Antagonism of stress-induced analgesia by D-phenylalanine, an anti-enkephalinase.
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 received respectively either 25, 50 or 100 mg/kg of D-phenylalanine intraperitoneally in three conditions: alone, with CWS (2 degrees 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.
D000698:Analgesia; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000037:antagonists & inhibitors*; D004745:Enkephalins / Q000037:antagonists & inhibitors*; D008297:Male; D009020:Morphine / Q000494:pharmacology; D010649:Phenylalanine / Q000494:pharmacology*; D005082:Physical Exertion; D051381:Rats
D004723:Endorphins; D004745:Enkephalins; D010649:Phenylalanine; D009020:Morphine