somatomedin-C/insulin-like Growth Factor I Research Articles

Evaluation of a radioimmunoassay for somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) in human plasma

Evaluation of a radioimmunoassay for somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) in human plasma

Cooperation of synthetic insulin-like growth factor I/somatomedin C and 1,25-dihydroxyvitamin D 3 on regulation of function in clonal osteoblastic cells

We investigated the effects of insulin-like growth factor I/somatomedin C (IGF-I/SM-C), and the interaction of IGF-I and 1,25-dihydroxyvitamin D 3 (1,25(OH) 2D 3) on mouse clonal osteoblasts, MC3T3-E1. IGF-I stimulated [ 3H]thymidine incorporation into the DNA of the cells at concentrations of 1.3 −130 × 10 −9. The alkaline phosphatase (ALP) activity in cultures was also raised by the hormone at the same concentrations. The optimal dose of IGF-I was 13 × 10 −9 M. Co-addition of IGF-I (1.3 −130 × 10 −9 M) and 1,25(OH) 2D 3 (10 −11 to 10 −10 M) to the culture of MC3T3-E1 cells caused a synergistic increase in ALP activity. 25(OH)D 3 and 24,25(OH) 2D 3 showed a similar effect with IGF-I at 1000–2000 times higher concentrations than 1,25(OH) 2D 3. [ 3H]Proline incorporation into collagenase digestible protein (CDP) in media was stimulated dose-dependently by 1GF-I up to 2.2-fold over the control levels at 130 × 10 −9 M. Addition of 1,25(OH) 2D 3 (5 × 10 −11 M) and IGF-I further elevated the proline incorporation into CDP. However, the increment in CDP synthesis, induced by the two hormones was less than the increment in ALP activity. Thus, we conclude (1) that IGF-I stimulates both cell replication and differentiated functions in cultured murine osteoblasts and (2) that IGF-I and 1,25(OH) 2D 3 have the synergistic effect on ALP activity and the additive effect on collagen synthesis in MC3T3-E1 cells.

Evidence for autocrine mitogenic stimulation by somatomedin-C/insulin-like growth factor I on an established human lung cancer cell line : Minuto F, Del Monte P, Barreca A, Alama A, Cariola G, Giordano G. Cattedra di Fisiopatologia Endocrina, Istituto Scientifico di Medicina Interna, I-16132 Genova. Cancer Res 1988;48:3716-9

The production of immunoreactive somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) by the established cell line derived from a human lung carcinoma CALU-6 has been evidenced in the serum-free medium in increasing concentrations as a function of the incubation time. Gel filtration in acid conditions of cell-conditioned medium collected after 72 h showed peaks of immunoreactive Sm-C/IGF-I in the elution volume corresponding to the molecular weight of the synthetic Sm-C/IGF-I, and in the high molecular weight region, where specific binding sites for Sm-C/IGF-I could be also demonstrated. These results indicate that this established cell line produces high amounts of immunoreactive Sm-C/IGF-I and of Sm-C/IGF-I carrier protein. The pooled fractions corresponding to the molecular weight of synthetic Sm-C/IGF-I showed a competitive binding curve parallel to the standard in the Sm-C/IGF-I RIA system, and a mitogenic activity on cells from the same line similar to the one observed using two different pure Sm-C/IGF-I preparations, obtained by chemical synthesis or by DNA recombinant technology. When a monoclonal antibody (sm-1.2) raised against Sm-C/IGF-I was added into the medium, the mitogenic effect observed by both synthetic and cell-derived Sm-C/IGF-I peptide was completely abolished; the monoclonal antibody also partially inhibited the effect of 10% fetal calf serum and the thymidine incorporation observed in serum-free medium without growth factors. In serum-free medium the monoclonal antibody produced a 45% reduction of cells in S phase by thymidine labeling index without modification of the growth fraction as determined by primer-dependent alpha-DNA polymerase labeling index. In conclusion it seems that Sm-C/IGF-I has a critical role in the autocrine stimulation of the replication of this cell line.

