Somatomedins (second of two parts)

The biology of posterolateral lumbar spinal fusion

This article reviews the existing knowledge base concerning the biology of spinal fusion, with the understanding that the focus is weighted toward posterolateral lumbar spinal fusion because of a relative paucity of biologic information on healing of other types of fusions. The discussion focuses first on the basic science of spinal fusion healing from the standpoint of animal modeling. Next, the discussion centers on the multitude of local factors that can affect fusion healing. Finally, the numerous systemic factors known to affect fusion healing are discussed.

The combined effects of TGF-β, IGF and PDGF on 5α-reductase activity on androgen substrates in human gingival tissue

The combined effects of the growth factors, PDGF, TGF-beta and IGF, on the metabolism of two androgen substrates by human gingival tissue were investigated. Having established their wet weight, duplicate incubations were performed in Eagle's MEM using [(14)C]testosterone/[(14)C]4-androstenedione as substrates and growth factors, PDGF, TGF-beta and IGF, alone and in combination. Steroid metabolites were then isolated, separated and quantified, using a radioisotope scanner. With [(14)C]testosterone as substrate, there were 3-5-fold decreases in 5alpha-reductase activity in response to individual growth factors, while the combinations, PDGF+TGF-beta, PDGF+IGF and TGF-beta-IGF, resulted in approximately half the stimulation, or similar to that of one of the growth factors, but still about 2-fold greater than control values. When [(14)C]4-androstenedione was used as substrate, there were approximately 2-6-fold increases in DHT synthesis in response to the growth factors alone. When used in combination, and intermediate response was seen. Growth factor combinations can enhance anabolic activity in the chronically inflamed periodontium.

Blood hormones as markers of training stress and overtraining

An imbalance between the overall strain experienced during exercise training and the athlete's tolerance of such effort may induce overreaching or overtraining syndrome. Overtraining syndrome is characterised by diminished sport-specific physical performance, accelerated fatiguability and subjective symptoms of stress. Overtraining is feared by athletes yet there is a lack of objective parameters suitable for its diagnosis and prevention. In addition to the determination of substrates (e.g. lactate, ammonia and urea) and enzymes (e.g. creatine kinase), the possibilities for monitoring of training by measuring hormonal levels in blood are currently being investigated. Endogenous hormones are essential for physiological reactions and adaptations during physical work and influence the recovery phase after exercise by modulating anabolic and catabolic processes. Testosterone and cortisol are playing a significant role in metabolism of protein as well as carbohydrate metabolism. Both are competitive agonists at the receptor level of muscular cells. The testosterone/cortisol ratio is used as an indication of the anabolic/catabolic balance. This ratio decreases in relation to the intensity and duration of physical exercise, as well as during periods of intense training or repetitive competition, and can be reversed by regenerative measures. Correlations have been noted with the training-induced changes of strength. However, it seems more likely that the testosterone/cortisol ratio indicates the actual physiological strain in training, rather than overtraining syndrome. The sympatho-adrenergic system might be involved in the pathogenesis of overtraining. Overtraining appears as a disturbed autonomic regulation, which in its parasympathicotonic form shows a diminished maximal secretion of catecholamines, combined with an impaired full mobilisation of anaerobic lactic reserves. This is supposed to lead to decreased maximal blood lactate levels and maximal performance. Free plasma adrenaline (epinephrine) and noradrenaline (norepinephrine) may provide additional information for the monitoring of endurance training. While prolonged aerobic exercise conducted at intensities below the individual anaerobic threshold lead to a moderate rise of sympathetic activity, workloads exceeding this threshold are characterised by a disproportionate increase in the levels of catecholamines. In addition, psychological stress during competitive events is characterised by a higher catecholamines to lactate ratio in comparison with training exercise sessions. Thus, the frequency of training sessions with higher anaerobic lactic demands or of competition, should be carefully limited in order to prevent overtraining syndrome. In the state of overtraining syndrome and overreaching, respectively, an intraindividually decreased maximum rise of pituitary hormones (corticotrophin, growth hormone), cortisol and insulin has been found after a standardised exhaustive exercise test performed with an intensity of 10% above the individual anaerobic threshold.(ABSTRACT TRUNCATED AT 400 WORDS)

Optic pathway glioma infiltrating into somatostatinergic pathways in a young boy with gigantism. Case report

The authors report gigantism in a 16-month-old boy with an extensive optic pathway glioma infiltrating into somatostatinergic pathways, as revealed by magnetic resonance imaging and immunocytochemical studies. Stereotactic biopsies of areas showing hyperintense signal abnormalities on T2-weighted images in and adjacent to the involved visual pathways provided rarely obtained histological correlation of such areas. The patient received chemotherapy, which resulted in reduction of size and signal intensity of the tumor and stabilization of vision and growth velocity.

