Radioimmunological determination of insulinlike growth factors I and II in normal subjects and in patients with growth disorders and extrapancreatic tumor hypoglycemia

Cardiovascular and metabolic responses during growth hormone treatment of lactating sheep

Pituitary-derived bovine growth hormone (bGH) was administered to six lactating Friesland ewes for 7 d. There was no consistent galactopoietic response, with changes in milk yield varying from 0 to 33% during treatment compared with the pretreatment period. The major effect of bGH on the concentration of milk constituents was to increase fat by 14.2% (P less than 0.05). Treatment resulted in significant increases in arterial plasma concentrations of growth hormone, insulin-like growth factor I and glucose, with decreases in the plasma arterial concentrations of acetate and certain amino acids. There was a marked reduction in haematocrit and in haemoglobin concentration which took at least 3 d to recover. The arterio-venous difference across the mammary gland decreased for O2 during treatment and the veno-arterial difference for CO2 decreased after treatment. Mammary respiratory quotient therefore decreased significantly after bGH treatment. The results suggest that bGH exerts effects at a number of separate loci.

Enhancement of erythropoiesis in vitro by human growth hormone is mediated by insulin-like growth factor I

Insulin-like growth factor I (IGF-I) is the presumed paracrine or autocrine growth-promoting mediator of growth hormone in peripheral tissues. In order to evaluate the role of IGF-I as mediator of human growth hormone (hGH) in erythropoiesis, we compared the effects of both peptides upon in vitro colony formation by primitive (BFU-E) and relatively mature (CFU-E) human erythroid precursors. Biosynthetic IGF-I (2 ng/ml) and hGH (25 ng/ml) induced a significant increase in the growth of both BFU-E and CFU-E. BFU-E growth was maximally enhanced by 6 ng/ml IGF-I and by 50 ng/ml hGH, resulting in an increase in burst numbers of 62 +/- 12% and 52 +/- 12%, respectively. Maximal enhancement of CFU-E growth was detected at higher concentrations of IGF-I (20 ng/ml) and hGH (150 ng/ml), with respective increases of 121 +/- 35% and 137 +/- 18% in colony numbers. Enhancement of bone marrow and peripheral blood erythroid progenitor cell growth by hGH required the presence of monocytes and was abrogated by specific monoclonal antibodies directed against IGF-I membrane receptors. The in vitro growth-promoting effect of hGH upon human erythroid precursors thus appears to be mediated by paracrine IGF-I.

Insulin-like growth factor I stimulates erythropoiesis in hypophysectomized rats

Stimulation of erythropoiesis during growth is necessary to ensure proportionality between erythrocyte mass and body mass. However, the way by which erythrocyte formation is adapted to body growth is still unknown. Growth arrest in hypophysectomized rats is accompanied by decreased erythropoiesis. We have, therefore, examined whether insulin-like growth factor I (IGF-I), the mediator of growth hormone effects on body growth, is able to restore erythropoiesis in these animals. Subcutaneous infusions of 120 micrograms of recombinant human IGF-I per day in hypophysectomized rats led to increases in body weight, 59Fe incorporation into erythrocytes, and the number of reticulocytes that were similar to increases caused by infusions of 28 milliunits of human growth hormone per day. Body weight gain and 59Fe incorporation were linearly correlated. Like growth hormone, IGF-I also caused a significant rise in serum erythropoietin concentrations. However, the stimulatory effect on erythropoiesis occurred before serum erythropoietin levels had risen. These results demonstrate that IGF-I mediates the stimulatory effect of growth hormone on erythropoiesis in vivo and thus further support the somatomedin concept. They also show that IGF-I can stimulate erythropoiesis in an endocrine manner, and they suggest two possible routes of action: a direct one and an indirect one by means of enhanced erythropoietin production.

Determination of circulating levels of insulin-like growth factor II (IGF-II) in swine

A heterologous radioimmunoassay system was developed for the determination of circulating IGF-II concentrations in swine. The assay utilized a monoclonal antibody against human IGF-II (Amano Intl. Ez, VA) and bovine IGF-II (Monsanto Co., MO) as the cold standard and iodinated ligand. Serial dilutions of acid-ethanol extracted normal swine sera resulted in a curve which was parallel to the bovine IGF-II standard curve. Recovery of unlabeled standard added to extracted swine sera was 101%. Neither IGF-I nor insulin were capable of cross-reacting in this assay at levels up to 100-fold excess. Using this assay, serum IGF-II levels were determined to be significantly lower when subnormal growth hormone (GH) levels existed such as in hypophysectomized swine. However, in contrast to serum IGF-I concentrations, supranormal levels of porcine GH (pGH) did not elevate serum IGF-II concentrations after 13 wk of treatment in 25 kg hogs (initial body wt). In addition, serum IGF-II levels were reduced in fasted swine, despite a significant increase in circulating GH concentrations. Thus, although normal concentrations of GH are required for maintenance of physiological levels of IGF-II in swine, the mechanism for stimulation of IGF-II secretion is less GH-dependent than IGF-I.

Presence and characterization of insulin-like growth factor 1 receptors in human benign breast disease

Insulin-like growth factor 1 binding sites were characterized in human benign breast disease. We demonstrated the presence of one high affinity binding site. Chemical cross-linking of [125I]IGF1 to benign breast disease membranes in reducing condition and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed one band with an apparent Mr of 130,000. The specificity of the binding was studied: IGF 2 was a good competitor whereas insulin competed for binding with a potency lower than 1/100 that of IGF1. This IGF1 binding corresponded to the previously described type I IGF receptor (IGF1-R). IGF1-R was assayed in 35 cases of benign breast disease and two samples of normal breast tissue. Forty-three per cent of the lesions were IGF1-R positive. The mean geometric level of specific binding was 1.98% in the whole population, it was significantly lower in adenofibromas (1.55%) than in epithelial hyperplasia (2.5%); it was 2% in dystrophic disease. IGF1-R was undetectable in normal tissue. Considering our previous results showing that almost all the breast cancers contained IGF1-R, these data suggest that the increase in IGF1-R could be a marker of malignant tumor development.

