Nitric Oxide Could Extend Fertility

The finding, by investigators at Wayne State University School ofMedicine in Detroit, was published in the Aug. 30 issue of the AmericanChemical Society's journal Biochemistry.

In their laboratory study, Anuradha Goud and colleagues gatheredmore than 1,500 eggs from mouse ovarian ducts one to two hours or fourto six hours after ovulation. Mouse eggs that aren't fertilized withinhours of ovulation begin to age rapidly. After about six hours, theseeggs are less likely to be fertilized properly, leading to chromosomalabnormalities in the embryos.

To prevent this, the researchers exposed the eggs to varyingconcentrations of nitric oxide, a multipurpose signaling molecule that,among other things, helps keep arteries supple and helps men achieveerections. In the "older" eggs, the compound appeared to slow thehardening of the eggs' outer shells, diminish the activity of ooplasmicmicrotubules (the structures that attach to chromosomes and guide themto different parts of a cell during division), increase the release ofcortical granules (the molecules responsible for preventing eggfertilization by more than one sperm) and delay other signs of aging.

In addition to possibly extending fertility in women, theresults suggest that nitric oxide could help prevent chromosome errorsduring early embryonic development. These errors can lead to Downsyndrome, spontaneous miscarriages and other problems associated withpregnancies later in life.

"Eggs from older women may be particularly sensitive to agingafter they are released from the ovaries," said Husam Abu-Soud, Ph.D.,a Wayne State University researcher and co-author of the study. "As aresult, the time available for optimal fertilization of these women'seggs may be quite a bit shorter than the time frame in younger women."But exposing the eggs to appropriate levels of nitric oxide "couldextend this fertilizable time window in both old and young women," hespeculates. The results also raise the possibility that nitric oxidecould be used to enhance the fertility of eggs harvested for use duringin vitro fertilization.

Although it is unclear how nitric oxide produced theseresults, the researchers theorize that the compound may preventirregularities in calcium release within the eggs. These irregularitieshave been linked to aging of mammalian eggs.

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