65 Zn Uptake from Blood into Brain in the Rat

Zinc is essential for the normal development and function of the CNS, although little is known about brain zinc homeostasis. Therefore, in this investigation we have studied 65 Zn uptake by brain from blood and have measured the blood‐brain barrier permeability to 65 Zn in the anaesthetised rat in vivo. Adult male Wistar rats within the weight range 500–600 g were used. 65 ZnCl 2 and 125 I‐albumin, the latter serving as a vascular marker, were injected intravenously in a bolus of normal saline. Sequential arterial blood samples were taken during experiments that lasted between 5 min and 5 h, after which the whole brain was removed, dissected, and analysed for radioisotope activity. Data have been analysed by graphical analysis, which suggests that after 30 min of circulation, 65 Zn uptake by brain from blood is unidirectional with an influx rate constant, K in , of ∼5 × 10 −4 ml/min/g. At circulation times of <30 min, 65 Zn fluxes between blood and brain are bidirectional, where influx has a K value of >5 × 10 −4 ml/min/g. In addition to the blood space, the brain appears to contain a rapidly exchanging compartment(s) for 65 Zn of ∼4 ml/100 g, which is not CSF.