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  • Title: Plasma beta-endorphin and cortisol levels in morphine-tolerant rats and in naloxone-induced withdrawal.
    Author: Antonio Martínez J, Vargas ML, Fuente T, Del Rio Garcia J, Milanés MV.
    Journal: Eur J Pharmacol; 1990 Jun 21; 182(1):117-23. PubMed ID: 2144820.
    Abstract:
    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.
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