Effect of somatomedin-C/insulin-like growth factor I and growth hormone on cultured growth plate and articular chondrocytes.

To determine whether growth hormone has a direct effect on skeletal tissues not mediated by somatomedins, and to better define the role of somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) in skeletal development, bovine growth plate, and rabbit articular and growth plate chondrocytes in primary culture were evaluated under a variety of experimental conditions designed to elicit growth hormone and Sm-C/IGF-I stimulation. Under none of these conditions did bovine growth plate chondrocytes respond to either homologous bovine growth hormone or heterologous hGH. Under the same conditions, these cells were highly responsive to human Sm-C/IGF-I with respect to both [3H]thymidine and [35S]sulfate incorporation, indices of mitotic and differentiated cell functions, respectively. Similarly, both rabbit articular and growth plate chondrocytes showed enhanced incorporation of [3H] thymidine and [35S]sulfate in the presence of Sm-C/IGF-I, but did not respond to either native or recombinant hGH. Cells at different stages of maturation within the bovine growth plate differed in their reaction to Sm-C/IGF-I with proliferative zone cells manifesting a greater response to the peptide than cells of the reserve zone. These results suggest that the action of Sm-C/IGF-I on growth plate and articular chondrocytes is direct and that the effect of GH on these cells is indirect. The data further suggest that within the growth plate, the transition from reserve to proliferative status is associated with an increased Sm-C/IGF-I responsiveness, a change which may contribute to the functional differences in these cells.

Growth factor stimulation of adult articular cartilage.

We have examined the effect of peptide growth factors on DNA and proteoglycan synthesis by adult bovine articular cartilage in organ culture. The actions of somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I), insulin, epidermal growth factor (EGF), and fibroblast growth factor (FGF) from bovine pituitary were investigated individually and in combination. FGF stimulated a 10-fold increase in tritiated thymidine incorporation while other factors used individually did not influence mitotic activity. Used in concert, insulin with EGF and insulin with FGF acted synergistically in stimulating DNA synthesis 20-fold and 40-fold, respectively. All of these growth factors, acting individually, significantly enhanced radiosulfate incorporation. This stimulation was additive for Sm-C/IGF-I in combination with EGF or FGF, but not with insulin. These data indicate that adult bovine articular chondrocytes possess the capacity to augment both mitotic and differentiated cell functions in response to growth factors. The data further suggest that, with the exception of insulin and Sm-C/IGF-I, which appear to share a common mechanism of action, these factors produce their cellular effects via different receptor or postreceptor pathways.

Early changes in serum concentrations of somatomedin-C induced by dietary protein deprivation in rats: contributions of growth hormone receptor and post-receptor defects.

To define the mechanism(s) for the decrease of somatomedin concentrations in acute protein malnutrition, we have assessed the relationships between serum immunoreactive somatomedin-C/insulin-like growth factor-I (Sm-C/IGF-I), serum immunoreactive GH and total (MgCl2-treated homogenates) as well as free (water-treated homogenates) liver somatogenic (GH) binding sites in growing rats fed a 5% protein diet for 12 or 24 h and given an s.c. injection(s) of rat GH (rGH) or saline. Control rats were fed a 15% protein diet and injected with rGH or saline. After 12 and 24 h of protein restriction, body weight was 6.9 and 8.2% below controls respectively (P less than 0.001), while Sm-C/IGF-I concentrations were reduced by 58 and 66% respectively (P less than 0.001 vs controls). Serum GH concentrations were not affected by the low protein intake. Furthermore, injection(s) of 50-100 micrograms rGH failed to raise serum Sm-C/IGF-I concentrations in the protein-deficient animals. The number of total and free GH-binding sites was modestly (15-20%) decreased at 12 and 24 h in the protein-restricted rats. Serum Sm-C/IGF-I concentrations correlated weakly with free and total binding sites (r = 0.48 and 0.38 respectively). Affinity constants of GH-binding sites were not changed by protein restriction. The profound reduction in Sm-C/IGF-I concentrations within a few hours of beginning protein restriction, and the discordance between this reduction and the small decline in somatogenic binding sites, suggests that, in addition to GH receptor loss, a postreceptor defect may participate in the GH resistance occurring in the early stages of protein deficiency.

