Plasma beta-endorphin and cortisol levels in morphine-tolerant rats and in naloxone-induced withdrawal.
The relationship between morphine tolerance and pituitary-adrenocortical activity was examined. In rats made tolerant to morphine by implantation of morphine-containing pellets, there was a significant reduction in plasma levels of beta-endorphin-like immunoreactivity (beta-END-LI), whereas no significant changes in cortisol levels were seen. Naloxone treatment induced an increase in plasma beta-END-LI and cortisol levels in morphine-tolerant animals. Additionally, acute morphine administration induced an increase in plasma levels of beta-END-LI and cortisol, an effect which was prevented by naloxone. These results are consistent with an increased release of pro-opiomelanocortin-derived peptides after acute morphine and with a decreased release of these peptides in tolerant rats, and suggest that opioid peptides play an important role in the regulation of pituitary-adrenocortical function.
Antonio Martínez
J
J
Department of Physiology and Pharmacology, University School of Medicine, Murcia, Spain.
Vargas
M L
ML
Fuente
T
T
Del Rio Garcia
J
J
Milanés
M V
MV
D000818:Animals; D004361:Drug Tolerance; D005260:Female; D006854:Hydrocortisone / Q000097:blood*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D011333:Pro-Opiomelanocortin / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013375:Substance Withdrawal Syndrome / Q000097:blood*; D001615:beta-Endorphin / Q000097:blood*
D009270:Naloxone; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D009020:Morphine; D006854:Hydrocortisone