title: Effects of treatment with the opioid antagonists naloxone and naltrexone on LH secretion and on sexual maturation in immature female rats.
abstract: The effects on sexual maturation of the opioid receptor antagonists naloxone and naltrexone were studied in the female rat. Neonatal treatment (days 1-10) with either naloxone (2.5 mg/kg at 6-h intervals) or naltrexone (20 or 50 mg/kg per day) did not advance sexual maturation as judged by age and body weight at vaginal opening and first ovulation. After treatment with naltrexone (20 mg/kg) first ovulation occurred 2.3 days earlier than in saline-treated control rats but this could be attributed to a growth-stimulating effect of naltrexone; the effect was not observed with 50 mg/kg. An effect of neonatal treatment with naloxone on serum LH levels was seen at 23 days of age (155 +/- 36 (S.E.M.) vs 14 +/- 4 micrograms LH/l in controls, P less than 0.01), but not at 29 or 33 days of age, at 2 days before first ovulation nor at first pro-oestrus. There were no differences in the number of ova released at first oestrus, nor in the length of the first cycle. Neonatal treatment with naltrexone (50 mg/kg per day) did not alter the response to treatment with human chorionic gonadotrophin at 28-31 days of age: ovulation of a mean of 7.3 ova was induced on day 32 in both naltrexone- and saline-treated rats. Naltrexone treatment (four daily injections of 20 mg/kg at 2-h intervals) at 28-32 days of age advanced first ovulation by 4.4 days in about 40% of the rats.(ABSTRACT TRUNCATED AT 250 WORDS)
authors: Department of Anatomy, Medical Faculty, Erasmus University, Rotterdam, The Netherlands.
authors: H M
authors: HM
authors: Meijs-Roelofs
authors: P
authors: P
authors: Kramer
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D005260:Female; D007986:Luteinizing Hormone / Q000378:metabolism*; D009270:Naloxone / Q000494:pharmacology*; D009271:Naltrexone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012741:Sexual Maturation / Q000187:drug effects*; D013997:Time Factors
chemical_list: D009270:Naloxone; D009271:Naltrexone; D007986:Luteinizing Hormone