Controlled release of estradiol-17β and bisphenol A from a silicone tube for long-term administration in mice

Silicone tubes filled with estradiol-17 beta (E2) or the xenestrogen, bisphenol A (BPA) were covered with a polyethylene tube and implanted into mice subcutaneously The releasing patterns from the tube in vivo were obtained from the volume of estrogen remaining in the tube by measurement with high performance lipid chromatography. E2 in glycerol was released in a few days from a silicone tube, which was not covered with a polyethylene tube (Type A). However, E2 in sesame oil was released very slowly from the silicone tube covered with a polyethylene tube (Type B) and approximately 10% of E2 remained in the tube at 56days after implantation into the mice. The mean linear regression equation for E2 was Y = 70.967 - 1.2271 X (R-2 = 0.9268) and the quadratic regression equation was Y = 77.97-2.2773X + 0.0194 x 2 (R-2 = 0.9864). The remainder rate curves of E2 and BPA were not significantly different throughout the experimental period of 56 days. The Type B tube in the present experiment might be useful for long-term administration of estrogens.