Multiple time-regression analysis of 125I-FGF19 transport from blood to brain. (A) The 125I-FGF19 clearance profile in blood was fitted with a two-phase exponential disappearance model. In the presence of 56-fold excess unlabeled FGF19, the area under curve of 125I-FGF19 was increased and the half-life of the slow phase of clearance was prolonged. (B) The influx rate Ki of 125I-FGF19 from blood to brain was not significant although the initial volume of distribution Vi was significantly higher than that of the co-administered vascular space marker 131I-albumin. The presence of excess unlabeled FGF19 resulted in the influx of 125I-FGF19 (p = 0.05). The influx of 131I-albumin remained non-significant. Each time point indicates an individual mouse (n = 8 /group).