title: Opioid modulation of prolactin secretion induced by stress during late pregnancy. Role of ovarian steroids.
abstract: BACKGROUND
  The opioid system modulates prolactin release during late pregnancy. Its role and the participation of ovarian hormones in this modulation are explored in ether stress-induced prolactin release.
  
  
  RESULTS
  Estrous, 3-day and 19-day pregnant rats were used. We administered the antagonist mifepristone (Mp) and tamoxifen to evaluate progesterone and estradiol action in naloxone (NAL, opioid antagonist) or saline treated rats. Ether stress had no effect on serum prolactin levels in controls but increased prolactin release in NAL-treated rats. Prolactin response to stress in NAL-treated rats was blocked by l-DOPA administration. Mp treatment on day 18 of pregnancy increased prolactin levels after stress without alterations by NAL. Tamoxifen on days 14 and 15 of pregnancy completely blocked Mp and NAL effects on prolactin release at late pregnancy. In contrast, stress significantly increased prolactin levels in estrous rats and pretreatment with NAL prevented this. On day 3 of pregnancy, at 6.00 p.m., stress and NAL treatment inhibited prolactin levels in saline-treated rat. No effect of stress or NAL administration was detected on day 3 of pregnancy at 9.00 a.m. icv administration of specific opioids antagonist, B-Funaltrexamine but not Nor-Binaltorphimine or Naltrindole, caused a significant increase in stress-induced prolactin release.
  
  
  CONCLUSIONS
  Opioid system suppression of prolactin stress response during late pregnancy was observed only after progesterone withdrawal, involving a different opioid mechanism from its well-established stimulatory role. This mechanism acts through a mu opioid receptor and requires estrogen participation. The opioid system and progesterone may modulate stress-induced prolactin release, probably involving a putative prolactin-releasing factor.
authors.affiliation: Laboratorio de Reproducción y Lactancia, IMBECU-CONICET, Mendoza, Argentina; Instituto de Ciencias Básicas, Universidad Nacional de Cuyo, Mendoza, Argentina.
authors.forename: Susana R
authors.initials: SR
authors.lastname: Valdez
authors.affiliation: Laboratorio de Reproducción y Lactancia, IMBECU-CONICET, Mendoza, Argentina.
authors.forename: Gisela E
authors.initials: GE
authors.lastname: Pennacchio
authors.affiliation: Laboratorio de Reproducción y Lactancia, IMBECU-CONICET, Mendoza, Argentina.
authors.forename: Dante F
authors.initials: DF
authors.lastname: Gamboa
authors.affiliation: Laboratorio de Reproducción y Lactancia, IMBECU-CONICET, Mendoza, Argentina.
authors.forename: Elina G
authors.initials: EG
authors.lastname: de Di Nasso
authors.affiliation: Departamento de Farmacología, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
authors.forename: Claudia
authors.initials: C
authors.lastname: Bregonzio
authors.affiliation: Laboratorio de Reproducción y Lactancia, IMBECU-CONICET, Mendoza, Argentina; Departamento de Morfofisiología, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, Mendoza, Argentina. Electronic address: msoaje@mendoza-conicet.gov.ar.
authors.forename: Marta
authors.initials: M
authors.lastname: Soaje
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004958:Estradiol / Q000378:metabolism; D005260:Female; D015735:Mifepristone / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010053:Ovary / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D011374:Progesterone / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013256:Steroids / Q000378:metabolism*; D013629:Tamoxifen / Q000494:pharmacology
chemical_list: D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D013256:Steroids; D013629:Tamoxifen; D015735:Mifepristone; D009270:Naloxone; C051844:norbinaltorphimine; D011374:Progesterone; D004958:Estradiol; D009271:Naltrexone; D011388:Prolactin; C055382:naltrindole
keywords: Naloxone; Opioid receptor subtypes; Pregnancy; Prolactin; Stress