Nociception, enkephalin content and dipeptidyl carboxypeptidase activity in brain of mice treated with exopeptidase inhibitors.

Thiorphan (60 micrograms intracerebrally) increased the met5-enkephalin content of mouse striatum by 30% in 30 min. This increase was no longer evident at 1 hr. If the dipeptidyl carboxypeptidase, inhibited by thiorphan, were located extraneuronally as suggested by De La Baume, Patey and Schwartz (1981), the met5-enkephalin accumulation represents the rate at which the pentapeptide is released extraneuronally. The increase in met5-enkephalin content was accompanied by an inhibition, greater than 80%, of the dipeptidyl carboxypeptidase that degrades striatal met5-enkephalin. Such an inhibition lasted longer then 2 hr. Thiorphan, given to mice intracerebrally, prolonged the latency time to jump off a 54 degree plate. The effects of thiorphan on brain met5-enkephalin content and hot plate latencies were significantly potentiated by bestatin, which inhibits aminopeptidase B and leucine aminopeptidase.