title: Lactation decreases mRNA levels of opioid peptides in the arcuate nucleus of the rat.
abstract: The state of lactation results in increased food intake to compensate for the increased energy expenditure to produce nutrients supplied to the offspring. In this study, Sprague-Dawley female rats lactating for 10-16 days, and rats 7 days post-lactation were implanted with osmotic minipumps infusing either naltrexone (NTX) (70 microg/h) or saline (0.9%) over a 48 h period. mRNA levels of pro-dynorphin (proDYN), pro-opiomelanocortin (POMC) and pro-enkephalin (proENK) were measured in the arcuate nucleus (ARC) and whole pituitary of both groups. In both saline- and NTX-treated lactating subjects, food intake was higher than in post-lactating subjects (P < 0.01). In post-lactating subjects, NTX decreased food intake by 27% during the infusion period (P < 0.05). There were no significant differences in body weight between the treatment groups; however, naltrexone decreased body weight gain in both lactating and post-lactating subjects. In both saline and NTX-treated lactating subjects, ARC mRNA levels of proDYN, POMC and proENK were significantly decreased compared with the saline or NTX-treated post-lactating subjects (P < 0.01). NTX did not significantly influence gene expression of opioid peptides in the ARC in either the lactating or the post-lactating subjects. Neither the lactation condition nor NTX administration significantly changed mRNA levels of proDYN, POMC or proENK in whole pituitary. Thus, as has been noted in energy-deprived rats, opioid peptide gene expression is decreased in the ARC of lactating rats, a period during which rats have increased energy requirements.
authors.affiliation: Department of Food Science and Nutrition, University of Minnesota, St. Paul 55108, USA.
authors.forename: E M
authors.initials: EM
authors.lastname: Kim
authors.forename: C M
authors.initials: CM
authors.lastname: Kotz
authors.forename: C C
authors.initials: CC
authors.lastname: Welch
authors.forename: M K
authors.initials: MK
authors.lastname: Grace
authors.forename: C J
authors.initials: CJ
authors.lastname: Billington
authors.forename: A S
authors.initials: AS
authors.lastname: Levine
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000378:metabolism*; D001835:Body Weight / Q000187:drug effects; D004435:Eating / Q000187:drug effects; D004958:Estradiol / Q000097:blood; D005260:Female; D007774:Lactation / Q000502:physiology*; D009271:Naltrexone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D018847:Opioid Peptides / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D009292:Narcotic Antagonists; D018847:Opioid Peptides; D012333:RNA, Messenger; D004958:Estradiol; D009271:Naltrexone