Effects of 3′,4′-dihydroxyflavonol on vascular contractions of rat aortic rings

1. 3′,4′-Dihydroxyflavonol (DiOHF) is an effective vasodilator with anti-oxidant activity. The aim of the present study was to elucidate the effects of DiOHF on vascular contractions. 2. Contractile and relaxation responses were determined in rat endothelium-denuded aortic rings mounted in organ baths. In addition, the phosphorylation of myosin light chain (MLC ₂₀), myosin phosphatase targeting subunit 1 (MYPT1) and protein kinase C (PKC)-potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase of 17 kDa (CPI-17) was determined using western blot analaysis. Levels of GTP RhoA, as a marker of RhoA activation, were also measured. 3. Cumulative addition of increasing concentrations of NaF (3.0-12.0 mmol/L) or U46619 (1.0-1000 nmol/L) concentration-dependently increased vascular tension. These responses were inhibited by pretreatment of aortic rings with DiOHF (10, 30 or 100 μmol/L), which dose-dependently decreased vascular contractions induced by 8.0 mmol/L NaF, 30 nmol/L U46619, 0.1 μmol/L phenylephrine and 50 mmol/L KCl. 4. The K⁺ channel blockers 4-aminopyridine (3 mmol/L), charybdotoxin (10 nmol/L), apamin (500 nmol/L) and glibenclamide (10 μmol/L) had no effect on vascular relaxation induced by DiOHF (1-30 μmol/L). 5. At 30 μmol/L, DiOHF decreased the activation of RhoA and subsequent phosphorylation of MYPT1, CPI-17 and MLC₂₀ to almost basal levels. 6. In conclusion, DiOHF decreases vascular contraction at least partly by inhibition of the RhoA/Rho-kinase pathway in rat endothelium-denuded aorta. These results suggest that DiOHF may have therapeutic potential in the treatment of cardiovascular diseases.