PERMEABILITY OF THE BLOOD-BRAIN-BARRIER TO THE NEUROTENSIN(8-13) ANALOG NT1

Neurotensin (NT) has been suggested to be a neuropeptide with therapeutic potential. We used multiple-time regression analysis to measure the unidirectional influx constant (K-i) of a tritiated analog of NT8-13, NT1, with improved metabolic stability. The K-i of [H-3]NT1 across the blood-brain barrier (BBB) was 5.12(10(-4)) ml/g-min and was decreased 66% by unlabeled NT1 system. The amount of NT1 crossing the BBB, 0.087% of the injected dose per gram of brain, is consistent with its exerting central effects after peripheral administration. The stable [H-3]NT1 crossed the BBB in intact form as assessed by HPLC and completely crossed the endothelial cells that comprise the BBB as assessed by the capillary depletion method. The presence of a transport system could be important for the development of NT analogs.