Mu and delta opioid receptor regulation of pro-opiomelanocortin peptide secretion from the rat neurointermediate pituitary in vitro.
We investigated the ability of selective opioid agonists and antagonists to influence pro-opiomelanocortin peptide secretion from the rat neurointermediate lobe in vitro. The mu-opioid agonist DAMGO ([D-Ala(2), N-Me-Phe(4), Gly(5)-ol]enkephalin) significantly stimulated beta-endorphin and alpha-melanocyte-stimulating hormone release relative to controls early (30 min) in the incubation period. Similar effects on beta-endorphin secretion were observed with the selective mu-opioid agonist dermorphin. The delta-opioid receptor agonist DPDPE ([D-Pen(2,5)]enkephalin) weakly inhibited beta-endorphin secretion relative to controls while the kappa-opioid receptor agonist U50488 had no effect. The mu-opioid selective antagonist CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2)) inhibited basal beta-endorphin secretion while kappa- and delta-opioid receptor antagonists had no effect. Our data support a role for local mu-opioid receptor control of intermediate lobe pro-opiomelanocortin peptide secretion. Peptide secretion from melanotropes appears to be tonically stimulated by activation of mu-opioid receptors in the absence of intact neuronal innervation to the intermediate lobe.
Carr
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Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409, USA. gtjac@ttacs.ttu.edu
Lovering
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D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009842:Oligopeptides / Q000494:pharmacology; D018847:Opioid Peptides; D010902:Pituitary Gland / Q000187:drug effects / Q000502:physiology*; D011333:Pro-Opiomelanocortin / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017465:Receptors, Opioid, delta / Q000502:physiology*; D017450:Receptors, Opioid, mu / Q000502:physiology*; D013004:Somatostatin / Q000031:analogs & derivatives / Q000494:pharmacology; D000521:alpha-MSH / Q000378:metabolism*; D001615:beta-Endorphin / Q000378:metabolism*
D000701:Analgesics, Opioid; D009842:Oligopeptides; D018847:Opioid Peptides; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; C049352:phenylalanyl-cyclo(cysteinyltyrosyl-tryptophyl-ornithyl-threonyl-penicillamine)threoninamide; C030058:dermorphin; D013004:Somatostatin; D000521:alpha-MSH; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D020881:Enkephalin, D-Penicillamine (2,5)-