Effect of a nonsteroidal antiandrogen, flutamide, on androgen receptor dynamics and ornithine decarboxylase gene expression in mouse kidney.

The mechanisms by which nonsteroidal antiandrogens such as flutamide (alpha, alpha, alpha-trifluoro-2-methyl-4'-nitro-m-propionotoluidide) influence androgen receptor distribution and androgen-regulated gene expression are poorly understood. Therefore, we studied acute and long-term effects of flutamide, administered alone or in combination with testosterone, on androgen receptor dynamics in mouse kidney. Nuclear androgen receptors were measured using 5 mM pyridoxal 5'-phosphate extracts of renal nuclei isolated with the hexylene glycol method. Androgen-regulated ornithine decarboxylase (ODC) and ODC-messenger RNA were used as biological markers for hormone action. A single dose of flutamide increased the measurable concentration of renal nuclear androgen receptors in a dose-dependent manner by 1 h after treatment, although to a lesser extent than a comparable dose of testosterone. When 5 mg flutamide was given concomitantly with a submaximal dose of testosterone (0.1 mg), nuclear androgen receptor concentration was similar to that achieved with flutamide alone; this inhibitory effect of the antiandrogen was reversed by a 10-fold higher dose of testosterone. The influence of flutamide on the steady-state receptor levels in renal nuclei achieved by continuous androgen administration was investigated by giving a single dose of this compound to mice with testosterone-releasing implants. In these animals, flutamide administration decreased nuclear androgen receptor concentration with an initial half-life of about 3.3 h. This half-life was similar to that after cycloheximide administration, but significantly longer than that measured (1.3 h) upon removal of the implant. During treatment of female mice for 8 days with testosterone-releasing implants (40 micrograms/day), both the immunoreactive and catalytically active ODC concentration increased about 300-fold. In contrast, there was no stimulation of ODC during the prolonged administration of flutamide, although this treatment resulted in a dose-dependent increase in the nuclear androgen receptor concentration. However, flutamide (up to 650 micrograms/day) given concomitantly with testosterone (40 micrograms/day) almost completely abolished the testosterone-induced increase in ODC. The changes in ODC-messenger RNA concentration, as measured by hybridization to a complementary DNA probe, paralleled those of the enzyme protein suggesting that flutamide action involves inhibition of transcription of androgen-regulated gene(s). We conclude that 1) nuclear androgen receptor turnover in mouse kidney is a relatively rapid process and 2) nonsteroidal antiandrogens such as flutamide have an intrinsic ability to form