Abstract
Summary
The duration of effectiveness of a single injection of aqueous suspensions of a crystalline ketonic estrogen preparation of 60, 100, 200 and 325 mesh particle size was compared with that of an oil solution of the same preparation. The dosages of the suspensions were varied from 50 I.U. to 2,000 I.U. Uterine weight or estrus smear were used as the criteria of effectiveness of the estrogens. 800 rats were used in the vaginal smear studies.
With the larger sized particles (60 and 100 mesh) 100 I.U. were as effective as 10,000 I.U. in oil solution. When the dosage level of 400 I.U. was used, estrus was maintained in 50% of the rats for 19 days with 60 mesh particles, 14 days with 100 mesh particles, 8 days with 200 mesh particles and 5-6 days with 325 mesh particles. Further increase in dosage levels up to 2,000 I.U. did not increase the duration of the estrus. This indicates the primary importance of particle size with this estrogen in controlling the duration of its effectiveness.
We wish to acknowledge the cooperation of Dr. R. F. Varney of the Biological Control Department in these studies.
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