Restoration of libido in castrated red deer stag (Cervus elaphus) with oestradiol-17β

Abstract

THE role of oestrogens in male reproduction remains an enigma. It is known that the stallion^1,2 and the boar³ excrete enormous amounts of oestrogen in their urine, and that this is of testicular origin^4,5; more modest amounts of oestrogen are secreted by the testis of the bull⁶, rat⁷, and man^8–10. Interest in male oestrogen was recently reawakened by the discovery that the hypothalami of rats, rabbits, monkeys and men are capable of aromatising testosterone to oestradiol-17β (ref. 11). This indicated that oestradiol-17β might be the central mediator of androgenic effects, an idea that is beginning to receive support from a number of different experiments. For example, it has been established that newborn female rats can be sterilised equally effectively by small doses of either androgen or oestrogen¹². In addition, the antioestrogen MER-25 will effectively inhibit this neonatal sterilisation even when it has been induced by testosterone¹⁹. It also seems significant that androgens which cannot be metabolised to oestrogen, such as dihydrotestosterone (DHT), have no apparent effect on the brain^13–16, although they are potent stimulators of male secondary sexual characteristics. Whilst DHT alone cannot restore libido to a castrated male rat, the addition of a few microgrammes of oestradiol will restore libido completely^17,18 and, recently, it has been shown that pharmacological doses of oestradiol benzoate are sufficient to restore all components of male reproductive behaviour to castrate male rats²⁰.