Interactions of "ultra-low" doses of naltrexone and morphine in mature and young male and female rats.
Sex and age influence morphine analgesia in humans and animals. Mature rats show greater morphine analgesia in males than in females. Ultra-low doses of naltrexone enhance morphine analgesia. In mature rats (18-22 weeks), naltrexone (0.002-2.0 mg/kg)-morphine (2 mg/kg) cotreatment enhanced morphine analgesia in females, an effect inversely related to naltrexone dose. Conversely, in mature male rats, naltrexone tended to decrease morphine analgesia with increasing dose. In young rats (8-10 weeks), morphine analgesia was unrelated to sex and in both sexes the naltrexone-morphine interaction was negligible. These data show that dose, age, and sex alter the naltrexone-morphine interaction in rats.
Hamann
Scott R
SR
Department of Anesthesiology, College of Medicine, University of Kentucky, Lexington, KY 40536-0293, USA. srhaman@uky.edu
Malik
Hammad
H
Sloan
Jewell W
JW
Wala
Elzbieta P
EP
D000367:Age Factors; D000701:Analgesics, Opioid / Q000008:administration & dosage; D000818:Animals; D004347:Drug Interactions; D005260:Female; D008297:Male; D009020:Morphine / Q000008:administration & dosage*; D009271:Naltrexone / Q000008:administration & dosage*; D009292:Narcotic Antagonists / Q000008:administration & dosage; D009294:Narcotics / Q000008:administration & dosage; D017288:Pain Threshold / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000187:drug effects; D012737:Sex Factors
D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D009294:Narcotics; D011957:Receptors, Opioid; D009271:Naltrexone; D009020:Morphine