Oestradiol synergizes with 5 alpha-dihydrotestosterone or 3 alpha- but not 3 beta-androstanediol in inducing sexual behaviour in castrated rats.

Castrated male rats were treated with constant-release implants filled with testosterone, oestradiol-17 beta, 17 beta-hydroxy-5 alpha-androstan-3-one (5 alpha-dihydrotestosterone; DHT), 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-Adiol) or 5 alpha-androstane-3 beta,17 beta-diol (3 beta-Adiol). Only testosterone activated the sexual behaviour of the rats. If combined with oestradiol, DHT or 3 alpha-Adiol induced the behaviour, but 3 beta-Adiol failed to have this effect. Oestradiol inhibited the in-vitro formation of [14C]Adiols from [14C]DHT by combined preoptic and hypothalamic tissue, but only when given in high doses. No effect on the formation of [14C]Adiols from [14C]DHT was found in rats treated in vivo with DHT or with the combination of DHT and oestradiol which effectively stimulated sexual behaviour. These results do not support the suggestion that oestradiol may synergize with androgens to induce sexual behaviour in castrated rats by inhibiting androgen metabolism.