Insulin-like growth factors are mitogens for rat pheochromocytoma PC 12 cells

We have addressed the issue of a mitogenic effect of insulin-like growth factors IGF-I and IGF-II on the PC 12 line of rat pheochromocytoma cells. The proliferation of PC 12 cells cultured in serum-free medium is stimulated threefold by IGF-I and IGF-II with significantly higher potency than epidermal growth factor, whereas platelet-derived growth factor, nerve growth factor, growth hormone and bombesin are inactive. Two types of IGF receptor are present in PC 12 cells and the dose-response curves suggest that the mitogenic responses to IGF's are mediated by the IGF-I receptor. These results suggest that IGF-I and IGF-II act as mitogens on pluripotent chromaffin cells in the development of the peripheral nervous system and adrenal medulla as well as in promotion of in vivo growth of neural crest-derived tumors.

Recombinant human insulin-like growth factor I stimulates growth and has distinct effects on organ size in hypophysectomized rats

Recombinant human insulin-like growth factor I (rhIGF-I) was infused subcutaneously into hypophysectomized rats for as long as 18 days. Three hundred micrograms (39 nmol) of rhIGF-I per day and 200 milliunits (4.5 nmol) of human growth hormone (hGH) per day increased body weight, tibial epiphyseal width, longitudinal bone growth, and trabecular bone formation similarly. Weight gains of the kidneys and spleen, however, were greater with rhIGF-I than with hGH, whereas the weight of the epididymal fat pads was reduced with rhIGF-I. The weight of the thymus was increased by rhIGF-I treatment. Thus, IGF-I administered over a prolonged period of time mimics GH effects in hypophysectomized rats. Quantitative differences between rhIGF-I and hGH treatment with respect to organ weights may be related to different forms of circulating IGF-I or may be due to independent effects of GH and IGF-I. The results support the somatomedin hypothesis, but they also stress the role of GH as a modulator of IGF-I action.

Mannose 6-phosphate/insulin-like growth factor II-binding proteins in human serum and urine. Their relation to the mannose 6-phosphate/insulin-like growth factor II receptor

Human serum and urine contain polypeptides which bind mannose 6-phosphate (M6P) and insulin-like growth factor II (IGF II) and crossreact with antibodies against the M6P/IGF II receptor. These polypeptides are considered to be fragments of the M6P/IGF II receptor. The major Mr approx. 205,000 fragment in serum and urine is about 10 kDa smaller in size than the membrane-associated receptor and is accompanied by minor forms with Mr values ranging from 104,000 to 180,000. The presence of receptor fragments in biological fluids indicates that shedding is one of the mechanisms contributing to the turnover of the M6P/IGF II receptor and that receptor fragments are part of the heterogenous group of serum proteins whic bind IGF II.

An effective method for the separation of insulin-like growth factors 1 and 2 during the purification process

The separation of human insulin-like growth factors hIGF-1 and hIGF-2 was greatly improved by an additional purification step using the cation exchanger Mono-S (FPLC) compared to previous studies. Cross-reactions between hIGF-1 and hIGF-2 were strongly reduced. The more highly purified hIGF-1 had a cross-reaction of less than 1% in the RIA for hIGF-2, and was equivalent to recombinant hIGF-1. The pure hIGF-2 had a cross-reaction of less than 1% in the RIA for hIGF-1. In the human placental hIGF-2 radioreceptor assay, the hIGF-1 polypeptide completed less than 1% with hIGF-2 when the type 1 IGF receptor was blocked with insulin.

Mannose 6-phosphate/insulin like growth factor II receptor: the two types of ligands bind simultaneously to one receptor at different sites

Pentamannose 6-phosphate/trilysine substituted aprotinin (PMP-lys-aprotinin) and insulin like growth factor II (IGF II) were used as affinity ligands for the mannose 6-phosphate (M6P) and IGF II binding sites of the M6P/IGF II receptor. Both ligands were cross linked to intact receptor and tryptic fragments of the receptor. The pattern of receptor fragments with M6P and IGF II binding sites differed indicating that the two binding sites are located on different segments of the receptor. The receptor was incubated with [125I]IGF II and pentamannose 6-phosphate substituted bovine serum albumin (PMP-BSA). From these mixtures [125I]IGF II receptor complexes could be precipitated with antibodies against the PMP-BSA indicating that the M6P/IGF II receptor can bind simultaneously IGF II and M6P-containing ligands.

Growth hormone deficiency and the measurement of somatomedin C/IGF-I: the influence of sexual maturation

Fifty-nine short children 2-19 years, 25 females and 34 males, were studied for clinical and biochemical evidence of growth hormone deficiency (GHD). Group 1 (n = 32), mean height SDS -3.26 +/- 1.5, mean retardation of bone age 2 years, had a mean peak GH of 6.1 +/- 3.7 mIU/l during tests of GH release, and were classified as GHD. Group 2 (n = 27), had a mean height SDS of -2.65 +/- 1, mean bone age retardation of 1.7 years and had a mean peak GH during provocation tests of 24.3 +/- 11.1 mIU/l and were classified as non-GHD. Basal IGF-I concentrations were correlated with height and bone age, for both groups and for GHD children, with pubertal score. Neither peak GH values nor integrated GH concentrations in a provocative test were correlated with IGF-I values. The minimum IGF-I concentrations occurred at a bone age of 8 years, the reference point that was taken as the average expected time of maturational change. IGF-I concentrations rose in five GHD children when their bone age exceeded 8 years and when their free testosterone was greater than 10 pmol/l. Eighty-nine per cent of the GHD children with a bone age at or below 8 years were identified as GHD from their basal IGF-I values, but for all bone ages this fell to 62.5%. Basal IGF-I values appear to be less discriminatory for identification of GHD as sexual maturity and bone age advance.

