Factors to be Considered in Immature Female Rat Titration of Pregnancy Urine. ∗

Abstract

The induction of precocious sexual maturity in the female rat or mouse has been used extensively as the foundation for both qualitative and quantitative studies of the gonadotropic activity of blood and urine and of extracts made from these and other substances. Considerable difficulty has been experienced in this and other laboratories in the application of reactions associated with this maturity phenomenon. For the purpose of evaluating several of the criteria suggested for use in estimating the gonad-stimulating potency of urine, an extended series of titrations of pregnancy urines was conducted in immature female rats. Analysis of the data yields information concerning the relative sensitivity of ovarian, vaginal, and uterine reactions; the conditions limiting their reliability and indications for their use, separately or in combination, as endpoints.

Two lots of urine were titrated. One of these (P.U.A.) was a composite of specimens from pregnancies of 2 to 12 weeks' duration. The other (P.U.B.) was a complete 24-hour collection obtained at approximately the seventh week of gestation in a woman with no evidence of malignancy or endocrinopathy. The follicular hormone was extracted with ether. Doses of less than 1 cc. of urine were prepared by so diluting the stock that each lower dose contained one-half as much urine as the preceding one. The test doses were made up to a volume of 5 cc. per animal. Female rats, of a highly inbred strain, weighing 35 to 45 gm. at 24 days of age were given daily subcutaneous injections for 5 days. During the injection period, observations were made for vaginal opening with estrus. The degree and character of uterine and of ovarian response was recorded at necropsy on the sixth day.