Estrogenic activity—
Dissolve a suitable quantity in
saline TS to obtain a test solution containing the equivalent of 1000 USP Chorionic Gonadotropin Units per mL. Into each of five rats that have been ovariectomized not less than 2 weeks previously, inject subcutaneously 0.25 mL of the test solution in the forenoon and in the afternoon of two successive days. On each of the three following days, take a vaginal smear from each animal: the requirements of the test are met if the cellular elements in the smears consist mainly of leucocytes, and a few nucleated epithelial cells, but no cornified epithelial cells.
Assay—
Standard preparations—
Dissolve a suitable quantity of USP Human Chorionic Gonadotropin RS in a diluent consisting of
saline TS, freshly prepared to contain 1 mg per mL of bovine serum albumin and adjusted with
sodium hydroxide TS to a pH between 6.9 and 8.0, to obtain a solution having a known concentration of 10 USP Chorionic Gonadotropin Units in each mL. Using the same diluent, prepare three
Standard preparations such that the respective concentrations of chorionic gonadotropin constitute a geometric series such as 1:1.2:1.44 or 1:2:4 and such that the activity in each mL lies within the range of 0.1 to 1.0 Unit.
Assay preparations—
Following the procedure outlined for the Standard preparations, prepare solutions of Chorionic Gonadotropin to obtain three Assay preparations corresponding to those of the Standard.
The animals—
Select 20- to 23-day-old female rats, but restrict the selection so that no rat is more than 30% heavier than the lightest. House the animals under uniform conditions of temperature, lighting, feeding, and watering. Mark the animals for identification, and divide them at random into groups of the same number but not fewer than 10 animals. Assign one group to each of the three Standard preparations and three Assay preparations, respectively.
Procedure—
Inject each rat subcutaneously in the dorsal area with 0.20 mL of the solution to which it was assigned, at approximately the same time on each of three consecutive days. On the afternoon of the fifth day, sacrifice the animals, and excise the uterus from each animal by cutting through the cervix, stripping off the surrounding tissue, and severing at the utero-tubal junction. Gently press out the uterine fluid on moistened absorbent paper, and weigh the uterus to the nearest 0.2 mg, using a suitable balance.
Calculation—
Tabulate the observed uterine weight for each rat, designated by the symbol
y, for each dosage group of
f rats. Proceed as directed in the
Assay under
Corticotropin Injection, beginning with “If the data from one or more rats.” Compute the log confidence interval
L (see
Confidence Intervals for Individual Assay 
111
). If the confidence interval is more than 0.1938, which corresponds at
P = 0.95 to confidence limits of 80% and 125% of the computed potency, repeat the assay until the combined data of two or more assays, redetermined as described under
Combination of Independent Assays 111, meet this limit.
