A quantitative test for oestrogenic activity using rat endometrium lactate dehydrogenase

In ovariectomized rats treatment with ethinyloestradiol (EOe) po started 1 week after castration and given for 4 days resulted in an increase of endometrial lactate dehydrogenase per DNA (LDH/DNA). The lambda of the dose-response curve was 0.178. In subsequent experiments EOe was used as a standard and the oestrogenic activity of four steroids given po was compared. The effect of testosterone was studied using oestradiol as a standard. If the activity of EOe is 1, the relative oestrogenic potencies of oestriol succinate, oestradiol decanoate, 11 beta-methyoxymethyl-17 alpha-ethinyl-delta 1,3,5(10)-oestratriene-3,17 beta-diol and 11 beta-methoxymethyl-delta 1,3,5(10)-oestratriene-3,16 alpha,17 beta-triol were 0.074, 0.7, 12.5 and 32, respectively. The results of the test were compared with the relative potencies of these four compounds in two biological tests, viz. the vaginal cornification in ovariectomized adult rats and stimulation of the uterine growth in immature intact rats. The relative oestrogenic potencies as measured by an increase in the endometrial LDH/DNA were in better agreement with those found in the vaginal cornification assay than with those in the uterine growth stimulation test. Testosterone caused no significant changes of LDH/DNA. We conclude that the increase in LDH/DNA in the endometrium of ovariectomized rats can be used as a quantitative assay for oestrogenic potency.