Growth and puberty in chronic inflammatory bowel disease

The consequences of IBD during childhood and adolescence may be devastating in terms of loss of growth potential, particularly if there has been a clinical course of frequent relapses resulting in inadequate nutrition and associated with repeated courses of steroid treatment. There is to date, however, a paucity of data recording final adult heights in such patients. The anticipation of relapse should become easier with increasing awareness of the importance of parameters of growth and pubertal development. Early and intensive nutritional support, and the use of steroid-sparing agents should help reduce the frequency and severity of any height deficit. The performance and timing of surgery must take into account the child's status in terms of height velocity and pubertal development. The importance of inducing the remission before the onset of puberty is stressed and this remission should be sustained at all costs during the pubertal years so that valuable height is not lost as a consequence of a missed pubertal growth spurt. Thus, increasing awareness of the issues of growth and development in these patients should improve the accuracy of initial diagnosis and early recognition of relapse, such that these children are ensured the best possible provision for achieving their full height potential.

Insulin like growth factor-I, insulin like growth factor binding protein-1, and insulin in childhood Crohn's disease

Twenty nine children with Crohn's disease were studied before and after treatment with steroids or an elemental diet to assess the effect of disease activity and treatment on serum insulin like growth factor I (IGF-I), insulin like growth factor binding protein (IGFBP-1), and insulin concentrations. The median serum IGF-I concentration was lower in patients with active disease than in matched controls, and lower in stunted than well grown patients, but insulin and IGFBP-1 concentrations were not significantly different between any group. After four weeks of either treatment there was an increase in the median serum IGF-I concentration; this was greater in the steroid group than the elemental diet group. The median serum insulin concentration increased and median serum IGFBP-1 concentration decreased in the steroid treated group but not in the elemental diet group. These changes were accompanied by a greater and more sustained increase in energy intake in the steroid group. Despite this the median height velocity SD score was greater in the elemental diet group than in the steroid group.

Gastrin, motilin, insulin, and insulin-like growth factor-I concentrations in very-low-birth-weight infants receiving enteral or parenteral nutrition

Blood concentrations of gastrin, motilin, insulin, and insulin-like growth factor-I were measured sequentially during the first 3 weeks of life in 22 very-low-birth-weight infants (birth weight 1.03 +/- 0.24 g; gestational age 28.3 +/- 1.9 weeks; mean +/- SD) who were in respiratory distress requiring mechanical ventilation and were receiving either total parenteral or enteral feedings. An increase in the blood concentration of motilin beyond the basal measurement was observed in enterally fed infants but not in infants receiving total parenteral nutrition. Motilin and gastrin concentrations were significantly increased in the enterally fed group compared with infants receiving total parenteral nutrition at 2 and 3 weeks and 1 and 3 weeks, respectively. There were no differences in serum insulin or plasma insulin-like growth factor-I concentrations between groups after the start of the study. The present data suggest that enteral nutrition in very-low-birth-weight infants is associated with a relative increase in peripheral motilin and gastrin concentrations compared with parenterally fed infants.

The effects of growth factors on DNA synthesis, proteoglycan synthesis and alkaline phosphatase activity in bovine dental pulp cells

Platelet-derived growth factor (PDGF), insulin-like growth factor-I and -II (IGF-I and -II), acidic fibroblast growth factor (aFGF), basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) stimulated [125I]-deoxyuridine incorporation about 13, 6.2-, 4.6-, 3.8-, 3.1- and 1.2-fold, respectively, above control values at a concentration of 50 ng/ml. Transforming growth factor-beta (TGF-beta) decreased incorporation about 30% at the same dose. aFGF, IGF-I, IGF-II, bFGF and TGF-beta increased [35S]-sulphate incorporation 231, 71, 64, 42 and 39%, respectively, in proliferating cells, while EGF, IGF-I, TGF-beta and PDGF decreased incorporation about 30%, and aFGF increased incorporation 80% in stationary-stage culture. TGF-beta, PDGF, aFGF and bFGF caused 65-40% inhibition of alkaline phosphatase activity in proliferating and stationary cultures. These findings suggest that the proliferation of pulp cells may be stimulated mainly by PDGF and IGF-I, and the production of extracellular matrix proteoglycan may be enhanced by aFGF, IGF-I and IGF-II. Furthermore, TGF-beta, PDGF, aFGF and bFGF may regulate the differentiation of pulp cells into odontoblasts.

Regulation and action of insulin-like growth factors at the cellular level

Present understanding of IGF-1 as a growth factor mediating integration of nutritional-hormonal interactions indicates that IGF-1 acts in both an endocrine mode on distant targets and an autocrine-paracrine mode on local targets. In the liver, the combined presence of GH, insulin, and critical metabolic fuels such as essential amino acids results in increased levels of IGF-1 messenger RNA, increased production of a high-MW IGF-1 precursor, and increased release of IGF-1 into the circulation, permitting action on distant target tissues bearing specific receptors for IGF-1. The net effect is distant amplification of anabolic hormone action via IGF-1 acting in an endocrine mode. In extrahepatic tissues, both 'general' anabolic hormones (insulin and GH) as well as 'specific' hormones (e.g. gonadotropins) acting on a wide variety of targets (including fibroblasts and chondrocytes as well as granulosa and Leydig cells) promote both local secretion of IGF-1 and an increase in IGF-1 receptors. Local actions of IGF-1 then result in a secondary increase in both hormone receptors and hormone responses. The net effect is local amplification of hormone action via IGF-1 acting as a growth factor in an autocrine-paracrine mode.

