Opioid modulation of thyrotropin releasing hormone induced prolactin secretion |
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Authors: | P Buydens B Velkeniers J Golstein E Finné L Vanhaelst |
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Institution: | 1. Division of Neonatology, Department of Pediatrics, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, Thailand;2. Department of Pediatrics, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, Thailand;1. Division of Gynecologic Oncology (Drs. Scott and Rimel);2. Department of Obstetrics and Gynecology (Dr. O''Connor), Cedars-Sinai Medical Center, Los Angeles, CA;1. Centre de compétences de l''hypertension pulmonaire (Pulmo Tension), service de pneumologie, Hospices Civils de Lyon, Hôpital Louis Pradel, Lyon, France;2. Centre de référence coordonnateur des maladies pulmonaires rares (RespiFil), service de pneumologie, Hospices Civils de Lyon, Hôpital Louis Pradel, Lyon, France;3. Université de Lyon, université Lyon 1, INRAE, EPHE, UMR754, IVPC, F-69007 , Lyon, France |
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Abstract: | It is known that opioids stimulate prolactin (PRL) secretion by an action on hypothalamic neurons, but in vitro studies have suggested a direct action on the lactotrophs. The present study was performed on male rats known to have little or no PRL response to TRH. A beta-endorphin (beta EP) injection in the third ventricle stimulated PRL secretion and induced furthermore a PRL secretory reaction to TRH injected intravenously 20 min later. Pretreatment with naloxone 10 min before beta EP injection abolished not only the PRL response to beta EP but also the conjugated effect of beta EP and TRH. Pretreatment with naloxone methyl bromide (Br-naloxone), a quaternary naloxone derivative, which does not cross the blood-brain barrier, had no effect on the PRL response to beta EP but prevented the conjugated effect of beta EP and TRH on PRL secretion. Pretreatment of the animals with -methyl-parathyrosine resulting in a dopamine depletion or with haloperidol, a dopamine antagonist, could not induce lactotroph responsiveness to TRH. These results suggest that beta EP in male rat sensitizes the PRL cell to TRH by a direct effect and not through an inhibition of the dopaminergic tone. |
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