BIOCHEMICAL STUDY OF CHINESE RHUBARB ⅩⅫ. INHIBITORY EFFECT OF ANTHRAQUINONE DERIVATIVES ON Na⁺-K⁺-ATPase OF RABBIT RENAL MEDULLA AND THEIR DIURETIC ACTION

Inhibitory effect of anthraquinone derivatives isolated from Chinese rhubarb on Na⁺-K⁺-ATPase of rabbit renal medulla and their diuretic action were investigated. The diuretic, natriuretic and kaliuretic effects of emodin were increased by 5.9, 4.4 and 3.2 times compared with the control respectively during 9. to 4 h after p. o. administration, while that of rhein were increased by 5.8 4.6 and 3.9 times respectively. Aloe-emodin and chrysophanol only showed weak effects.Emodin, rhein and aloe-emodin exhibited strong competitive inhibition on Na⁺-K⁺-ATPase activity with IC₅₀ of 9.8 μg/ml, 11.0 μg/ml and 19.3 μg/ml and Ki value of 1.33×10^-6, 1.41×10^-6 and 7.41×10^-6 mol/L respectively. It seems that the diuresis of emodin and rhein are probably due to the inhibition of Na⁺-K⁺-ATPase actitvity.