Induction of precocious puberty in the female rat after chronic naloxone administration during the neonatal period: the opiate 'brake' on prepubertal gonadotrophin secretion

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Abstract
Studies were undertaken using the opiate receptor antagonist naloxone to examine the hypothesis that endogenous opiates may have a restraining effect on prepubertal gonadotrophin secretion and may be involved in the maturation of the central nervous system mechanisms regulating the onset of puberty in the female rat. Naloxone (2·5 mg/kg) administered intraperitoneally every 6 h to female rats from day 1 to day 10 of postnatal life significantly (P P < 0·001) higher levels of FSH (761·4 ± 87·6 vs 483·8± 57·2 μg/l in control animals) and LH (562·8 ± 57·4 vs 351·3 ± 43·3 μg/l in control animals) at the first late pro-oestrus and a significantly (P < 0·001) higher number of ova released at first oestrus (12·4 ± 0·4 vs 8·1±0·3 in controls). Body weight at first oestrus was significantly (P P J. Endocr. (1985) 104, 299–307