Growth and somatomedins

The insulin-like growth factor-I receptor stimulating activity (IRSA) in health and disease

Determination of true IGF-I bioactivity in serum and other biological fluids is still a substantial challenge. The IGF-IR Kinase Receptor Activation assay (IGF-IR KIRA assay) is a novel tool to asses IGF-IR stimulating activity (IRSA) and has opened a new era in studying the IGF system. In this paper we discuss many studies showing that measuring IRSA by the IGF-IR KIRA assay often provides fundamentally different information about the IGF system than the commonly used total IGF-I immunoassays. With the IGF-IR KIRA assay phosphorylation of tyrosine residues of the IGF-IR is used as read out to quantify IRSA in unknown (serum) samples. The IGF-IR KIRA assay gives information about net overall effects of circulating IGF-I, IGF-II, IGFBPs and IGFBP-proteases on IGF-IR activation and seems especially superior to immunoreactive total IGF-I in monitoring therapeutic interventions. Although the IRSA as measured by the IGF-IR KIRA assay probably more closely reflects true bioactive IGF-I than measurements of total IGF-I in serum, the IGF-IR KIRA assay in its current form does not give information about all the post-receptor intracellular events mediated by the IGF-IR. Interestingly, in several conditions in health and disease IRSA measured by the IGF-IR KIRA assay is considerably higher in interstitial fluid and ascites than in serum. This suggests that both the paracrine (local) and endocrine (circulating) IRSA should be measured to get a complete picture about the role of the IGF system in health and disease.

Relationships between insulin-like growth factor i and selected clinico-morphological parameters in colorectal cancer patients

Insulin Like Growth Factor (IGF I) as the one of the strongest growth factors which can affect cancers development including colorectal cancer. IGF I induces processes of the cells growth and division. It regulates cells cycle and inhibits apoptosis. There is limited data about correlation between IGF I and staging of the tumor. The aim of the study was estimation of the clinical usefulness of IGF I concentration in the serum of the patients with colorectal cancer.

MATERIAL AND METHODS

We have examined 125 individuals with colorectal cancer. The age range was 36 to 92 years. They have been operated in the 2nd Departament of The Gastrointestinal Surgery of the Medical University in Białystok. Serum concentration of the IGF I have been estimated using immunoassay ELISA before and after operation. Correlation between serum level of IGF I and clinicopathologic features: age, gender, localisation of the primary tumor, TNM stage of tumor, histological type and histological grade (G) of the cancer have been estimated.

RESULTS

Our study revealed statistically significant increased serum concentration of IGF I in patients with locally advanced colorectal cancer (pT3 and pT4) comparing to less advanced (pT2) The investigations showed higher serum concentration of IGF I in patients with poorly differentiated cancers (G3) than in moderately differentiated. Similarly higher serum concentration of IGF I were found in male, in patients older than 60 years and in mucigenous colorectal cancers.

CONCLUSIONS

Our results indicated that IGF I can be one of the factors of the prognosis in colorectal cancer development.

Brain tissue volume segmentation in patients with anorexia nervosa before and after weight normalization

OBJECTIVE

To examine whether gray and white matter volumes are preferentially reduced and cerebral spinal fluid (CSF) increased with starvation in patients with anorexia nervosa compared with healthy controls and to determine what changes occur with weight normalization.

METHOD

Whole intracranial volumes of patients and controls were segmented into gray matter, white matter, and CSF volumes and results compared. A subgroup of patients were rescanned after weight normalization.

RESULTS

Total white matter and several regional white matter volumes were significantly reduced and total and regional CSF volumes were significantly increased in patients versus controls whereas gray matter was not significantly reduced. Total and regional CSF volumes were significantly decreased in patients upon weight normalization whereas white and gray matter volumes increased.

DISCUSSION

These changes in brain tissue may be related to a variety of pathophysiologic mechanisms. We hypothesize that insulin-like growth factor-1 may be involved.

Insulin-like growth factor-I gene expression in the tibial epiphyseal growth plate of growth hormone-treated uremic rats

To identify the molecular mechanisms involved in long bone growth of uremic animals, we evaluated the effects of recombinant human growth hormone (rhGH) supplementation on whole body growth, growth plate morphometrics, and insulin-like growth factor-I (IGF-I) gene expression in the tibial epiphyseal growth plates of uremic rats. Uremia was induced by a two-stage subtotal nephrectomy (Nx) of 30-day-old rats, followed by rhGH (N = 6) or saline (N = 6) treatment from day 56 to day 70 of age. Controls (N = 4) were sham decapsulated. Treatment with rhGH on Nx animals caused: (1) a significant increase in weight, (2) longitudinal growth similar to controls, and (3) increased total growth plate width predominantly due to an increase in hypertrophic zone width. rhGH increased IGF-I mRNA abundance in both zones, but the increase was greater in the proliferative zone. These changes were accompanied by concomitant alterations in IGF-I immunoreactivity. In uremic animals, therefore, rhGH treatment induces local IGF-I gene expression in the growth plate and increases the hypertrophic zone width but not the proliferative zone width. The latter suggests resistance to IGF-I action in that zone.

