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Career situation of first and presenting author Student for a master or a PhD. Introduction Prominent features of rheumatoid arthritis (RA) are pain, joint swelling and erosion induced by massive infiltration of immune cells into the inflamed tissue. Among these immune cells, granulocytes and monocytes play a crucial role. Both express sialic acid-binding immunoglobulin-like lectins (Siglecs) −7 and −9 (in mice Siglec-E), trans-membrane proteins generally transmitting inhibitory signals through immunoreceptor tyrosine-based inhibitory motifs in their cytoplasmic tails. So far, there has been only limited research on the effects of Siglecs in RA. Objectives To evaluate the potential role of Siglec 7- and −9 during disease progression in RA by comparing the expression on blood leukocytes with disease activity in RA patients. Additionally we monitored Siglec-E knockout mice in an experimental arthritis model. Methods Blood samples from 45 healthy donors (HD) and 37 RA patients were analyzed by flow cytometry for Siglec-7 and −9 expressions on NK cells (CD14+/CD56+/CD3-), granulocytes (CD16+/CD19-) and monocytes (CD14+/CD16-). Expression was correlated with autoantibody positivity and disease severity. Siglec-E knockout mice and wildtype controls were used in a serum transfer induced arthritis model and disease manifestation was monitored by measurement of paw swelling. Additionally we performed functional ex vivo assays to study Siglec impact on granulocytes and monocytes. Results There was a diminished Siglec-7/9 expression on NK cells from RA patients, especially in highly CCP positive patients (>500 U/ml), while no differences were observed in neutrophils and monocytes compared to healthy controls. Interestingly we observed a correlation between a higher DAS28 score and lower Siglec-9 expression levels on granulocytes in seropositive patients. Siglec-E knockout mice displayed higher disease scores and paw swelling in serum transfer induced arthritis, especially at the peak and the resolution phase. Functional studies unraveled that granulocytes are in a more active state if Siglec-7 and −9 are missing. Conclusions Together our data support that Siglec-7/9 expression negatively correlates with pathogenesis and disease manifestation in RA patients. We showed in vivo and ex vivo, that Siglecs possess an important role concerning granulocyte and monocyte function and are capable of dampening immune response. Due to their inhibitory potential, Siglecs should be considered as potential therapeutic starting point in future studies. Acknowledgements This work was supported by DFG (HA 8163/1–1) and STAEDTLER Stiftung (WW/eh20/17). Disclosure of Interest None declared.

Aim of the study was to investigate the possible mechanisms leading to stunted growth and osteoporosis in experimental arthritis. Fourty-two female rats of 7-8 weeks of age were randomly assigned to three groups of 14 animals each: (a) controls; (b) adjuvant-inoculated (AA); and (c) adjuvant-inoculated rats receiving 10 mg cyclosporin A (CsA) orally for 30 days. Biological parameters studied were: hindpaw swelling; vertebral length progression expressed as Delta increments between days 1 and 30 as a parameter of skeletal growth, and estimation of total skeletal mineral content by dual energy X-ray absorptiometry (n=10 each group) on day 30. Endocrine parameters measured were pulsatile release of growth hormone (rGH) on day 30 following jugular cannulation and measurement of insulin-like growth factor (IGF-1) in pooled plasma from rGH profiles. Results can be summarized as follows: Untreated AA rats exhibited local signs of inflammation in comparison with controls (hindpaw diameter 8.1-8.9 mm vs. 5.3-5.6 mm in controls). Treatment with CsA normalized this parameter (4.9-5.6 mm). Vertebral growth was significantly retarded in AA rats in comparison with controls (214+/-32 vs. 473+/-33 microm; p

The peripheral actions of growth hormone (STH) are mediated by somatomedins or "insulin-like growth factors" (IGF I and II). In untreated acromegaly (n = 24) IGF I was always found increased, IGF II, however, was unchanged. The mean IGF-I-level (+/- SEM) was 553 +/- 75 (range 319-1066) ng/ml in active acromegaly and 193 +/- 10 (range 120-300) ng/ml in control persons. The corresponding IGF-II-values were 533 +/- 38 (range 187-720) and 647 +/- 21 (range 400-900) ng/ml. After treatment of acromegaly IGF I followed changes of the basal STH level with a delay of 4-8 weeks independent of the mode of treatment. This was in contrast to behaviour of IGF II. When STH was suppressible below 1 ng/ml after oral administration of 100 g glucose IGF I was never increased. STH after glucose of more than 5 ng/ml was always associated with increased IGF I. STH values between 1 and 5 ng/ml after glucose were combined with IGF-I-increases in 3 out of 6 cases. Thus, IGF I represents a valuable diagnostic criterion for assessment of activity of acromegaly, particularly in borderline cases, in contrast to IGF II. The criterion of normal somatotrophic function is suggested to be suppressibility of STH level below 1 ng/ml after oral administration of 100 g glucose.

It was investigated if IGF-1 levels in cats which experience diabetic remission (i.e. transient diabetes mellitus) differ from those in cats with permanent disease. Thirteen of 32 diabetic cats showed remission within 16 weeks after initiating insulin therapy, 19 cats continued to need insulin therapy. IGF-1 concentrations were measured before (t(0)), 1-3 (t(1)) and 4-8 (t(2)) weeks after initiating insulin therapy. No difference in IGF-1 levels was found between cats with transient and permanent diabetes at any point in time. In both groups of cats IGF-1 concentrations were significantly lower compared to those of controls before insulin administration. After starting insulin therapy IGF-1 increased significantly in both groups. In cats with transient diabetes IGF-1 levels were not different from controls already at t(1), whereas in cats with permanent diabetes it took until t(2). Although IGF-1 levels seem to normalize faster in cats with transient diabetes mellitus, measurement is not helpful to predict the course of the disease.

