Sterilization of Silastic Capsules Containing 17β-Estradiol for Effective Hormone Delivery in Mus musculus.

Silastic capsules are frequently used to study the physiologic effects of estrogen exposure in animal models. The Officeof Laboratory Animal Welfare requires the sterilization of nonpharmaceutical-grade compounds before use. We compared 2commonly used terminal sterilization methods-ionizing radiation (IR) and ethylene oxide (EO)-for their utility in sterilizingsilastic capsules containing 0.05 or 0.1 mg 17β-estradiol (E2). E2-specific ELISA demonstrated that serum estrogen levelsdid not differ between mice implanted with 0.05-mg E2 capsules that were sterilized with IR or EO and those implanted withnonsterilized capsules. Likewise, mammary gland morphology and progesterone receptor expression and proliferation inmammary epithelium were similar among mice treated with E2 capsules, regardless of sterilization method, and pregnant day15 mice. In addition, IR-sterilized 0.1-mg E2 pellets provided high serum E2. We conclude that neither ionizing radiation norethylene oxide degraded E2 or the cellulose matrix, suggesting that these methods of sterilization are appropriate to provideeffective sterile hormone capsules for animal research.