Release of alpha-neoendorphin from the anterior pituitary gland of conscious rats.
alpha-Neoendorphin (alpha-NEO) is a proenkephalin B-derived opioid peptide and kappa type opioid receptor agonist. In the present study, we used a combination of microdialysis and a highly sensitive radioimmunoassay to measure the extracellular levels of immunoreactive (ir)-alpha-NEO from the anterior pituitary gland of conscious free-moving rats. When rats were given water ad libitum under a 12:12 h light-dark cycle with lighting from 06.00 to 18.00 h, ir-alpha-NEO showed circadian rhythmicity that peaked at 00.00-03.00 h and reached a minimum at 12.00-15.00 h. Furthermore, we investigated whether naloxone (10(-6) to 10(-8) M) affected ir-alpha-NEO level. The alpha-NEO release induced by naloxone was optimum at 10(-7) M, and 10(-6) M naloxone seemed to induce alpha-NEO release to a lesser degree. These results suggested that alpha-NEO release by naloxone might be mediated via anterior pituitary cell auto-receptor (kappa type) inhibition.
Konya
H
H
2nd Department of Internal Medicine, Hyogo College of Medicine, Japan.
Masuda
H
H
Nagai
K
K
Kakishita
E
E
D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D004723:Endorphins / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D009270:Naloxone / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D004723:Endorphins; D011498:Protein Precursors; D009270:Naloxone; C025681:alpha-neoendorphin