The sections in this article are: 1 Indirect Evidence that Insulin-Like Growth Factor I Participates in the Regulation of Somatic Growth 1.1 Clinical: Correlations Between Growth and Insulin-Like Growth Factor I Levels in Serum 1.2 Experimental: Growth Hormone-Dependent Regulation of Insulin-Like Growth Factor I mRNA and Protein Expression in Various Tissues and the Autocrine/Paracrine Versus Endocrine Role of Insulin-Like Growth Factor I 2 Direct Evidence that Insulin-Like Growth Factor I Promotes Growth 2.1 Insulin-Like Growth Factor I as a Growth and Differentiation Factor In Vitro 2.2 Effects of Insulin-Like Growth Factor I Administration on Growth In Vivo 2.3 Transgenic Animals Overexpressing Growth Hormone or Insulin-Like Growth Factor I 2.4 Insulin-Like Growth Factor I and Type 1 Insulin-Like Growth Factor Receptor Knock-Out Animals 2.5 The Somatomedin Hypothesis Revisited

To examine whether insulin-like growth factor I (IGF I) or growth hormone (GH) influences leptin in vivo we measured leptin mRNA in epididymal fat pads and serum leptin of normal rats infused subcutaneously for 6 days with recombinant human (rh)IGF I (1 mg/day), rhGH (200 mU/day), or vehicle. In addition, we determined fat pad weight and food consumption as well as IGF I, insulin, glucose, non-esterified fatty acid (NEFA), glycerol, β-hydroxybutyrate and triglyceride (TG) serum concentrations. Food intake was identical during all three treatments. RhIGF I but not rhGH raised IGF I serum concentrations, reduced fat pad weight (60.3 ± 7.4 % of control rats, p = 0.019), and suppressed leptin mRNA (38.8 ± 11.9 % of control rats, p = 0.002), serum leptin (51.6 ± 10.5 % of control rats, p = 0.0028) and serum triglycerides (39.3 ± 8.0 % of control rats, p = 2.6 × 10–6). Both rhIGF I and rhGH reduced non-esterified fatty acids (NEFA) (p = 0.00 001 and 0.0007, respectively), whereas serum glycerol, β-OH butyrate and glucose concentrations remained unchanged. Serum insulin concentrations during rhIGF I were lower than during rhGH infusion and correlated with leptin mRNA (r = 0.589, p = 0.016) and fat pad weight (r = 0.643, p = 0.007). Reduction of adipose tissue mass and suppression of leptin by IGF I appear to be due to reduced circulating insulin leading to enhanced fat mobilization and NEFA oxidation as well as to increased gluconeogenesis from glycerol. In contrast, decreased NEFA concentrations during rhGH in the presence of unchanged fat pad weight, serum glycerol and triglycerides might result from more efficient re-esterification of released fatty acids within the triglyceride-fatty acid cycle. The results also show that exogenously infused IGF I and GH act on lipid metabolism by different mechanisms and suggest an IGF-independent, probably direct, metabolic effect of GH. Finally, in agreement with previous studies in GH-infused hypophysectomized rats, it appears unlikely that GH regulates leptin in the rat. [Diabetologia (1999) 42: 160–166]

Non-islet cell tumour hypoglycaemia (NICTH) is characterised by severe and recurrent fasting hypoglycaemia, and is usually caused by secretion of insulin-like growth factor-II (IGF-II) by the tumour. This induces secondary changes in the circulating levels of insulin, growth hormone (GH), and the IGF-binding proteins (IGFBPs), resulting in an increased insulin-like hypoglycaemic activity of IGF-II. A participating role of IGF-I is not established. We measured serum levels of free IGF-I and free IGF-II, total IGF-I, total IGF-II, big IGF-II and IGFBP-1, IGFBP-2 and IGFBP-3 in patients with NICTH before (n = 14) and after surgical removal of the tumour (n = 3). A control group (n = 20) was included for comparison. In NICTH patients, free IGF-II was 20-fold increased (26.8 ± 8.1 [mean ± SEM] vs. 1.3 ± 0.1 μg/l), and free IGF-I was four fold increased (2.8 ± 0.4 vs. 0.7 ± 0.1 μg/l), as compared to control subjects (p < 0.0001). In accordance with earlier observations levels of total IGF-I, total IGF-II, and IGFBP-3 were decreased, whereas IGFBP-1 and IGFBP-2 were increased in NICTH (all p-values < 0.05). The highly elevated levels of free IGF-I and free IGF-II most likely imply a considerable hypoglycaemic insulin-like activity, and may, by negative feedback explain the marked suppression of the GH/IGF-I axis observed in NICTH. Finally, free IGF-II seems to be a powerful biochemical marker in the diagnosis of NICTH. [Diabetologia (1998) 41: 589–594]

Leptin is thought to exert its actions on energy homeostasis through the long form of the leptin receptor (OB-Rb), which is present in the hypothalamus and in certain peripheral organs, including adipose tissue. In this study, we examined whether leptin has direct effects on the function of brown and white adipose tissue (BAT and WAT, respectively) at the metabolic and molecular levels. The chronic peripheral intravenous administration of leptin in vivo for 4 d resulted in a 1.6-fold increase in the in vivo glucose utilization index of BAT, whereas no significant change was found after intracerebroventricular administration compared with pair-fed control rats, compatible with a direct effect of leptin on BAT. The effect of leptin on WAT fat pads from lean Zucker Fa/ fa rats was assessed ex vivo, where a 9- and 16-fold increase in the rate of lipolysis was observed after 2 h of exposure to 0.1 and 10 nM leptin, respectively. In contrast, no increase in lipolysis was observed in the fat pads from obese fa/fa rats, which harbor an inactivating mutation in the OB-Rb. At the level of gene expression, leptin treatment for 24 h increased malic enzyme and lipoprotein lipase RNA 1.8+/-0.17 and 1.9+/-0.14-fold, respectively, while aP2 mRNA levels were unaltered in primary cultures of brown adipocytes from lean Fa/fa rats. Importantly, however, no significant effect of leptin was observed on these genes in brown adipocytes from obese fa/fa animals. The presence of OB-Rb receptors in adipose tissue was substantiated by the detection of its transcripts by RT-PCR, and leptin treatment in vivo and in vitro activated the specific STATs implicated in the signaling pathway of the OB-Rb. Taken together, our data strongly suggest that leptin has direct effects on BAT and WAT, resulting in the activation of the Jak/STAT pathway and the increased expression of certain target genes, which may partially account for the observed increase in glucose utilization and lipolysis in leptin-treated adipose tissue.

