The effect of phenolphthalein and other purgative drugs on rat intestinal (Na + + K +) adenosine triphosphatase

Abstract

Phenolphthalein noncompetitively inhibited the (Na + + K +)-adenosine triphosphatase (ATPase) activity of microsomes from the rat small intestine ( K i = 6 × 10 −5 M). Quinone, hydroquinone and the purgative drugs, danthron and bisacodyl, were also inhibitory at 10 −4 M, while phlorizin, phenolphthalein disulfate and phenolphthalein monoglucuronide were without effect. It is suggested that inhibition of intestinal sodium transport by purgative drugs results from inhibition of intestinal (Na + + K +)-ATPase. Since danthron inhibited the intestinal (Na + + K +)-ATPase, but did not affect glucose transport across the intestine, it appeared unlikely that (Na + + K +)-ATPase was directly involved in glucose transport.