The discovery of the reversible antifertility action of an extract from Tripterygium
wilfordii both in male rats and in men in 1986 stimulated worldwide interest. International
and national collaborations aimed at the bioassay-directed sub-fractionation of materials
extracted from the plant was then organized and to date, a series of six male antifertility
diterpene epoxides have been isolated. Their chemical structures have been identified
and found to be triptolide, tripdiolide, triptolidenol, tripchlorolide, 16-hydroxytriptolide
and T7/19 (structure not yet published). At the ED95 dosage levels, they act mainly
on metamorphosing spermatids and testicular and epdidymal spermatozoa with exfoliation
and inhibition of basic nuclear protein turnover of late spermatids, delayed spermiation
and sperm head-tail separation and microtubule, microfilament and membrane damages.
A preliminary toxic evaluation indicated that these compounds were immunosuppressive
at dose levels 5-12 times their antifertility doses. Immuno-suppression is an important
weakness for an antifertility agent, but if the immuno-suppressive dose of a drug
is much higher than its antifertility dose, it could yet be regarded as a safe contraceptive.
Therefore, in the safety evaluation of compounds isolated from Tripterygium wilfordii,
it warrants our attention to probe deeply into their precise dose/immuno-effect relationship.