The effect of ovarian function on insulin-like growth factor I plasma levels and hepatic IGF-I mRNA levels in diabetic rats treated with insulin

When insulin was administered to streptozotocin-induced diabetic female rats, the percentage of glycohemoglobin, growth rate, ovulatory cycle, uterus to body weight ratio, and insulin-like growth factor (IGF-I) level returned to near normal. In untreated diabetic rats there were no normal estrous cycles, and hepatic IGF-I mRNA (7.94 +/- 1.02 O.D. units per micrograms total RNA) levels were significantly lower than the control or insulin-treated groups in proestrus (16.47 +/- 0.91 and 17.15 +/- 1.84, respectively). Insulin therapy restored the hypothalamic-pituitary-ovarian axis with the reinstitution of normal estrous cycles. Plasma IGF-I levels were highest in non-diabetic proestrous animals (277 +/- 36.9 ng/ml), significantly higher than IGF-I levels in insulin-treated diabetic rats in diestrus (174 +/- 23.1 ng/ml), non-diabetic diestrus rats (165 +/- 18.4 ng/ml) and untreated diabetic rats (135 +/- 19.7 ng/ml). Plasma IGF-I levels were elevated in insulin-treated diabetic rats in proestrus (221 +/- 78.3 ng/ml), however this was not significantly different from any other group. The increases observed in plasma IGF-I and hepatic IGF-I mRNA after insulin therapy correlate with the normalization of sex hormone secretion. Though this study does not prove a causal relationship between restoration of ovarian function and normalization of circulating IGF-I levels, a relationship has been established, as evidenced by higher levels of IGF-I in both the control and insulin-treated diabetic proestrous groups when compared to the diestrus groups.

Circulating insulin-like growth factor I in type 1 (insulin-dependent) diabetic patients with retinopathy

The relationship between insulin-like growth factor I (IGF I) and diabetic retinopathy was investigated. This somatomedin circulates bound to at least two large carrier proteins with molecular weights of approximately 150,000 and 35,000. Total and protein binding profiles of insulin-like growth factor I were determined in the serum of 18 patients who had had Type 1 (insulin-dependent) diabetes for 15-20 years, but had no signs of nephropathy and a similar degree of mild subclinical neuropathy. Nine had preproliferative or proliferative retinopathy and 9 had little or no background retinopathy but there was no difference in diabetes duration, insulin doses or glycaemic control between the two groups. In the latter group, the amounts of the somatomedin I and the serum profiles were similar to those in 9 healthy control subjects. In patients with advanced retinopathy, however, binding of insulin-like growth factor I to the carrier proteins was significantly altered. Binding to the low molecular weight protein increased to 140% whereas binding to the large molecular weight protein decreased to 70% of the normal level. In the latter Type 1 diabetic patients total serum insulin-like growth factor I was decreased to 60% of the normal level (p less than 0.02). When the alteration in serum profile was adjusted for, the level of somatomedin associated with the small carrier complex was normal whereas that associated with the large carrier complex was reduced by almost 60% in Type 1 diabetic patients with retinopathy. It is proposed that the total circulating somatomedin level is low in advanced diabetic retinopathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Nutrition and somatomedin: nutritionally regulated release of somatomedins and somatomedin inhibitors from perfused livers in rats

Circulating somatomedin activity reflects the presence of both somatomedins and somatomedin inhibitors, factors which antagonize the growth-promoting actions of somatomedins. Although both are regulated by nutrition, somatomedin inhibitors respond more rapidly than somatomedins to refeeding in fasted animals. To explore the role of the liver in such responses, release of somatomedin activity and somatomedin inhibitor activity was assessed during perfusion of livers from normal, fasted, and fasted-refed rats. Size-exclusion high-performance liquid chromatography (HPLC) revealed that liver perfusates contain both somatomedin and somatomedin inhibitor activity of apparent molecular weight (mol wt) comparable to that found in the circulation (approximately 7,000 and approximately 30,000, respectively), as well as activity of apparently higher wt. In subsequent studies, responses to nutrition were evaluated as fluctuations in bioactivity only of mol wt comparable to that found in the circulation. Release of both somatomedin and somatomedin inhibitor activity was progressive over at least two hours of recirculating perfusion. Perfusates of livers from normal fed rats had somatomedin activity (stimulation of cartilage SO4 uptake) 94 +/- 19% above buffer (P less than .01), which fell to undetectable levels after three days of fasting. With refeeding, perfusate somatomedin activity rose within three hours to approximately 25% of levels in fed rats, but did not become significant until after 12 hours (29 +/- 7%, P less than .02). Perfusates of livers of fed rats also contained somatomedin inhibitor activity (42 +/- 10% inhibition of cartilage stimulation by normal serum), which rose after three days of fasting to 114 +/- 22% (P less than .02).(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoid effects on IGF-1/somatomedin-C and somatomedin inhibitor in streptozotocin-diabetic rats