Patterns of growth deficiency in rats exposed in utero to undernutrition, ethanol, or the neuroteratogen methylazoxymethanol (MAM)

Children and experimental animals exposed to ethanol (EtOH) in utero commonly have low birthweights, and many remain small at maturity. Low body weight or small stature in adulthood may reflect an inability to recover from in utero growth retardation, or it may reflect a separate, postnatal growth deficiency. In this study, daily body weights (postnatal days 1 to 60) were compared among the offspring of the following groups of Long Evans rats: dams fed liquid diet containing 35% EtOH-derived calories; their pair-fed and chow-fed controls; and dams exposed to methylazoxymethanol (MAM) in two previous studies, in which offspring exhibited reduced numbers of growth hormone releasing factor (GRF) neurons. All treatments produced a number of offspring with weight deficits beginning after birth and persisting into maturity. Three distinct patterns of growth deficiency were observed: (1) weight loss relative to controls in the first weeks of life, seen in offspring exposed to EtOH, pair feeding, or MAM on gestation day 13 (G13); (2) a delay in the onset of the prepubertal growth spurt, seen in all EtOH-exposed offspring and in G13 MAM-exposed dwarfs; and (3) failure to sustain the prepubertal growth spurt, seen only after exposure to MAM on G14. The results of this study support the view that prenatal EtOH exposure is capable of affecting postnatal growth specifically; moreover, the pattern of growth deficiency seen in EtOH-exposed offspring was distinct from that of the undernourished offspring of pair-fed dams.

Dihydrotestosterone (DHT) regulation of insulin-like growth factor II mRNA in neonatal rats

Insulin-like growth factors (IGFs) are well known as peptide mitogens and important growth factors in fetal as well as in early postnatal development. In particular, IGF II is strongly expressed during fetal life and in neonatal animals. Very little is known about the regulation of IGF II gene expression. In order to study in detail the regulation of IGF II mRNA levels in the liver by the potent nonaromatizable androgen dihydrotestosterone (DHT), we have used quantitative in situ hybridization to detect the mRNA encoding for this growth factor. Pups were separated into 4 groups and injected twice a day immediately after birth with 3 different doses of DHT: 0.1 mg DHT/day, 0.25 mg DHT/day, 0.5 mg DHT/day for 4 and 7 days, and the control groups were injected with the vehicle alone. Animals were perfused with 4% paraformaldehyde and sections from the liver, heart, kidneys and brain were cut with a cryostat. A [35S]-labeled cDNA probe was used to detect IGF II mRNA levels. After hybridization, sections were autoradiographed with X-ray films and then coated with liquid photographic emulsion. Densitometric measurement revealed that, at 4 days of age, IGF II mRNA levels were lower in DHT-treated rats than in control animals. No statistically significant differences in IGF II mRNA levels were observed among the three groups treated with the different doses of DHT, thus revealing that even the lowest dose of DHT (0.1 mg/day) used was sufficient to inhibit IGF II gene expression in neonatal rats. Moreover, at 7 days of age, DHT-treated rats showed the same levels of IGF II mRNA as those observed in rats treated with DHT for 4 days. These results suggest that DHT may play an important role in the regulation of IGF II gene expression in the rat liver during the neonatal period.

Insulin-like growth factor II and nonsuppressible insulin-like activity levels in newborns

We measured insulin-like growth factor II and nonsuppressible insulin-like activity levels in the sera of newborn infants with different birth weights and gestational ages to determine the significance of these peptides in fetal growth. Our results obtained by use of one-way analysis of variance showed that the insulin-like growth factor II and nonsuppressible insulin-like activity levels in premature, average-weight-for-gestational-age, large-for-gestational-age, and small-for-gestational-age newborns were significantly different (p less than 0.01). Although levels in the premature neonates were less than the other three groups and large-for-gestational-age neonates had a higher insulin-like growth factor II level than the other three groups, maternal insulin-like growth factor II levels in all groups were similar. These results suggest that insulin-like growth factor II may play a major role in fetal growth.

