Identification of low molecular weight immunosuppressor molecules in human in vitro fertilization supernatants predictive of implantation as a polyamine—possibly spermine**Supported by grant MA 9707 from the Medical Research Council of Canada, Ottawa, Ontario, Canada; and by Natural Sciences and Engineering Research Council, Ottawa, Ontario, Canada.††Presented in part at the 35th Annual Meeting of the Canadian Fertility and Andrology Society, Vancouver, British Columbia, Canada, November 8 to 11, 1989.

Suppressor activity in in vitro fertilization (IVF) culture medium correlates with successful implantation. High performance liquid chromatography fractionation revealed peak(s) of inhibitory activity in the 1,000- to 5,000-Da molecular weight range. Inhibitory activity was dependent on the presence of fetal bovine serum (FBS) and was abrogated both by heat treatment of the serum and by pretreatment with monoamine oxidase inhibitors. Spermine becomes toxic when oxidized by monoamine oxidase to spermine dialdehyde or acrolein. Spermine also shows suppressive activity in the same molecular weight range as IVF supernatants. These data suggest IVF-associated inhibitory activity may be attributable to oxidation of a polyamine, possibly spermine, by monoamine oxidase in FBS. The biological significance is discussed.