Somatomedin-C/insulin-like growth factor I as an enhancer of androgen biosynthesis by cultured rat ovarian cells.

The ovarian granulosa cell has recently been shown to be a site of somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) production, reception, and action. These observations have generally been interpreted to suggest the existence of an autocrine loop concerned with granulosa cell physiology. It is the objective of the in vitro studies reported herein to extend these observations by evaluating the interaction of Sm-C/IGF-I with the adjacent thecal-interstitial cell. Treatment of collagenase-processed whole ovarian dispersates or highly enriched (greater than 90%) thecal-interstitial cells from immature rats with Sm-C/IGF-I (50 ng/ml) or hCG (1 ng/ml), resulted in 2.1- and 4.0-fold increments in the accumulation of androsterone (3 alpha-hydroxy-5 alpha-androstane-17-one), the main androgenic steroid identified in culture media. However, combined treatment with both agents unmasked a synergistic interaction producing a 3.3-fold increase in the hCG-stimulated accumulation of androsterone, an effect consequent to enhanced androgen biosynthesis rather than diminished degradation. Unaccounted for by an increase in viable ovarian cell numbers and independent of the hCG dose (0.1-10 ng/ml) used, the Sm-C/IGF-I effect proved time and dose dependent, with a projected minimal effective dose of 3 ng/ml and a minimal time requirement of 72 h. [125I]Iodo-Sm-C/IGF-I binding to untreated highly enriched thecal-interstitial cells proved saturable, with a single class (Hill coefficient = 0.98 +/- 0.01) of high affinity (Kd = 3.0 nM), low capacity (maximum binding = 10,840 +/- 2,108 sites/cell) binding sites. Limited specificity studies using related peptides produced a rank order of competitive potency of: Sm-C/IGF-I greater than multiplication stimulating activity greater than insulin, a pattern compatible with the presence of type I IGF receptors. Other related peptides, such as porcine proinsulin and porcine desoctapeptide insulin, proved weakly effective in inhibiting Sm-C/IGF-I binding to its receptor; unrelated peptides such as porcine relaxin and erythropoietin were without effect. Taken together, these findings suggest that 1) the thecal-interstitial cell, like the granulosa cell, may be a site of Sm-C/IGF-I reception and action, and 2) the ability of high dose insulin to stimulate ovarian androgen biosynthesis may be due to its capacity to act as a Sm-C/IGF-I surrogate, its high dose requirements reflecting cross-interaction with the type I receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

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

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

Further Characterization of the Keratinocyte Somatomedin-C/Insulin-like Growth Factor I (SM-C/IGF-I) Receptor and the Biological Responsiveness of Cultured Keratinocytes to SM-C/IGF-I

Somatomedin-C/insulin-like growth factor I (SM-C/IGF-I) binds to both cultured keratinocytes trypsinized to single-cell suspensions and fresh epidermal sheets derived from 1 M NaBr-treated 6-mm punch biopsies. A gradual increase of 1-4% in specific binding of SM-C/IGF-I to fresh epidermal sheets was observed during a 5-hour incubation period at 15 degrees C. The human keratinocyte SM-C/IGF-I receptor was isolated by polyacrylamide gel electrophoresis after cross-linking with iodinated SM-C/IGF-I and migrated at 135,000 daltons under reducing conditions. Both a partially purified preparation of SM-C/IGF-I, as well as recombinant DNA-derived thr-59-SM-C/IGF-I (25-100 ng/ml), stimulated keratinocyte replication in a serum-free system, with an approximately equivalent effect as insulin (10 micrograms/ml). Since fibroblasts produce SM-C/IGF-I, our data suggest that some dermal-epidermal interactions in diseases such as psoriasis may be mediated, in part, by SM-C/IGF-I.

