Newborn rabbit blood-brain barrier is selectively permeable and differs substantially from the adult.

Examination of blood-brain barrier (BBB) function by the intracarotid injection technique has been utilized in studies of newborn (6-30 h) and adult rabbits. The exclusion of mannitol (mol. wt. 182), dextran (mol. wt. 60,000-90,000), and indium-bound EDTA indicate that the newborn BBB has restrictive properties similar to the adult. At birth, saturable, carrier-mediated transport mechanisms are present, regulating the entry of glucose, amino acids, organic acids, purines, nucleosides, and choline. No difference in brain uptake of glucose was observed between adult and newborn, but considerably higher uptake rates for arginine, choline, and adenine were seen in the newborn. In contrast to suggestions of an immature barrier in young animals, these studies indicate that a sophisticated, selective BBB is operative at birth. Furthermore, the specific selectivity and dramatic increases seen for certain metabolites imply a vital function in the newborn for these carrier systems.