In vivo steroid regulation of aromatase and 5 alpha-reductase in goldfish brain and pituitary.

The full expression of testosterone (T) actions in neuroendocrine tissues requires aromatization and 5 alpha-reduction to estradiol (E2) and 5 alpha-dihydrotestosterone (DHT), respectively. Recently, we documented striking changes in aromatase and 5 alpha-reductase during the annual reproductive cycle of goldfish (Carassius auratus). To investigate possible regulatory effects of sex steroids, goldfish were implanted with hormone-filled silastic capsules for 2-5 weeks. Conversion of [3H]androstenedione to estrone or 5 alpha-androstanedione by homogenates of anterior hypothalamus/preoptic area, remaining telencephalon, and whole pituitary (PIT) was used to estimate aromatase and 5 alpha-reductase, respectively. Gonadosomatic index and plasma E2, T, and DHT were monitored as an index of reproductive status and capsule effectiveness. In reproductively inactive fish in which plasma steroids and aromatase were basal (October), E2 or T increased aromatase activity in brain of both sexes but stimulated activity in PIT of females only; DHT was not effective. In a subsequent experiment initiated close to the spawning peak and prior to the seasonal decline in plasma steroids and brain aromatase (April), T increased or maintained brain aromatase in a time-dependent manner. 5 alpha-Reductase activity was unaffected by steroid treatment in both reproductively active and inactive fish. These results indicate that variations in circulating steroids are responsible, at least in part, for changes in brain aromatase during the annual reproductive cycle of goldfish and provide the first evidence for steroid control of pituitary aromatase. The steroid specificity of the induction suggests that an estrogen receptor mechanism is involved.(ABSTRACT TRUNCATED AT 250 WORDS)