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|Title:||Vascular myorelaxing activity of isolates from South African Hyacinthaceae partly mediated by activation of soluble guanylyl cyclase||Authors:||Fusi, Fabio
CROUCH N., R
MULHOLLAND D., A
|Issue Date:||2008||Project:||None||Journal:||JOURNAL OF PHARMACY AND PHARMACOLOGY||Abstract:||
The vasorelaxing effect of isolates (compounds 1, 2, 3, and 4 (homoisoflavanones), compound 5 (sesquiterpenoid), compounds 6 and 7 (bufadienolides)) from the South African Hyacinthaceae has been assessed using rat aortic ring preparations. Compounds 2, 3, and 4 inhibited the tonic contraction induced by both 60 mM K(+) (K60) and phenylephrine, compound 3 being the most potent. Compounds 5, 6, and 7 caused a modest concentration-dependent relaxation, whereas compound 1 was ineffective. Under K25- or K60-induced depolarization, compound 3 displayed antispasmodic effects not reversed by tetraethylammonium. Under precontraction induced with phenylephrine, compound 3 shifted to the left the concentration-relaxation curves of either isoprenaline or sodium nitroprusside. 1 H-[1,2,4] oxidazolol [4,3-a] quinoxalin-1-one shifted to the right the concentration-relaxation curve of compound 3, while 3'-isobutyl-1-methylxanthine had no effect. In the absence of extracellular Ca(2+), compound 3 (estimated pIC50 = 4.66) and ryanodine reduced the response to phenylephrine. Phenylephrine-stimulated influx of extracellular Ca(2+) was markedly reduced when tissues were pretreated with compound 3 (pIC50 = 5.14) or nifedipine, but stimulated by ryanodine. Compound 3 partially antagonized the contraction induced by phorbol 12-myristate-13-acetate. To our knowledge, this has been the first account describing the vasodilating activity of homoisoflavonoids: compound 3 proved an effective vasorelaxing agent, partly acting via the activation of soluble guanylyl cyclase.
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