Activation of iberiotoxin-sensitive, Ca2+-activated K+ channels of porcine isolated left anterior descending coronary artery by diosgenin

The objective of this study was to determine the vasodilating effect of 3beta-hydroxy-5-spirostene (diosgenin), a phytoestrogen found in wild yams, using porcine resistance left anterior descending coronary artery. In 5-hydroxytryptamine (3 muM) pre-contracted preparation, diosgenin caused a concentration-dependent (0.01 to 1 muM), endothelium-independent relaxation, with a maximum relaxation of similar to72% at 1 muM. No apparent effect was observed with 17beta-oestradiol and progesterone with concentrations less than or equal to0.3 muM, and a relaxation of similar to15% and similar to23% caused by 17beta-oestradiol (1 muM) and progesterone (1 muM), respectively. Diosgenin-elicited relaxation was not altered by 7alpha,17beta-[9[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol (ICI 182,780), mifepristone, (+)-bicuculline, cis-N-(2-phenylcyclopentyl)azacyclotridec-1-en-2-amine (MDL 12330A), glibenclamide and scavengers of reactive oxygen species. The iberiotoxin-sensitive, Ca2+-activated K+ (BKCa) current of single vascular myocytes recorded, using patch-clamp techniques, was markedly enhanced by diosgenin, 17beta-oestradiol and progesterone. Application of (9S, 10R, 12R)-2,3,9,10,11,12-hexahydro-10-methoxy-2,9-dimethyl-1-exo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid methyl ester (KT 5823, 300 nM) eradicated the enhancement of BKCa amplitude. Diosgenin, 17beta-oestradiol and progesterone did not affect whereas phloretin, biochanin A and zearalanone (1 muM each) significantly suppressed [Ca2+](o)-induced contraction. In oestrogen competition essay using human breast cancer cell (MCF-7 cells), diosgenin (0.001 nM to 10 muM) did not interact with oestrogen receptor-alpha, and no displacement of [H-3]17beta-oestradiol was observed. In oestrogen receptor alpha- and beta-fluorescence polarization competitor assay, diosgenin (100 muM) demonstrated a greater competition with the beta-isoform of oestrogen receptor. These results suggest that diosgenin caused an acute, endothelium-independent coronary artery relaxation via protein kinase G signalling cascade and an activation of BKCa channel of arterial smooth muscle cells. The oestrogen receptor (alpha and beta-isoforms) and progesterone receptor are probably not involved. (C) 2004 Elsevier B.V. All rights reserved.