Ultrastructural study on the interaction of insulin-albumin-gold complex with mouse brain microvascular endothelial cells.

The interaction between the brain microvascular endothelium and bovine serum albumin complexed with insulin and colloidal gold (insulin-BSA-gold) was studied in adult and newborn mice. The results suggest: (a) the modification of albumin enhances its binding to the luminal front of the endothelial cells, as compared to unmodified albumin used in previous studies from this laboratory; (b) the binding density of insulin-BSA-gold complex to blood-brain barrier microvessels is approximately 2.5 times higher in newborn than in adult mice; (c) in adult mice, fenestrated endothelia of the median eminence and choroid plexus demonstrate the highest binding capacity (over five and two times higher, respectively, than in blood-brain barrier endothelia); (d) in the median eminence only, the gold-labelled tracer particles may be transported across the vessel wall. Our observations offer new ultrastructural evidence that: (1) the modification of BSA molecules by complexing with insulin does not enhance the transport of BSA across the blood-brain barrier in mouse brain, and (2) insulin-BSA-gold complex appears adequate for ultrastructural localization of blood-brain barrier insulin receptors but is of questionable value as a tracer for demonstration of increased transendothelial transport in blood-brain barrier microvasculature.