Osteopenia and retarded skeletal growth are consistent features of juvenile polyarthritis. Although the former has also been described in the experimental animal, the consequences of induced joint inflammation on skeletal growth have not yet been documented. In order to investigate the effect of experimental arthritis on these parameters, we studied female rats with adjuvant arthritis (AA) subjected to chronic treatment with cyclosporin A (CsA, Sandimmun ® ). This compound has been found to prevent the development of articular swelling and also repair joint and skeletal lesions in AA rats. Five groups of 8 animals each received oral CsA, 2.5, 5, 10, 20, or 30 mg/kg daily for 30 days. Eight normal and eight diseased, untreated rats served as placebo controls. The parameters studied were (a) measurement of hindpaw swelling, (b) radiometric assessment of vertebral growth, (c) vertebral trabecular density, (d) weight control and nutritional status. At the end of the investigational period, AA-rats on no therapy had severe osteopenia and growth retardation. Treatment with CsA, 2.5 mg/kg, was ineffective, but doses between 5 and 20 mg/kg prevented the development of articular and osseous lesions and normalized growth. A catch-up phenomenon was also observed. The 20 mg/kg dose showed no better effect than 10 mg/kg, and 30 mg/kg produced a significant reduction in bone density and skeletal growth, an effect thought to be toxic in nature. Body weight paralleled growth profiles, and average food consumption was stable in all groups with the exception of somewhat low records in the animals receiving 30 mg/kg. A comparison with classical features of human juvenile arthritis indicated that the clinical and radiological profiles concerning joint swelling, osteopenia, skeletal growth, and response to treatment, occur in a similar fashion, although it cannot be inferred that the operating mechanisms are common to both situations. It is concluded that skeletal growth measurements may represent a sensitive additional parameter in the evaluation of experimental arthritis and its response to potential therapeutic agents.

Adult rat cardiomyocytes in long-term culture express type 1 insulin-like growth factor (IGF) receptors. In contrast to insulin receptors, type 1 IGF receptors are up-regulated during culturing. IGF-I added to the cells at plating increased granular density and pseudopodia number per cell after 7 days. After 16 days, IGF-I-treated cells showed, as compared with controls, a dramatic increase of the number of newly built sarcomeres and were packed with myofibrils. At the same time, IGF-I suppressed the accumulation of smooth muscle alpha-actin (sm-alpha-actin) in a dose-dependent manner. Under the conditions of this in vitro system, growth hormone had no effect on cell morphology or sm-alpha-actin. sm-alpha-Actin, a nonsarcomeric isoform of actin expressed in early fetal cardiac development, reappears both during long-term culture of adult rat cardiomyocytes and during heart hypertrophy. This study shows that type 1 IGF receptors are up-regulated in adult rat cardiomyocytes in long-term culture and that IGF-I enhances myofibril development and concomitantly down-regulates sm-alpha-actin. This protein forms stress-fiber-like structures and may temporarily serve as a scaffold for the formation of new sarcomeres until myofibrils have developed throughout the cell and the scaffold is no longer needed. Our findings thus allow us to propose another hypothesis for the mechanism leading to overload heart hypertrophy.

Day 1 human colostrum contains 5 times more IGF I than IGF II. By day 3 postpartum, IGF I drops by 80% to constant levels whereas IGF II increases 3-fold up to day 7. Colostrum contains mainly IGFBP-2, little IGFBP-3 and no detectable IGFBP-1 or IGFBP-4. IGFBP-2 rises 20-fold up to day 6 of lactation. The major IGFBPs of newborn serum are IGFBP-2, -3 and -4. Early maternal serum contains only small amounts of IGFBP-2 and -3 and no detectable IGFBP-4. The pronounced differences between the IGFBP patterns of colostrum and early maternal serum suggest that IGFBP-2 does not pass from maternal blood into colostrum but is produced and secreted by mammary tissue itself. On the other hand, most of the IGF I, but not IGF II, in day 1 colostrum appears to stem from the maternal circulation.

Our results show that an insulin-like growth factor binding protein, IGFBP-3, purified from rat serum, is an inhibitor of chick embryo fibroblast (CEF) growth. It abolished DNA synthesis in CEF stimulated by IGF-I as well as by human serum. Rat IGFBP-3 and IDF45 (an inhibitory diffusible factor secreted by mouse cells) had the same activities, confirming that they have an intrinsic capacity to inhibit serum stimulation and may be considered as growth inhibitors. Our data show that inhibition by IGFBP-3 of serum stimulation was not simply the result of its inhibition of IGF present in the serum: 1) While anti-IGF-I IgG was able to completely inhibit stimulation induced by added IGF-I, it did not decrease stimulation induced by 1% human serum. Anti-IGF-II IgG inhibited the stimulation induced by added IGF-II, but only 25% decreased the stimulation induced by 0.7% serum. The percent inhibition was not significantly increased when the concentration of serum was decreased to 0.2%, which induced 140% stimulation of DNA synthesis; 2) stimulation by 0.2% serum was much more inhibited by IGFBP-3 than by IgG anti IGF-II; 3) after separation of IGF-I and IGF-II from serum by chromatography of acidified serum proteins on BioGel P150, the remaining serum proteins (with a molecular mass greater than 45 kDa) which were depleted in IGF-I and -II (verified by RIA determination) still stimulated DNA synthesis, and this stimulation was 80% inhibited by IGFBP-3.

Isolated cells produce insulin-like growth factors (IGFs) and their binding proteins (IGFBPs). Two distinct cell types were studied with regard to IGFBP-2 expression: (i) rat hepatocytes, which produce IGF I at a high rate and thus regulate its plasma concentration; and (ii) rat osteoblasts, which are targets of IGF I action. IGFBP-2 expression is low in hepatocytes prepared from normal adult rats and high in calvaria cells from newborn rats. Retinoic acid stimulates IGFBP-2 production by liver cells. Insulin suppresses both basal and retinoic acid-induced IGFBP-2 mRNA expression in hepatocytes and has no such effect on osteoblasts. Retinoic acid and insulin regulate IGFBP-2 expression in a tissue-specific manner.

Tumor necrosis factor alpha (TNF-alpha), a major mediator of inflammation, also possesses a wide pleiotropism of actions, suggesting its involvement in physiological conditions. TNF-alpha mRNA is present in mouse embryonic tissues and also in fetal thymus and spleen. Repeated injections of a monospecific polyclonal rabbit anti-mouse TNF-alpha antibody in mice, starting either during pregnancy or at birth, led to a severe but transient growth retardation, already present at birth, reaching a 35% decrease in body weight at 3 wk, with complete recovery at 8 wk. The insulin growth factor I (IGF-I) blood levels were decreased to about 50%; growth hormone release and other endocrine functions were unaltered. A marked atrophy of the thymus, spleen, and lymph nodes was also observed, with lymphopenia and impaired development of T and B cell peripheral lymphoid structures. The pathways involving TNF-alpha in IGF-I release and early body growth are probably distinct from those by which TNF-alpha participates in early development of lymphoid tissues, where its low physiological release may contribute to enhance lymphoid cell expansion.

