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 cytokine 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 saturably enters the brain from the blood. We found that CNTF crosses the BBB rapidly, with a rate of entry (K-i) of 4.60 (+/-0.78)x 10(-4) ml/g min, considerably faster than that of the Tc-99m-albumin control. The K-i was reduced more than 3-fold by addition of excess unlabeled CNTF. The results indicate that CNTF is saturably transported across the BBB from blood to brain. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.