Circulating Molecular Variants of Growth Hormone in Childhood

Abstract

ABSTRACT. Human growth hormone (hGH) is known to "bioinactive hGH" as a basis for growth failure (13,14). Recent consist of several molecular forms. We examined the mo-improvements in the sensitivity of analytical techniques have lecular nature of circulating hGH in 18 normal children made it possible to achieve that goal. and compared the resulting patterns to those previously obtained in adults. hGH secretion was stimulated with L-MATERIALS A N D METHODS dopa, the hormonal forms were extracted from plasma by hmunoadsorbent chromatography, and their molecular Subjects. Eighteen prepubertal children, aged 6-1 3 yr, particnature was analyzed by polyacrylamide gel electrophoresis. ipated in the study. Eleven were boys and seven were girls. All Circulating monomeric hGH consisted of 73% hGH22~, underwent a standard L-dopa test (500 mg/m2) and blood was 16% hGH20~, and 10% of an acidic hGH from (N,-acylated drawn at 30. 60, and 90 min after administration of the secretaor deamidated hGH). These relative proportions are indis-gogue. The tests were performed as part of the diagnostic procetinguishable from those found in the plasma of adults. No dures for short stature. All children had normal growth age or sex differences in the circulating hGH Pattern were velocity. Ethical considerations prompted us to perform pharfound. We conclude that the types and proportions of hGH macological testing and venipunctures only in children where a forms in the blood of normal children are the same as those medical indication existed. Following full diagnostic work-up, all previously established in adults. These data provide a children were found to have normal endocrine function and no framework against which children with postulated struc-identifiable disease. The subsequent clinical course over a 2-yr turally abnormal ("bioinactive") hGH can be compared. period confirmed this assessment. All children had peak hGH (Pediatr Res 22: 21 -22, 1987) responses exceeding 7 ng/ml (range 9.7-35.6 ng/ml) after Ldopa. Blood samples obtained at the time of spontaneous elevaAbbreviations tion of hGH in two children were also included. The procedures had been approved by the Institutional Review Boards for HuhGH, human growth hormone man Experimentation at both participating institutions. PAGE, polyacrylamide gel electrophoresisAnalysis. Plasma from one to three time points was pooled to SDS, sodium dodecyl sulfate yield a minimum quantity of hGH of 20 ng (range 20-108 ng). hGH and all its variants were then extracted from plasma by immunoadsorbent chromatography as described in detail previously (3). The extracted hGH was analyzed for molecular variants hGH consists of several distinct moIecuIar forms (1,2). Recent by PAGE under nondenaturing conditions at pH 7.5 in a disconevidence has shown that in adult man, at least three monomeric tinuous TES-acetate-chloride-Bistris buffer system. Experimental species and several hGH oligomers circulate in blood (3-7). The details of these procedures have been reported previously (3, 15). three ~G H m...

Growth Hormone Binding Proteins and Various Forms of Growth Hormone: Implications for Measurements

“…After a secretory stimulus, the following GH variants appear in plasma: 22 kDa, 20 kDa, one or more not fully characterized 'acidic' forms (deamidated and/or acylated GH), and oligomers composed of these variants (dimeric to pentameric GH) (7,8,33,(36)(37)(38)(39). Oligomers are either non-covalent aggregates (approximately 65 %) or disulphide-linked (approximately 35%) (36,37).…”

“…Oligomers are either non-covalent aggregates (approximately 65 %) or disulphide-linked (approximately 35%) (36,37). The mixture of GH forms released appears to be independent of the type of stimulus, or the age or sex of the subject (38,39). In addition, 16 kDa, 12 kDa and 30 kDa forms are found in plasma (8), but it is not known whether they are secreted or are fragments derived from peripheral metabolism of GH.…”

Factors Modifying Growth Hormone Estimates in Immunoassays

“…1], of which the 22-and the 20-kD variants predominate. The 20-kD molecule has reduced bioactivity and reduced affinity for the GH receptor compared to the 22-kD variant [2,3], It has been demonstrated that the relationship in the circulation be tween the two variants (and some posttranslation-modi fied forms) is the same independently of the form of secre tion (i.e., spontaneous or stimulated), gender, and age [4,5]. This reduces the number of variables contributing to the uncertainty of GH estimates in the individual GH assay.…”

Metabolism of Growth Hormone (GH) and Different Molecular Forms of GH in Biological Fluids

“…20K and one or more acidic [deamidated and acylated] forms) in plasma shortly after a spontaneous or pharmacologically in duced secretory burst [29,[46][47][48], Their relative propor tions are the same regardless of the secretory stimulus used [49], they are age-and sex-independent. Children secrete the same GH forms as adults [50]. In addition to the monomeric forms just listed, an oligomeric series up to pentameric GH.…”