Evidence for the involvement of central opioidergic systems in L-tyrosine methyl ester-induced analgesia in the rat.
Intraperitoneal administration of L-tyrosine (used as methyl ester HCl) produced dose-dependent analgesia in male Sprague-Dawley rats as measured by the tail-flick test. The maximal analgesic response was obtained with 200 mg/kg dose of tyrosine. Administration of morphine also produced a dose-dependent analgesic response. Tyrosine in doses of 50 mg/kg or higher potentiated morphine-induced analgesia. The analgesic response of tyrosine (200 mg/kg) was antagonized by naloxone (1 mg/kg), an opiate antagonist. Subcutaneous administration of methyl naltrexone bromide (MRZ 2663 BR, 1 and 10 mg/kg) had no effect on tyrosine-induced analgesia. Intracerebroventricular injection of MRZ 2663 BR (1 and 10 micrograms/rat) effectively blocked tyrosine-induced analgesia. It is concluded that tyrosine-induced analgesia and its potentiation of analgesic response to morphine may be mediated via either the opiate receptors or activation of endogenous opioidergic systems of central origin.
Department of Pharmacodynamics, University of Illinois, Chicago.
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Ramarao
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Bhargava
D000698:Analgesia; D000818:Animals; D004723:Endorphins / Q000502:physiology*; D007276:Injections, Intraventricular; D007279:Injections, Subcutaneous; D008297:Male; D009020:Morphine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds; D051381:Rats; D011919:Rats, Inbred Strains; D014443:Tyrosine / Q000494:pharmacology*
D004723:Endorphins; D009292:Narcotic Antagonists; D000644:Quaternary Ammonium Compounds; C032257:methylnaltrexone; D009270:Naloxone; D014443:Tyrosine; D009271:Naltrexone; D009020:Morphine