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  • Title: Development and control of the opioid inhibition of gonadotropin secretion during the sexual maturation of the male rat.
    Author: Nazian SJ.
    Journal: Neuroendocrinology; 1992 Jun; 55(6):613-20. PubMed ID: 1630582.
    Abstract:
    The endogenous opioid system tonically inhibits the LH-releasing apparatus in adult male rats but not in immature animals. To determine the relationship between the onset of this effect and the peripubertal testosterone rise, male rats were examined at 5-day intervals from day 25 through day 65. They were injected subcutaneously with saline, 0.25 or 1.0 mg/kg body weight naloxone and sacrificed 20 min later. Another group of immature males was castrated, implanted with testosterone-filled capsules and tested with naloxone 4 days later. The peripubertal increase in testosterone and the ability of naloxone to increase serum LH concentrations were both first statistically significant on day 45. Testosterone treatment of immature rats did not induce a naloxone effect. The ability of hypothalamic fragments to release LHRH in vitro in response to naloxone also appeared to occur at the same time as the peripubertal testosterone rise. Hypothalamic fragments obtained from immature male rats treated in vivo with testosterone were capable of responding to naloxone with LHRH release in vitro. These data suggest that in the rat the maturation of the endogenous opioid system is a component of male puberty that is induced by the peripubertal testosterone rise.
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