ABSTRACT. Castrated goats were treated with dihydrotestosterone (DHT) for four weeks. Skin samples were collected from the head and the rump regions before and after the DHT treatment. The primer pheromone activities of these samples were assessed neurophysiologically by recording electrophysiological manifestations of the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator activity. Pheromone activity was detected in both the head and rump skin samples following the DHT treatment, although the development of sebaceous glands was limited to the head region. Taken together with our previous finding that testosterone treatment results in the appearance of primer pheromone activity in the skin sample of the head region but not of the rump region, these observations suggests that the regional difference of pheromone production would be ascribed to intrinsic expression levels of 5α-reductase, an enzyme converting testosterone to DHT.KEY WORDS: caprine, dihydrotestosterone, pheromone.J. Vet. Med. Sci. 63(3): 347-348, 2001 Dihydrotestoserone (DHT) is a target tissue-produced androgen, which is converted from testosterone by 5α-reductase. DHT is known to have higher affinity with androgen receptors (AR) than testosterone and to play a major role for the development of sebaceous glands and sebum production in the skin [13,14]. The results of our previous study [16] imply the involvement of DHT in the production of primer pheromone in sebaceous glands of the male goat, which is responsible for the "male effect" [1,3] of the male goat. Specifically, four weeks treatment of castrated goats with testosterone resulted in the appearance of primer pheromone activity in the skin sample of the head region but not of the rump region. Much higher immunoreactivities to 5α-reductase and androgen receptor were expressed at the sebaceous glands of the head region than those of the rump region. Based on these findings we assumed that the regional difference of the responsiveness to testosterone was due to different enzymatic activities of 5α-reductase determining local DHT availability. In order to test this hypothesis, skin samples were collected from the head and the rump regions of castrated male goats which had been treated for 4 weeks with DHT. These samples were then assessed for pheromone activity and the development of sebaceous glands as an indicator of sebum production.For the present study, three long-term (>1 year) castrated Shiba goats were obtained from the closed colony at the experimental station of the University of Tokyo. Each animal was implanted subcutaneously with six Silastic capsules (1 cm × 1 cm, Dow Corning, Midland, MI, U.S.A.) each of which contained 1 g of DHT (Wako Co., Osaka, Japan). Skin sampling was conducted on Day 0 (the day of DHT implantation) and on Day 28. For sampling, the goat was anesthetized, and a square (1 cm × 1 cm) of skin was excised from the head and the rump region using a scalpel as described previously [7,16].The bioassay for pheromone activity in skin sample was carri...