Gossypol has been proven to be a very effective male contraceptive. However, clinical trials showed that the major side effect of gossypol was hypokalemia. Gossypol occurs naturally as enantiomeric mixtures of (+)-gossypol and (-)-gossypol. The (-)-gossypol is found to be the active component of antifertility. 11beta-Hydroxysteroid dehydrogenase 2 (11betaHSD2) has been demonstrated to be a mineralocorticoid receptor (MR) protector by inactivating active glucocorticoids including corticosterone (CORT) in rats, and therefore mutation or suppression of 11betaHSD2 causes hypokalemia and hypertension. In the present study, the potency of gossypol enantiomers was tested for the inhibition of 11betaHSD1 and 2 in rat and human. Both (+) and (-)-gossypols showed a potent inhibition of 11betaHSD2 with the half maximal inhibitory concentration (IC(50)) of 0.61 and 1.33 microM for (+) and (-)-gossypols, respectively in rats and 1.05 and 1.90 microM for (+) and (-)-gossypols, respectively in human. The potency of gossypol to inhibit 11betaHSD1 was far less; the IC(50) was > or =100 microM for racemic gossypol. The gossypol-induced hypokalemia is likely associated with its potent inhibition of kidney 11betaHSD2.