Postpubertal maturation of endogenous opioid regulation of luteinizing hormone secretion in the female sheep.
This study investigated whether the role of endogenous opioid peptides in the suppression of LH secretion during seasonal anestrus in the sheep changes with age. The experimental approach was to determine the effect of blockade of opioid receptors with naloxone on LH secretion at different times of year within the anestrous season, and to compare responses between seasonally anestrous sheep of different ages. Sheep, all past the normal age of puberty, were ovariectomized before the study and treated s.c. with estradiol implants to provide a fixed estradiol feedback signal. One-year-old females responded to naloxone with a rapid increase in LH pulse frequency in the early (April) and late (August) phases of their first anestrous season. This response was similar to that previously found in prepubertal female sheep. Only 5 of the 8 females responded to the same naloxone challenge in mid anestrus (June), suggesting that the contribution of opioid pathways to the inhibition of LH secretion at this time of year is not necessarily the same as that in early and late anestrus. None of the older anestrous sheep (greater than or equal to 2 yr) responded to naloxone in June, indicating age-related changes in the role of endogenous opioid mechanisms in the inhibition of LH secretion. Ovary-intact mature sheep did not respond to naloxone, in contrast to our previous observations in intact prepubertal females. We infer that the neural mechanisms underlying the superficially similar hypogonadotropic states that occur during the prepubertal period, first anestrous season, and later anestrous seasons are not identical.(ABSTRACT TRUNCATED AT 250 WORDS)
Schall
R E
RE
Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor 48109-0404.
Ebling
F J
FJ
Karsch
F J
FJ
Foster
D L
DL
D000367:Age Factors; D000780:Anestrus / Q000502:physiology; D000818:Animals; D004723:Endorphins / Q000037:antagonists & inhibitors / Q000502:physiology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000378:metabolism*; D009270:Naloxone / Q000494:pharmacology; D012621:Seasons; D012741:Sexual Maturation / Q000502:physiology*; D012756:Sheep
D004723:Endorphins; D007987:Gonadotropin-Releasing Hormone; D009270:Naloxone; D007986:Luteinizing Hormone