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occur. However, effects on the critical window of neonatal pituitary gland development in mice have not been explored. Therefore, this study determined baseline gene expression in male and female pituitaries and consequences of environmental exposure to 17beta-estradiol (E2) and BPA on transcription of genes exhibiting sex differences during the neonatal period. Through microarray and quantitative RT-PCR analysis of pituitaries at postnatal day (PND)1, 3 genes were differentially expressed between males and females: Lhb, Fshb, and intracellular adhesion molecule-5 (Icam5). To see whether E2 and BPA exposure regulates these genes, pituitaries were cultured at PND1 with 10(-8) M E2 or 4.4 x 10(-6) M BPA. E2 decreased expression of Lhb, Fshb, and Icam5 mRNA in females but only significantly decreased expression of Icam5 in males. BPA decreased expression of Icam5 similarly to E2, but it did not affect Lhb or Fshb. Importantly, in vivo exposure to 50-mug/kg . d E2 from PND0 to PND7 decreased expression of Lhb, Fshb, and Icam5 mRNA in both males and females, whereas 50-mg/kg . d BPA exposure during the same time frame decreased expression of Icam5 in females only. Overall, we have uncovered that genes differentially expressed between the sexes can be regulated in part by hormonal and chemical signals in vivo and directly at the pituitary and can be regulated in a sex-specific manner.