Sex steroids interact in vitro with DNA and can act as "nongenotropic" factors, but the in vivo relevance of these mechanisms has been unclear. In October 25 Science, S. Kousteni and colleagues at the University of Arkansas for Medical Sciences, Little Rock, USA, show that sex steroids protect the adult murine skeleton through a mechanism that is distinct from that used to preserve the mass and function of reproductive organs (Science, 298:843-846, October 25, 2002).

Kousteni et al. used a synthetic ligand (4-estren-3,17β-diol) that reproduces the nongenotropic effects of sex steroids, without affecting classical transcription. They observed that this estren increased bone mass and strength in ovariectomized females above the level of the estrogen-replete state. The estren was at least as effective as dihydrotestosterone in orchidectomized males, without affecting reproductive organs.

"The favorable effects of estren on bone and its lack of effect on reproductive tissues...

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