Diabetes is associated with a fall in serum levels of insulin-like growth factor-1/somatomedin-C (IGF-1/Sm-C) and a rise in somatomedin inhibitor, a factor which antagonizes somatomedin action. We attempted to determine if the presence of glucocorticoids was required for diabetes-related alterations in these circulating growth factors. Diabetes was induced with streptozotocin in intact or adrenalectomized rats. Adrenalectomized-nondiabetic and adrenalectomized-diabetic rats were given either no glucocorticoids or daily hydrocortisone acetate at 0.5 or 50 mg/kg body weight, and killed 48 hours after streptozotocin treatment. After serum fractionation via size exclusion high performance liquid chromatography (HPLC), IGF-1/Sm-C was determined by radioimmunoassay, and somatomedin inhibitor by bioassay according to the ability of serum fractions to blunt cartilage stimulation by normal serum. Intact-diabetic rats had 22% weight loss, glucose 427 mg/dL, and beta-hydroxybutyrate 7.2 mmol/L (all P less than .001 v control). Serum IGF-1/Sm-C levels in intact-diabetic rats were decreased 71%, while somatomedin inhibitor rose to 470% of the control values (both P less than .004). Adrenalectomized-diabetic rats displayed comparable hyperglycemia (greater than 400 mg/dL) and decline in IGF-1/SmC, with or without glucocorticoid replacement. However, adrenalectomized-diabetic rats had greatly reduced weight loss (10%), beta-hydroxybutyrate (1.5 mmol/L), and somatomedin inhibitor (59% of control), all P less than .01 v intact-diabetic. Hydrocortisone 0.5 mg/kg in these animals increased weight loss but had no significant effect on beta-hydroxybutyrate or somatomedin inhibitor levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrine functions in Huntington's disease. A two-and-a-half years follow-up study

An oral glucose tolerance test (OGTT) was performed in 1985 in 10 patients with Huntington's disease (HD), while 10 healthy age-matched volunteers served as controls. Two-and-a-half years later, in 1988, 8 of the original 10 patients were reinvestigated. Apart from glucose, insulin and growth hormone (sampled at 30 min intervals) the following parameters of endocrine function were assessed: C-peptide (at times 0 and 60 min), glycosylated haemoglobin (HbAlc), somatomedin-C, and basal prolactin. In 1985 one female patient was considered to have impaired glucose tolerance, and this same patient, as well as another male patient, had a paradoxical rise in GH secretion. None of the other measurements of endocrine function differed significantly from control. In 1988 the HD patients had clinically deteriorated significantly, as measured by the Shoulson and Fahn Scale. Six of them completed a repeat OGTT. Of these 6, the same female as in 1985 showed impaired glucose tolerance. Now none of the participants had a paradoxical GH rise. The HD patients did not show any deterioration of the parameters of glucose metabolism, nor of GH secretion. The basal prolactin level, however, decreased significantly in these 2.5 years, from 9.3 +/- 3.2 micrograms/l to 6.1 +/- 3.0 micrograms/l (P less than 0.01).

Neuroendocrine profile in bulimia nervosa

The neuroendocrinology of bulimia nervosa has only recently been investigated, with initial research suggesting some biological overlap with both anorexia nervosa (AN) and depression. Similarities among AN, depression, and bulimia include a nonsuppressed Dexamethasone Suppression Test and an abnormal growth hormone (GH) response to thyrotropin-releasing hormone (TRH). Bulimics and anorectics both tend to have a delayed thyrotropin (TSH) response to TRH and elevated basal GH levels. Bulimics, however, have a normal GH response to clonidine, a nonblunted TSH response to TRH, low basal prolactin (PRL) levels, and may have an exaggerated PRL response to TRH. Unpublished data suggest bulimics may have a gonadotropin profile distinct from either AN or depression, as well as a variety of other endocrinopathies. Although many of these abnormalities may reflect malnutrition despite normal weight, other factors that are as yet unidentified are likely to be contributing to the neuroendocrine abnormalities seen in bulimia.

Salt stimulation of serum insulin-like growth factor binding protein activity

Insulin-like growth factors (IGF)-I and -II are bound to carrier or binding proteins in serum. There are at least two classes of binding protein: a high molecular weight complex and a low molecular weight species that is relatively unsaturated. Total binding capacity in serum generally is determined by incubating [125I]IGF with protein that has been stripped of IGF by acid gel filtration. We found that addition of NaCl to the assay increased binding to stripped guinea pig binding protein to about two to four times the level measured in the absence of salt. Stimulation by NaCl was optimal between concentrations of 0.6 and 1.4 M and also was observed when fetal calf or human sera were used as sources of stripped binding protein or when IGF-II was the ligand. Using chloride salts, the order of activity with respect to cations was Na+ greater than K+ greater than Li+. Na2HPO4 at 0.6 M was as stimulatory as 1.2 M NaCl but 0.6 M Na2SO4 was less effective. NH4HCO3 was as effective as NaCl at 0.6 M. Scatchard plots of data from competitive dilution experiments with [125I]IGF-I and unlabeled IGF-I showed that binding was heterogeneous in the absence of 0.6 M NaCl but linear in its presence. NaCl did not stimulate binding when whole serum was used, but after gel filtration of serum on Sephacryl 200 at pH 8, which does not dissociate IGFs from binding protein, binding to individual fractions was stimulated three- to fourfold by NaCl. Fractions stimulated included those containing the large complex or the unsaturated binding protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Nutritional consequences of inflammatory bowel disease on growth