Enhancement of human granulopoiesis in vitro by biosynthetic insulin-like growth factor I/somatomedin C and human growth hormone

The effect of biosynthetic recombinant insulin-like growth factor I/somatomedin C (IGF-I/Sm-C) and human growth hormone (hGH) on the in vitro growth and maturation of human marrow myeloid progenitors was investigated. Myeloid colony formation was maximally enhanced by 60 ng/ml IGF-I/Sm-C and by 250 ng/ml hGH, resulting in an increase in colony numbers of 41 +/- 7 and 38 +/- 4%, respectively (P less than 0.001). Both peptides induced a 1.5-2.5-fold increase in the frequency of colonies composed of granulocytes alone, but did not alter the numbers of monocyte/macrophage or mixed granulocyte/macrophage colonies. IGF-I/Sm-C and hGH were also found to enhance myeloid maturation towards mature granulocytes in suspension cultures of human marrow cells. The effect of both peptides on human marrow granulopoiesis was similarly demonstrable in serum-free cultures stimulated with human recombinant granulocyte/macrophage colony-stimulating factor. Enhancement of human marrow granulopoiesis in vitro by hGH required the presence of marrow adherent cells and was abrogated by specific monoclonal antibodies directed against IGF-I/Sm-C receptors. The effect of hGH on marrow myeloid progenitors thus appears to be mediated by paracrine IGF-I/Sm-C.

Growth hormone dependent stimulation of osteoblast-like cells in serum-free cultures via local synthesis of insulin-like growth factor I

Gene-recombinant human growth hormone (rhGH) elicited a dose-dependent stimulation of the proliferation of osteoblast-like cells (OB), when grown in strictly serum-free longterm cultures. A half-maximal effect was observed at concentrations of 15-20 ng/ml and the maximal stimulation was 160% of hormone-free controls. The rhGH-induced effect on proliferation could be inhibited dose-dependently by the addition of an insulin-like growth factor (IGF) I-antiserum to the medium. Moreover, IGF I and rhGH had additive effects only when the exogenous IGF I concentration exceeded that of endogenously produced IGF I by a large margin. Thus, direct stimulation of OB proliferation by rhGH is, at least in part, mediated by IGF I-like immunoreactivity.

Mannose 6-phosphate/insulin-like growth factor II receptor: distinct binding sites for mannose 6-phosphate and insulin-like growth factor II

Pentamannosyl phosphate substituted bovine serum albumin (PMP-BSA) and insulin like growth factor II (IGF II) bind specifically to immobilized mannose 6-phosphate/insulin like growth factor II receptor. An excess of IGF II inhibited binding of PMP-BSA by less than or equal to 20%, and an excess of PMP-BSA inhibited binding of IGF II by less than or equal to 10%. Polyclonal antibodies against the receptor purified from human liver inhibited preferentially the binding of PMP-BSA, and a monocloncal antibody 2C2 inhibited only the binding of IGF II to the receptor. Similar results were obtained for binding of PMP-BSA and IGF II to human skin fibroblasts. These results suggest that the binding sites for mannose 6-phosphate and IGF II reside in different portions of the receptor.

Improvement of growth and food utilization by human recombinant growth hormone in uremia

We compared growth rate, food conversion ratio and morphology of the growth zone in female Sprague-Dawley rats with subtotal nephrectomy or sham operation. Both groups were either given vehicle or 1.4 IU/day recombinant human growth hormone (GH) by s.c. osmotic minipump, or 2.5 IU twice daily intraperitoneally for 14 or 20 days, respectively. Compared to uremic rats infused with vehicle, infusion of GH significantly (P less than 0.01) improved growth; that is, it increased gain of weight (delta 27.0 +/- 7.7 g vs. 11.6 +/- 4.9 g) and length (delta 1.8 +/- 0.3 cm vs. 1.12 +/- 0.44 cm) in ad libitum fed uremic rats. This was accompanied by increased food utilization ratio (0.146 vs. 0.065 g weight gain per g food intake). A similar increment of growth and food utilization ratio was also observed in GH versus solvent infused controls, either pairfed as for the uremic animals or fed ad libitum. Despite administration of GH, growth was not completely restored to normal in uremic animals. Circulating immunoreactive IGF I was not significantly increased by GH infusion in either uremic animals or controls. Histological analyses of the proximal tibia showed increased rate of longitudinal growth, as evaluated by tetracyclin-labeling, and increased volumetric density of primary spongiosa with unchanged width of primary spongiosa trabecules when GH was infused in uremic animals. The data suggest that growth impairment in the uremic rat is partially responsive to GH, and this is not accompanied by an increase of circulating IGF I. Therapeutic trials with recombinant GH in uremic children appear justified.

Polycystic ovarian disease: endocrinological parameters with specific reference to growth hormone and somatomedin-C

Thirty-three women (22-38 years old) with polycystic ovarian disease (PCOD) were included in this study. The criteria for diagnosis were: an LH/FSH ratio greater than 2.0; polycystic ovaries, diagnosed by means of palpation and ultrasound; androgenism and menstrual cycle abnormalities. Using endocrine parameters, we attempted to define distinct forms of PCOD. The patients were placed in three groups according to serum levels of testosterone (T) and 17 alpha-hydroxyprogesterone (17 alpha OHP) and the estrone/androstendione (E1/delta 4A) ratio. Patients in group I (n = 18) had an elevated T level (greater than 1.0 ng/ml) and a 17 alpha OHP level under 4.0 ng/ml. This type of POCD was called the "androgen" type. Patients in group II (n = 7) had normal T- and 17 alpha OHP levels under 4.0 ng/ml and an elevated (E1/delta 4A) ratio. This type of PCOD was called the "estrogen" type. Group III (n = 8) comprised patients with 17 alpha OHP levels over 4.0 ng/ml. This type of PCOD was called the "adrenocortical" type. In two patients of this group, a modified ACTH test revealed late-onset congenital hyperplasia. The endocrine parameters of the patients with PCOD were compared with those of 17 adult without signs of PCOD. Statistical evaluation was done by variance analysis. Women with acromegaly often show signs of androgenism as well as menstrual cycle abnormalities. This may indicate an association between the growth factors human growth hormone (HGH) and somatomedin-C (Sm-C) and the biosynthese and metabolism of steroid hormone. Recent experiments have demonstrated such associations. Our study showed an association between the HGH and Sm-C levels and abnormal steroid hormone concentrations in women with androgen type PCOD (group I). These patients had a significantly decreased HGH level, a significantly decreased HGH/Sm-C ratio, and an increased average Sm-C level. These data suggest that elevated Sm-C levels can, by a negative-feedback mechanism, inhibit pituitary HGH production. We discuss the possible mechanisms causing elevation of plasma Sm-C, HGH, steroid hormones, excessive food intake, and possibly prolactin seem responsible for the clinical manifestation of increased Sm-C production in adolescence and for its level in the fertile years of patients.