The mechanism of tumor-associated hypoglycemia was investigated in 10 (six hypoglycemic and four normoglycemic) southern African blacks with hepatocellular carcinoma. The mean basal blood glucose concentration was significantly lower (2.4 +/- 0.1 v 3.6 +/- 0.2 mmol/L; P less than .01) and steady-state exogenous glucose requirements were increased fourfold (3.6 +/- 0.6 v 0.97 +/- 0.2 mg/kg/min; P less than .01) in the hypoglycemic compared with the normoglycemic patients. Plasma insulin and C-peptide levels were suppressed to the lower limit of sensitivity of each of the assays in both groups of patients. The concentrations of insulin-like growth factors (IGF) I and II were lower (19 +/- 1.6 v 25 +/- 4.6 insulin-like growth factors (IGF) I and II were lower (19 +/- 1.6 v 25 +/- 4.6 ng/L) and higher (230 +/- 42 v 173 +/- 40 ng/L), respectively, in the hypoglycemic patients, although the differences were not statistically significant. Of the counterregulatory hormones measured, only the growth hormone (GH) concentration was significantly lower in the hypoglycemic patients (0.9 +/- 0.2 v 18.6 +/- 5.6 micrograms/L; P less than .01). Correction of the plasma GH level into the high-normal physiological range in two hypoglycemic patients failed to reduce steady-state exogenous glucose requirements. However, the glucose requirements were reduced from 2.6 to 1.1 mg/kg/min in the same two patients when "acromegalic" plasma concentrations of GH were achieved. We conclude that steady-state glucose requirements are increased in black patients with hypoglycemia complicating hepatocellular carcinoma, and that short-term correction of the associated hyposomatotropism fails to reduce the enhanced requirements.

Insulin-like growth factors (IGF) I and II produce acute insulin-like effects or promote growth indices in hypophysectomized rats, depending on their mode of administration. Intravenous bolus injections of IGF I and II, like insulin, lower the blood sugar level and lead to a pronounced stimulation of glycogen synthesis in skeletal muscle. The two factors are equipotent in this respect. Continuous subcutaneous infusions of IGF I or II over six days have no hypoglycaemic effect. They mimic the effects of growth hormone, increasing the width of the tibial epiphysis and stimulating the thymidine-incorporating activity of costal cartilage in the absence of growth hormone. IGF I (identical to somatomedin C) is more potent than IGF II and causes a dose-dependent increase in body weight at concentrations where IGF II is still ineffective. The absence of acute insulin-like effects in long-term experiments is explained by the presence in serum of highly specific carrier proteins that interfere with the insulin-like properties of IGF I and II and restrict their capillary permeability. Growth hormone induces the formation of both IGF and the major IGF carrier protein in the liver. Thus, while IGFs mediate the actions of growth hormone on growth, growth hormone appears to modulate these actions via IGF carrier proteins.

The goal of this study was to find out whether GH or insulin regulate the mRNA expression of the fetal binding protein of insulin-like growth factor (IGFBP-2). Primary hepatocytes from adult rats were used as a test system. IGFBP-2 mRNA was abundant in cells cultured in the absence of hormones and markedly reduced in cultures containing insulin. Addition of GH had no effect on IGFBP-2 mRNA levels although the cells are responsive to GH as demonstrated by a GH mediated elevation of IGF l mRNA levels. Half-maximal down-regulation of IGFBP-2 mRNA levels occurred at an insulin concentration of 1 to 2 x 10(-10) M. The finding that insulin is a potent negative regulator of hepatic IGFBP-2 mRNA levels suggests a physiologically important regulatory link between the two hormones insulin and IGF l.

Serum concentrations of insulin-like growth factor 1 (IGF-1) and growth hormone were measured in 25 cats with untreated diabetes mellitus (11 of which were used for follow-up measurements, one to three, four to eight, nine to 12 and 13 to 16 weeks after their treatment with insulin began), 14 diabetic cats that had previously been treated with insulin, and seven diabetic cats that also had hypersomatotropism, two of which had not previously been treated with insulin; 18 healthy cats were used as controls. In the untreated diabetic cats the concentration of IGF-1 ranged from 13.0 to 433.0 ng/ml (median 170.5 ng/ml), which was significantly lower than the concentrations in the control cats (196.0 to 791.0 ng/ml, median 452.0 ng/ml). Their IGF-1 concentrations increased significantly when they were treated with insulin and after four to eight weeks were not different from those in the control cats. In the diabetic cats that had previously been treated with insulin the IGF-1 concentrations were 33.0 to 476.0 ng/ml (median 316.0 ng/ml), which was significantly lower than the concentrations in the control cats, but significantly higher than in the untreated diabetic cats. The IGF-1 concentrations in the two previously untreated diabetic cats with hypersomatotropism were low and low-normal but increased markedly after treatment with insulin. In the five previously treated cats with hypersomatotropism the concentration of IGF-1 was above the normal range. The concentrations of growth hormone in the treated and untreated diabetic cats without hypersomatotropisms were not significantly different and there was an overlap in its concentrations in the diabetic cats with and without hypersomatotropism.

The so-called somatomedin hypothesis (1) states that growth hormone (GH) acts on skeletal tissues indirectly by inducing the production of a growth factor, somatomedin, circulating in blood and mediating the effects of GH on growth. After the isolation and amino sequencing of insulin-like growth factor I (IGF I) and its biological characterization it became evident that this polypeptide was the postulated somatomedin. IGF I consists of 70 amino acids and has a molecular weight of 7649 (2). It is mainly produced and secreted by the liver. However, many other tissues synthesize IGF I which acts locally on these tissues. The significance of endocrine versus auto-/paracrine actions of IGF I is still under debate. Two recent publications provide evidence that in mice liver-derived circulating IGF I is not required for growth (3, a). IGF I tissue expression is under the control of GH (5), but other factors, like insulin or nutrition, also influence IGF I production. Both endogenous and administered IGF I mimic trophic effects of pituitary GH. In contrast, some effects of administered IGF I on intermediary metabolism are opposite to those of GH (6, 7). Moreover, the two hormones act by different mechanisms, which implies that endogenous IGF I induced by GH does in general not mediate the effects of GH on intermediary metabolism. Cardiac effects of IGF were first investigated by Meuli and Froesch in 1975 in the perfused rat heart (8). IGF, like insulin, stimulated glucose transport and lactate production. The biological potency ratio between IGF and insulin in this model was higher than in adipose tissue. Based on this finding and on competitive binding studies, it was concluded that insulin and IGF act on the heart separately via the insulin and the type 1 IGF receptor, respectively (9). In 1986 Borner and Froesch showed that IGF I stimulated the contractility of the isolated perfused rat heart (Figure 1). Since the availability of pure IGF I was limited at that time the positive inotropic effects of IGF I could not be extensively tested, and the data remained unpublished.

