Appropriately substituted 8-9 (Psi CH2NH) isosteres of neurotensin (NT
) 8-13 have been found which are active as NT agonists in vitro and in
vivo. SAR studies suggest that preventing amide bond hydrolysis at th
e 8-9 and 11-12 positions of NT(8-13) mimetics is important for produc
ing compounds with potent activity in vivo. Other simplified replaceme
nts for the Arg-Arg portion of NT(8-13) are reported.