estrogen receptor, and female rats, which have the estrogen receptor. In conclusion, we have shown for the first time that estrogen at physiological concentrations modulates negatively the stimulatory actions of Iso on the heart rate and cardiac contractility. The effects may result from activation of an unknown membrane receptor and the adenylate cyclase/cAMP pathway, which enhances Ca(2+) influx across the L-type Ca(2+) channel.

Adrenergic beta-Agonists↗

PubMed2000

Cardiovascular actions of Radix Stephaniae Tetrandrae: a comparison with its main component, tetrandrine.

A comparison of the cardiovascular actions of the extract of Radix Stephaniae Tetrandrae (RST), the root of a Chinese hero Stephania tetrandra S Moore, in rats with those of tetrandrine (Tet), the best known active component of RST was reviewed. The RST extract inhibits Ca2+ influx into the myocyte and reduces protein release during reperfusion with a Ca2+ containing solution following perfusion with a Ca2+ free solution (Ca2+ paradox), and arrhythmia during reperfusion in the isolated perfused heart. It also reduces the infarct size induced by ischemia/reperfusion in vitro and in vivo. In addition, the RST extract suppresses elevation of arterial blood pressure in DOCA-salt hypertensive rats. It does not further reduce the heart rate and coronary flow significantly during myocardial ischemia. The effects are similar to those of Tet. When compared with the same doses of Tet alone, the RST extract, of which 9% is Tet, produces equally potent effects on infarction, arrhythmias, coronary flow and heart rate, and has a greater inhibitory effect on protein release during Ca2+ paradox. The combination at 1:1 ratio of Tet and fangchinoline (Fan), another main component, which constitutes 6% of the RST extract and has no significant effects on the heart, produces comparable effects on protein release during Ca2+ paradox as Tet alone. The observations suggest that the efficacy of the RST extract cannot be accounted for by Tet alone. Some of the effects may be due to an interaction between the components of the extract. The RST extract also produces similar effects as verapamil, a prototype Ca2+ channel antagonist widely used in the treatment of ischemic heart diseases and hypertension, except that verapamil, at 1 mumol/L, a concentration that produces similar cardiac effects as the RST extract, further reduces heart rate significantly during ischemia. So the RST extract may be a therapeutically better agent in the treatment of ischemic heart diseases and hypertension than Ca2+ channel antagonists because of the absence of the inhibitory effect on heart rate during myocardial ischemia.

Alkaloids↗

PubMed1999

Cardioprotection of preconditioning by metabolic inhibition in the rat ventricular myocyte. Involvement of kappa-opioid receptor.

To determine whether opioid receptors (ORs) are involved in the delayed cardioprotection of ischemic preconditioning (IP), the effect of severe metabolic inhibition (MI) with a glucose-free buffer that contained sodium cyanide and 2-deoxy-D-glucose on the viability of isolated rat ventricular myocytes was first determined 20 hours after preconditioning with a sublethal metabolic inhibition (MIP) with a glucose-free buffer that contained 2-deoxy-D-glucose and lactate for 30 minutes in the presence of OR antagonists. With the use of trypan blue exclusion as an index of cell viability, severe MI killed >60% of the cells and the value increased significantly after MIP. In the presence of 5x10(-6) mol/L nor-binaltorphimine (nor-BNI), a selective kappa-OR antagonist, but not 5x10(-6) mol/L CTOP, a selective mu-OR antagonist, or 5x10(-6) mol/L naltrindole, a selective delta-OR antagonist, the cardioprotection of MIP was significantly attenuated. To verify the role of kappa-OR, we studied the effects of severe MI after pretreatment with the kappa-OR agonist U50,488H (UP) for 30 minutes. U50,488H at 3x10(-6) to 1x10(-4) mol/L increased cell viability concentration-dependently with an EC50 of 3.311x10(-6) mol/L. In the presence of 5x10(-6) nor-BNI, the cardioprotection of UP (3x10(-5) mol/L) was blocked. A time course study showed that UP-induced cardioprotection occurred in 2 windows: the first occurred approximately 1 hour later and the other occurred 16 to 20 hours later. Additional studies on cell contraction and intracellular Ca2+ ([Ca2+]i) revealed that both UP and MIP attenuated the inhibitory effects of severe MI on contractility and electrically induced [Ca2+]i transient in single ventricular myocytes. On blockade of protein kinase C, the delayed cardioprotections of UP and MIP were significantly attenuated. In conclusion, the results of the present study have provided evidence that kappa-OR mediates the cardioprotection of MIP, which may involve protein kinase C and [Ca2+]i.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1999

Cross-talk between cardiac kappa-opioid and beta-adrenergic receptors in developing hypertensive rats.

The kappa-opioid receptor exerts a negative modulatory action on the beta-adrenoceptor and the action is blunted in adult spontaneously hypertensive rats (SHR). In order to determine whether the blunted negative modulation of the beta-adrenoceptor by the kappa-opioid receptor contributes to the development of hypertension, the electrically induced intracellular calcium ([Ca2+]i) transient was measured in single ventricular myocytes of SHR at 4, 6, 8 and 13-week-old and the age-matched Wistar Kyoto (WKY) rats. The electrically induced [Ca2+]i transients were augmented by norepinephrine (NE), a beta-adrenoceptor agonist, over four-fold in WKY rats of all ages studied and in SHR of 4 and 6 weeks of age. The enhancing effect of NE in 8- and 13-week-old SHR was, however, only approximately three-fold, significantly lower than the corresponding values in age-matched WKY rats. Similarly, the electrically induced [Ca2+]i transients were also augmented by forskolin, an activator of adenylate cyclase, by approximately two-fold in WKY rats of all ages and SHR aged 4 and 6 weeks. In SHR aged 8 and 13 weeks, the effect of forskolin was only 1.5-fold, significantly lower than the two-fold increase in the corresponding WKY rats. The enhancing effects of NE and forskolin were attenuated by U50,488H, a selective kappa-opioid agonist, by approximately 50 and 25%, respectively, in both types of rats of all ages studied, with the exception of 13-week-old rats. In rats of this age group, the attenuations by U50,488H on the enhancing effects of NE and forskolin were 17 and 9% in SHR, respectively, significantly less than the corresponding 54 and 29% in WKY. The fact that attenuation of U50,488H on the enhancing effects of NE and forskolin only occurs in 13-week-old SHR when hypertension has been fully developed indicates that the attenuated inhibitory modulation of kappa-opioid receptor stimulation does not contribute to the initiation of hypertension. Interestingly, the enhancing effects of NE and forskolin on the electrically induced [Ca2+]i transient was attenuated in SHR aged from 8 weeks when the blood pressure was rapidly increasing. The different time courses of altered responses to U50,488H, and NE and forskolin suggest that the attenuated negative modulation of kappa-receptor stimulation on the beta-adrenergic receptor is not due to the signal transduction pathway activated by beta-adrenergic stimulation. In 13-week-old SHR with the arterial blood pressure restored to normal by pharmacological manipulations, the blunted responses to NE, U50,488H and forskolin still occurred, indicating that the altered responses to activation of beta-adrenergic and kappa-opioid receptors and adenylate cyclase are not secondary to hypertension.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