title: A puberty-related attenuation of opiate peptide-induced inhibition of LH secretion.
abstract: The long-acting synthetic enkephalin FK 33-824 (FK) potently inhibits LH secretion in gonadectomized prepubertal male and female rats. The effect is reversible by coinjection of naloxone. We have observed an age-related decrease in the ability of FK to reduce LH secretion in the 48 h post-gonadectomized rat. Thus, the IC50 values (i.e. the dose required to give 50% reduction in LH levels) for 12, 23 and 33-day old female rats were 0.03, 0.04 and 0.17 mg/kg BW, respectively. The figures for pre- and post-pubertal male rats (ages 26 and 70 days) were 0.25 and 0.89 mg/kg BW, respectively. This attenuation of opiate-induced inhibition of LH release may provide a neurochemical basis for the well-described shift in sensitivity of gonadal steroid feedback which occurs with the approach of puberty.
mesh_terms: D000818:Animals; D002369:Castration; D005405:D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000494:pharmacology*; D004745:Enkephalins / Q000494:pharmacology*; D005260:Female; D006728:Hormones / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012741:Sexual Maturation
chemical_list: D004723:Endorphins; D004745:Enkephalins; D006728:Hormones; D005405:D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; D007986:Luteinizing Hormone