Opioid peptides modulate luteinizing hormone secretion during sexual maturation.

Subcutaneous injections of naloxone, an opiate antagonist, lead to an increase in serum luteinizing hormone concentrations in female but not in male rats before they reach puberty. In addition, estradiol benzoate specifically blocks the luteinizing hormone response to naloxone in prepubertal female rats, suggesting that the opioid peptides have a physiological role in the endocrine events leading to sexual maturation.