This review summarizes much of the current information concerning the problem of growth failure in children and adolescents with inflammatory bowel disease. Growth impairment is discussed as a dynamic process and ways of recognizing and monitoring subtle changes in growth velocity are presented. Factors which contribute to growth delay are described, with special attention to prolonged insufficient nutrient intake. Studies using different methods of nutritional intervention to reverse growth failure are presented as a guide to the management of this challenging group of patients.

Serum IGF-1 concentration in diabetic retinopathy

Growth factors such as growth hormone and insulin-like growth factor 1 (IGF-1) may be important in the pathogenesis of diabetic retinopathy. We measured serum IGF-1 in 371 diabetic patients attending a diabetic retinopathy clinic and in 73 non-diabetic control subjects. No significant difference was observed in IGF-1 level between the diabetic and control groups (168 +/- 3.9 vs 177 +/- 7.4 micrograms/l [mean +/- SE]). Within the diabetic group, there was no difference between patients with no retinopathy and those with proliferative change (198.7 +/- 8.8 vs 190.5 +/- 11 micrograms/l). After adjusting for differences in age, duration of diabetes, and presence of proteinuria, only the inactive previously proliferative group showed any significant difference from the other patient subgroups (151.8 +/- 11.5 micrograms/l; p less than 0.05). Serum IGF-1 correlated with age in the control group (r = 0.49; p less than 0.001) and to a lesser extent in the diabetic group (r = -0.23; p less than 0.05). IGF-1 levels were higher in patients with proteinuria than in those without proteinuria (196.8 +/- 10.3 vs 138.8 +/- 4.4 micrograms/l; p less than 0.001).

Central nervous system inhibition of pentagastrin-stimulated acid secretion by insulin-like growth factor II

The ability of intracisternal insulin-like growth factor II (IGF II) to inhibit gastric acid secretion was studied in rats. Centrally-administered IGF II dose-dependently inhibited acid secretion stimulated by pentagastrin. The effect was abolished by vagotomy. IGF II did not inhibit acid secretion stimulated by histamine or PCP-GABA.

Growth hormone and somatomedin-C in bulimia

Somatomedin-C (SOM-C) concentrations are regulated by circulating growth hormone (GH) concentrations; however, other factors, such as nutrition, also influence SOM-C concentrations. We evaluated the GH-SOM-C axis in seven normal-weight female bulimics one day after hospital admission, and in seven age-, sex-, and weight-matched normal controls. Subjects were medication-free for at least one month. Fasting morning serum GH concentrations were higher in all bulimics (range 2.5-13.3 ng/ml) than in all controls (range less than 1.0-1.8 ng/ml). The mean (+/- SD) maximum GH response to TRH (500 micrograms) was greater in the bulimics (12.9 +/- 4.9 ng/ml) than in the controls (3.7 +/- 2.7 ng/ml) (p less than .001). Despite this GH elevation, the mean (+/- SD) SOM-C concentration was comparable in the bulimics (2.0 +/- 0.6 U/ml) and the controls (1.6 +/- 0.8 U/ml). This suggests that SOM-C generation is resistant to the elevated circulating GH in bulimia and that SOM-C is not inhibiting GH secretion in the pituitary-hypothalamic axis.

Initiation and enhancement of bone formation. A review

Knowledge of some of the fundamental biochemical factors that may influence the initiation and continued growth of bone-forming cell lines is presented. The discussion is limited to those factors shown experimentally to be present locally in bone tissue and synthesized in the environment of bone-forming cells. The current state of knowledge of basic research findings on osteogenic factors is given in detail. Cooperative actions of these locally produced and systemic factors are the primary stimuli that result in increased bone growth and volume.

Extracellular matrices and polypeptide growth factors as mediators of functions of cells of the periodontium. A review

This is a review of the interactions between cells and their extracellular matrices and polypeptide growth factors. The review not only attempts to provide a basic understanding of the functions of extracellular matrices and polypeptide growth factors but, in addition, suggests the role these biological molecules may play in periodontal regeneration. It is conceivable that future periodontal therapy will include the treatment of a scaled root with biological response modifiers to predictably attain a true new connective tissue attachment.

