We previously created the Alb-DsRed2 transgenic (Tg) rat that specifically expresses the red fluorescent protein, DsRed2, in the liver. Herein, we demonstrate that the DsRed2 expression is sexually dimorphic and exhibits a male-specific pattern. The profiling of sexual dimorphism in DsRed2 expression during pre-pubertal development was investigated using an in vivo fluorescent imaging analysis. The DsRed2 expression decreased gradually in both sexes until 28 days after birth. While DsRed2 expression was not persistent in the female liver, the male hepatic expression increased again at 35 days. Sexual dimorphic DsRed2 expression did not change in gonadectomized male and female Tg-rats. However, female hepatic DsRed2 was induced 72 h after the hypophysectomy. Hepatocytes isolated from the female Tg-rats also revealed DsRed2 induction by 96 h in culture. These results suggest that the pituitary hormone suppresses the female hepatic DsRed2 expression causing the sexual dimorphism of DsRed2 expression. (C) 2009 Elsevier Inc. All rights reserved.