Effects of age and weaning on the immature rat uterotrophic assay using ethynylestradiol

The intact immature rodent uterotrophic bioassay: possible effects on assay sensitivity of vomeronasal signals from male rodents and strain differences

The vomeronasal organ in rodents is an important social and sexual signaling pathway. We have investigated whether the housing of intact immature females in close proximity to mature males would interfere with the sensitivity of the immature rodent uterotrophic bioassay as the result of vomeronasal signals transmitted by male urinary proteins. The hypothesis was that the proximity of males might induce early puberty, thereby increasing mean uterine weight and reducing the responsiveness of the assay. The hypothesis was tested in both rats and mice by housing mature males above immature females, separated only by a wire screen, for 3 days and determining possible changes in uterine weight. The results were negative. Neither the mean uterine weight nor the group mean standard deviation of the uterine weights were changed in the uterotrophic bioassay. Given that the timing of sexual maturation may vary with the strain of mouse used, we also evaluated the sensitivity of the immature mouse uterotrophic assay to diethylstilbestrol (DES) using four strains of mice. Similar sensitivity was observed for the CD-1, C57Bl6, and Alpk strains, but B6CBF(1) mice were marginally less sensitive to DES than were the other strains. These findings add to earlier data indicating the robustness of the rodent uterotrophic assay protocol.