Leptin is thought to play important roles in pubertal development and reproductive function in the female. Leptin receptor is expressed in various tissues including the pituitary and hypothalamus. We investigated the transition of leptin receptor (Ob-R) expression in female rat pituitary during pubertal development. Real-time RT-PCR was performed for long-form leptin receptor (Ob-Rb) and short-form leptin receptor (Ob-Ra) in the pituitary and cerebrum of the rats aged 4 (juvenile), 6 (pubertal), and 8 weeks (adult). Double immunohistochemical colocalization of Ob-R and luteinizing hormone (LH) was performed in pituitaries from 4-week-old female rats. Serum leptin concentrations of 4-, 6-, and 8-week-old rats were measured by radioimmunoassay. In the pituitary, expression of Ob-Rb mRNA in 4-week-old rats (1.00 +/- 0.16) was significantly higher than in 8-week-old rats (0.61 +/- 0.07, p<0.05), although expression of Ob-Ra mRNA did not differ among 4-, 6-, and 8-week-old rats. In cerebrum, Ob-Ra and Ob-Rb mRNA expressions did not differ significantly among 4-, 6-, and 8-week-old rats. Intense staining of Ob-R and colocalization of Ob-R and LH were seen in 4-week-old rat pituitary. On the other hand, serum concentrations of leptin in 6- and 8-week-old rats were significantly higher than those in 4-week-old rats (p<0.05, p<0.01, respectively). In conclusion, since the pituitary gonadotroph is a potential target of leptin, the juvenile rat pituitary might prepare for a subsequent increase of serum leptin concentration by expressing Ob-Rb.