Synthetic peptide octarphin (TPLVTLFK), a selective agonist of nonopioid β-endorphin receptor, stimulates nitric oxide synthesis in macrophages.

Synthetic peptide octarphin (TPLVTLFK, a selective agonist of nonopioid β-endorphin receptor) was able to activate in a dose-dependent manner murine macrophages to express nitric oxide (NO) synthase and to produce NO. Octarphin required lipopolysacharide for the optimal induction of NO production. Octarphin-dependent NO production was sensitive to inhibition by dexamethasone and the NO synthase specific inhibitor NG-monomethyl-L-arginine. In the concentration range of 1-1000 nM, octarphin increased the cyclic 3',5'-guanosine monophosphate (cGMP) content in macrophages stimulated with lipopolysacharide. The effect was dependent on the peptide concentration and was maximal at a concentration of 100 nM. Thus, octarphin stimulates both NO and cGMP production in macrophages.