Twin very low birth weight infants: a study of nutritional and hormonal status

Nonidentical twin male infants (twin 1,950 g birth weight, twin 2,970 g) had their nutritional and hormone status studied for up to 59 days. Both infants received parenteral nutrition up to 32 days postnatally; enteral feeding was then established in twin 1; in twin 2 parenteral feeding was recommenced on day 35, for the remainder of the study. Serial 72-hr metabolic balances were performed in both infants at 4, 32, 45, and 56 days postnatally. Insulin-like growth factor I (IGF-I) and growth hormone were assayed on day 2 of each balance. During the course of the study growth was similar in each infant. Overall mean daily energy intakes were 90 kcal/kg/day and 84 kcal/kg/day and percentage nitrogen retention was 62% and 55% in twin 1 and twin 2, respectively. No differences were observed between the two infants in IGF-I or growth hormone. Despite low energy intakes incremental weights were within an acceptable range for both infants.

Biological activity of insulin-like growth factor-I purified from chicken serum

This study describes a rapid purification of insulin-like growth factor-I from chicken serum and the immunological, biological and receptor binding activity of the peptide. It was purified after initial extraction, by cation exchange chromatography, hydrophobic interaction chromatography and reverse phase chromatography up to 1.4 x 10(6)-fold with an overall yield ranging from 10-30%. The N-terminal amino acid sequence was the same as predicted from the nucleotide sequence of a chicken IGF-I cDNA and the partial sequence obtained from a previously reported purification. The material was both immunologically and biologically active. It had a 50% potency compared to human IGF-I in a radioimmunoassay using an antiserum raised against human IGF-I, stimulated the incorporation of [3H]-thymidine into DNA in cultured chick embryo myoblasts with a half-maximum effective dose of 5 ng/ml and displaced [125I]-labelled human IGF-I and IGF-II from binding sites in microsomal membranes prepared from both the chicken liver and the lactating rabbit mammary gland in a dose dependent manner.

Therapeutic potential of insulinlike growth factor i

Human recombinant insulinlike growth factor I is a promising therapeutic agent for diseases characterized by relative insulin resistance, e.g., diabetes mellitus, obesity, and hypertriglyceridemia, since it suppresses growth hormone, insulin, C-peptide, and triglyceride levels and lowers the total cholesterol to high-density lipoprotein-cholesterol ratio. Moreover, insulinlike growth factor administration increases kidney function in healthy subjects (glomerular filtration rate, renal plasma flow) and may prove useful in the treatment of degenerative disorders of cartilage and bone (arthrosis, osteoporosis) as well as in catabolic states.

Insulin-like growth factor I (somatomedin C) in goats during normal lactation and in response to somatotropin treatment

1. Two experiments were performed. In Experiment 1, IGF-I concentrations in serum were followed in four lactating dairy goats during normal lactation and before, during and after 14 days of daily administration of 10 IU recombinant bovine somatotropin, starting 10 weeks post-partum. In Experiment 2, IGF-I was measured in single blood samples obtained from 40 dairy goats in the first part of lactation. 2. Measured IGF-I concentrations ranged from 4.4-9.0 nM. Concentrations varied during the day with coefficients of variation from 8.9 to 18.4% in the four goats in Experiment 1. There were no systematic trends in the diurnal variations (P greater than 0.75). 3. Concentrations of IGF-I remained fairly constant in all goats in Experiment 1 during the lactational period, and were not related to the changes in milk yield (P greater than 0.65). Similarly, no relationship was found in Experiment 2 between level of milk production and IGF-I concentration in serum. 4. Somatotropin treatment stimulated milk yields by 14 +/- 2.9% (P less than 0.05) and IGF-I concentration by 27.9 +/- 6.7% (P less than 0.05). 5. IGF-I is the most likely factor which increases mammary gland synthetic capacity in response to somatotropin treatment, and thus is responsible for the galactopoietic effect of this hormone being exerted. 6. However, serum IGF-I may primarily be involved in regulation of nutrient partitioning during normal lactation, but a paracrine synthesis with local effect on the mammary gland cannot be ruled out.

Fetal hypophysectomy causes a decrease in preadipocyte growth and insulin like growth factor-1 in pigs

Fetal pigs in one uterine horn of each of five gilts were hypophysectomized (HX) in utero by electrical cauterization at 72-74 days of gestation and sera collected at 110 days of gestation. Sera from HX fetuses had lower levels of insulin-like growth factor-1 compared to control littermates (P less than .05). Sera were tested for their effects on primary cultures of stromal-vascular cells from adipose tissue. The soluble protein concentration/dish was lower when pig cells were cultured in sera from HX fetuses compared to sera from control fetuses (P less than .01). Sera from HX fetuses inadequately supported growth of stromal-vascular cells so subsequent experiments utilized pooled sera from normal and HX adult pigs. Sera from HX and control fetuses were mixed with sera from the two adult pools and tested for incorporation of tritiated thymidine into rat preadipocytes and the appearance of adipocytes (determined histochemically) in pig stromal-vascular cultures. In cultures fed sera from HX fetuses there was a lower (P less than .05) number of pig fat cells/culture and a lower level (P less than .06) of preadipocyte proliferation in rat cell cultures when compared to control fetal sera. Fetal pig serum contains factors (adipogenic) which promote the proliferation and differentiation of adipocytes in culture. Serum from HX fetuses has a lower level of adipogenic factors.