The relationship between insulin-like growth factors (IGFs) and insulin has been known since the discovery of nonsuppressible insulin-like activity (NSILA) in serum at the beginning of the 1960s (1), and was derived from the similarities of their biological actions. In the mid-1970s it was found that NSILA consisted of two polypeptides termed IGF-I and IGF-II. They turned out to be not only biologically but also structurally closely related to insulin (2,3). This finding was at first surprising, because the discovery of NSILA had been based on a most prominent feature that essentially distinguished it from insulin: its complete lack of cross-reactivity with insulin antibodies. However, after the elucidation of the primary and tertiary structures of IGF-I and -II (2–4),the reason for this lack of cross-reactivity became apparent (Fig. 1). Insulin contains two main antibody binding sites. One of them comprises the amino (N)-terminal region of the B chain (B2, B3, and B4) plus an adjacent region of the A chain (A8, A9, and A10). This region is completely different in the IGFs. The second antibody binding site of insulin comprises residues Al and A19–A21 and the carboxyl (C)-terminal region of the B chain, but this region is covered in the IGFs by the C domain and by a C-terminal extension called the D domain.

Insulin-like growth factor-II (IGF-II) is thought to play a critical role in the development of embryonic tumors such as Wilms' tumor. However, despite highly elevated IGF-II mRNA levels in tumors, IGF-II is not elevated in the serum of patients with Wilms' tumors. Recently high molecular weight forms of IGF-II ('big'- or pro-IGF-II) have been found to be produced by some tumors. In order to prove whether or not high molecular weight forms of IGF-II are produced by Wilms' tumor cells and secreted into the culture medium, we established Wilms' tumor cell lines. After column chromatography of the culture medium, IGF-II and pro-IGF-II concentrations were measured. For pro-IGF-II measurement we established a pro-IGF-II RIA using a rabbit polyclonal antiserum directed against amino acids 7-21 (E7-21) of the E-domain of pro-IGF-II. Gel electrophoresis and Western blotting with anti-IGF-II antibodies revealed a band at 7.5 kDa corresponding to fully processed IGF-II and bands between 10 and 20 kDa. Using pro-IGF-II antiserum, bands between 10 and 25 kDa were detected. We conclude that in vitro cultured Wilms' tumor cells produce and release various forms of 'big IGF-II' with molecular masses between 10 and 25 kDa. It remains uncertain whether these high molecular weight forms of IGF-II represent normal precursors of IGF-II or incorrectly processed IGF-II.

In the sheep, follicular growth is characterized by both an increase and a decrease in the level of intrafollicular insulin-like growth factor-binding protein-3 (IGFBP-3) and IGFBPs less than 40 kDa (IGFBP-2, -4, and -5), respectively. In contrast, follicular atresia is associated with a decrease and a large increase in levels of IGFBP-3 and IGFBPs less than 40 kDa, respectively. To assess whether intrafollicular proteases are involved in such changes, follicular fluid from follicles of different sizes and degrees of atresia was incubated alone or with pure human IGFBP-3, -4, or -5 or serum (as a source of exogenous IGFBP-2) for 20 h at 37 C. Samples were then analyzed by Western ligand blotting and by immunoblotting using specific antisera. Ovine follicular fluid from different classes of follicles contained proteolytic activity degrading IGFBP-2, -3, -4, and -5. Degradation of IGFBPs was accompanied by the generation of small proteolytic fragments visualized by immunoblotting or after autoradiography using radiolabeled IGFBP-4. Moreover, follicular growth and atresia were characterized by changes in IGFBP proteolytic activity. Indeed, follicular growth (between 2 and 6 mm in diameter) was characterized by 1) a decrease in IGFBP-3 proteolytic activity and 2) a dramatic increase in proteolytic activity degrading IGFBP-4 and, to a lesser extent, IGFBP-2 and -5. Atresia, in contrast, was associated with a strong increase in IGFBP-3 proteolytic activity in small (3-mm diameter) follicles and a decrease in IGFBP-4 and -5 proteolytic activity in large (5-mm diameter) follicles. Regardless of the follicle class, IGFBP proteolytic activity was strongly inhibited by EDTA and 1,10-phenanthroline, but very slightly or not at all inhibited by tissue inhibitor of matrix metalloprotease-1 and-2 and BB-2116 (natural and synthetic inhibitors of matrix metalloproteases, respectively) as well as cysteine and serine proteases inhibitors, with the exception of phenylmethylsulfonylfluoride (1 mM) in atretic follicles. In addition, IGFBP proteolytic activity was dependent on the presence of zinc and calcium chloride. Zymography experiments showed the presence of 72- and 92- to 96-kDa gelatinases in follicular fluid; their levels were dramatically increased during follicular atresia. These results suggest that 1) changes in intrafollicular IGFBP proteolytic activity could be at least partly responsible for the changes in intrafollicular IGFBP levels that occur during follicular growth and atresia in the sheep; and 2) metalloprotease(s) in healthy and atretic follicles as well as serine protease(s) in atretic follicles are involved in IGFBP degradation.

Beckwith-Wiedemann syndrome is a rare condition ( 1 13 700 live births) occurring in both inherited and sporadic forms in the population. It is manifest as a fetal overgrowth syndrome, in which hypertrophy dominates the clinical picture. An additional complication is that these children are predisposed to a specific subset of childhood neoplasms, amongst which are Wilms' tumour and adrenocortical carcinoma. We report here the synthesis by an associated adrenal tumour of large quantities of a high molecular weight form of insulin-like growth factor II (IGF-II), associated with profound suppression of circulating IGFs in the patient's serum. As with other tumours of this type, the tumours showed loss of material on chromosome 11p.

Removal of a craniopharyngioma usually results in panhypopituitarism. Some children, however, grow normally or even excessively after extirpation of the tumor despite a proven lack of GH and have so far not been treated with hGH. We studied the effects of short (2-day) and long term (1-yr) administration of hGH on metabolism and growth in six patients receiving regular hormonal replacement therapy. During short term human (h) GH treatment, 15N retention was not significantly increased (mean +/- SEM, 115.4 +/- 9.6% of basal balance) and was not different from the control value. In contrast, 15N retention was 210.3 +/- 20.7% in children with GH deficiency from other causes. Long term administration of hGH (2 IU/m2.day, sc, for 12 months) did not influence growth velocity, but increased the calf circumference and decreased the body mass index and skinfold thickness in prepubertal patients. Insulin-like growth factor-I (IGF-I), IGF-binding protein-3 (IGFBP-3), and the 150-kilodalton IGFBP complex were decreased before and restored to normal during treatment. The reverse was observed for the 50-kilodalton IGFBP complex. Growth (velocity) in these patients did not correlate with any of the usual indicators of the growth status and remains unexplained. Although hGH did not affect growth, it had other beneficial effects and is recommended for these patients.

