Pharmacological Evaluation of Ocoteine, Isolated from Cassytha Filiformis, as an α_1 : Adrenoceptor Antagonist in Rat Thoracic Aorta

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Abstract

Ocoteine, isolated from Cassytha filiformis, was found to be an α<SUB>1</SUB>-adrenoceptor blocking agent in rat thoracic aorta as revealed by its competitive antagonism of phenylephrine-induced vasoconstriction (pA<SUB>2</SUB>=7.67±0.09). Removal of endothelium from the aorta did not affect its antagonistic potency (pA<SUB>2</SUB>=7.97±0.07). [<SUP>3</SUP>H]-Inositol monophosphate formation caused by noradrenaline (3 μM) was suppressed by ocoteine (10 μM) and prazosin (3 μM). Ocoteine did not affect the contraction induced by U46619, prostaglandin F<SUB>2α</SUB> or angiotensin II, but inhibited slightly those by high K<SUP>+</SUP> and endothelin I. Neither the cyclic AMP nor cyclic GMP content of rat thoracic aorta was changed by ocoteine (10 μM). Comparing the EC<SUB>50</SUB> values, the potency of ocoteine against 5-hydroxytryptamine (5-HT) was about 60 times less than that against phenylephrine. Ocoteine (10 μM)also slightly antagonized the clonidine-induced inhibition of the twitch response evoked by field stimulation in rat vas deferens. In guinea pig trachea, the contraction caused by carbachol, histamine, neurokinin A or leukotriene C<SUB>4</SUB> and β<SUB>2</SUB>-adrenoceptor-mediated relaxing responses induced by isoprenaline were not affected by ocoteine (10 μM). The voltage clamp study in rat ventricular single myocytes revealed that ocoteine (3, 10 μM) inhibited steady state outward currents, but not transient outward currents or slow inward Ca<SUP>2+</SUP> currents. It is concluded that ocoteine is a selective α<SUB>1</SUB>-adrenoceptor antagonist in isolated rat thoracic aorta. At high concentrations, it also blocks 5-HT receptors and Na<SUP>+</SUP> and steady state outward currents in rat ventricular myocytes.

Journal

  • The Japanese Journal of Pharmacology

    The Japanese Journal of Pharmacology 73(3), 207-214, 1997-03-01

    The Japanese Pharmacological Society

References:  33

Codes

  • NII Article ID (NAID)
    10008677380
  • NII NACSIS-CAT ID (NCID)
    AA00691188
  • Text Lang
    ENG
  • Article Type
    ART
  • ISSN
    00215198
  • NDL Article ID
    4196915
  • NDL Source Classification
    ZS51(科学技術--薬学)
  • NDL Call No.
    Z53-D199
  • Data Source
    CJP  NDL  J-STAGE 
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