Responses to divergent selection for plasma concentrations of insulin-like growth factor-1 in mice

A divergent selection experiment with mice, using plasma concentrations of insulin-like growth factor-1 (IGF-1) at 42 days of age as the selection criterion, was undertaken for 7 generations. Lines were not replicated. To obtain sufficient plasma for the IGF-1 assay, blood from four individuals was volumetrically bulked to obtain a litter mean IGF-1 concentration. This necessitated the use of between family selection. Although inbreeding accumulated in a linear fashion in each of the high, control and low lines, the rates were different for each line (3.6, 1.6 and 5.3% per generation for the high, control and low lines, respectively). As a consequence, the effects of selection and inbreeding are confounded in this experiment. Divergence between the high and low lines in plasma concentrations of IGF-1 continued steadily until generation 5. In generations 6 and 7, there was a reduced degree of divergence and this contributed towards the low realized heritability value of 0.15 +/- 0.12. Six-week liveweight showed a steady positive correlated response to selection for or against plasma concentrations of IGF-1 until generation 4 (high-low difference = 1.7 g = 12%). In generation 5, a substantial drop in 6-week liveweight in the low line relative to both the high and control lines occurred (high-low difference, 3.9; g, 25%). This difference was maintained until generation 7.(ABSTRACT TRUNCATED AT 250 WORDS)

The study of insulin-like growth factors in Tilapia, Oreochromus mossambicus

Whole and acid-separated serum samples from fed, starved, and refed Tilapia were analyzed for insulin-like growth factors 1 (IGF-1) and 2 (IGF-2) using human fetal brain radioreceptorassay (RRA-IGF-1), rat liver membrane radioreceptorassay (RRA-IGF-2), and radioimmunoassay (RIA-IGF-1). Triidothyronine (T3) and thyroxine (T4) levels were measured by commercial kits for RIA. For serum separation, acid Sephadex G-50 and G-100 and neutral Sephadex G-200 columns were used. Whole serum and separated serum cross-reacted in RRA-IGF-1, but only slightly in RRA-IGF-2. IGF activity eluted in two peaks after acid G-50 chromatography. Peak I eluted at the void volume, and peak II eluted with an apparent molecular weight of approximately 7 kDa. The 7 kDa activity did not cross-react in RIA-IGF-1 excluding identity with human intact or truncated IGF-1, but did suggest the presence of an IGF-1 variant form. Whole serum was separated over a neutral G-200 column, and all activity eluted at the void volume indicated an apparent molecular weight equal to or greater than 250 kDa. No IGF-binding activity was displayed by either whole serum or peak I after acid G-50 chromatography. Despite significant changes in body weight, an influence of starvation and refeeding on serum IGF activity could not be established. No correlation was seen between serum IGF and T3 and T4 levels.

Binding proteins for the insulin-like growth factors: structure, regulation and function

Binding proteins for the insulin-like growth factors (IGF-I and IGF-II) are increasingly being recognized as modulators of IGF actions in both inhibitory and stimulatory ways. At least three distinct classes of binding protein are thought to exist, differing in their primary structures and binding characteristics, although all are able to bind both IGF-I and IGF-II. This review outlines the purification and characterization of the binding proteins that have been identified to date, and describes the regulation of their production and of their levels in the circulation. Current views on their potential biological roles are also discussed.

Wiedemann-Beckwith syndrome

The Wiedemann-Beckwith syndrome (WBS) comprises an accumulation of multiple congenital anomalies. Exomphalos, macroglossia and gigantism are considered the most common manifestations, hence the alternative designation EMG-syndrome. The syndrome carries with it an increased risk of developing specific tumours. One of the more frequent metabolic changes is transient neonatal hypoglycaemia, the result of increased insulin secretion. Inheritance of the syndrome remains uncertain. Most cases are sporadic, but a number of familial cases have been reported. Present evidence suggests that WBS is an autosomal dominant trait with variable expressivity. This review summarizes the abundant literature on the subject and discusses recent molecular genetic developments that may explain the interrelationship between the clinical abnormalities, metabolic disturbances and development of tumours.

