The expression of cyclin D1 in the mammary gland of parous rats treated with insulin-like growth factor (IGF)-I (P-IGF-I), untreated parous rats (P-Un), and age-matched virgin rats (AMV). The IGF-I treatment (0.66 mg/kg body weight/day) was continued for 7 days before samples were collected. Protein samples (100 μg/lane) were electrophorized on a 10% SDS-PAGE, transferred to a PVDF membrane, and specific protein bands detected using a specific cyclin D1 antibody (sc-450; Santa Cruz Biotechnology, Santa Cruz, CA, USA) and enhanced chemiluminescence reagents. The upper image shows the results of the Western blot analysis and the bar chart shows the quantitation and statistical analysis of the results. Values are expressed as mean ± standard error. *P < 0.05 versus P-Un and P-IGF-I.