Somatomedin C/insulin-like growth factor I production by human fetal lung tissue maintained in vitro

The production of somatomedin C/insulin-like growth factor I (Sm-C/IGFI) by human fetal lung tissue maintained in vitro was examined in the present study. We have shown that epithelial cells in human fetal lung explants maintained in vitro differentiate into type II cells within 4-6 days. During the first 24 h of culture, the fetal lung explants released 2.74 +/- 0.14 ng Sm-C/IGFI/mg tissue protein into the culture medium. At this time the explants contained 0.24 +/- 0.02 ng Sm-C/IGFI/mg tissue protein. During the next 4 days of culture, explant Sm-C/IGFI content and the rate of Sm-C/IGFI secretion into the medium declined by approximately 50%. Sm-C/IGFI secretion was inhibited significantly when fetal lung explants were cultured in media that contained cortisol (10(-7) M), a hormone that is known to stimulate fetal lung type II cell differentiation. The effect of cortisol was both concentration- and time-dependent. While insulin, bovine prolactin, and human growth hormone had no apparent effect on Sm-C/IGFI production by the explants, human prolactin and human placental lactogen both decreased Sm-C/IGFI production. These findings are unprecedented and are suggestive that Sm-C/IGFI synthesis may be regulated in a unique fashion in the fetal lung. The decline in Sm-C/IGFI production by fetal lung tissue temporally correlates with the initiation of fetal lung type II cell differentiation in the human fetal lung explants.

Somatomedin-C levels in growth-impaired children and adolescents with chronic inflammatory bowel disease

The relationship between caloric insufficiency and impaired growth in children with chronic inflammatory bowel disease has been increasingly recognized in recent years. The mechanism by which nutritional insufficiency leads to decreased growth in these children is unclear. Our study suggests that chronic undernutrition lowers circulating somatomedin-C, which is known to exert anabolic effects on peripheral tissues. Therapeutic intervention that increases caloric intake results in improved somatomedin-C levels and growth velocity. Monitoring somatomedin-C levels in growth-impaired children with inflammatory bowel disease provides an important marker of nutritional sufficiency and reversibility of growth retardation.

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.

The measurement of insulin-like growth factor I: clinical applications and significance

Of the somatomedins so far measured, the selective quantitation of insulin-like growth factor I (IGF-I) appears to have the greatest potential in clinical diagnosis. There have been two approaches to the development of immunoassay systems. One type uses antibodies raised against synthetic fragments of IGF-I which exhibit cross-reactivity with the whole hormone. Such assay systems may be adequate for measuring normal adult plasma IGF-I levels, but the potential for the higher sensitivity required for detecting sub-normal plasma levels in young children is apparent only in methods using antibodies raised against the complete hormone. IGF-I in plasma exists as part of a high molecular weight complex in which it is bound to carrier proteins. The binding proteins may interfere with plasma IGF-I measurements by radioligand assays. Direct analysis of untreated plasma samples is claimed to be possible using disequilibrium assay conditions but in order to maximise assay sensitivity it is necessary to employ an initial extraction stage in order to eliminate binding protein interference. Whether the measurement of plasma IGF-I can or should be used in addition to, or as a replacement for, plasma growth hormone (GH) measurement in the clinical assessment of growth disorders remains a controversial issue. Available evidence indicates that a single, random plasma IGF-I level provides an accurate reflection of GH secretion. Adequate discrimination between the elevated levels in acromegaly and normal reference values has been demonstrated. However, in the investigation of growth-retarded children available radioimmunoassay (RIA) methods have proved only partially successful because of the age-related nature of normal plasma IGF-I concentrations. Existing assays appear capable of identifying sub-normal plasma levels after the age of approximately 4 years. In younger subjects an improvement in assay sensitivity is required in order to establish with greater accuracy the relevant normal ranges. Improvements in the identification of the particular lesion responsible for retarded growth in a child can be achieved by measurement of both plasma GH and IGF-I concentrations. The predictive value of the acute plasma IGF-I response to single-dose GH therapy may identify patients who will respond to long-term GH therapy. Better, more informed decisions on subsequent treatment may therefore be made. Apart from GH control, several other factors influence circulating IGF-I levels. Nutritional status can be assessed through reference to IGF-I analysis, overall catabolic or anabolic processes being associated with decreasing or increasing plasma IGF-I levels respectively.

Insulin-like growth factor I/somatomedin C: a potent inducer of oligodendrocyte development

Cell cultures established from cerebrum of 1-day-old rats were used to investigate hormonal regulation of the development of oligodendrocytes, which synthesize myelin in the central nervous system. The number of oligodendrocytes that developed was preferentially increased by insulin, or by insulin-like growth factor I (IGF-I), also known as somatomedin C. High concentrations (5 micrograms/ml) of insulin were required for substantial induction of oligodendrocyte development, whereas only 3.3 ng of IGF-I per ml was needed for a 2-fold increase in oligodendrocyte numbers. At an IGF-I concentration of 100 ng/ml, oligodendrocyte numbers were increased 6-fold in cultures grown in the presence of 10% fetal bovine serum, or up to 60-fold in cultures maintained in serum-free medium. IGF-I produced less than a 2-fold increase in the number of nonoligodendroglial cells in the same cultures. Type I IGF receptors were identified on oligodendrocytes and on a putative oligodendrocyte precursor cell population identified by using mouse monoclonal antibody A2B5. These results indicate that IGF-I is a potent inducer of oligodendrocyte development and suggest a possible mechanism based on IGF deficiency for the hypomyelination that results from early postnatal malnutrition.