The insulin-like growth factors and their binding proteins

1. This review provides a brief overview of the structure of the insulin-like growth factors (IGFs or somatomedins), their mRNA and genes; the regulation and sites of production of these peptides; their binding and actions in target tissues; and the structure and biological role of their binding proteins. 2. Molecular cloning techniques have allowed the prediction of precursor forms of IGF-I and IGF-II, have provided tools to study the regulation of the synthesis and translation of IGF mRNAs, and have recently yielded the primary sequence of the IGF-I receptor, supplementing other rapidly-accumulating structural data. 3. Several of the IGF binding proteins have also been purified, and initial structural studies performed. 4. The increased knowledge of the structures of the IGFs, their receptors and binding proteins should now permit rapid progress in understanding the physiology and functions of these proteins.

A novel system for mammary epithelial cell culture

A method is described for the isolation and density gradient enrichment of mammary epithelial fragments from pregnant, nonlactating bovine tissue. Immunocytochemical analysis prior to and following culture revealed specific staining with antibodies to keratin, indicating that these cells are epithelial in nature. Fragments enriched for epithelium could be stored in liquid nitrogen for extended periods prior to culture. When cast within a three-dimensional matrix of collagen gel, the mammary fragments grew as branching, duct-like structures and displayed a 4-fold increase in cell number during 10 to 12 d of culture.

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.

Hydrocortisone stimulates the development of oligodendrocytes in primary glial cultures and affects glucose metabolism and lipid synthesis in these cultures

Cultures of glial cells were prepared from the brains of one-week-old rat pups. After one day in culture, serum was omitted from the medium and replaced by a combination of growth-stimulating hormones and other factors that enhanced the percentage of oligodendrocytes in the cultures. We investigated the effects of hydrocortisone on the development of oligodendrocytes, on the activities of oligodendrocyte-specific enzymes and on glucose- and lipid-metabolism of the glial cells. Hydrocortisone greatly enhanced the survival of glial cells in culture. The development of galactocerebroside-positive cells and the specific activity of 2',3'-cyclic-nucleotide 3'-phosphodiesterase were stimulated by 50 nM hydrocortisone, whereas these effects were partly reversed at higher concentrations of the hormone. The specific activity of glycerol-3-phosphate dehydrogenase was markedly stimulated by hydrocortisone; 1 microM or higher concentrations of hydrocortisone were required for an optimal effect. The consumption of glucose and the production of lactate were lowered by hydrocortisone whereas the oxidation of [6-14C]glucose to 14CO2 was not affected. Incorporation of [35S]sulfate into sulfolipids was greatly enhanced by hydrocortisone and [14C]incorporation from [1-14C]acetate into cholesterol and fatty acids was also stimulated but to a smaller extent. These results show that hydrocortisone exerts a general trophic function on glial cells in our culture system; enhances the ratio of oligodendrocytes over astrocytes, possibly by directing bipotential progenitor cells to develop into oligodendrocytes; specifically induces glycerol-3-phosphate dehydrogenase in oligodendrocytes.

Somatomedins in tumour cyst fluid, cerebrospinal fluid, and tumour cytosol in patients with glial tumours

In the present study, the levels of the growth-promoting hormones, somatomedins, were analysed in tumour cyst fluid, CSF, and tumour cytosol, collected from 22 unselected patients with intracranial tumours. All samples contained somatomedin activity. 5/7 CSF samples, taken from patients with tumour mass visible on CT, showed elevated concentrations. 6/9 cyst fluid samples, taken from patients with glioma were elevated compared with normal serum somatomedin levels. Tumour cytosol, taken from 7 patients with malignant glioma contained somatomedins in an elevated level compared with values previously analysed from normal adult brains. These preliminary findings demonstrate for the first time the presence of somatomedins in brain tumours and suggest the use of somatomedins as a possible brain tumour marker.

Sequences of liver cDNAs encoding two different mouse insulin-like growth factor I precursors

Complementary DNAs encoding mouse liver insulin-like growth factor I (IGF-I) have been isolated and sequenced. Alternative RNA splicing results in the synthesis of two types of mouse IGF-I precursor that differ in the size and sequence of the COOH-terminal peptide. The sequences of the signal peptides, IGF-I moieties and the first 16 amino acids of the COOH-terminal peptides or E-domains of the two precursors are identical. The sequence difference results from the presence in preproIGF-IB mRNA of a 52 base insertion which introduces a 17 amino acid segment into the COOH-terminal peptide of preproIGF-IB and also causes a shift in the reading frame of the mRNA. As a consequence of this insertion, the COOH-terminal 19 and 25 amino acids of mouse preproIGF-IA and -IB, respectively, are different. The sequences of mouse and human preproIGF-IA are highly conserved and possess 94% identity. In contrast, the sequences of mouse and human preproIGF-IB are quite different in the region of the COOH-terminal peptide. A comparison of the sequences of mouse and human preproIGF-IB mRNA indicates that they are generated by different molecular mechanisms.

