Antagonism of stress-induced analgesia by D-phenylalanine, an anti-enkephalinase

Richard J. Bodnar, Michael Lattner, Margaret M. Wallace

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


Methionine- and leucine-enkephalin produce mild and transient analgesic effects, presumably because of enzymatic degradation. Administration of high (250 mg/kg) doses of D-phenylalanine retards the degradation process and elicits analgesia which is reversed by naloxone and which summates with electroacupuncture analgesia. The present study evaluated D-phenylalanine's dose-dependent effects upon a non-opioid analgesic treatment, cold-water swims (CWS), and compared this with morphine. Following determination of flinch-jump baselines, three groups of rats recieved respectively either 25, 50 or 100 mg/kg of D-phenylalanine intraperitoneally in three conditions: alone, with CWS (2°C for 3.5 min), and with morphine (5 mg/kg, SC). Parallel controls with saline were also tested. Simultaneous exposure with each minimally analgesic dose of D-phenylalanine reduced significantly the analgesic, but not hypothermic effects of CWS. By contrast, morphine analgesia was unaffected by D-phenylalanine. These data provide further support that different pain-inhibitory systems mediate CWS and morphine analgesia and suggest that activation of one system is capable of exerting collateral inhibition upon the other.

Original languageEnglish
Pages (from-to)829-833
Number of pages5
JournalPharmacology Biochemistry and Behavior
Issue number6
StatePublished - Dec 1980
Externally publishedYes


  • Analgesia
  • Cold-water swims
  • Collateral inhibition
  • D-Phenylalanine
  • Enkephalins
  • Morphine
  • Pain


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