Silastic implants for delivery of oestradiol to mice

Silastic implants containing oestradiol were developed for delivering a range of physiological concentrations of oestradiol to mice over long periods. The implants consisted of discrete lengths of Silastic tubing containing oestradiol in arachis oil, with a small reservoir of the oestradiol solution at either end of the implant. Studies showed that the release of oestradiol in vitro was proportional to the concentration of steroid within the implant. Implants containing oestradiol at concentrations from 1 to 100 micrograms ml-1 could induce biological responses in ovariectomized mice, ranging from minimal effects on uterine weight and vaginal smears to supraphysiological increases in uterine weight and rapid vaginal cornification. Studies of uterine vascular permeability indicated that significant effects occurred within a few hours of initial placement of the implant. These results suggest that the design of the Silastic implants described in this study provides a useful method for delivering controlled and easily manipulated physiological doses of oestradiol to mice.