Characterization of somatomedins from human fetal brain: identification of a variant form of insulin-like growth factor I

A fetal form of somatomedin (insulin-like growth factor) that crossreacts in the fetal brain radioreceptor assay has been proposed to exist in humans. Using this assay to monitor activity during purification, we have isolated a variant form of insulin-like growth factor I (IGF-I) from human fetal brain tissue. The variant IGF-I showed potent crossreaction in the fetal brain radioreceptor assay and stimulated DNA synthesis in fetal brain cells in vitro. Structural analysis revealed the variant IGF-I to have a truncated NH2-terminal region compared to IGF-I isolated from serum. An additional peptide, which displayed less potent crossreaction in the fetal brain radioreceptor assay, was also isolated from the human fetal brain. Partial amino acid sequence analysis revealed identity to insulin-like growth factor II.

Isolation and characterization of variant IGF-1 as well as IGF-2 from adult human brain

The forms of somatomedin present in the adult human brain have been characterized in this study. Two peptides were purified by acidification, size exclusion chromatography, affinity chromatography, FPLC and HPLC. Structural analysis identified these peptides as the variant form of IGF-1 with a truncated N-terminal region earlier isolated from human fetal brain and IGF-2. The presence of the truncated IGF-1 variant and IGF-2 in the human CNS suggests their role as neuropeptides.

Mitogenic response of human SH-SY5Y neuroblastoma cells to insulin-like growth factor I and II is dependent on the stage of differentiation

Human insulin-like growth factor I and II (IGF-I and IGF-II) in concentrations of 1-30 ng/ml, were shown to stimulate ornithine decarboxylase activity and [3H]thymidine incorporation in human SH-SY5Y neuroblastoma cells. Proliferation of these cells was also stimulated by IGF-I and II when added to RPMI 1640 medium, fortified with selenium, hydrocortisone, transferrin, and beta-estradiol. Labeled IGF-I and II bound to SH-SY5Y cells. The cross-reaction pattern of IGF-I, IGF-II, and insulin in competing with the binding of labeled IGF-I and IGF-II, respectively, indicated that SH-SY5Y cells express both type I and type II IGF receptors. Treatment of SH-SY5Y cells for 4 d with 12-O-tetradecanoylphorbol-13-acetate (TPA), which resulted in morphological and functional differentiation and growth inhibition, abolished the mitogenic response to both IGF-I and II. Concomitantly, the binding of IGF-II disappeared almost totally, which offers a possible explanation for the reduced biological response to IGF-II after TPA treatment. In contrast, the IGF-I binding in TPA-treated cells was only reduced to approximately 70% of the binding to control cells. It is therefore not excluded that the IGF-I receptor could be uncoupled by TPA, with persistent binding capacity for IGF-I.

Affinity chromatography with amniotic fluid somatomedin binding protein in the purification of insulin-like growth factor I

A simplified procedure has been developed for the isolation of insulin-like growth factor I from human plasma by use of affinity chromatography with the somatomedin binding protein. After acidification of human plasma and separation of insulin-like growth factor I and endogenous binding protein by cation exchange chromatography on SP-Sephadex the material was passed through a column packed with pure human amniotic fluid binding protein covalently coupled to Sepharose. The bound insulin-like growth factors I and II were eluted by 1M acetic acid and separated on a Mono S cation exchange column by use of a salt gradient. The 30 micrograms insulin-like growth factor I and 18 micrograms insulin-like growth factor II recovered from 1 liter plasma gave an overall recovery of 30% for insulin-like growth factor I but only 2.5% for insulin-like growth factor II.