Differentiating effects of somatomedin-C/insulin-like growth factor I and insulin on Leydig and Sertoli cell functions.

Using an in vitro system of pig Leydig cells (LC) and Sertoli cells (SC) we have demonstrated that: 1) LC contained specific receptors for both somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) and insulin, whereas SC contained only Sm-C/IGF-I receptors; 2) pretreatment of LC with insulin or Sm-C/IGF-I increased hCG receptor number and the cAMP and testosterone responses to this hormone. The enhanced steroidogenic capacity was related to an increased activity of several enzymes of the steroidogenic pathway. At physiological concentrations Sm-C/IGF-I was more potent than insulin, but the effects of the latter peptide at micromolar concentrations were similar to those produced by nanomolar concentrations of Sm-C/IGF-I. However, at maximal concentrations of both peptides, there was no additive effect; 3) the specificity of the effect of Sm-C/IGF-I was proven by the fact that all the effects induced by this peptide, but not by insulin, were blunted by an anti-Sm-C/IGF-I antibody; 4) pretreatment of SC with Sm-C/IGF-I at nM concentrations or with insulin (but only at microM concentrations) enhanced the stimulatory effect of FSH on cAMP production and the secretion of plasminogen activator; 5) in both LH and SC, Sm-C/IGF-I had small mitogenic effects but potentiated the mitogenic action of fibroblast growth factor (FGF). The effect of insulin was observed only at microM concentrations; 6) SC secreted a factor which had physico-chemical and biological properties similar to that of Sm-C/IGF-I. The secretion of this factor was stimulated by FGF and EGF.

Effects of platelet-derived growth factor and somatomedin-C/insulin-like growth factor I on the deoxyribonucleic acid replication of fetal rat islets of Langerhans in tissue culture.

The effects of platelet-derived growth factor (PDGF) on DNA replication and release of insulin and somatomedin-C/insulin-like growth factor I (SM-C/IGF-I) from cultured fetal rat islets have been studied. In medium containing 1% fetal calf serum and 16.7 mM glucose, both PDGF (2-10 ng/ml) and SM-C/IGF-I (100 ng/ml) stimulated DNA replication 2-fold. The growth stimulatory effects of the two peptides were additive. In the absence of serum, SM-C/IGF-I, but not PDGF, stimulated DNA replication. Under conditions of PDGF-stimulated DNA replication there was no increased release of either insulin or SM-C/IGF-I into the culture medium. An antibody against SM-C/IGF-I which inhibited SM-C/IGF-I-stimulated DNA replication did not affect PDGF-stimulated DNA replication. Similarly, an antibody against PDGF did not affect DNA replication stimulated by SM-C/IGF-I. It is concluded that PDGF stimulates islet cell DNA replication. This is the first demonstration of a tissue of nonmesodermal origin responding to PDGF. Stimulation of DNA replication appears to be independent of SM-C/IGF-I release, and furthermore, the results indicate that the islets do not produce PDGF-like substances themselves. It is suggested that PDGF is of importance for fetal islet development.

Characterization and regulation of a specific cell membrane receptor for somatomedin-C/insulin-like growth factor I in cultured rat granulosa cells.

