Equol and other compounds from bovine urine as monoamine oxidase inhibitors.

Equol, its methylated derivative, and a carbazole, all isolated from bovine urine, are relatively potent inhibitors of monoamine oxidase with IC50 values of 158, 28, and 16 microM respectively (using 83 microM tyramine as substrate). The probable dietary origin of these compounds suggests that "natural" monoamine oxidase inhibitors may be more widespread than had previously been suspected.