The effects of different total parenteral nutrition fuel mixes on skeletal muscle composition of infant miniature pigs

Two groups of 10-day-old miniature pigs were maintained on isocaloric and isonitrogenous total parenteral nutrition (TPN) regimens for nine days. One group received nonprotein energy as glucose, whereas the second group received a mixture of fat and glucose. The administration of the amino acid/glucose fuel mix resulted in higher plasma insulin but lower glucagon concentrations compared to the amino acid/glucose/fat mix. Differences also were observed in the composition of skeletal muscle, which contained higher concentrations of alkali-soluble (AS) proteins (chiefly cellular protein) and DNA, when glucose was the only source of nonprotein energy. Intracellular sodium and water content and nonalkali-soluble proteins (largely extracellular proteins) were lower in the skeletal muscle of the amino acid/glucose group than in that of the group receiving the fat regimen. No differences in RNA concentration, RNA/AS protein, or AS protein/DNA ratios were observed. These data suggest that conditions of high insulin production in the postnatal growth period favored increased DNA replication and accretion of AS protein. The differences in water and electrolyte composition indicate that the rate of chemical maturation of skeletal muscle was slower in the piglets receiving amino acids/glucose/fat than in those on the glucose regimen. This study has demonstrated that the source of nonprotein energy can influence skeletal muscle maturation in the postnatal period.

The influence of maternal protein deprivation on the developmental pattern of serum immunoreactive insulin-like growth factor 1 (IGF-1) levels

The influence of maternal protein deprivation on body and brain growth and on serum immunoreactive insulin-like growth factor I (IGF-I) levels was examined in rats during development. The offspring of protein-deprived mothers were significantly growth-retarded postnatally and showed an altered developmental pattern of serum immunoreactive IGF-I levels. In contrast to control animals, between days 5 and 20 postnatally, a significant elevation in serum immunoreactive IGF-I levels which peaked at day 15 was found. However, in adult growth-retarded rats a significant reduction in serum immunoreactive IGF-I levels was found. These findings suggested the preweaning period to be critical for the development of the mature somatomedin system.

Binding properties and biological potencies of insulin-like growth factors in L6 myoblasts

Protein synthesis in rat L6 myoblasts is stimulated and protein breakdown inhibited in a co-ordinate manner by insulin-like growth factors (IGF) or insulin. For both processes, bovine IGF-1 was somewhat more potent than human IGF-1, which was effective at a tenth the concentration of insulin, rat IGF-2 or human IGF-2. A similar order of potency is noted when DNA synthesis or protein accumulation is monitored over a 24 h period, but between 20- and 50-fold higher concentrations of each growth factor are required than those needed to produce effects in the 4 h protein-synthesis or -breakdown measurements. Binding experiments with labelled human or bovine IGF-1 as ligand demonstrated competition at concentrations of IGF-2, especially human IGF-2, lower than that of either IGF-1 preparation. This pattern was much more pronounced when the radioligand was either human IGF-2 or rat IGF-2. Insulin competed 10-15% for the binding of labelled IGF-1, but not at all with labelled IGF-2. Ligand-receptor cross-linking experiments showed that labelled bovine IGF-1 bound approximately equally to the type 1 IGF receptor (Mr 130000 after reduction) and to the type 2 IGF receptor (Mr 270000 after reduction), and that unlabelled IGF-1 competed equally with radioligand binding to both receptors. On the other hand, rat IGF-2 competed more effectively for binding to the type-2 receptor, and insulin competed only for binding to the type-1 receptor. Further cross-linking experiments with rat IGF-2 as radioligand demonstrated binding only to the type-2 receptor and to proteins with Mr values after reduction of 230000 and 200000. This binding was prevented by high rat IGF-2 concentrations, less effectively by bovine IGF-1 and not at all by insulin. The apparently conflicting biological potencies and receptor binding of the different growth factors can be explained if all the biological actions are mediated via the type-1 IGF receptor, rather than through the abundant type-2 receptor.

Growth and somatomedin responses to growth hormone in Down's syndrome

Five growth retarded children with Down's syndrome, three girls and two boys aged between 3 1/2 and 6 1/2 years with trisomy 21, were treated with human growth hormone for six months. Before treatment the growth hormone response to sleep and insulin-arginine load, as well as serum concentrations of insulin, thyroid hormones, and cortisol was found to be in the normal range. During the treatment with human growth hormone the growth velocity increased in all the children with Down's syndrome from 2.3-2.8 cm to 3.3-5.8 cm per six months. The serum concentrations of immunoreactive insulin like growth factor 1 (IGF-1) were low before treatment and increased during the treatment with human growth hormone. The serum concentrations of immunoreactive insulin like growth factor 2 (IGF-2), which were within the normal range, however, increased during treatment with human growth hormone. Children with Down's syndrome respond to treatment with human growth hormone, with an increase in both growth velocity and serum somatomedin concentrations.

Effects of growth hormone substitution on mental performance in adults with growth hormone deficiency: a pilot study

Five patients ages 22 to 36 years with growth hormone deficiency received substitution with native human growth hormone and biosynthetic methionyl human growth hormone, 8 IU i.m. three times weekly, for two separate 4-week periods. Before and at the end of each treatment period, five psychometric tests evaluating cognitive functions were performed. The results suggest a beneficial effect of growth hormone on certain cognitive functions. The results were similar for the two hGH preparations.

