Relaxant effect of an estrone derivate EA303 on isolated colonic smooth muscle of rabbits

Aim To study the effect and mechanism of estrone EA303 on isolated ascular smooth muscle of rabbits.Methods we investigated the effect of EA303 on the isolate aorta contracted by noradrenalin(NE),high-K+ solution and CaCl2.Moreover,the activity of EA303 was investigated by comparing with verapamil,a well-known calcium antagonist.To assess whether the spasmolytic activity of EA303 was through ATP-sensitive potassium channels blockade,the smooth muscle preparations from rabbits were exposed to glibenclamide(10-5mol·L-1) and the effects on the preparations contracted by KCl and NE were observed.Results In concentration between 3×10-5 and 3.0×10-3mol·L-1,EA303 concentration dependently relaxed NE and high-K+ induced contractions.At the concentration of 1.0×10-5mol·L-1,EA303 caused a dose-dependent rightward shift in the Ca2+ dose-response curve which was similar to verapamil.When exposed to glibenclamide,the relaxing effect of EA303 on the preparation contracted by KCl,NE was obviously inhibited.Conclusion EA303 has the effect of relaxing the isolated ascular smooth muscle of rabbits and it seems that EA303 may act on smooth muscle as a K+ channel blocker and inhibiter of calcium release from calcium store.