20K is bound with high affinity by one rat and one of two rabbit growth hormone receptors.

A naturally occurring variant of human (h)GH, designated 20K, is equipotent with hGH(22K) in stimulating growth in hypophysectomized rats. However, despite high growth-promoting activity in vivo, 20K is a poor inhibitor of 125I-hGH(22K) binding to GH receptors in radioreceptor assays. In order to resolve the differences between bioassay and radioreceptor assay data, we have examined the binding of 20K to rat and rabbit liver GH receptors. Our data indicate that the GH receptor in rat liver binds 20K with an affinity only slightly lower than that for hGH(22K), in accordance with bioassay data. In the rabbit, however, 20K is bound with high affinity by only a small subset of the GH receptors which bind hGH(22K) with high affinity. The GH receptors which bind 20K appear to belong to the same of subset of receptors which bind rat and rabbit GH with high affinity.

Comparative study of serum human growth hormone measurement with NB2 lymphoma cell bioassay, IM-9 receptor modulation assay, and radioimmunoassay in children with disorders of growth.

The biological activity of GH in serum from 10 adult volunteers, 6 children with normal stature, and 26 children with growth retardation was assessed using the Nb2 rat lymphoma cell bioassay and the IM-9 human lymphocyte receptor modulation assay. The bioassay/RIA ratios for both bioassays varied widely but the range of ratios found in the normal stature adults and children was not different than that found in the group of children with growth retardation, which included 4 children with a presumptive diagnosis of bioinactive GH. We conclude that the use of these two bioassays is a valid approach to the assessment of the bioactivity of the circulating molecular forms of GH and that a large number of children with disorders of growth can be screened to identify patients with bioinactive GH.

Serum levels of 20-kilodalton human growth hormone (GH) are parallel those of 22-kilodalton human GH in normal and short children.

Twenty-kilodalton human GH (20K), which is one of the human GH (hGH) variants, is thought to be produced by alternative premessenger ribonucleic acid splicing. However, its physiological role is still unclear due to the lack of a specific assay. We have measured serum 20K and 22-kDa hGH (22K) by specific ELISAs to investigate the physiological role of 20K in children. The subjects were 162 normal children, aged 1 month to 20 yr; 12 patients with GH deficiency (GHD), aged 11 months to 13 yr; 57 children with non-GHD short stature, aged 2-17 yr; and 13 girls with Turner's syndrome, aged 5 months to 15 yr. Samples were collected at random from normal children and were collected after hGH provocative tests and 3-h nocturnal sleep from GHD, non-GHD short stature, and Turner's syndrome children. The mean basal serum concentrations of 22K and 20K were 2.4 +/- 2.8 ng/mL and 152.3 +/- 184.0 pg/mL in normal boys and 2.5 +/- 3.1 ng/mL and 130.6 +/- 171.5 pg/mL in normal girls, respectively. The percentages of 20K (%20K) were 5.8 +/- 2.1% and 6.0 +/- 3.2% in 83 normal boys and 79 normal girls, respectively. There was no significant difference in %20K either among ages or between the prepubertal stage and the pubertal stage in normal boys and girls. The mean %20K values in basal samples of provocative tests in 12 patients with GHD, non-GHD short stature, and Turner's syndrome were 6.5 +/- 2.4%, 6.5 +/- 3.8%, and 5.9 +/- 3.2%, respectively. There was no significant difference in %20K among normal children and these growth disorders, and there was no significant difference in %20K throughout the hGH provocative tests and 3-h nocturnal sleep in these growth disorders. There was also no significant correlation between the percentage of 20K and the height SD score or body mass index in either normal children or subjects with these growth disorders. In conclusion, the %20K is constant, regardless of age, sex, puberty, height SD score, body mass index, and GH secretion status. The regulation of serum 20K levels remains to be established.

Sequence analysis of the thyrotropin (TSH) receptor gene in congenital primary hypothyroidism associated with TSH unresponsiveness.

Congenital primary hypothyroidism due to thyrotropin (TSH) unresponsiveness is a very rare disorder and only a few cases have been documented previously. To elucidate whether structural abnormalities in the TSH receptor (TSHR) could be a primary underlying mechanism of this disorder, we analyzed nucleotide sequence of the entire coding region of the TSHR gene in three patients diagnosed with congenital primary hypothyroidism associated with TSH unresponsiveness. Diagnosis of TSH unresponsiveness was largely made based on the following criteria: (a) congenital primary hypothyroidism with autosomal recessive inheritance, (b) a nongoitrous thyroid gland in a normal position with low thyroidal radioactive iodine uptake, (c) normal in vitro TSH bioactivity or absent in vivo response to exogenous TSH, and (d) absence of thyroid autoantibodies. The TSHR cDNA was successfully obtained from RNA of peripheral mononuclear leukocytes with reverse transcription and polymerase chain reaction, and was sequenced directly. Comparison of these nucleotide sequences with the normal TSHR sequence revealed no difference in the predicted amino acid sequence with a heterozygous polymorphism in codon 601 in one patient, indicating absence of TSHR structural abnormalities in these patients. Our results indicate that congenital primary hypothyroidism associated with TSH unresponsiveness is unlikely to be due to mutations in the TSHR-structure gene.

Measurement of the skin urocanic acid content in normal and histidinemic infants.

The urocanic acid content of the skin was measured photometrically in a large number of normal and histidinemic infants. A very high content was demonstrated in the normal newborn infants, followed by a rapid decrease throughout early infancy. In contrast, 36 measurements in 17 infants with histidinemia revealed a much lower content even in their newborn periods. Thus, the quantification of skin urocanic acid was considered to be simple and useful for confirming the diagnosis of histidinemia, especially in a neonatal mass-screening program.

Serum insulin-like growth factor I (somatomedin-C) level in normal subjects from infancy to adulthood, pituitary dwarfs and normal variant short children.

Serum levels of IGF-I were radioimmunoassayed after acid ethanol extraction in 1075 normal subjects from infants through young adults, and the normal range for each age was established. The mean value for infants which was relatively low increased gradually with age, and rose sharply after that reaching the peak levels at mid adolescence, then it decreased slowly to the young adult levels. Significantly higher mean values were observed in females at the age of 9, 10, 11 and 12 years. Each of 23 cases with pituitary dwarfism exhibited a lower concentration than the lower limit of the bone age matched normal range. All of the 59 normal variant short children except three showed normal values, but the values were distributed over the lower side of the range.

A new form of insulin resistance with growth retardation, fatty liver, and hypogonadotropic hypogonadism.

A 17-year-old boy presented with growth retardation, marked hepatomegaly, and sexual infantilism. Elevated fasting serum insulin levels and a blunted hypoglycemic response to exogenous insulin (up to 0.35 unit/kg) demonstrated severe insulin resistance. Neither anti-insulin nor anti-insulin receptor antibodies were present. The molecular size of his circulating insulin and its binding to IM-9 lymphocytes was normal. Despite high circulating insulin values, both erythrocytes and cultured skin fibroblasts showed normal insulin binding capacity and affinity. Tissue responsiveness was examined by measuring the insulin-induced increase in 2-deoxyglucose uptake into fibroblasts. Although the basal glucose transport rate was slightly lower than that of controls, the insulin-induced increase was normal. However, the normal increase in thymidine incorporation in response to insulin was blunted, as were the thymidine incorporation responses to epidermal growth factor and fibroblast growth factor. These studies demonstrate the possible existence of a new form of post-insulin receptor defect as a cause of insulin resistance, but underscore the difficulty that exists in defining the exact nature of the defect in these disorders.