Developmental and hormonal regulation of mRNAs for insulin-like growth factor II and steroidogenic enzymes in human fetal adrenals and gonads

Insulin-like growth factor II (IGF-II) is regulated developmentally and hormonally in human fetal gonads and adrenals. The abundance of IGF-II mRNA is greatest in RNA from human fetal adrenals, followed by fetal liver, testis, placenta, and ovaries. Fetal testicular IGF-II mRNA decreases significantly with increasing gestational age, in parallel with our previous measurements of the mRNAs for the steroidogenic enzymes P450scc (cholesterol side-chain cleavage enzyme) and P450c17 (17 alpha-hydroxylase/17,20 lyase) (J. Clin. Endocrinol. Metab. 63, 1145, 1986). The abundances of P450scc and P450c17 mRNAs in cultured fetal testis cells rose 2.5-fold (p less than 0.01) and 9.2-fold (p less than 0.001), respectively, in response to 0.5 mM cAMP, but the abundance of IGF-II mRNA was not affected. This suggests that the IGF-II gene is regulated differently in fetal testes than it is in fetal adrenals, placenta, or adult granulosa cells, where we have previously shown that ACTH, cAMP, and gonadotropins, respectively, increase IGF-II mRNA accumulation (Proc. Natl. Acad. Sci. USA 84, 1590, 1987). Exogenously added IGF-I and IGF-II had no effect on mRNAs for P450c17 or P450c21 (21-hydroxylase), but decreased IGF-II mRNA in ACTH-stimulated fetal adrenal cells. Thus, the IGFs appear to exert short-loop feedback inhibition on accumulation of IGF-II mRNA.

Heterogeneity of insulin-like growth factor binding proteins and relationships between structure and affinity. 1. Circulating forms in man

Circulating insulin-like growth factors (IGFs) are bound to specific, high-affinity binding proteins (BPs), and form complexes with relative molecular masses of about 150,000 ('large' complex) and 40,000 ('small' complex). The large complex appears to be under growth-hormone control and its proportions vary with those of the IGFs. Molecular heterogeneity among the binding proteins was revealed by polyacrylamide gel electrophoresis (SDS-PAGE) of serum in which they were cross-linked to 125I-labelled IGF I or II. Out of the six specific bands observed, of 150,000, 120,000, 49,000, 40,000 and 37,000 Mr, the last three appeared in both complexes, whereas the first three were visible only in the large complex. Some or all of the 49,000-37,000-Mr species may constitute the subunits of 150,000-Mr and/or 120,000-Mr IGF-BP complexes. With electrophoresis followed by transfer onto nitrocellulose and incubation with either 125I-labelled IGF I or II (western blot), the different binding proteins were identified per se. There were five molecular forms with Mr of 41,500, 38,500, 34,000, 30,000 and 24,000. In normal serum the 41,500 and 38,500-Mr forms were the major binding proteins. They appeared in both complexes, but were predominant in the large complex where they constitute the elementary binding units. These two proteins therefore bind to IGFs to form both 'monomeric' IGF-BP and 'oligomeric' (IGF-BP)n complexes. The 34,000, 30,000 and 24,000-Mr forms, by contrast, were visible only in the small complex. Different mechanisms appear to regulate the different binding proteins: in acromegalic serum the 41,500 and 38,500-Mr forms were augmented and the 34,000-Mr form diminished, whereas in hypopituitary serum the reverse was true and, in addition, the 30,000-Mr form was augmented. With chromatofocusing, the 34,000, 30,000 and 24,000-Mr forms eluted in three peaks between pH 6.0 and 4.0, whereas the 41,500 and 38,500-Mr forms eluted throughout the gradient, principally at pH 7.5 and 7.0. Competitive binding studies, done on binding proteins separated either by chromatofocusing or by SDS-PAGE and transfer onto nitrocellulose, revealed different affinities for the IGFs among the different molecular forms. The 41,500 and 24,000-Mr binding proteins preferentially bound IGF I and the 38,500, 34,000 and 30,000-Mr proteins preferentially bound IGF II. Our findings demonstrate the molecular heterogeneity of the binding proteins and the existence of a relationship between their structure and their affinities for the IGFs.(ABSTRACT TRUNCATED AT 400 WORDS)

Tissue-specific expression of insulin-like growth factor II mRNAs with distinct 5' untranslated regions

We have used RNA from human hypothalamus as template for the production of cDNAs encoding insulin-like growth factor II (IGF-II). The prohormone coding sequence of brain IGF-II RNA is identical to that found in liver; however, the 5' untranslated sequence of the brain cDNA has no homology to the 5' untranslated sequence of the previously reported liver cDNAs. By using hybridization to specific probes as well as a method based on the properties of RNase H, we found that the human IGF-II gene has at least three exons that encode alternative 5' untranslated regions and that are expressed in a tissue-specific manner. A probe specific to the brain cDNA 5' untranslated region hybridizes to a 6.0-kilobase transcript present in placenta, hypothalamus, adrenal gland, kidney, Wilms tumor, and a pheochromocytoma. The 5' untranslated sequence of the brain cDNA does not hybridize to a 5.3-kilobase transcript found in liver or to a 5.0-kb transcript found in pheochromocytoma. By using RNase H to specifically fragment the IGF-II transcripts into 3' and 5' fragments, we found that the RNAs vary in size due to differences in the 5' end but not the 3' end.

