title: Opioids and the pulsatile prolactin secretory pattern: effects of hyperprolactinemia.
abstract: It is well known that opioids regulate prolactin secretion through unknown mechanisms. The present study describes the effects of morphine and naloxone administration on pulsatile prolactin secretion in adult sham-operated and pituitary-grafted female rats. Animals were rendered hyperprolactinemic by transplanting 2 pituitary glands beneath the kidney capsule. Naloxone (2 mg/kg/h), morphine (50 mg/kg/h)+naloxone or saline (0.5 ml/h) were administered i.v. through a jugular cannula and bled at 7-min intervals for a period of 3 h. Pituitary grafting increased mean serum prolactin levels, the absolute amplitude and the duration of the pulses, but decreased their frequency. Naloxone, in sham-operated rats, reduced mean serum prolactin levels, the absolute amplitude and the frequency of the pulses. However, morphine+naloxone administration increased mean serum prolactin levels and the absolute amplitudes of prolactin pulses in pituitary-grafted rats. Naloxone administration did not decrease previously increased mean serum levels of prolactin in pituitary-grafted rats. These results suggest that opioids synchronize the pulsatile pattern of prolactin and that these effects are blunted in pituitary-grafted animals.
authors.affiliation: Departamento de Toxicologia, Facultad de Ciencias, Universidad de Vigo, Orense, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Lafuente
authors.forename: J
authors.initials: J
authors.lastname: Marco
authors.forename: A I
authors.initials: AI
authors.lastname: Esquifino
mesh_terms: D000818:Animals; D005260:Female; D006966:Hyperprolactinemia / Q000209:etiology / Q000378:metabolism*; D007262:Infusions, Intravenous; D007601:Jugular Veins; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D016377:Organ Transplantation; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism / Q000637:transplantation; D011388:Prolactin / Q000097:blood / Q000378:metabolism*; D011673:Pulsatile Flow / Q000187:drug effects; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D009270:Naloxone; D009020:Morphine; D011388:Prolactin