3.4.1.2. Enkephalins
Similar to their effects on beta-endorphin, androgens increase concentrations of enkephalin peptides in many brain regions. In intact male rats, chronic treatment with nandrolone increases met-enkephalin concentrations in the hypothalamus and striatum (Johansson et al., 2000a) and under some (but not all) conditions in the periaqueductal gray area (cf., Johansson et al., 2000a; 2000b). Intact male rats also have greater concentrations of met- and leu-enkephalin in the anterior pituitary than intact female rats, and castration reduces these concentrations to those observed in females (Hong et al, 1982; Yoshikawa & Hong, 1983). Chronic administration of the testosterone metabolite, DHT, (but not testosterone) increases concentrations of both met- and leu-enkephalin in the anterior pituitary following castration (Yoshikawa & Hong, 1983). One exception to these findings is the observation that chronic treatment with testosterone in intact males decreases met- and leu-enkephalin concentrations in the anterior pituitary (Yoshikawa & Hong, 1983).