Publication: The presence and actions of opioid receptors in bovine pineal gland
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Issued Date
1992-01-01
Resource Type
ISSN
1600079X
07423098
07423098
Other identifier(s)
2-s2.0-0027068106
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Mahidol University
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SCOPUS
Bibliographic Citation
Journal of Pineal Research. Vol.13, No.3 (1992), 124-132
Suggested Citation
P. Govitrapong, M. Pariyanonth, M. Ebadi The presence and actions of opioid receptors in bovine pineal gland. Journal of Pineal Research. Vol.13, No.3 (1992), 124-132. doi:10.1111/j.1600-079X.1992.tb00066.x Retrieved from: https://repository.li.mahidol.ac.th/handle/123456789/22267
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Title
The presence and actions of opioid receptors in bovine pineal gland
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Abstract
Abstract: The mammalian pineal gland and its main hormone, melatonin, working in conjunction with the hypothalamic suprachiasmatic nuclei, synchronize circadian rhythm and hence refine numerous physiological and biochemical parameters. An interaction among melatonin, opioids, and analgesia has been suspected for many years, since during nighttime, when the level of melatonin is high, the mammals are less sensitive to pain. In studying this phenomenon further, we have identified a single population of opioid receptors in the bovine pineal gland using [3H]‐diprenorphine and other ligands. The receptors have a dissociation equilibrium constant (Kd) of 1.36 ± 0.31 nM and a density (Bmax) of 17.93 ± 5.22 fmol/mg protein. In competitive experiments, the concentration of drugs required to inhibit 50% of the [3H]‐diprenorphine binding (IC50) in descending order of potency was found to be naltrexone > fentanyl > naloxone > nalbuphine > morphine > nalorphine > DAGO > dynorphin > metenkephalin. In order to delineate the function of the opioid system in the pineal gland, the effects of both opioid receptor agonists and antagonists on the basal activity of N‐acetyltransferase were examined in the bovine pineal expiants in culture. Morphine, an opioid receptor agonist, increased significantly the activity of N‐acetyltransferase in a dose‐dependent fashion. In addition, the stimulatory effect of morphine was inhibited by naloxone, an opioid receptor antagonist. The results of these studies indicate the existence of pineal opioid receptors, which play a pivotal role in the synthesis of melatonin and its action in synchronizing pineal events. Copyright © 1992, Wiley Blackwell. All rights reserved