The protracted absence of muscle activation initiates complex cellular and molecular reactions aimed at restoring functional neuromuscular transmission and preventing degenerative processes. A central aspect of these reactions is the sprouting of intramuscular nerves in the vicinity of inactivated muscle fibers. Sprouts emerging from terminal nerve branches and nodes of Ranvier can reestablish functional contacts with inactive muscle fibers, and this is an essential restorative process in pathological conditions of the neuromuscular system. Due to their rapid upregulation in inactive skeletal muscle fibers and their ability to induce nerve sprouting in adult muscle, insulin-like growth factors (IGFs) are candidate signaling molecules to promote restorative reactions in the neuromuscular system. In this study we have exploited the high affinity and specificity of IGF-binding protein 4 (IGF-BP4) and IGF-BP5 for IGF1 and IGF2 to determine whether these growth factors are involved in the nerve sprouting reaction in paralyzed skeletal muscle. In tissue culture experiments with sensory- and motoneurons we demonstrate that the neurite promoting activity of IGF1 is blocked by IGF-BP4, and that a similar IGF-BP-sensitive activity is detected in muscle extracts from paralyzed, but not from control muscle. In in vivo experiments, we show that local delivery of IGF-BP4 to Botulinum toxin A-paralyzed skeletal muscle effectively prevents nerve sprouting in that muscle. Our findings indicate that muscle IGFs play an essential role in intramuscular nerve sprouting. In addition, these findings suggest that IGFs are major signaling factors from inactivated muscle to promote local restorative reactions, including interstitial cell proliferation and nerve sprouting.

Skeletal growth depends upon enchondral ossification in growth plate cartilage, within which chondrocytes undergo well defined stages of maturation. We infused IGF-I or growth hormone (GH), two key regulators of skeletal growth, into hypophysectomized rats and compared their effects on growth plate chondrocyte differentiation using qualitative and quantitative autoradiography, stereology, and incident light fluorescence microscopy. Stem cell cycle time was shortened from 50 to 15 and 8 d after treatment with IGF-I and GH, respectively. Proliferating cell cycle time decreased from 11 to 4.5 and 3 d, and duration of the hypertrophic phase decreased from 6 to 4 and 2.8 d. Average matrix volume per cell at each differentiation stage was similar for normal, hormone-treated, and untreated hypophysectomized groups. Mean cell volume and cell height were significantly reduced by hypophysectomy at the proliferative and hypertrophic stages, but were restored to physiological values by IGF-I and GH. In contrast, cell productivity, i.e., increases in cell volume, height, and matrix production per unit of time, did not reach normal values with either IGF-I or GH, and this parameter was inversely proportional to cell cycle time or phase duration. IGF-I and GH are thus capable of stimulating growth plate chondrocytes at all stages of differentiation, albeit to variable degrees with respect to individual cell activities. Although it is generally accepted that GH acts at both the stem and proliferating phases of chondrocyte differentiation, our data represent the first evidence in vivo that IGF-I is also capable of stimulating stem cells.

IGFBP-3 is the predominant IGFBP in serum and the major IGFBP secreted by osteoblasts. Native and recombinant IGFBP-3 and a truncated form lacking the carboxyterminal third were tested for their effects on 2 osteoblastic cell lines. Intact but not truncated IGFBP-3 blocked IGF I-stimulated DNA and glycogen synthesis. Inhibition was dose-dependent and found whenever the concentration of intact IGFBP-3 exceeded the concentration of IGF I. Truncated IGFBP-3 appears to result from proteolytic cleavage and does occur in vivo. The loss of inhibition by IGFBP-3 may be regulated at the site of IGF target cells and thus be essential for IGF I-induced osteoblast growth.

Lipolysis is regulated, at least in part, by the intracellular level of cyclic AMP [ 1,2] . The effects of several hormones and of lipolytic and antilipolytic agents on CAMP accumulation in adipose tissue and adipocytes have been extensively studied [3-61. Most experiments were carried out with isolated fat cells [4-81. Little attention has been paid to CAMP release from intact adipose tissue [3]. During liver perfusion CAMP is released into the perfusion medium in response to glucagon and to epinephrine [9, lo] . Therefore, we examined to what extent CAMP was released from adipose tissue in response to these lipolytic hormones and whether lipolysis was correlated with CAMP release, which may reflect metabolically available ‘free’ CAMP in the cell [9] . Furthermore, we were interested to find out whether partially purified nonsuppressible insulin-like activity (NSILA-S) which has been shown to exert the same metabolic effects on adipose tissue as insulin (for review see [ 111) affects epinephrine-induced CAMP release. The results of this study show that: 1) Considerable amounts of CAMP are released from adipose tissue only when theophylline is present in addition to lipolytic hormones. After 30 min CAMP, which has accumulated in the medium, rapidly disappears possibly due to enhanced degradation. 2) CAMP release is inhibited by insulin and NSILA-S. 3) Concomitant inhibition by insulin of epinephrine-induced lipolysis and of CAMP release is observed only at low epinephrine concentrations, whereas at higher epinephrine concentrations lipolysis

Adipose tissue from streptozotocin-diabetic rats exhibits half-maximal lipolytic responses (FFA, glycerol release, increase in tissue FFA) to epinephrine at hormone concentrations 5–10 times lower than those required for half-maximal stimulation of lipolysis in adipose tissue from normal rats. The lipolytic response to epinephrine also occurs more promptly and the antilipolytic effect of insulin in the presence of submaximal epinephrine concentrations is much less pronounced than in normal tissue. In contrast, diabetic adipose tissue is less responsive to ACTH and glucagon than normal tissue. Half-maximal lipolytic responses are elicited by similar dibutyryl cyclic AMP concentrations in both tissues. Insulin treatment of diabetic rats during 24 hrs restores the lipolytic response of their adipose tissue to epinephrine to nearly normal. Our findings point to an abnormality of diabetic adipose tissue possibly related to the hypersensitivity of catecholamines encountered in denervated organs which are adrenergically innervated. They are consistent with the present concept of different hormone discriminators on the fat cell membrane and offer a further explanation for increased FFA mobilization in the diabetic state.

