RESUMO
BACKGROUND: Endogenous opioids have roles in various functions in different parts of the body, including intestinal motility, suppression of pain, reinforcement of behavior, and regulation of the hypothalamic-pituitary-gonadal axis. The endogenous opioid system is also recognized to be involved in the negative-feedback regulation of the release of LH and testosterone. AIM: The reviewed articles herein show the development of the current model of this regulation, the evidence supporting it, and also the observed effects of opioid antagonist (naloxone, naltrexone, and nalmefene) on the system. MATERIALS AND METHODS: Review of the studies published during the years 1979-1996 (no significant studies made after that). Search from databases Pubmed, SciFinder, and Medline with search words opioid antagonists, hormones, LH, testosterone, and GnRH, in different combinations. RESULTS/CONCLUSIONS: Opioid antagonists seem to increase the secretion of GnRH in the hypothalamus which then causes a pulsatile release of LH in the pituitary and secretion of testosterone. According to the experiments, the frequency of pulses and concentration of LH and testosterone in plasma seem to increase. These effects are seen in both men and women (at early follicular phase). More research is needed to investigate the consequences of these effects in general.