Nutrition, somatomedins, and the brain

Conditions of decreased nutrient supply (malnutrition) and/or decreased nutrient utilization (diabetes) are attended by impairment of growth despite an increase in circulating levels of growth hormone (GH). Growth involves the actions of somatomedins, circulating insulinlike polypeptides with anabolic effects on cartilage, fat, and muscle. In malnutrition and diabetes, mechanisms of growth impairment appear to include a decrease in GH-induced generation of somatomedins, together with an increase in somatomedin inhibitors, factors which antagonize somatomedin action. Brain mediation of these alterations involves a rise in GH secretion due to decreased negative feedback from somatomedins, perhaps accentuated by blunting of feedback via actions of somatomedin inhibitors. In combination these processes lead to shunting of metabolic fuels toward vital processes and away from growth (via decreased somatomedin action) and to protein-sparing and increase in alternate metabolic fuels (via direct GH actions on muscle and fat). Further study of involved hypothalamic and pituitary mechanisms should yield additional insights into the role of the brain in metabolic homeostasis.

Exogenous growth hormone inhibits growth hormone-releasing factor-induced growth hormone secretion in normal men

Previous studies from this laboratory and by others in rats, monkeys, and humans support the concept that growth hormone (GH) can regulate its own secretion through an autofeedback mechanism. With the availability of human growth hormone-releasing factor (GRF), the possible existence of such a mechanism was reexplored by examining the effect of exogenous GH on the GH response induced by GRF-44-NH2 in six normal men (mean age, 32.4 yr). In all subjects the plasma GH response evoked by GRF-44-NH2 (1 microgram/kg i.v. bolus) was studied before and after 5 d of placebo (1 ml normal saline i.m. every 12 h), and then before and 12 h after 5 d of biosynthetic methionyl human GH (5 U i.m. every 12 h). The GH response to GRF (maximal increment over time 0 value) was significantly inhibited after GH treatment (0-1.3 vs. 2.3-11.2 ng/ml before treatment, P = 0.05), but was not significantly affected by placebo. This impaired pituitary response to GRF persisted for at least 24 h following exogenous GH treatment in two subjects who underwent further study. Serum somatomedin-C concentrations were significantly increased after 5 d of GH treatment (2.66-5.00 vs. 0.92-1.91 U/ml before treatment, P = less than 0.01). The impaired pituitary response to GRF may be mediated indirectly through somatomedin, somatostatin, by a direct effect of GH on the pituitary somatotropes, or by all of these mechanisms. These data suggest that after GH treatment, the blunted GH response to synthetic GRF is not solely a consequence of the inhibition of hypothalamic GRF secretion.

Insulin and new bone formation in diffuse idiopathic skeletal hyperostosis

The tendency of patients with DISH towards obesity or an adult onset of diabetes has been reflected in marked hyperinsulinaemia following glucose challenge. It is hypothesized that insulin at prolonged and high physiologic levels promotes new bone growth, particularly in the entheseal regions. These areas are also subject to various mechanical forces. The resulting new bone produces the radiological changes which characterise DISH.

Nutrition and somatomedin. XIV. Altered levels of somatomedins and somatomedin inhibitors in rats with streptozotocin-induced diabetes

Diabetes is associated with poor growth despite elevated levels of growth hormone (GH). Skeletal GH effects are mediated by somatomedins; in diabetes, somatomedins measured by radioassay are normal, yet somatomedin activity measured by bioassay is low. Since bioassay measurements reflect the presence of both somatomedins and somatomedin inhibitors, we asked if diabetes might be associated with discordant regulation of these circulating factors. Graded severity of diabetes was induced in rats by injection of streptozotocin at 37, 73, 146, and 293 mg/kg. After two days, metabolic derangement varied from normal serum beta-hydroxybutyrate with slight increase in glucose and minimal weight loss at 37 mg/kg streptozotocin to beta-hydroxybutyrate 10.6 mmol/L, glucose 447 mg/dL, and 33 g weight loss at 293 mg/kg streptozotocin. After fractionation of serum on Sephacryl S-300 pH 7.0, somatomedins and somatomedin inhibitors were measured by rat cartilage bioassay. Somatomedins (Kav 0.25 to 0.50) were comparable to control levels despite beta-hydroxybutyrate 2 mmol/L, glucose 534 mg/dL, and weight loss 11 g at 73 mg/kg streptozotocin and fell only at higher streptozotocin dosage. In contrast, somatomedin inhibitors (Kav 0.62 to 0.88) began to rise at 37 mg/kg streptozotocin and increased with higher dosage. Levels of somatomedins were correlated weakly only with beta-hydroxybutyrate (r = 0.48, P less than 0.05), while somatomedin inhibitors were correlated significantly with all indices, particularly beta-hydroxybutyrate (r = 0.78, P less than 0.0001). The early rise in somatomedin inhibitors but late fall in somatomedins could explain low somatomedin activity (and poor growth) despite normal levels of somatomedins measured by radioassay; measurement of somatomedin inhibitors may provide an index of growth potential in diabetes mellitus.

