Decreases in mediobasal hypothalamic and preoptic area opioid ([3H]naloxone) binding are associated with the progesterone-induced luteinizing hormone surge.
In view of evidence implicating hypothalamic opioid systems in the control of LH release, we have examined the binding of [3H]naloxone (NAL) to slices of mediobasal hypothalamus (MBH) and preoptic area (POA) during the induction of an afternoon LH surge (1630-1700 h) in estradiol benzoate (EB)-primed ovariectomized (OVX; day 0) rats by treatment with progesterone (P; day 2). Such a surge was invariably accompanied by a decrease from early morning (1000 h) values in the number of NAL-binding sites detectable in the MBH, while the affinity of the binding site was not affected over the course of the day. Time-course studies indicated that P injection at 1000 h on day 2 was followed by a transient midday elevation in the amount of NAL bound to slices of MBH; the binding decreased significantly before the onset of and during the LH surge. A similar diurnal change was not observed in MBH slices of either oil-treated OVX rats (controls) or EB-treated OVX rats, which displayed only a 2-fold increase in LH release in the afternoon. Further studies indicated a similar change in NAL binding to slices of the POA of EBP-treated rats. Since hypothalamic opioid systems inhibit LH release, the decrease in opioid binding to MBH as well as POA slices suggests that P may curtail the existing opioid inhibitory influence in these areas before and during the course of the afternoon LH surge.
Jacobson
W
W
Department of Obstetrics and Gynecology, University of Florida College of Medicine, Gainesville 32610.
Kalra
S P
SP
D000818:Animals; D005260:Female; D007033:Hypothalamus, Middle / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D007986:Luteinizing Hormone / Q000378:metabolism*; D009270:Naloxone / Q000378:metabolism*; D010052:Ovariectomy; D011301:Preoptic Area / Q000187:drug effects / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000378:metabolism*
D011957:Receptors, Opioid; D009270:Naloxone; D011374:Progesterone; D007986:Luteinizing Hormone