The use of steroid-containing Silastic implants in male nude mice: plasma hormone levels and the effect of implantation on the weights of the ventral prostate and seminal vesicles.

The effects of implantation of steroid-containing capsules into male nude mice on steroid concentrations in plasma and weight of accessory sex organs were studied. Intact male nude mice had plasma levels of testosterone (T) of 8.0 +/- 2.4 ng/ml, while T implantation (length 1.0 cm) of a group with castrated male mice resulted in a mean level of 8.1 +/- 0.3 ng/ml. This level was reached within 2 days after implantation and lasted for at least 40 days. After longer periods of application (up to 75 days) physiological levels could still be attained. Treatment of intact male nude mice with estradiol (E2)-containing implants (length 0.5 cm) resulted in constant levels of plasma-E2 (250 pg/ml) also lasting for at least 32 days. This treatment resulted in a mean plasma-T level of 1.0 +/- 0.2 ng/ml, which was still significantly higher than that obtained after castration (0.14 +/- 0.03 ng/ml). Up to 16 days after implantation E2 did not cause a decrease of the weights of the accessory sex glands in intact male mice, while after 32 days a significant reduction (50% of the control animals) of the organ weights was observed. The present data obtained with T and E2 implantation show that this route of administration of hormones is also very applicable in the nude mouse model.