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Excretion and binding of tritium-labelled oestradiol in mice (Mus musculus): implications for the Bruce effect

Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ontario, Canada L8S 4K1

Correspondence should be addressed to D deCatanzaro; Email: decatanz{at}mcmaster.ca

Male mouse urine contains 17β-oestradiol (E₂) and other steroids. Given that males actively direct urine at proximate females and intrauterine implantation of blastocysts is vulnerable to minute amounts of exogenous oestrogens, males' capacity to disrupt early pregnancy could be mediated by steroids in their urine. When male mice were implanted with osmotic pumps containing tritium-labelled E₂ (³H-E₂) or injected i.p. with ³H-E₂, radioactivity was reliably detected in their urine. Following intranasal administration of ³H-E₂ to inseminated females, radioactivity was detected in diverse tissue samples, with there being significantly more in reproductive tissues than in brain tissues. When urine was taken from males injected with ³H-E₂, and then intranasally administered to inseminated females, radioactivity was detected in the uterus, olfactory bulbs, and mesencephalon and diencephalon (MC+DC). When inseminated and ovariectomised females were perfused at the point of killing to remove blood from tissues, more radioactivity was detected in the uterus than in muscle, olfactory bulbs, MC+DC and cerebral cortex. Pre-treatment with unlabelled E₂ significantly reduced the uptake of ³H-E₂ in the uterus. Taken with evidence that males deliver their urine to the nasal area of females, these results indicate that male urinary E₂ arrives in tissues, including the uterus, where it could lead to the disruption of blastocyst implantation.