L-Kyotorphin (L-KTP), an endogenous analgesic neuropeptide, is a substrate for aminopeptidases and a proton-coupled oligopeptide transporter, PEPT2. This study examined the CSF efflux, antinociceptive response, and hydrolysis kinetics in brain of L-KTP and its synthetic diastereomer D-kyotorphin (D-KTP) in wild-type and Pept2 null mice. CSF clearance of L-KTP was slower in Pept2 null mice than ...