title: Naloxone administration does not relieve the inhibition of gonadotropin release in food-restricted, lactating rats.
abstract: Lactational anovulation is an important factor in determining birth spacing in women living in developing countries. Therefore, a more comprehensive understanding of the mechanisms involved in the relationships among lactation, nutrition and ovulation is important. This study was designed using the food-restricted, lactating rat to examine whether endogenous opioids might be involved in depressing gonadotropin release. Females were mated after 65 d of age and, beginning on d 42 of life, offered food in unrestricted amounts (control) or were food restricted to 50% of what the controls consumed. On d 15 of lactation, dams were injected with either naloxone hydrochloride (3 mg/kg body weight) or saline and killed 0, 15, 30 or 60 min later. Plasma was analyzed for luteinizing hormone, follicle-stimulating hormone and prolactin. Food restriction decreased plasma concentrations of luteinizing hormone and follicle-stimulating hormone (P < 0.005). Naloxone administration marginally influenced follicle stimulating hormone (P < 0.1), but not luteinizing hormone concentration regardless of diet group. The interaction among diet group, drug group and time of killing was significant for plasma prolactin concentration (P < 0.05). Food restriction lowered prolactin concentrations, but this effect was diminished with increasing time after injection of naloxone. Furthermore, the magnitude of the effect of food restriction was lessened and even reversed with treatment of naloxone. These results indicate that endogenous opioids are not the primary mechanism suppressing luteinizing hormone release in food-restricted lactating rats.
authors.affiliation: Division of Nutritional Sciences, Cornell University, Ithaca, NY 14853, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: McGuire
authors.forename: T R
authors.initials: TR
authors.lastname: Myers
authors.forename: W R
authors.initials: WR
authors.lastname: Butler
authors.forename: K M
authors.initials: KM
authors.lastname: Rasmussen
mesh_terms: D000818:Animals; D004435:Eating / Q000502:physiology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D005508:Food Deprivation / Q000502:physiology; D006062:Gonadotropins / Q000378:metabolism*; D007774:Lactation / Q000502:physiology*; D008098:Litter Size; D007986:Luteinizing Hormone / Q000097:blood; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology; D010060:Ovulation / Q000502:physiology; D011247:Pregnancy; D011388:Prolactin / Q000097:blood / Q000378:metabolism; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D006062:Gonadotropins; D009292:Narcotic Antagonists; D009294:Narcotics; D009270:Naloxone; D011388:Prolactin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone