Arosio M, Nissim M, Ballabio M, Orefice R, Bazzoni N, Faglia G
Institute of Endocrine Sciences, University of Milan, Italy.
Acta Endocrinol (Copenh). 1991 Aug;125(2):150-9. doi: 10.1530/acta.0.1250150.
Circulating GH consists of several molecular size species with different biological activity. A reduced sensitivity of some monoclonal antibodies towards high-molecular weight GH variants has been reported. The aim of the present work was to evaluate the molecular size species of circulating GH using Sephadex G-100 gel filtration chromatography in acromegalic patients and in normal subjects employing both RIA and an immunoradiometric assay for all GH determinations. In 6 normal subjects, studied under GHRH stimulation, little GH was 69.8 +/- 6% (mean +/- SD), big GH (44 kD) 26.4 +/- 6% and big-big GH (greater than 80 kD) 2.8 +/- 4%, in IRMA, with a good correspondence with RIA results (70.8 +/- 8, 27.0 +/- 4, and 3.2 +/- 2%, respectively). In 13 untreated acromegalic patients, studied in basal conditions, the little form constituted 76.2 +/- 7%, the big form 18.3 +/- 4%, which is significantly lower than in normals (p less than 0.05), and the big-big form 5.5 +/- 7%. Similar results were obtained with RIA. A clear elevation of big-big GH (21% for both in IRMA, and 15.7 and 27.8% in RIA) was found in 2 patients with IGF-I levels lower than expected on the basis of mean GH concentrations. The study was extended to an additional acromegalic patient, previously operated and irradiated on, characterized by discrepant serum GH levels in RIA (4.6 micrograms/l), and in IRMA (1.4 micrograms/l), and by normal IGF-I levels. Serum GH showed a lack of parallelism to standard GH in RIA, but not in IRMA. RIA immunoreactivity was almost completely composed (92%) of a high molecular weight GH form (greater than 90 kD), not recognized by IRMA. All IRMA immunoreactivity eluted with a Kav corresponding to 19-50 kD.
a. the three main molecular size isomers of serum GH are similarly recognized by IRMA and RIA methods in normal subjects. b. in acromegaly, both quantitative and qualitative modifications of the GH chromatographic profile may be present. In particular, increased amounts of big-big forms, whether or not recognized by monoclonal antibodies, have been observed. Their lower bioactivity, suggested by the normal or lower than expected IGF-I levels, can account for the discrepancy between serum GH levels and the clinical picture or IGF-I levels sometimes observed in acromegaly.
循环中的生长激素（GH）由几种具有不同生物活性的分子大小种类组成。据报道，一些单克隆抗体对高分子量GH变体的敏感性降低。本研究的目的是使用Sephadex G - 100凝胶过滤色谱法，通过放射免疫分析（RIA）和免疫放射分析（IRMA）测定肢端肥大症患者和正常受试者循环中GH的分子大小种类。在6名接受生长激素释放激素（GHRH）刺激研究的正常受试者中，小GH在IRMA中占69.8±6%（平均值±标准差），大GH（44kD）占26.4±6%，大大GH（大于80kD）占2.8±4%，与RIA结果具有良好的一致性（分别为70.8±8%、27.0±4%和3.2±2%）。在13名未经治疗的肢端肥大症患者的基础状态研究中，小形式占76.2±7%，大形式占18.3±4%，显著低于正常受试者（p＜0.05），大大形式占5.5±7%。RIA也得到了类似结果。在2名胰岛素样生长因子 - I（IGF - I）水平低于根据平均GH浓度预期水平的患者中，发现大大GH明显升高（IRMA中两者均为21%，RIA中分别为15.7%和27.8%）。该研究扩展至另一名曾接受手术和放疗的肢端肥大症患者，其RIA（4.6微克/升）和IRMA（1.4微克/升）测定的血清GH水平存在差异，IGF - I水平正常。血清GH在RIA中与标准GH缺乏平行性，但在IRMA中并非如此。RIA免疫反应性几乎完全由一种高分子量GH形式（大于90kD）组成（92%），IRMA无法识别。所有IRMA免疫反应性以对应于19 - 50kD的分配系数（Kav）洗脱。
a. 在正常受试者中，IRMA和RIA方法对血清GH的三种主要分子大小异构体的识别相似。b. 在肢端肥大症中，GH色谱图可能存在定量和定性改变。特别是，已观察到大大形式的量增加，无论单克隆抗体是否能识别。IGF - I水平正常或低于预期所提示的其较低生物活性，可以解释肢端肥大症中有时观察到的血清GH水平与临床表现或IGF - I水平之间的差异。
