Fletcher T P, Thomas G B, Willoughby J O, Clarke I J
Prince Henry's Institute of Medical Research, Clayton, Vic., Australia.
Neuroendocrinology. 1994 Jul;60(1):76-86. doi: 10.1159/000126722.
The effect of hypothalamopituitary disconnection (HPD) on growth hormone (GH) secretion was studied in sheep. Plasma GH levels were measured in serial blood samples (10 min x 6-8 h) taken from 12 Romney wethers and 5 ewes which had undergone HPD 40-506 days earlier and from 4 wethers (10 min x 7 h) to serve as controls. Five wethers and 5 ewes were taken approximately 300 days after HPD and injected with vehicle or 10 micrograms/kg of the synthetic hexapeptide growth hormone-releasing peptide 6 (GHRP-6); GH responses were monitored. In a second series of sheep, 4 wethers and 6 HPD wethers were given saline, 0.5 micrograms/kg of synthetic growth hormone-releasing factor (GRF) or 5 micrograms/kg GHRP-6 and were blood-sampled to measure the plasma GH response. A further group of 4 HPD wethers and 3 control wethers were killed and the anterior pituitary glands collected for the quantification of GH and LH beta mRNA by Northern analysis. Three HPD wethers and 1 HPD ewe and 1 control ewe were killed and their brains were perfused; the hypothalami were sectioned and immunostained for the presence of GRF-containing fibres in the median eminence. Normal episodic GH secretion was abolished by HPD in both wethers and ewes but plasma values did not fall below the assay detection limit, indicating constitutive secretion. Northern blot analyses showed that the GH mRNA was detectable in HPD wethers at a lower (p < 0.05) level than in control animals but mRNA for LH beta was undetectable in the HPD wethers. Immunohistochemistry revealed GRF-positive staining in the median eminence of the controls but GRF-positive staining was not seen below the operation site in the median eminence of the HPD animals. In the first series, 3/5 wethers and 3/5 of the ewes responded to GHRP-6 challenge; the magnitude of the response was similar in both sexes. In the second series, responses to GRF were lower (48%) (p < 0.03) in HPD wethers than in control wethers, and responses to GHRP-6 were much lower (p < 0.01) than those to GRF in both controls and HPD wethers. These studies show that HPD removes GRF inputs to the pituitary gland and abolishes pulsatile GH secretion in most cases but constitutive non-pulsatile secretion continues. The HPD wether pituitary glands had lower GH mRNA levels than controls. Accordingly, HPD sheep were able to respond to a single injection of GRF although the response was half that seen in control animals.(ABSTRACT TRUNCATED AT 400 WORDS)
在绵羊中研究了下丘脑 - 垂体切断术（HPD）对生长激素（GH）分泌的影响。对12只罗姆尼阉羊和5只母羊（40 - 506天前接受了HPD）以及4只作为对照的阉羊（10分钟×7小时）采集连续血样（10分钟×6 - 8小时），测量血浆GH水平。在HPD后约300天选取5只阉羊和5只母羊，分别注射溶媒或10微克/千克的合成六肽生长激素释放肽6（GHRP - 6）；监测GH反应。在另一组绵羊中，给4只阉羊和6只接受HPD的阉羊注射生理盐水、0.5微克/千克的合成生长激素释放因子（GRF）或5微克/千克GHRP - 6，然后采血样以测量血浆GH反应。再选取4只接受HPD的阉羊和3只对照阉羊处死，收集垂体前叶，通过Northern分析定量GH和LHβmRNA。处死3只接受HPD的阉羊、1只接受HPD的母羊和1只对照母羊，对其大脑进行灌注；将下丘脑切片并进行免疫染色，以检测正中隆起中含GRF纤维的存在。HPD使阉羊和母羊的正常GH脉冲式分泌消失，但血浆值未降至检测限以下，表明存在组成性分泌。Northern印迹分析显示，接受HPD的阉羊中GH mRNA水平低于对照动物（p < 0.05），但接受HPD的阉羊中未检测到LHβmRNA。免疫组织化学显示对照动物正中隆起有GRF阳性染色，但接受HPD动物的正中隆起手术部位以下未见GRF阳性染色。在第一组实验中，3/5的阉羊和3/5的母羊对GHRP - 6刺激有反应；两性反应幅度相似。在第二组实验中，接受HPD的阉羊对GRF的反应低于对照阉羊（48%）（p < 0.03），且接受HPD的阉羊和对照阉羊对GHRP - 6的反应均远低于对GRF的反应（p < 0.01）。这些研究表明，HPD消除了垂体的GRF输入，在大多数情况下消除了GH的脉冲式分泌，但组成性非脉冲式分泌仍继续存在。接受HPD的阉羊垂体中GH mRNA水平低于对照。因此尽管接受HPD的绵羊对单次注射GRF有反应，但其反应仅为对照动物的一半。（摘要截短至400字）