Relationship between growth hormone and somatomedin-C levels in untreated acromegaly, after surgery and radiotherapy and during medical therapy with sandostatin (SMS 201-995)

Several conflicting reports have been published with regard to the relationships between circulating growth hormone (GH), Somatomedin-C (SM-C) levels and clinical activity during different stages of therapy of acromegaly. We did not find a significant correlation between (fasting, post-prandial and mean 24-h) plasma GH and SM-C concentrations in twenty-two untreated acromegalic patients. There was a statistical significant correlation, however, if only the GH levels below 100 micrograms 1(-1) were considered (n = 18 patients, P less than 0.01). The distribution of molecular forms of GH ('little', 'big' and 'big-big') did not differ between the four patients with GH levels above 100 micrograms 1(-1) and in four patients with levels between 40 micrograms 1(-1) and 80 micrograms 1(-1). Therefore, it is suggested that GH levels of 80-100 micrograms 1(-1) maximally activate Somatomedin-C production in man and that further increases in GH in general will not result in a further increase in SM-C generation. There was a significant correlation between GH and SM-C levels in forty-nine acromegalic patients after surgery and/or radiotherapy (P less than 0.001). In twenty-three of thirty-one patients with elevated SM-C levels the disease was subjectively still active, while this was the case in none of the patients with normal SM-C levels. In eight patients the disease was considered not to be clinically active any more, despite slightly increased SM-C levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term metabolic effects of recombinant human insulin-like growth factor I in healthy adults

Insulin-like growth factor I (IGF I) is structurally similar to insulin and shares many of its biologic properties. We compared the short-term metabolic effects of recombinant IGF I (100 micrograms [13.3 nmol] per kilogram of body weight) and insulin (0.15 IU [1 nmol] per kilogram) in eight healthy volunteers (four men and four women). The hypoglycemic responses to both hormones were nearly identical in the doses used. The lowest blood glucose levels were reached after 30 minutes: 1.98 +/- 0.44 mmol per liter after IGF I and 1.78 +/- 0.29 after insulin. On a molar basis, IGF I was only 6 percent as potent as insulin in the production of hypoglycemia. Insulin also inhibited lipolysis more effectively than IGF I. Levels of epinephrine, norepinephrine, growth hormone, glucagon, and cortisol responded similarly to both agents. The hypoglycemia produced by IGF I is probably due to the supraphysiologic concentrations of the free peptide that result from its rapid intravenous injection. Fifteen minutes after injection, the serum level of IGF I increased from 144 +/- 38 ng per milliliter at base line to 424 +/- 56, of which 80 percent was free in the plasma (not bound to IGF carrier proteins). The determination of whether any of the short-term metabolic effects of IGF I have any clinical application will require further investigation.

Hollow fiber-encapsulated pituitary cells for the study of adenohypophyseal regulation of growth in poultry: 2. Recipient growth responses

A technique for the encapsulation and transplantation of viable, functionally active adenohypophyseal cells to pituitary-intact poultry by means of hollow fiber units has been developed. Endogenous pituitary glands of broiler pullets that received high density capsules (1.2 X 10(6) cells) were observed 30 days after fiber implantation at 2 weeks of age. Glands were reduced in size and immunoreactive growth hormone (I-GH) concentration in comparison to sham and low density (.3 X 10(6) cells) groups. Although these changes were not significant, the combined reduction in mass and I-GH concentration equates to a 25 to 35% reduction in total pituitary I-GH content for the high density group, in comparison with sham and low density group birds, respectively. These changes suggest a feedback effect of high density cell implants on endogenous pituitary function. Relative gains of each group reflect apparent differences in pituitary I-GH content: high density group birds gained less than shams (P greater than .05) and significantly less than low density group birds. In a second study of older birds, cell implants (.73 X 10(6) cells) resulted in a significantly greater average relative gain (52%) in comparison with shams (33%) over the 6 week implantation period. Mixed adenohypophyseal cell populations transplanted to the hypophysiotropic region of pituitary-intact broiler pullets resulted in changes in endogenous pituitary function and growth of recipient birds. These studies suggest that dosage administered (e.g., cell density) may interact with age at application in determining the ultimate response of birds to exogenous manipulation of endocrine regulation of growth.

Insulin-like growth factors in pygmies. The role of puberty in determining final stature

We measured the serum concentrations of insulin-like growth factors (IGF) I and II and testosterone in pygmy children, adolescents, and adults, as well as in controls, to determine more precisely the role of these factors in controlling growth. We had previously shown that growth hormone levels were normal in pygmies. Prepubertal pygmy children and controls did not differ in linear growth or in serum concentrations of IGF I and II. In pygmy adolescent boys, the mean (+/- SEM) serum concentration of IGF I was only one third that in control adolescents, who were similar to the pygmies in age and Tanner stage of development (154 +/- 22 vs. 435 +/- 37 ng per milliliter; P less than 0.01). A similar difference in IGF I concentration was observed in girls (278 +/- 18 vs. 570 +/- 25 ng per milliliter; P less than 0.01). IGF II and testosterone levels were normal in all groups. There was a significant difference in growth between controls and pygmies only during puberty. There was a marked acceleration of growth in the controls during adolescence, but such an acceleration was absent or blunted in the pygmies. These findings suggest that the short stature of adult pygmies is due primarily to a failure of growth to accelerate during puberty. We postulate that IGF I is the principal factor responsible for normal pubertal growth and that testosterone does not accelerate growth appreciably in the absence of an increase in the level of IGF I.

