Ghuman S P S, Jones D N, Prabhakar S, Smith R F, Dobson H
Department of Veterinary Clinical Science, University of Liverpool, Wirral, UK.
Reprod Domest Anim. 2008 Oct;43(5):531-41. doi: 10.1111/j.1439-0531.2007.00948.x. Epub 2008 Feb 25.
The present study examines the involvement of GABA(A or B) receptors in gonadotrophin-releasing hormone (GnRH) release in vitro and determines whether oestradiol modulates gamma-aminobutyric acid (GABA)-GnRH interaction. Within 10 min after ewe killing, hypothalamic slices were dissected and placed in oxygenated Minimum Essential Media (MEM)-alpha at 4 degrees C; within 2 h, slices were singly perifused at 37 degrees C with oxygenated MEM-alpha (0.15 ml/min), with or without oestradiol (24 pg/ml). After 4 h equilibration, fractions were collected for 4 h interposed with a 10 min exposure to specific GABA(A or B) receptor ligands (0.1-10 mM). The GABA(A or B) agonists (muscimol or baclofen) did not greatly influence GnRH release. However, GnRH increased (p < 0.05) after exposure to 10 mM GABA(A or B) antagonists (bicuculline or CGP52432, respectively). The GABA(A) antagonist stimulated greater sustained GnRH release (p < 0.05) in the absence of oestradiol than in its presence. The bioactivity of the released GnRH was studied using a hypothalamus-pituitary sequential double-chamber perifusion. Only after exposure of hypothalamic slices to the GABA(A) antagonist, did the hypothalamic eluate stimulate luteinizing hormone release from pituitary fragments (p < 0.05) confirming that the GABA(A) antagonist stimulated release of biologically active GnRH. In summary, GnRH release from the hypothalamus is predominantly under GABA(A) receptor inhibitory control and this is attenuated in the presence of oestradiol.
本研究检测了γ-氨基丁酸A（GABA(A)）或B（GABA(B)）受体在体外促性腺激素释放激素（GnRH）释放中的作用，并确定雌二醇是否调节γ-氨基丁酸（GABA）与GnRH的相互作用。在母羊处死10分钟内，解剖下丘脑切片并置于4℃的充氧α-最低必需培养基（MEM）中；在2小时内，将切片在37℃下以充氧的MEM-α（0.15毫升/分钟）单独灌流，添加或不添加雌二醇（24皮克/毫升）。平衡4小时后，收集馏分4小时，期间穿插10分钟暴露于特定的GABA(A)或B受体配体（0.1 - 10毫摩尔）。GABA(A)或B激动剂（蝇蕈醇或巴氯芬）对GnRH释放影响不大。然而，暴露于10毫摩尔的GABA(A)或B拮抗剂（分别为荷包牡丹碱或CGP52432）后，GnRH增加（p < 0.05）。在没有雌二醇存在时，GABA(A)拮抗剂比有雌二醇存在时刺激GnRH释放更持久（p < 0.05）。使用下丘脑-垂体顺序双室灌流研究释放的GnRH的生物活性。只有在下丘脑切片暴露于GABA(A)拮抗剂后，下丘脑洗脱液才刺激垂体碎片释放促黄体生成素（p < 0.05），证实GABA(A)拮抗剂刺激了生物活性GnRH的释放。总之，下丘脑GnRH的释放主要受GABA(A)受体抑制性控制，且在有雌二醇存在时这种抑制作用减弱。
