EFFECTS OF KYOTORPHIN (L-TYROSYL-L-ARGININE) ON [H-3] N-G-NITRO-L-ARGININE BINDING TO NEURONAL NITRIC-OXIDE SYNTHASE IN RAT-BRAIN

L-Tyrosyl-L-arginine (kyotorphin) is known as an endogenous analgesic neuropeptide. We examined whether kyotorphin and other arginine-contai ning neuropeptides were endogenous substrates for neuronal nitric oxid e synthase (NOS) in the rat brain. Cytosol fractions of the rat cerebe llum contained higher concentrations of neuronal NOS (nNOS) than endot helial NOS. In rat cerebellar cytosol, the binding activity of [H-3]N- G-nitro-L-arginine (NNA) was inhibited equally by L-arginine (L-Arg), kyotorphin, and L-leucyl-L-Arg (a kyotorphin receptor antagonist). Bin ding activities were inhibited to lesser degrees by fibronectin active fragments, bradykinin, and dynorphin A, but were not inhibited by L-t yrosyl-D-Arg or substance P. Interestingly, the inhibition of [H-3]NNA binding by kyotorphin was attenuated by inhibitors of kyotorphin-hydr olyzing peptidases (KTPases) such as bestatin and arphamenine B. These results suggest that kyotorphin is degraded to L-Arg by KTPases, whic h in turn may act as substrate for nNOS. (C) 1997 Elsevier Science Ltd .