Kerrigan J R, Dalkin A C, Haisenleder D J, Yasin M, Marshall J C
Department of Pediatrics, University of Virginia Health Sciences Center, Charlottesville 22908.
Endocrinology. 1993 Nov;133(5):2071-9. doi: 10.1210/endo.133.5.8404655.
Gonadotropin subunit gene transcription and messenger RNA (mRNA) levels are differentially regulated by GnRH pulse frequency and amplitude in the male rat. The rapid changes of subunit mRNA levels and LH and FSH secretion during the estrous cycle, particularly the rapid rise in LH-beta subunit mRNA on proestrus afternoon, suggest that physiological changes in the pattern of GnRH action may also be important in female rats. However, in the absence of a GnRH-deficient female model the role of varying GnRH stimulation remains to be determined. We have characterized a GnRH-deficient model by administering the alpha-adrenergic antagonist phenoxybenzamine (PBZ) to ovariectomized (OVX) rats. Initial experiments showed that PBZ given 24 h earlier abolished the afternoon LH surge in OVX estradiol (E2) replaced rats whereas LH responses to exogenous GnRH were preserved. A PBZ regimen of 15 mg/kg ip at OVX followed by 10 mg/kg at 24 h and 5 mg/kg at 48 h prevented the increase in alpha, LH-beta, and FSH-beta mRNAs and LH and FSH secretion for 72 h post-OVX. LH and FSH responses to GnRH pulses were preserved suggesting that PBZ blocked the post-OVX increase in hypothalamic GnRH secretion. The suppressive effect of PBZ appeared to be specific to the hypothalamic-pituitary-ovarian axis as plasma PRL, TSH, and corticosterone were not decreased compared to controls. We have used this GnRH-deficient OVX female model to investigate the effects of exogenous GnRH pulses on subunit mRNA expression. GnRH pulses (5-250 ng/30 min for 12-24 h) were administered via an intraatrial catheter beginning 24 h after OVX and the first PBZ injection (OVX+PBZ+saline pulses to controls). Expression of alpha and FSH-beta mRNAs and LH and FSH secretion were increased by GnRH pulse doses of 5-25 ng to values similar to or greater than those in OVX controls though the higher doses of GnRH/pulse did not increase FSH-beta mRNA or plasma FSH. However, LH-beta mRNA levels were not increased by GnRH pulses. GnRH pulses were also given to rats replaced with proestrus concentrations of estradiol alone or in combination with progesterone (P). Again, no demonstrable increases in LH-beta mRNA expression were observed. alpha-mRNA concentrations were further increased in the presence of E2 alone, and P in combination with E2, produced an augmented response of FSH-beta subunit mRNA. These data suggest that ovarian steroid hormones act directly on the gonadotrope to augment alpha and FSH-beta mRNA responses to GnRH.(ABSTRACT TRUNCATED AT 400 WORDS)
促性腺激素亚基基因转录及信使核糖核酸（mRNA）水平在雄性大鼠中受促性腺激素释放激素（GnRH）脉冲频率和幅度的差异调节。发情周期中，亚基mRNA水平以及促黄体生成素（LH）和促卵泡生成素（FSH）分泌的快速变化，尤其是发情前期下午LH-β亚基mRNA的迅速升高，表明GnRH作用模式的生理变化在雌性大鼠中可能也很重要。然而，由于缺乏GnRH缺陷雌性模型，不同GnRH刺激的作用仍有待确定。我们通过给去卵巢（OVX）大鼠注射α-肾上腺素能拮抗剂酚苄明（PBZ）来建立GnRH缺陷模型。初步实验表明，提前24小时给予PBZ可消除OVX雌二醇（E2）替代大鼠的下午LH峰，而LH对外源性GnRH的反应得以保留。在OVX时腹腔注射15mg/kg的PBZ方案，随后在24小时时注射10mg/kg，48小时时注射5mg/kg，可在OVX后72小时内阻止α、LH-β和FSH-β mRNA以及LH和FSH分泌的增加。LH和FSH对GnRH脉冲的反应得以保留，表明PBZ阻断了OVX后下丘脑GnRH分泌的增加。PBZ的抑制作用似乎对下丘脑-垂体-卵巢轴具有特异性，因为与对照组相比，血浆催乳素（PRL）、促甲状腺激素（TSH）和皮质酮并未降低。我们利用这个GnRH缺陷的OVX雌性模型来研究外源性GnRH脉冲对亚基mRNA表达的影响。在OVX和首次注射PBZ后24小时开始，通过心房内导管给予GnRH脉冲（5 - 250ng/30分钟，持续12 - 24小时）（OVX + PBZ + 生理盐水脉冲作为对照）。5 - 25ng的GnRH脉冲剂量可使α和FSH-β mRNA的表达以及LH和FSH的分泌增加，达到与OVX对照组相似或更高的值，尽管更高剂量的GnRH/脉冲并未增加FSH-β mRNA或血浆FSH。然而，GnRH脉冲并未增加LH-β mRNA水平。也给仅用发情前期浓度的雌二醇或雌二醇与孕酮（P）联合替代的大鼠给予GnRH脉冲。同样，未观察到LH-β mRNA表达有明显增加。单独存在E2时，α-mRNA浓度进一步升高，P与E2联合使用时，FSH-β亚基mRNA的反应增强。这些数据表明，卵巢甾体激素直接作用于促性腺细胞，增强α和FSH-β mRNA对GnRH的反应。（摘要截断于400字）