The influence of purified somatomedins and insulin on foetal rat brain DNA synthesis in vitro

The two main forms of somatomedins, termed insulin-like growth factor I and II (IGF-I and IGF-II), have been isolated from human plasma. Pure IGF-I or IGF-II was incubated with foetal rat brain cells and found to be equipotent in stimulating the [3H]thymidine incorporation into DNA, despite the fact that IGF-I not is present during foetal life.

Isolation of the human insulin-like growth factor genes: insulin-like growth factor II and insulin genes are contiguous

Overlapping recombinant clones that encompass the insulin-like growth factor (IGF) I and II genes have been isolated from a human genomic DNA library. Each gene is present once per haploid genome; the IGF-I gene spans greater than 35 kilobase pairs (kbp) and the IGF-II gene is at least 15 kbp. The exon-intron organization of these genes is similar, each having four exons, which is one more than the related insulin gene. Comparison of the restriction endonuclease cleavage maps of the IGF-II and insulin genes, including their flanking regions and hybridization with an IGF-II cDNA probe, revealed that they are adjacent to one another. The IGF-II and insulin genes have the same polarity and are separated by 12.6 kbp of intergenic DNA that includes a dispersed middle repetitive Alu sequence. The order of the genes is 5'-insulin-IGF-II-3'.

Increased levels of somatomedins in human lumbar and central cerebrospinal fluid after subarachnoid haemorrhage

The somatomedins, multitargit growth-promoting peptide hormones, were measured with radio receptor assay in cerebrospinal fluid (CSF) after subarachnoid haemorrhage (SAH) in 21 patients and after head injury in 2 patients. In the first group of 10 patients, lumbar (n = 8) or central (n = 2) CSF was collected on days three, six and nine after SAH. 6 of the 8 patients with SAH showed an increase in somatomedin concentrations ranging between 0.52-1.26 U/ml while 2 patients fell within the normal range between 0.19-0.48 U/ml. In the 2 patients with head injury, the somatomedin concentrations were scarcely detectable. In the second group of 13 patients with SAH, CSF was collected preoperatively during surgical clipping of an aneurysm. These patients fell into two groups: 6 patients who had CSF somatomedin levels within the normal range and 7 patients with pathologically increased somatomedin concentrations ranging between 0.38-1.26 U/ml. Neither the neurological condition nor the cerebral vascular diameter correlated with the somatomedin concentrations. It is suggested that the increased somatomedin levels in CSF after SAH could be a compensatory response in order to stimulate cerebral anabolism after injury.

Degradation of somatomedins by the thioredoxin system

The insulin disulfide reducing thioredoxin system from E. coli was used to investigate a possible mechanism of degradation for the two somatomedins, insulin-like growth factor I and II (IGF-I and -II). The amounts of IGF-I and -II remaining after degradation were measured by use of human placenta radioreceptor assay. The results show that both IGF-I and -II were as sensitive to disulfide reduction as insulin.

The characterization of somatomedin A, isolated by microcomputer-controlled chromatography, reveals an apparent identity to insulin-like growth factor 1

The polypeptide termed somatomedin A (SMA) was isolated from outdated human plasma by a new purification procedure, not using acid ethanol extraction. Fractions containing SMA were monitored by a placenta radioreceptorassay and a radioimmunoassay for SMA. The purification method utilized a microcomputer-controlled chromatography system, yielding both SMA (identified as insulin-like growth factor 1 (IGF-1) or a deamidated derivative) and insulin-like growth factor 2 (IGF-2). The first step of CM-Affigel blue adsorbed at neutral pH the majority of somatomedins detectable by the radioreceptorassay for SMA. Exclusion chromatography on Sephadex G-50 in 0.1 M acetic acid separated this active material from albumin and NaCl. Separation between SMA and IGF-2 was achieved on two different cation-exchange columns, but not in the final high-performance liquid chromatography step. The isoelectric points, determined by chromatofocusing, were 8.0 for SMA and 6.2 for IGF-2. The amino acid compositions of the two isolated peptides were indistinguishable from the known compositions of IGF-1 and IGF-2. Sequence analysis up to position 39 of the peptide with a pI of 6.2 also proved identity with IGF-2 for all positions examined. The peptide with a pI of 8.0, corresponding to SMA, was degraded directly as well as after CNBr cleavage. The results show that it is identical to IGF-1, with the possible exception of acid/amide assignment, which could correspond to a deamidation. If occurring in the native preparation before analysis, it could explain the chromatographic properties and isoelectric point of SMA versus IGF-1 isolated by other techniques.