Analgesic activity of the lysozyme peptide N-(N-L-threonyl-L-alpha-aspartyl)-L-tyrosine in the monkey and the dog.

N-(N-L-Threonyl-L-alpha-aspartyl)-L-tyrosine (CAS 115053-54-8, SPA-S-646) was originally derived from lysozyme. It has previously been found to have analgesic properties following oral and intravenous administration to laboratory rodents. In the rhesus monkey, intramuscular administration of SPA-S-646 caused a dose-related analgesia. This effect was not seen following oral administration, but when given via the rectum, analgesia was again observed. In the dog, a single dose of 50 mg/kg was active by the intramuscular route but not the oral route. It is thought that unlike the rat, the digestive systems of the rhesus monkey and the dog degrade the tripeptide into inactive constituents.