INDIVIDUAL VARIABILITY IN TYR-GLY-GLY FORMATION FROM ENKEPHALIN HYDROLYSIS IN MOUSE PLASMA

We examined the effects of captopril (an angiotensin-converting enzyme inhibitor) and phosphoramidon (a selective enkephalinase inhibitor) o n Tyr-Gly-Gly production during Met-enkephalin hydrolysis in plasma sa mples taken from individual outbred Swiss-Webster and inbred C57BL/6J and DBA/2J mice. Discriminant analysis procedures identified three dis tinct plasma profiles of Tyr-Gly-Gly production in all strains of mice : a captopril-sensitive/phosphoramidon-insensitive profile, a captopri l-insensitive/phosphoramdion-sensitive profile, and a moderate captopr il and phosphoramidon sensitivity profile. The abilities of captopril and phosphoramidon to inhibit Tyr-Gly-Gly production in the same mouse plasma sample were highly inversely correlated (r = -0.938). Plasma o f Swiss-Webster mice whose cages and bedding had been changed 24 h pri or to sample collection was significantly more likely to exhibit the c aptopril-sensitive/phosphoramidon-insensitive profile than the plasma of mice whose cages/bedding had not been changed for at least 5 days. The results suggest that environmental novelty may dramatically alter the activity of a plasma dipeptidyl carboxypeptidase system, and there by regulate behavioral and physiological responses to novel experience s