thromboxane-a2 and daidzein

The present study was undertaken to determine whether treatment with genistein, the plant-derived estrogen-like compound influences agonist-induced vascular smooth muscle contraction and, if so, to investigate related mechanisms. The measurement of isometric contractions using a computerized data acquisition system was combined with molecular experiments. Genistein completely inhibited KCl-, phorbol ester-, phenylephrine-, fluoride- and thromboxane A(2)-induced contractions. An inactive analogue, daidzein, completely inhibited only fluoride-induced contraction regardless of endothelial function, suggesting some difference between the mechanisms of RhoA/Rho-kinase activators such as fluoride and thromboxane A(2). Furthermore, genistein and daidzein each significantly decreased phosphorylation of MYPT1 at Thr855 had been induced by a thromboxane A(2) mimetic. Interestingly, iberiotoxin, a blocker of large-conductance calcium-activated potassium channels, did not inhibit the relaxation response to genistein or daidzein in denuded aortic rings precontracted with fluoride. In conclusion, genistein or daidzein elicit similar relaxing responses in fluoride-induced contractions, regardless of tyrosine kinase inhibition or endothelial function, and the relaxation caused by genistein or daidzein was not antagonized by large conductance K(Ca)-channel inhibitors in the denuded muscle. This suggests that the RhoA/Rho-kinase pathway rather than K(+)-channels are involved in the genistein-induced vasodilation. In addition, based on molecular and physiological results, only one vasoconstrictor fluoride seems to be a full RhoA/Rho-kinase activator; the others are partial activators.

Topics: Animals; Aorta; Blotting, Western; Carcinogens; Cardiotonic Agents; Genistein; Isoflavones; Male; Muscle Contraction; Muscle Relaxation; Peptides; Phenylephrine; Phorbol Esters; Phosphorylation; Phytoestrogens; Potassium Channel Blockers; Potassium Channels, Calcium-Activated; Potassium Chloride; Protein Phosphatase 1; Rats; Rats, Sprague-Dawley; rhoA GTP-Binding Protein; Sodium Fluoride; Thromboxane A2; Toxins, Biological

An isoflavone compound, genistein, which is known as a protein tyrosine kinase inhibitor, concentration-dependently (0.1-30 micrograms/ml) suppressed human platelet aggregation, serotonin secretion, and protein tyrosine phosphorylation induced by collagen or stable thromboxane A2 analogs [U46619 and 9,11-epithio-11,12-methano-thromboxane A2 (STA2)]. However, genistein did not inhibit these thrombin (0.1 unit/ml)-induced platelet responses. Although thrombin induced an increase in the platelet phosphotyrosine content, genistein at 100 micrograms/ml only slightly attenuated thrombin-induced protein tyrosine phosphorylation. Genistein competitively inhibited [3H]U46619 binding to washed platelets, in a concentration-dependent fashion. Daidzein (another isoflavone compound), which does not have a hydroxyl group at the 5-position of genistein and lacks inhibitory activity for protein tyrosine kinase, was found to suppress [3H]U46619 binding, leading to the inhibition of collagen- or STA2-induced platelet responses. These results indicate that the blockage by genistein of platelet responses induced by collagen or thromboxane A2 is due to its preventive action on thromboxane A2 binding to the receptor, rather than via inhibition of protein tyrosine phosphorylation, and that the drug does not appear to be a particularly good inhibitor of tyrosine phosphorylation in intact platelets.

Topics: Anti-Bacterial Agents; Benzoquinones; Blood Platelets; Cinnamates; Genistein; Humans; Isoflavones; Lactams, Macrocyclic; Phospholipids; Phosphorylation; Platelet Activation; Platelet Aggregation; Platelet Aggregation Inhibitors; Protein-Tyrosine Kinases; Quinones; Rifabutin; Serotonin; Signal Transduction; Sulfides; Thromboxane A2; Tyrosine