PERMEABILITY OF NS-3, A THYROTROPIN-RELEASING-HORMONE ANALOG, INTO THE BRAIN AFTER ITS SYSTEMIC ADMINISTRATION IN RATS - A MICRODIALYSIS STUDY

The concentration of NS-3 (montirelin hydrate, CG 3703), a thyrotropin -releasing hormone (TRH) analogue, in the cerebral cortex of urethane- anaesthetized rats was measured after its systemic administration (1 m g kg(-1), i.v.), using in-vivo microdialysis coupled with a radioimmun oassay. The concentration in microdialysates was highest (24 nM) durin g the first 20 min after injection, and it fell below the detection li mit (3.5 nM) 100 min after treatment. The maximal interstitial concent ration was estimated to be 0.51 mu M. From these results, it is sugges ted that NS-3 can readily penetrate into the brain.