Saturable entry of ciliary neurotrophic factor into brain

Ciliary neurotrophic factor (CNTF), like tumor necrosis factor-alpha (TNF) and granulocyte-macrophage colony-stimulating factor (GM-CSF), is a cytokin e with neurotrophic properties. Since all three cytokines are found in the periphery as well as brain, and since TNF and GM-CSF cross the blood-brain barrier (BBB) by a saturable mechanism, we investigated whether CNTF also s aturably enters the brain from the blood. We found that CNTF crosses the BB B rapidly, with a rate of entry (K-i) of 4.60 (+/-0.78)x 10(-4) ml/g min, c onsiderably faster than that of the Tc-99m-albumin control. The K-i was red uced more than 3-fold by addition of excess unlabeled CNTF. The results ind icate that CNTF is saturably transported across the BBB from blood to brain . (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.