Coordinate tropic hormone regulation of mRNAs for insulin-like growth factor II and the cholesterol side-chain-cleavage enzyme, P450scc [corrected], in human steroidogenic tissues

Insulin-like growth factors (IGFs) are single-chain polypeptides important for cell proliferation and growth. IGFs are produced in several tissues, suggesting that they function in a paracrine or autocrine fashion as well as functioning as endocrine hormones. We studied the hormonal regulation of IGF-I and IGF-II mRNA in human steroidogenic tissues. In cultured human ovarian granulosa cells, follicle-stimulating hormone, human chorionic gonadotropin, and dibutyryl cAMP increased IGF-II mRNA, but corticotropin [adrenocorticotropic hormone (ACTH)], chorionic somatomammotropin, growth hormone, prolactin, dexamethasone, estradiol, and progesterone had no effect. In cultured human fetal adrenal cells, ACTH and dibutyryl cAMP increased IGF-II mRNA accumulation, but human chorionic gonadotropin and angiotensin II did not. The same five size species of IGF-II mRNA were detected in transfer blots of RNA from granulosa cells and fetal adrenal cells, and all of these increased after hormonal stimuli. Dibutyryl cAMP also increased IGF-II mRNA accumulation in cultured human placental cells. Accumulation of mRNA for the cholesterol side-chain-cleavage monooxygenase [P450scc [corrected]; cholesterol, reduced-adrenal-ferredoxin:oxygen oxidoreductase (side-chain-cleaving), EC 1.14.15.6] was regulated in parallel with IGF-II mRNA in all these steroidogenic tissues. IGF-I mRNA was not detected in transfer blots of these RNAs, and the minimal amounts detected in dot blots showed no detectable change after any of the hormonal stimuli studied. The data indicate that the IGF-II gene is expressed in human steroidogenic tissues and is regulated by cAMP. These data suggest that IGF-II may act in an autocrine or paracrine fashion to stimulate the adrenal and gonadal growth stimulated by ACTH and gonadotropins, respectively.

Somatomedin-C levels in treated and untreated patients with acromegaly

With the aid of a recently developed commercially available radioimmunoassay for Somatomedin-C (Sm-C) we measured the Sm-C levels in 38 controls, 24 untreated acromegalics, 45 inactive acromegalics and five pituitary dwarfs. With the exception of the dwarfs, the age and sex distributions for the various groups were similar. In inactive acromegalics the basal GH level (calculated as the mean of four blood samples taken during the day) was less than 5 mU/l; it was depressed to, or less than, 2.5 mU/l during the 100 g oral glucose tolerance test. The mean Sm-C level found for control subjects was 20.4 +/- 5.1 nmol/l and for untreated patients 85.6 +/- 25.7 nmol/l (mean +/- SD, P less than 0.001). The mean Sm-C level for inactive patients who had undergone surgery and invariably showed a normalized paradoxical reaction to TRH was 18.2 +/- 7.1 nmol/l (NS) vs 16.1 +/- 8.2 nmol/l (NS) for those who underwent surgery plus postoperative pituitary radiation therapy. Only one out of 45 inactive acromegalics exhibited an increased Sm-C level. The Sm-C levels correlated significantly not only with the log GH levels (r = 0.82) but also with the fasting insulin/glucose ratio the integrated incremental insulin levels, the maximal insulin increase and the integrated glucose levels during the oral glucose tolerance test as well as the 24-h urinary excretion of calcium and hydroxyproline.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiology of the somatotropic axis with particular reference to the ruminant

The physiology of growth hormone and the insulin-like growth factors are reviewed with particular reference to the dairy industry. Growth hormone secretion in the ruminant is pulsatile in nature and nutritional factors have a major impact on its secretion. Isolation of growth hormone-releasing factor has allowed further progress in understanding the mechanisms underlying growth hormone release. The receptors appear to be under active endocrine and metabolic control, and nutritional influences on the somatotropic axis are in large part mediated through changes in somatotropic receptors. The mode of action of growth hormone to induce acute metabolic affects and lipolysis remains to be resolved, but there is increasing evidence that its anabolic actions are mediated by the insulin-like growth factors. Recent studies of measurement of insulin-like growth factor-1 and -2 in the ruminant and the role of growth hormone, nutrition, insulin, and sex steroids in their regulation are reviewed. The relative role of the two factors and the multiple forms of their receptors remain to be resolved. It is well-documented that growth hormone is galactopoietic. The evidence that this effect is largely due to enhanced nutrient supply to the mammary gland is not convincing. Effects of growth hormone are indirect and may be mediated by the insulin-like growth factors. The potential is considerable for manipulating the growth hormone insulin-like growth factor axis to enhance lactation.

Preferential association of the insulin-like growth factors I and II with metabolically inactive and active carrier-bound complexes in serum

Ion-exchange chromatography of serum on DEAE-Sephadex A-50 using a stepwise NaCl gradient showed that complexes enriched with insulin-like growth factors I and II (IGF-I and IGF-II) could be preferentially eluted. A fraction eluted with 0.075 M-NaCl preferentially contained immunoreactive IGF-I with peak levels appearing in fractions of Mr approx. 110,000. The IGF-I-binding protein complex itself had low bioactivity as measured in a non-suppressible insulin-like (NSILA) bioassay. On conversion to free IGF-I by gel-permeation chromatography on Sephadex G-75 in 1% formic acid, however, the IGF-I did express its intrinsic NSILA bioactivity. In contrast, an IGF-II-enriched complex was eluted from the DEAE-Sephadex with 0.15 M-NaCl. Practically all of the recovered NSILA of the original serum was present in this fraction, in the Mr range 70,000-300,000 with a peak of 150,000. Chromatography on Sephadex G-75 in 1% formic acid separated this high-Mr NSILA into low-Mr (less than 15000) IGF-II and high-Mr acid-stable NSILA-P. The high-Mr IGF-II complex bound to concanavalin A-Sepharose, suggesting that it was a glycoprotein. The results confirm previous reports that a large portion of the NSILA of whole serum can be accounted for by a biologically active acid-dissociable complex. These data show for the first time that this active complex consists of an IGF-II-preferring binding protein. In direct contrast, the IGF-I-preferring complex does not express NSILA bioactivity until the IGF-I is liberated through acidification. The presence of a metabolically active IGF-II complex in serum raises questions as to its possible biological role in the adult.