The influence of Dowex-50 adsorption chromatography on the recovery of two different forms of serum NSILA, large and small mol. wt. NSILA, and on the recovery of the binding protein of the small mol. wt. form was studied and compared with another extraction procedure, gel filtration on Sephadex G-50 in 1 m acetic acid. Partially purified NSILA-S is adsorbed to Dowex-50 at pH 6.8. It can be eluted with 20 mm NH4OH and appears unchanged with regard to its biological activity and molecular weight. Adsorption of 125I-labelled NSILA-S to Dowex-50 does not change its binding characteristics to serum. When serum is chromatographed on Sephadex G-50 in 1 m acetic acid, NSILA is obtained in a large and in a small molecular weight form (NSILA-S). After recombination of the small molecular weight NSILA fraction with the "stripped" serum fraction, which contains large mol. wt. NSILA and a specific carrier protein for NSILA-S, re-chromatography of this mixture on Sephadex G-50 at neutral pH yields NSILA mostly in the void volume. It adsorbs to Dowex-50. After elution from Dowex, acidic gel filtration on Sephadex G-50 results in an elution pattern which is completely different from that of NSILA-S. Adsorption of serum to Dowex-50 results in a dramatic decrease of the NSILA-S binding activity. It is concluded that Dowex-50 adsorption chromatography of serum inactivates most of the serum NSILA-S binding protein leads to the loss of acid dissociable small mol. wt. NSILA (NSILA-S). Therefore, Dowex-50 adsorption chromatography is not suitable for the subsequent determination or further purification of NSILA-S from whole serum.

Rat insulin-like growth factor-I (IGF-I), a serum polypeptide with growth promoting activity, was isolated from rat serum by a combination of acid/ethanol extraction, affinity chromatography, and a series of reversed phase high performance liquid chromatography, cation exchange, and reversed phase. All peptide fragments produced by chymotrypsin digestion of reduced and carboxymethylated rat IGF-I were amino acid sequenced and compared with the sequence of human IGF-I. Three out of 70 of the rat amino acid residues differed from those of human IGF-I as follows: Asp20→Pro, Ser35→Ile and Ala67→Thr. Purified rat IGF-I cross-reacted with polyclonal anti-human IGF-I antibody 75% as compared to human IGF-I, but it cross-reacted only 3% with monoclonal anti-human IGF-I antibody. Thus, it is possible to monitor the metabolic fate of human IGF-I, when injected into rats, without interference by endogenous rat IGF-I. Rat IGF-I showed 65% activity in the radioreceptor, 28.6% activity in the lipogenesis and 22.5% activity in the free fatty acid release inhibition assays as compared to human IGF-I on a protein quantity basis.

IGF-I and -II share specific serum carrier proteins which elute on neutral Sephadex G-200 gel permeation chromatography at apparent molecular masses of 50 and 200 kD. The half-lives of free and carrier protein-bound 125I-IGF-I and -II were determined after bolus injections of the tracers into two normal adults. Labelled IGF-I and -II migrated first with the 50-kD and later with the 200-kD complex. In these complexes their apparent half-lives were 20–30 min and 12–15 h, respectively. The apparent half-life of free 125I-IGF-I and -II was 10–12 min. In a second set of experiments, recombinant human insulin-like growth factor I was infused during 6 days in two healthy adults at a dose of 20 μg · kg−1 · h−1 (corresponding to around 30 mg/day). Serum obtained before and during the infusion was subjected to neutral Sephadex G-200 gel permeation chromatography and fractions were pooled according to the apparent molecular masses at which the carrier protein complexes elute. IGF-I and -II in these pools were determined by RIA. Before the IGF-I infusion, 92 and 272 μg/l of IGF-I and -II were found in the 200-kD complex, 45 and 91 μg/l in the 50-kD complex, and 15 and 5 μg/l were present in the free form. Corresponding figures during the IGF-I infusion were 389 and 18 μg/l for the 200-Kd complex, 201 and 54 μg/l for the 50-kD complex, and 80 and < 1 μg/l for free IGF-I and -II. Using the half-lives of the tracer studies and the levels of the different molecular weight forms of IGF in serum, the production rates for IGF-I and -II were calculated to be 10 mg and 13 mg per day.

IGF-I infused at pharmacological doses in healthy men markedly decreases C-peptide levels, whereas insulin levels remain within the normal range. One possible explanation is decreased insulin removal. As the liver is the major site of insulin degradation, we studied insulin degradation by HepG2 cells in the presence of IGF. We found that IGF-I at a concentration of 130 nmol/l inhibits insulin degradation by HepG2 cells when the initial insulin concentration is 0.34 nmol/l. The effect of IGF-I on insulin degradation is dose-dependent and the rate of insulin degradation is dependent on the insulin concentration. IGF-II is 6 to 10 times more potent than IGF-I in inhibiting 125I-insulin binding to HepG2 cells and in protecting insulin from being degraded. Thus, IGF-I and IGF-II inhibit insulin degradation most likely by competing for binding at insulin binding sites of liver cells.

The human septal cartilage is of ectodermal origin and contributes to midfacial growth and development. Acromegaly is an endocrine disease due to growth hormone (Gh) excess originating from a somatotrophic adenoma of the pituitary gland. Excessive Gh levels lead to high insulin-like growth factor I (IGF I) concentrations, which are known to stimulate cartilage growth in vivo and in vitro. One of the salient clinical pictures is coarsening of the midface and enlargement of the septal cartilage. Septal cartilage was obtained from 8 acromegalic patients during transnasal hypophysectomy and from 10 healthy adults during septoplasty to analyse the following aspects of cartilage biochemistry, metabolism and growth. 1. Intracellular glycogen, the major source of energy of chondrocytes, was determined enzymatically and found to be drastically reduced in acromegaly. 2. Several intracellular enzymes, related to biomatrix degradation, showed a strict local pattern of distribution. Cathepsin B activity, a neutral proteinase degrading both the helical and nonhelical region of the collagen molecule was significantly increased in acromegaly, whereas alkaline phosphatase activity, an enzyme related to mineralization of the cartilage at the chondroosseous junction was depressed in acromegaly. 3. The cell density in some areas of the septal cartilage was increased in acromegaly, whereas the clonal proliferation rate of its chondrocytes in response to serum and growth factors was decreased. Chondrocytes both of healthy adults and acromegalic patients could be effectively stimulated by insulin-like growth factor I and II and to a lesser extent by epidermal growth factor.

