Cytoplasmic and nuclear metabolism of testosterone in the brains of neonatal and prepubertal rats.

The metabolism of testosterone (T) in neonatal rat brains was measured following in vivo and in vitro incubations with 3H-testosterone.Steroids associated with nuclear and cytoplasmic fractions of brain tissue from 4, 12, and 32-day-old male and female rats were identified. Although there are quantitative differences under different methods of incubation, in all cases more than 95% of the radioactivity was recovered and identified as T, or the 5alpha-reduced metabolities, DHT and 3alpha-androstanediol. Most of the metabolism of T occurred in the cytoplasm but 5alpha-reduced metabolities were also associated with purified nuclei. Reaction kinetics indicate that the metabolic sequence is T leads to DHT leads to 3alpha DIOL. DHT levels were similar in the cytoplasmic fractions from the neonates (4 and 12-day-old animals) and prepubertal animals (32-day-old animals), but 3alpha-androstanediol was significantly reduced in these fractions from prepubertal animals compared to those from neonates. Sex differences in the metabolism of T in the various subcellular fractions were not detectable.