title: Methoxychlor modifies the ultradian secretory pattern of prolactin and affects its TRH response.
abstract: BACKGROUND
  Methoxychlor (MTX) is an insecticide characterized by both estrogenic and antiandrogenic properties that may modify the secretory pattern of prolactin. The objective of the present work was to analyze MTX's effects on changes in the episodic secretion of prolactin induced by thyrotropin-releasing hormone (TRH).
  
  
  METHODS
  Adult male Sprague-Dawley rats (400-420 g body weight) were administered 25 or 50 mg/kg/day of MTX s.c. in sesame oil for 30 days. Control animals received the vehicle only.
  
  
  RESULTS
  In animals treated with 50 mg/kg/day of MTX, mean serum prolactin levels and absolute pulse amplitude increased (p< or = 0.05 and p< or = 0.001 respectively). TRH administration (two pulses of 2 Kg) increased both mean serum prolactin levels and the absolute amplitude of the prolactin peaks in all groups studied (p< or = 0.001). The response to TRH was greatly increased in the animals treated with 50 mg/kg/day. TRH reduced the mean life of the hormone in control rats (p< or = 0.01) and in animals treated with 50 mg/kg/day (p< or = 0.001). After TRH administration, the duration of prolactin peaks was increased in the MTX-treated animals (p< or = 0.05 and p< or = 0.001 for 25 and 50 mg/kg/day respectively). TRH reduced the frequency of prolactin pulses in the animals treated with 50 mg/kg/day (p< or = 0.05).
  
  
  CONCLUSIONS
  These data suggest that MTX sensitizes the pituitary to TRH, indicating a direct effect of MTX on the pituitary gland.
authors.affiliation: Toxicology Laboratory, Faculty of Sciences, University of Vigo, Campus de Orense, Las Lagunas, Orense, Spain. lafuente@uvigo.es
authors.forename: Anunciación
authors.initials: A
authors.lastname: Lafuente
authors.forename: Aníbal
authors.initials: A
authors.lastname: González-Carracedo
authors.forename: Alejandro
authors.initials: A
authors.lastname: Romero
authors.forename: Ana I
authors.initials: AI
authors.lastname: Esquifino
mesh_terms: D000204:Activity Cycles / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D007306:Insecticides / Q000008:administration & dosage / Q000633:toxicity*; D008297:Male; D008731:Methoxychlor / Q000008:administration & dosage / Q000633:toxicity*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology* / Q000502:physiology
chemical_list: D007306:Insecticides; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D008731:Methoxychlor