When 125 I-labeled nonsuppressible insulinlike activity—soluble in acid/ethanol (NSILA-S) is incubated with human serum between 10 and 20% of the radioactivity are bound to serum proteins and can be displaced specifically by cold NSILA-S. Chromatography of the incubation mixture on Sephadex G-200 at pH 7.5 reveals three peaks of radioactivity in the large molecular weight region and a fourth one corresponding to low molecular unbound labeled NSILA-S. An excess of cold NSILA-S during preincubation leads to the disappearance of the two major large molecular weight peaks and to a concomitant increase of the peak eluting in the low molecular weight range. Binding of 125 I-labeled NSILA-S is highly sensitive to small concentrations of cold NSILA-S, whereas insulin, ACTH and human growth hormone are completely ineffective in displacing bound 125 I-labeled NSILA-S. NSILA-S preparations of different purity show displacement according to their specific biological activities. Furthermore, binding of 125 I-labeled NSILA-S to serum pH- and time-dependent and displays saturation characteristics. Chromatography of serum on Sephadex G-200 with 0.15 m acetic acid/0.15 m NaCl localizes the binding fraction in the 50,000–70,000 molecular weight range. Boiling of serum for 5 min abolishes binding completely. These studies help explain why the molecular weight of NSILA varied considerably from one group of investigators to the other.

Insulin-like growth factors (IGFs) I and II are polypeptides with an insulin-like chemical structure and insulin-like biological properties (Rinderknecht and Humbel, 1978a, 1978b). They have been isolated from human serum. Their molecular weights are 7649 and 7471. However, they do not circulate in blood as free polypeptides, but are non-covalently bound to specific carrier protein(s) (Zapf, Waldvogel and Froesch, 1975; Hintz and Liu, 1977; Zapf et al, 1978). As shown in Figure 1, 75 to 80 per cent of total immunoreactive IGFs I and II are recovered in a 150000200 000 molecular weight protein fraction after neutral Sephadex G-200 gel filtration of serum (gamma globulin-sized IGF peak, Kav 0.22-0.24), whereas the rest is found in a second protein fraction (molecular weight 50 000, Kav 0.48-0.50) which elutes after the albumin peak (albumin-sized IGF peak). Total bioassayable IGF shows the same distribution (Zapf et al, 1978). So far it has not been possible to identify free IGF in serum. Whereas the biological, immunological and receptor-binding properties of the purified polypeptides have been relatively well characterized, there is only scanty information on the properties of the native, i.e., the complexed forms of IGFs. The main reason for this is that all efficient purification procedures of IGF start with an acid-ethanol extraction or acidic gel filtration of serum in order to remove the bulk of serum proteins and to facilitate further purification. Under these conditions the IGF-carrier complexes dissociate and release low molecular weight IGFs. The latter differ essentially from the IGF-carrier complexes: the carrier protein abolishes the acute insulin-like actions typical of the free polypeptides (Meuli, Zapf and Froesch, 1978; Zapf et al, 1979), it restricts their permeability through capillaries and it inhibits their access to membrane receptors (Meuli, Zapf and Froesch, 1978; Zapf et al, 1979; Daughaday, Mariz and Blethen, 1980) and immunobinding sites (Daughaday, Mariz and Blethen, 1980). These peculiarities ought to be kept in mind when

We studied insulin-like growth factors (IGF) I and II, prolactin, and the insulin response to arginine in 19 children with craniopharyngioma and documented growth hormone deficiency. Patients were divided into three groups according to their growth rate during the first postoperative year. Seven patients with excessive growth (Group A) had hyperinsulinism, normal IGF values, elevated basal prolactin levels, and a delayed thyrotropin response to thyrotropin-releasing hormone, which was compatible with hypothalamic lesions. In the six patients with normal growth (Group B), the insulin level was low; all other hormone values were similar to those of Group A. In the six patients with decreased growth (Group C), levels of IGF I, insulin, prolactin, and thyrotropin were low, indicating the presence of severe pituitary damage and explaining the failure to grow. Patients in all groups had low or undetectable basal levels of growth hormone. We conclude that in Group B, normal IGF permitted normal growth, and prolactin hypersecretion may have been responsible for normal IGF I values. Excessive growth in Group A may have been caused by hyperinsulinism associated with hyperphagia and obesity of hypothalamic origin.

We describe a sensitive protein-binding assay for non-suppressible insulin-like activity in human serum. It can detect as little as 0.2 microunits (corresponding to 0.5 ng) of the activity in 0.4 ml of the assay mixture. It is measured in a low-molecular-weight fraction (termed "biological material") obtained by chromatography of serum on Se¬phadex G-50 in 1 mol/liter acetic acid. This fraction has been shown earlier to contain nearly all this biologically active material that is present in serum. A partially purified carrier protein from human serum is used as the binding protein; different concentrations of a partially purified preparation of material with the activity serve as standards, which compete with 1251-labeled tracer for binding. Bio¬logical material dilutes more or less in parallel with the standard over a 10-fold concentration range. In the chro¬matographed serum fractions, displacing activity appears between 50 and 80% bed volume, with the peak at 60%, and coincides with the distribution and the peak of radio¬activity obtained by chromatography of tracer. A good correlation (γ = 0.88) is observed between the values determined for this activity in the rat fat-pad assay and the protein-binding assay, although the latter yields about twofold higher results (160 ± 37 milliunits/liter vs. 345 ± 65 milliunits/liter, mean values for 18 normal sera). Values determined in the protein-binding assay are decreased in hypopituitary patients (183 ± 27 milliunits/liter) and in¬creased in acromegalics (486 ± 88 milliunits/liter), in accord with the results of the bioassay (68 ± 21 milli-units/liter for hypopituitary patients, 293 ± 53 for acro¬megalics).

Insulin-like growth factors (IGFs, somatomedins) are structural homologues of insulin with insulin-like biological activity. They are mainly synthesized and secreted by the liver, but may also be produced by extrahepatic tissues. In their native from in blood they are bound to specific carrier protein(s). This determines essentially their biological actions. The complexed factors stimulate growth indices in vitro and in vivo, but, in contrast to the free factors, do not exert acute effects on insulin target tissues.

IGF I and IGF II are two insulin-like growth factors resembling insulin in many respects. They stem from a common precursor, act through receptors similar to the insulin receptor with which they cross-react. When administered in large amounts they produce hypoglycemia. Their major effects, however, are on replication and differentiation of cells of mesodermal origin. IGF I is the major growth promoting factor in vivo. The synthesis and secretion of IGF I by the liver depend on the growth hormone status, insulin and nutrition. In contrast to insulin, the IGFs circulate in blood bound to the carrier proteins. Their half-life in man is in the order of 16 h. IGF I deficiency results in dwarfism (pygmy, Laron dwarf, toy poodle) despite normal or elevated growth hormone secretion. The anabolic actions of insulin and of the IGFs appear to complement each other as shown in Figure 7.