THE WEANLING GUINEA PIG AS TEST OBJECT FOR ESTROGEN ASSAYS

Abstract

A method of assaying estrogen by hypodermic injn. of the vulvar region of weanling guinea pigs is here described. The technique is simple and the animals are not injured, hence need not be sacrificed. The endpoint consists of the disappearance of part or all of the vaginal closure membrane. The greater the dosage administered, the less time is required for the vagina to open and the more extensive is the involvement of the closure membrane. The threshold dose in these expts. was between 4 X 10-7 and 2 X 10-7 mg. of the estrogen. The normal adult [female] is less well adapted to the test than weanlings about 200 gs. in wt. Exploratory tests (not here detailed) indicate that the primed castrated adult [female] guinea pig is exceedingly sensitive; and since it may be used over and over, may prove to be the animal of choice for these assays. Indications are that progesterone in the normal cycle antagonizes estrogen, since, for example, in the preadolescent the vagina remains open for more than 2 wks., only about 4 days in the normal adult.