[The effects of digitalis compounds on K(+)-induced relaxation in aortic rings].

It has been shown that, changes in the structure of the cardiac glycoside, are related to changes in their biological effects. In the present study we compared the effects of two structurally different digitalis compound (ouabain and ouabagenin), on K+ induced vascular relaxation as an index of the Na+K+ ATPase activity. Ouabain was the most potent compound tested, and had vasoconstrictor effect on the rat aortic rings, as, well as inhibitory effect on the K(+)-induced relaxation. Ouabagenin did not affect either the vascular tone or K(+)-induced relaxation. It is well known that changes in the part of the structure of the cardiac glycoside that contain the sugar, are important to maintain some of their biological effects. In this paper we demonstrate that elimination of the 1-rhamnose in ouabagenin reduces its vascular effects associated to the inhibition of the Na+ K+ ATPase pump.