The Uterotrophic Bioassay is an in vivo short-term screening test. It is based on the increase in uterine weight or uterotrophic response.

The Uterotrophic Bioassay relies for its sensitivity on an animal test system in which the hypothalamic-pituitary-ovarian axis is not functional. Two oestrogen sensitive states in the female rodent meet this requirement: i) immature females after weaning and prior to puberty and ii) young adult females after ovariectomy with adequate time for uterine tissues to regress. The test substance is administered daily by oral gavage or subcutaneous injection. Each treated and control group should include at least 6 animals. Graduated test substance doses are administered to a minimum of two treatment groups of experimental animals using one dose level per group and an administration period of three consecutive days for immature method and a minimum administration period of three consecutive days for ovx-adult method. The animals are necropsied approximately 24 hours after the last dose. For oestrogen agonists, the mean uterine weight of the treated animal groups relative to the vehicle group is assessed for a statistically significant increase. A statistically significant increase in the mean uterine weight of a test group indicates a positive response in this bioassay. The report should include: the daily body weights, the daily record of status of animal, the wet and blotted uterine weight, the daily food consumption.