Insulin-like growth factor II in human adrenal pheochromocytomas and Wilms tumors: expression at the mRNA and protein level

Two forms of insulin-like growth factor (IGF) II with molecular masses of 10 and 7.5 kDa, respectively, were found in tumor tissue from human adrenal pheochromocytomas. The tumors contained 5.3-7.1 micrograms of immunoreactive IGF-II per g of tissue, which is about 20 times more than in adrenal medulla. The total bioactive IGF in the pheochromocytomas exceeded that in normal liver or kidney, which contained only the 7.5-kDa IGF-II species, by a factor of approximately equal to 100. By contrast, the amount of IGF-I was just measurable and did not vary significantly between tumor and normal tissue. The high amounts of IGF-II in the pheochromocytomas were not reflected, however, by a corresponding increase of mRNA. The opposite situation was found in Wilms tumors, where IGF-II content was in the same range as in nontumor tissues despite increased expression of IGF-II mRNA.

Insulin-like growth factors (IGF) I and II in diabetic pregnancy: suppression of normal pregnancy-induced rise of IGF-I

The concentrations of somatomedins/insulin-like growth factors were measured by a specific radioimmunoassay for insulin-like growth factor-I and a specific radioreceptor assay for insulin-like growth factor-II in sera of term normal and Type 1 (insulin-dependent) diabetic pregnant women and in various cord sera of their newborn infants. Serum insulin-like growth factor-I levels in normal (non-diabetic) maternal serum were higher than in non-pregnant women (486 +/- 26 versus 215 +/- 26 ng/ml). The normal pregnancy-induced increment of insulin-like growth factor-I was markedly reduced in diabetic pregnancy. It was not different in patients with good or poor glycaemic control, as judged by normal or elevated blood levels of haemoglobin A1c content. Insulin-like growth factor-I levels in cord serum of infants of diabetic women with good glycaemic control (86 +/- 11 ng/ml) and poor glycaemic control (91 +/- 19 ng/ml) were significantly higher (p less than 0.01) than in infants of non-diabetic women (43 +/- 42 ng/ml). The fetal birth weight ratios were not significantly correlated with insulin-like growth factor-I levels in cord serum. Serum insulin-like growth factor-II levels in maternal and cord serum in diabetic and normal pregnancy were not different from each other or from normal non-pregnant women. The increment in insulin-like growth factor-I levels in maternal serum in pregnancy may influence placental structure and function. Lack of this increment in maternal diabetes may have direct implication in placental abnormalities in diabetes and indirect implications on fetal development and metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of insulin-like growth factor-II in human seminal and follicular fluids

Antisera raised in rabbits against synthetic insulin-like growth factor-II (IGF-II) were used to develop a specific radioimmunoassay (RIA) for IGF-II. Affinity purified antibodies showed 6% cross-reactivity with IGF-I but failed to recognize insulin even at 10 micrograms/tube. Utilizing this RIA system, immunoreactive IGF-II was identified in the pooled samples of human follicular fluid and seminal plasma. The acid-ethanol precipitates of human seminal and follicular fluids were chromatographed on Sephadex G-50 column and the IGF-II immunoreactive fractions were subjected to reversed-phase high performance liquid chromatography. It was found that immunoactive IGF-II was eluted in the same location as that of synthetic IGF-II. The data indicate for the first time that human seminal plasma and follicular fluid contain significant amounts of IGF-II.

Insulin-like growth factors I and II in evaluation of growth retardation

Plasma samples from 68 growth hormone (GH)-deficient children (provocative serum GH level less than 7 ng/ml), 44 normal short children, and 197 children with normal height were assayed by specific radioimmunoassays for the somatomedin peptides, insulin-like growth factors (IGF)-I and -II. Eighteen percent of the GH-deficient children had IGF-I levels within the normal range for age, whereas 32% of normal short children had low IGF-I levels. Low IGF-II levels were found in 52% of GH-deficient children, but also in 35% of normal short children. However, only 4% of GH-deficient children had normal plasma levels of both IGF-I and IGF-II. Furthermore, only 0.5% of normal children and 11% of normal short children had low plasma levels of both IGF-I and IGF-II. We conclude that plasma levels of either IGF-I or IGF-II overlap in GH-deficient and normal short children, but that the combination of radioimmunoassays may permit better discrimination among normal, normal short, and GH-deficient children.

Characterization of affinity-purified type I insulin-like growth factor receptor from human placenta

The binding affinities of type I IGF receptor, purified to near homogeneity from human placental membranes, were characterized. For this receptor preparation, free of type II IGF receptor and essentially free of insulin receptor, dissociation constants of Kd = 0.05 nM for IGF I and of Kd = 0.2 nM for IGF II (linear Scatchard plots) were determined. Competitive binding studies indicated a cross-reactivity of approximately 40% for IGF II to the type I IGF receptor.

