Release of 4-nonylphenol from a silicone tube implanted in mice.

Silicone tubes are commonly used as a tool for long-term steroid treatment in animals. However, the release rates of steroids from these tubes have not yet been accurately determined. We measured the amounts of 4-nonylphenol (NP) remaining in tubes implanted in mice to obtain accurate release rates for original amounts of 20 or 1,000 microg NP in silicone tube implants. We achieved an accurate figure for the release rate from the tube, calculated using the total recovery from both the contents of the tube and the silicone matrix of the tube. The regression curve for the remaining amount of NP, as a percentage of the original amount (1,000 microg) was calculated as y (%) = 83.033 - 3.4722t + 0.0375t(2), where t is the number of days after implantation. The mean release rate over 56 days was 1.6% of the original amount per day.