Turzillo A M, Nett T M
Department of Physiology, Colorado State University, Fort Collins 80523, USA.
Biol Reprod. 1997 Jun;56(6):1537-43. doi: 10.1095/biolreprod56.6.1537.
In cultured ovine pituitary cells, inhibin increases concentrations of mRNA encoding GnRH receptor and numbers of GnRH receptors. The objective of this study was to test the hypothesis that inhibin increases concentrations of ovine GnRH receptor mRNA in vivo. Ovariectomized ewes were used to eliminate effects of endogenous ovarian hormones, and passive immunization against GnRH was employed to avoid possible confounding influences of GnRH on GnRH receptor gene expression. Two groups of ewes (n = 5/group) were treated with 50 ml GnRH antiserum on Days 0 and 3 of the experiment. One group of immunized ewes received 10 ml charcoal-extracted bovine follicular fluid (bFF) as a source of inhibin every 8 h for 48 h on Days 4-6 of the experiment. A third group of ewes was not passively immunized and was treated only with bFF, and control ewes received no treatments. Anterior pituitary glands were collected from all ewes on Day 6. Passive immunization against GnRH, alone or in combination with treatment with bFF, decreased mean concentrations of LH (p < 0.01) and LH pulse amplitude (p < 0.001). In ewes treated only with GnRH antiserum, number of LH pulses was also reduced (p < 0.03). Circulating concentrations of FSH tended to be lower (p = 0.06) in passively immunized ewes compared to controls. Treatment with bFF, alone or in combination with GnRH antiserum, reduced circulating concentrations of FSH (p < 0.02) and amounts of FSHbeta subunit mRNA (p < 0.001) to less than 30% and 10% of control values, respectively. Despite effects of bFF on concentrations of FSHbeta mRNA and secretion of FSH, concentrations of GnRH receptor mRNA were similar among controls, ewes treated with bFF alone, and passively immunized ewes treated with bFF. Passive immunization against GnRH did not affect concentrations of GnRH receptor mRNA but resulted in a reduction (p < 0.05) in amount of LHbeta mRNA. Treatment with bFF did not affect amounts of either alpha subunit or LHbeta subunit mRNA except when combined with treatment with antiserum, when amounts of both alpha and LHbeta subunit mRNA were reduced (p < 0.05). These results do not support the hypothesis that inhibin increases concentrations of GnRH receptor mRNA in the ewe, and they provide evidence that inhibin is not an acute regulator of ovine GnRH receptor gene expression in vivo.
在培养的绵羊垂体细胞中，抑制素可增加编码促性腺激素释放激素（GnRH）受体的mRNA浓度以及GnRH受体的数量。本研究的目的是验证抑制素在体内可增加绵羊GnRH受体mRNA浓度这一假说。采用去卵巢母羊以消除内源性卵巢激素的影响，并采用GnRH被动免疫来避免GnRH对GnRH受体基因表达可能产生的混杂影响。在实验的第0天和第3天，对两组母羊（每组n = 5）给予50 ml GnRH抗血清。在实验的第4 - 6天，一组免疫母羊每8小时接受10 ml经活性炭处理的牛卵泡液（bFF）作为抑制素来源，持续48小时。第三组母羊未进行GnRH被动免疫，仅接受bFF处理，而对照组母羊未接受任何处理。在第6天从所有母羊采集垂体前叶。单独或与bFF处理联合进行的GnRH被动免疫降低了LH的平均浓度（p < 0.01）和LH脉冲幅度（p < 0.001）。在仅用GnRH抗血清处理的母羊中，LH脉冲次数也减少了（p < 0.03）。与对照组相比，被动免疫母羊的促卵泡激素（FSH）循环浓度有降低趋势（p = 0.06）。单独或与GnRH抗血清联合使用bFF处理，可使FSH的循环浓度（p < 0.02）和FSHβ亚基mRNA量（p < 0.001）分别降至对照值的30%和10%以下。尽管bFF对FSHβ mRNA浓度和FSH分泌有影响，但对照组、单独接受bFF处理的母羊以及接受bFF处理的被动免疫母羊之间，GnRH受体mRNA浓度相似。对GnRH进行被动免疫不影响GnRH受体mRNA浓度，但导致LHβ mRNA量减少（p < 0.05）。单独使用bFF处理不影响α亚基或LHβ亚基mRNA量，但与抗血清联合处理时，α和LHβ亚基mRNA量均减少（p < 0.05）。这些结果不支持抑制素可增加母羊GnRH受体mRNA浓度这一假说，并且提供了证据表明抑制素在体内不是绵羊GnRH受体基因表达的急性调节因子。
