AIM: With the changes of vascular tension as the index, this study was aimed to investigate the effect of genistein and 17β-estradiol
on cardio-vessel and study the correlated mechanisms. METHODS: ① The
experiment were completed at Functional Laboratory of Hunan College from April to October 2005. All of the selective animals were male mongreal dogs. Hearts were collected from a local abattoir and rinsed in cold modified Krebs-Henseleit solution. Genistein (a phytoestrogen existing in soy bean), 17β-estradiol, indomethacin, Nω-L-nitro-arginine, Cycloheximide, Prostaglandin F2α and bradykinin, and sodium orthovanadate were all purchase from Sigma Company Methylene blue was obtained from Runjie Chemistry Reagent Co. Ltd. (Shanghai) and dissolved in distilled water. Genistein, 17β-estradiol and Tamoxifen were dissolved in dimethylsulfoxide (Me2SO). Indomethacin was dissolved in an ethanol solution with 0.2 volume fraction. ② Coronary rings were prepared and then mounted in the organ bath, the experiments were carried through as follow: Relaxant effects of genistein and 17β-estradiol on KCl- contraction response of isolated coronary arteries: Samples were allowed an equilibration period of 30 minutes and treated with 50 mmol/L KCl and washed out with Krebs-Henseleit solution when contractile responses had reached a stable plateau. Then the solution was changed every 20 minutes. After 30 minutes equilibration, the experiment above was repeated, cumulative concentrations 1, 4, 8, 40 and 80 μmol/L were applied, the arterial ring tension changes were observed. Effects of various inhibitors and
endothelium on two estrogens' relaxant response of isolated coronary arteries: The experiment above was repeated and rings were sluiced out with Krebs-Henseleit solution, then the solution was changed at the interval of 20 minutes. After 1.5 hours equilibration, inhibitor of nitric oxide synthase Nω-L-nitro-arginine 1×10-4 mol/L, sodium orthovanadate 1×10-5 mol/L, cycloheximide 1×10-5 mol/L, indomethacin 1×10-5 mol/L, tamoxifen 1×10-5 mol/L were added respectively 15 minutes prior to the experiment above being repeated or endothelium removed by gentle rubbing with a cotton lot, and compared with earlier work. ③ Antagonist concentration were determined with linear regression when agonist effect decreased 50%. Students' t-test was used for comparing two groups. When three or more groups were compared, one-way analysis of variance was used. RESULTS: ① Similarly to 17β-estradiol, genistein could dose-dependently attenuate 50 mmol/L KCl elicited-contraction in canine coronary rings (r = 0.96, P < 0.01) with antagonist concentration of (16.37±5.19) μmol/L and (22.64±8.26) μmol/L respectively, when agonist effect decreased 50%. ② After incubation with inhibitor of nitric oxide synthase Nω-L-nitro-arginine 1×10-4 mol/L, Methylene blue (MB) 1×10-5 mol/L and sodium orthovanadate (SOV) 1×10-5 mol/L, genistein induced-relaxation had no change (P > 0.05), however, 17β-estradiol induced-relaxation decreased significantly (P < 0.01). Indomethacin (INDO) 1×10-5 mol/L, cycloheximide (CYC) and tamoxifen (TAM) failed to affect the relaxant responses of both estrogens (P > 0.05).CONCLUSION: ① The relaxations induced by genistein and 17β-estradiol in isolated coronary rings are not related to prostaglandins and the conventional estrogen receptor as well as the genomic pathways. ② The vasorelaxant effect of 17β-estradiol is probably endothelium-dependent and related to NO partly. ③ Tyrosine protein kinase may play a role in the control of coronary vascular tone.