FP04-5 Release of Estradiol in the Hypothalamus of Ovariectomized Female Monkeys (Macaca Mulatta): A Possible Role in Control of Gonadotropin Releasing Hormone Release

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: FP04-GnRH & Gonadotroph Biology & Signaling
Saturday, June 15, 2013: 11:00 AM-11:30 AM
Presentation Start Time: 11:20 AM
Room 135 (Moscone Center)

Poster Board SAT-135
Brian P Kenealy*, Amita Kapoor, Kathryn A Guerriero, Kim L Keen, Toni E Ziegler and Ei Terasawa
University of Wisconsin-Madison, Madison, WI
Estrogens play a pivotal role in regulating GnRH neuronal function in female mammals. In primates, systemic administration of estradiol benzoate (EB) induces negative feedback effects with a latency of ~2 h and positive feedback effects with a latency of ~24 h. Earlier in vitro studies from this lab, however, show that estradiol (E2) results in a rapid stimulatory action, similar to a neurotransmitter effect, in cultured GnRH neurons derived from fetal olfactory placodes. Therefore, in the present study, we examined whether 1) brief infusion of EB into the hypothalamus induces GnRH release in vivo, and if so, 2) whether there is any physiological significance in the hypothalamus using a microdialysis method. A microdialysis probe was inserted into the median eminence-stalk region of the medial basal hypothalamus (MBH) in ovariectomized (OVX) female rhesus monkeys through a cranial pedestal as described previously. EB at 10-100 nM was infused into the MBH through the microdialysis probe for 20 min, while dialysate samples were continuously collected at 10 or 20 min intervals for up to 12 h. GnRH and E2 in the same dialysates were measured by RIA and liquid chromatography-mass spectrometry (LC/MS), respectively. Results indicate that infusion of EB into the MBH for 20 min stimulated GnRH release with a latency of 10 min, similar to those seen in vitro. To our surprise, EB also induced an increase in the release of E2 immediately following the EB-induced GnRH increase and following each subsequent GnRH pulse. While E2 levels prior to EB challenge were either not seen or were seen as sporadic increases peaking at 100-250 pg/ml, EB induced pulsatile E2 release with uniform peaks reaching 700-2000 pg/ml. Elevated levels of E2 were of hypothalamic origin, because 1) animals were OVX for several months, 2) LC/MS distinguishes E2 from EB, 3) E2 release became pulsatile with uniform peaks after EB infusion, and 4) a series of experiments examining if EB metabolizes into E2 indicated that this was not the case. Accordingly, we focused on examining the concept that E2 release observed in our studies is hypothalamic neuroestrogen. First, we found that electrical stimulation of the MBH in OVX monkeys stimulated not only GnRH release, but also E2 release. Second, infusion of the aromatase inhibitor, letrozole (100 nM), through the microdialysis probe resulted in suppression of pulsatile GnRH release and letrozole blocked EB-induced GnRH as well as EB-induced E2 increases. It is concluded that neuroestrogen is synthesized and released in the MBH and appears to play a role in regulating pulsatile GnRH release. How circulating ovarian E2 interacts with hypothalamic neuroestrogen in control of GnRH release remains to be investigated.

Nothing to Disclose: BPK, AK, KAG, KLK, TEZ, ET

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: Wisconsin National Primate Research Center base grant, P51OD011106 / P51RR000167; NIH grants HD15433 and HD11355 awarded to ET; NIH T32 training grant 5T32HD041921-09 awarded to BPK