Changes in immunoreactive basic somatomedin in conscious and anaesthetized male rats

Basic somatomedin (B-SM) like insulin-like growth factor-I or somatomedin-C belongs to the basic group of somatomedins. In preliminary studies on the control system for B-SM, we have found that plasma levels of immunoreactive B-SM (IRSM) fluctuate in conscious adult male rats. The peaks average 85% of the local baseline level (minimum of 6 points) and occur with an interpeak interval of 2.1 h. In rats anaesthetized with nembutal (50 mg/kg) very few peaks were found. After approximately 3.4 hr. of anaesthesia, plasma IRSM levels dropped precipitously with a calculated T1/2 of 50 minutes. These results suggest that IRSM levels may be related to serum CH levels which occurred 4 hr previously and that part of variation seen in serum levels in conscious rodents may be due to physiological fluctuations.

Nutrition and somatomedin. XIII. Usefulness of somatomedin-C in nutritional assessment

Malnutrition is common in hospitalized patients, but current measures of nutritional status are limited. Because levels of somatomedins are regulated by nutrition, the utility of somatomedin-C measurement in nutritional assessment was studied. Thirty-seven malnourished patients had measurement of somatomedin-C and conventional nutritional indexes. In 28 patients seen before therapy, the somatomedin-C level was reduced (38 percent of normal) and was lower than the albumin level (66 percent, p less than 0.01), transferrin level (59 percent, p less than 0.05), and lymphocyte count (43 percent, p = NS). Somatomedin-C level was lowest with combined "kwashiorkor-marasmus" (25 percent of normal) and also reduced with "kwashiorkor" (51 percent) or "marasmus" (57 percent) alone. Somatomedin-C was correlated with albumin, transferrin, and lymphocyte count (p less than 0.02 for each). In six patients given nutritional therapy, somatomedin-C levels rose by more than 70 percent in each (mean increase 181 percent), whereas lymphocyte counts rose in four (increase 78 percent for all patients), transferrin levels rose in four (increase 33 percent), and albumin levels rose in one (-6 percent). In 20 patients with detailed dietary analysis, only somatomedin-C was correlated with intake of protein and calories (p less than 0.005 for each). Somatomedin-C may be a sensitive marker of malnutrition and the response to nutritional therapy.

Steindler lecture. Binding sites in fetal and growth plate cartilage

In addition to genetic and nutritional factors, linear growth during the prenatal and postnatal periods is controlled by peptide, steroid, and thyroid hormones interacting with the receptors present on the membrane or in the cytosol and nuclei of growth plate cartilage. Using standard procedures, insulin and "nonsuppressible insulin-like activity" (a somatomedin) showed significant binding in 600, 15,000, and 105,000 g membrane fractions of epiphyseal cartilage of immature animals. The binding of growth hormone and prolactin was small and probably not significant. Specific uptake of glucocorticoid was demonstrated in viable canine chondrocytes, but not of androgen, estrogen, or vitamin D3 metabolite. A triiodothyronine receptor was present in nuclei from dog epiphyseal cartilage. Hormones that lack binding may affect cartilage only indirectly. Hormone receptors were studied in those portions of fetal growth cartilage that will later evolve into an ossification center, articular cartilage, and epiphyseal cartilage. Cytosol fractions contained a receptor for glucocorticoid but not for androgen or estrogen. Zonal analysis showed a higher level in the peripheral and central sections than in the palisade section. Triiodothyronine binding was also detected in nuclei prepared from whole fetal cartilage. Heterogeneity of cell function was obvious in fetal cartilage. Cell division was high in the central and peripheral zones as well as the upper half of the palisade zone, but low in the lower palisade section. Proline and sulfate incorporation predominated in the palisade section compared with the central and peripheral sections. Disease states with changes of metabolic activities in the cartilage may perhaps be better understood with a clearer knowledge of receptor levels and interactions.

Nutrition and somatomedin--XII. Fractionation of somatomedins and somatomedin inhibitors in normal and diabetic rats

Bioassayable somatomedins and somatomedin inhibitors were examined after chromatographic separation, using serum from normal rats (enriched in somatomedins) and diabetic rats (enriched in somatomedin inhibitors). At neutral pH, gel filtration on Sephacryl S-300 revealed somatomedins at mol. wt approximately 140,000 (presumably carrier-bound) and inhibitors at mol. wts approximately 250,000, approximately 24,000 and approximately 1,000. At acid pH, gel filtration on Sephadex G-50 revealed somatomedins at mol. wt approximately 8,000 (presumably carrier-free) and a single inhibitor at mol. wt approximately 21,000. Ion exchange chromatography revealed that the inhibitor(s) may be more acidic than the somatomedins, but only low quantities of somatomedins were recovered. Sephadex G-50 fractionation was applied to pathophysiologic models in rats: 3 days of fasting were associated with a 62% fall in somatomedins and a 159% rise in inhibitors; 2 days of diabetes were associated with a 60% fall in somatomedins and a 344% rise in inhibitors. Since chromatography on Sephadex G-50 at pH 2.4 appears to provide adequate separation of somatomedins and somatomedin inhibitors with good estimated recovery of biological activity, this simple approach may be a probe useful in examining the regulation of somatomedins and somatomedin inhibitors in vivo.