BCRP activity regulation at the blood–brain barrier through activation of endothelin-1 signaling. Twenty-hours after endothelin-1 (ET-1) intracerebroventricular (icv) treatment, prazosin, a BCRP substrate, was administered intravenously in adult brain (A) and juvenile brain (B) during four hours (steady state (ss) achievement) at a concentration of 1 mg/kg/h. At the end of the infusion period, blood was sampled, brain was isolated and the administered substrate was quantified using mass spectrometry. BCRP transport activity was estimated by the ratio between unbound prazosin brain concentrations and unbound plasma prazosin concentrations. Unbound plasma prazosin concentration in adult (C) and juvenile rat (D). Data represent the mean concentration for three or five rat brains/plasma. Variability is given by bars ± S.E.M. Data were analyzed using Student’s t-test. Statistical comparisons: *P <0.05.