R_CorrTissue% (ml × 100 g⁻¹) of [³H]corticosterone in the absence and presence of unlabeled digoxin in wild-type mice using in situ brain/choroid plexus perfusion technique. [³H]cortisol (3.8 nm), along with [¹⁴C]sucrose (vascular space marker; 0.5–1.0 nm), was administered by a slow-drive syringe pump into the artificial plasma containing unlabeled digoxin (25 μm). After a perfusion time of 20 min, the mouse was decapitated, and selected brain regions (open white bar, frontal cortex; light gray bar, hippocampus; closed black bar, hypothalamus; dark gray bar, cerebellum) (A) and choroid plexus and pituitary gland (open white bar, choroid plexus; closed black bar, pituitary gland) (B) were sampled. The concentration of [³H] or [¹⁴C] radioactivity in the tissues (dpm g⁻¹) is expressed as a percentage of that in the artificial plasma (dpm ml⁻¹). The uptake of [³H]corticosterone was not significantly different in the absence or presence of unlabeled digoxin in any of the brain regions (P > 0.05, Student's t tests, vascular space corrected). However, the uptake of [³H]corticosterone was significantly decreased in the choroid plexus and pituitary gland in the presence of unlabeled digoxin compared with wild-type controls (P = 0.019 and P = 0.020, respectively, Student's t tests, corrected for extracellular space) (n = 14–26).*, Significance (P < 0.05) compared with controls.