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The metabolism in vitro of [4-¹⁴C]testosterone to reduced derivatives was studied in the pituitary gland, hypothalamus and hyperstriatum dorsale of cockerels from hatch to sexual maturity. The most important metabolites were 5β-dihydrotestosterone (5β-DHT), 5β-androstane-3,17β-diol (5β-3-diol) and 5β-androstane-3β,17β-diol. Trace amounts of androstenedione and, in the hypothalamus only, of 5-DHT were also detected. The amounts of 5β-reduced metabolites produced by all neuroendocrine tissues declined progressively during maturation with the steepest fall occurring during the first 2 weeks after hatch. At all ages studied, 5β-DHT was formed to the greatest extent by the hyperstriatum dorsale, to a lesser extent by the hypothalamus and in the smallest quantities by the pituitary gland. In the three tissues studied, 5β-3-diol tended to be formed to the greatest extent by the pituitary gland.

No significant change was observed in the metabolism of testosterone to reduced derivatives in any of the neuroendocrine tissues after castration.

It was concluded that in the cockerel, unlike the rat, a change in 5-reductase activity of the neuroendocrine tissues is unlikely to be involved in the initiation of puberty. The physiological significance of 5β-reductase activity in the neuroendocrine tissues remains to be established.