Endogenous lignans--a potential endogenous digitalis.

Lignans are natural products formed by oxidative dimerization of monomeric phenols. A few were recently discovered in human and animal urine, semen and blood plasma but their role has never been assessed. We investigated the actions of mammalian lignans obtained by total synthesis or extracted from the urine of pregnant women, on the Na+K+-pump in human red cells. Some of the tested lignans (enterolactone, prestegane B and 3-O-methylenterolactone) inhibited the Na+K+-pump activity with IC50 ranging from 5 to 9 X 10(-4) mol/l. The IC50 for ouabain (7 X 10(-7) mol/l) was not modified by addition of lignans suggesting a non-competitive inhibition.