Estrogen (a) and STX (b) significantly attenuate the body weight gain in female guinea pigs after ovariectomy. The female guinea pigs were ovariectomized (on day 0) and allowed to recover for 1 week before being given bi-daily subcutaneous injections of oil (OIL), estradiol benzoate (EB), or STX (see Materials and Methods). A two-way ANOVA (repeated measures) revealed an overall significant effect of both estrogen and STX (p < 0.001), and post hoc Newman–Keuls analysis revealed daily significant differences between estrogen and oil-treated, and STX and oil-treated groups (**p < 0.01). Bars represent the mean ± SEM of six and four animals per group for estrogen and STX treatment, respectively. c, Uteri are enlarged after estradiol, but not after STX or oil-vehicle treatment (inset). After the treatment period, the uteri of the guinea pigs were harvested and examined. There was a significant increase in uterine size after EB, compared with oil-vehicle or STX treatment. Bar graphs represent mean uterine weights. ***p < 0.001, EB versus oil-treated females; n = 6 guinea pigs/group.