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.
Ramarao
P
P
Department of Pharmacodynamics, University of Illinois, Chicago.
Bhargava
H N
HN
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