Treatment of growth hormone deficiency

According to the results reported in the literature and from our own experience, the following recommendations for the treatment of children with GHD can be given: In order to start GH replacement therapy in early childhood the diagnosis of GHD should be made as early as possible. The growth hormone dose during prepubertal age should not fall short of 12 IU/m2 per week. During spontaneous or induced puberty, the dose needs to be increased, possibly by a factor of two. Daily subcutaneous injections appear most suitable. Treatment with growth hormone releasing factors in cases with hypothalamic GHD, although a promising alternative to the treatment with hGH (Thorner et al, 1985), must be considered experimental at this point. Thyroxine replacement at a daily dose of 75-100 micrograms/m2 should be given in cases of secondary hypothyroidism. Glucocorticoid replacement, if required, should be given at low doses (e.g. hydrocortisone 10 (to 15) mg/m2 per day in divided doses). In cases with additional gonadotropin deficiency, sex steroids (or anabolic steroids) should be given with frequent monitoring of bone maturity not before the age of 13 in girls or 15 years in boys. In boys depot testosterone starting at low doses (e.g. 50-100 mg/month i.m.) will induce a puberty-like increment in height velocity. Since the effect of oestrogens--even in low doses--on growth is uncertain, their administration before achievement of near-normal adult height should be avoided. With the advancement of diagnostic techniques and with the experience in treatment accumulated over the past 25 years, patients with GHD need no longer become dwarfs.

Hormonal control of the replication of human fetal fibroblasts: role of somatomedin C/insulin-like growth factor I

Sparse cultures of fetal and postnatal human fibroblasts were equivalent in their responsiveness to the mitogenic action of somatomedin C/insulin-like growth factor I (SM-C/IGF-I). At both developmental stages, the addition of SM-C/IGF-I (100 ng/ml) increased cell number at day 3 1.4-fold in serum-free medium and 2-fold in the presence of 0.25% human hypopituitary serum. Furthermore, dose-response curves indicated that there was no difference in the sensitivity of fetal and postnatal fibroblasts to the growth-promoting effects of SM-C/IGF-I, with a half-maximal response occurring at 6 ng/ml SM-C/IGF-I. This biological action of SM-C/IGF-I correlated with SM-C/IGF-I binding to fetal and postnatal fibroblast monolayers. Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) also stimulated replication of fetal and postnatal fibroblasts. The mitogenic effects of SM-C/IGF-I, EGF, and PDGF were additive. Dexamethasone, which alone had no effect, was synergistic with SM-C/IGF-I in stimulating replication of postnatal fibroblasts. The combination of SM-C/IGF-I (100 ng/ml), dexamethasone (10(-7) M), EGF (10 ng/ml), and PDGF (5 ng/ml) had the same mitogenic effectiveness as 10% calf serum (CS) in postnatal cells. In marked contrast, there was no mitogenic interaction between SM-C/IGF-I and dexamethasone in fetal fibroblasts. In fetal cells, SM-C/IGF-I + EGF + PDGF +/- dexamethasone could only account for 50% of the activity of 10% CS. Moreover, fetal cells were 50-100% more responsive than postnatal cells to the proliferative effect of serum.

Insulin-like growth factor I (IGF-I) in healthy children, adolescents and adults as determined by a radioimmunoassay specific for the synthetic 53-70 peptide region

A radioimmunoassay (RIA) specific for the synthetic 53-70 peptide region of human insulin-like growth factor I (IGF-I) was used to determine IGF-I in the serum of 191 healthy newborns, children and adolescents and in 26 adults. The results compare favourably with reported values obtained using RIA systems for the native IGF-I molecule. Intra- and inter-assay CV were 3.3 and 7.2% respectively. In childhood, mean +/- SD IGF-I levels rise from 6.0 +/- 3.5 nmol/l in newborns to 16.5 +/- 4.0 nmol/l at 8-11 years in both sexes. At the onset of puberty, IGF-I levels in females (24.9 +/- 6.6 nmol/l) are significantly (P greater than 0.005) higher than in males (17.2 +/- 4.2 nmol/l). With further pubertal development IGF-I levels continue to rise, reaching peak values at pubertal stage P4 (40.6 +/- 4.5 nmol/l in males, 42.8 +/- 5.1 nmol/l in females) and decline thereafter to lower values during adulthood: 16.5 +/- 5.8 nmol/l (males) and 24.2 +/- 7.0 nmol/l (females) (P greater than 0.001). In pubertal males, IGF-I correlates significantly with height (r = 0.66, P less than 0.001), bone age (r = 0.69, P less than 0.001) and growth velocity (r = 0.64, P = 0.025) as well as with testosterone levels (r = 0.69, P less than 0.001). In pubertal females a significant correlation is found between IGF-I and height (r = 0.55, P less than 0.020). The ready availability of a simple, precise and reproducible IGF-I RIA, should contribute much to evaluating the importance of IGF-I measurements in normal growth and in the diagnosis and therapy of various growth disorders.

Direct stimulatory effects of insulin-like growth factor-I on Leydig cell steroidogenesis in primary culture

Insulin-like growth factor-I (IGF-I) in concentration as low as 10 ng/ml significantly increased basal testosterone formation and 100 ng/ml of IGF-I increased testosterone production more than two fold in primary cultures of purified mature Leydig cells. IGF-I also markedly potentiated hCG-induced testosterone formation in a dose-dependent manner. Furthermore, IGF-I enhanced 8-bromo cyclic AMP induced steroidogenesis and hCG-stimulated cyclic AMP formation. The binding of 125I-IGF-I to purified Leydig cells was linear with a binding affinity of 0.56 +/- 0.07 X 10(9) M-1 and a capacity of 167 +/- 10.2 fmol/mg protein. Insulin and multiplication-stimulating activity were less potent than IGF-I in competing the binding of 125I-IGF-I to purified Leydig cells. This suggests that Leydig cells contain specific type I IGF receptor and IGF-I could modulate Leydig cell steroidogenesis.

Purification of the type I insulin-like growth factor receptor from human placenta

The type I IGF receptor from human placental membranes was purified to near homogeneity by affinity chromatography on IGF I-Sepharose. SDS-polyacrylamide gel electrophoresis of the affinity purified type I IGF receptor demonstrated a high molecular weight protein with Mr greater than or equal to 300,000 under non-reducing conditions. After reduction with 2-mercaptoethanol two protein bands were found of Mr = 125,000 and 95,000, representing the alpha- and beta-subunits of the receptor molecule, respectively. A co-purification of the insulin receptor through the IGF I-affinity column could be avoided by a preincubation step with insulin.