The ovarian granulosa cell has recently been found to be a site of somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) production, reception, and action, thereby raising the prospect of a novel autocrine control mechanism concerned with granulosa cell ontogeny. It is the objective of the in vitro studies reported herein to explore the characteristics of the murine granulosa cell membrane Sm-C/IGF-I receptor and its regulation by gonadotropic, lactogenic, and beta 2-adrenergic signalling. Provision of FSH (150 ng/ml) to granulosa cells from immature rats cultured for 72 h under serum-free conditions resulted in a 3.1-fold increase over control values in specific cell-bound [125I]iodo-Sm-C/IGF-I. Binding to FSH-primed cells proved time, temperature, and pH dependent; optimal steady state conditions were achieved after an 8-h incubation at 15 C and a pH of 8.0. Although subject to regulation by the cellular density of plating, the binding of [125I]iodo-Sm-C/IGF-I to its receptor proved saturable (apparent Kd = 3.3 X 10(-9) M) as well as reversible; complete or partial tracer displacement was effected by competitive inhibition and dilution, respectively. Specificity studies revealed the competition for [125I]iodo-Sm-C/IGF-I binding to follow a relative rank order of potency of Sm-C/IGF-I much greater than multiplication-stimulating activity greater than insulin, but disclosed limited or no displacement by a series of chemically related and unrelated polypeptides. By Scatchard and Hill analysis, both control and FSH-treated cells displayed a single class of noninteracting binding sites; the FSH-enhanced binding represented largely increased binding capacity, rather than affinity. Significantly, up-regulation of granulosa cell Sm-C/IGF-I binding was not limited to FSH; qualitatively comparable increments in [125I]iodo-Sm-C/IGF-I binding were obtained after treatment with luteotropic, and beta 2-adrenergic (but not lactogenic) granulosa cell agonists. Taken together, these studies provide further evidence for the existence of high affinity, low capacity, specific cell membrane receptors for Sm-C/IGF-I in cultured rat granulosa cells. Our findings further indicate that the ability of FSH to enhance granulosa cell Sm-C/IGF-I binding largely reflects increased binding capacity rather than affinity and that this heterologous up-regulatory phenomenon may not be limited to FSH. As such, our observations of comparable up-regulation after luteotropic and beta 2-adrenergic (but not lactogenic) stimulation are in keeping with the view that cAMP may play an intermediary role in the regulation of granulosa cell type I IGF receptors.

Somatomedin-C/Insulinlike Growth Factor I (Sm-C/IGF-I) and Insulinlike Growth Factor II (IGF-II) mRNAs during Lung Development in the Rat

Somatomedins/insulinlike growth factors (Sm/IGFs) are peptide growth factors that are synthesized in multiple tissues and have been implicated in organ growth. Poly(A +)RNAs from lungs of fetal and postnatal rats were examined by dot and Northern blot analyses to investigate the local synthesis of IGFs during lung organogenesis. Blots were successively hybridized with 32P-labeled human IGF-II and mouse Sm-C/IGF-I cDNAs followed by human ubiquitin cDNAs (a control). Multiple IGF-II mRNA species of 4.7, 3.9, 3.1, 2.2, 1.75, and 1.2 kb were observed. Prenatally, the 3.9 kb species was predominant. In adult lung, the 4.7 kb species was the major species, and the 1.2 kb species was not detectable. Multiple Sm-C/IGF-I mRNA species of estimated sizes 7.5, 4.7, 1.7, and 1.0 kb were observed and their relative abundance did not change discernibly throughout development. Densitometric quantification revealed that IGF-II mRNAs were 7-20 fold more abundant in fetal lung than adult lung. In addition, they were 5-8 times more abundant than Sm-C/IGF-I mRNAs in embryonic lung, and were slightly less abundant than Sm-C/IGF-I mRNAs in adult lung. These data suggest synthesis of both Sm-C/IGF-I and IGF-II throughout lung organogenesis. Developmental changes in IGF-II mRNA abundance during lung organogenesis imply regulation at the level of gene transcription and/or mRNA stability.

Quantitation of urinary somatomedin-C in children with normal and abnormal growth.

The renal excretion of radioimmunoassayable somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) was measured in 12-h overnight urine samples obtained from 88 subjects, aged 3-19 yr. The participants included 34 healthy children (group 1), 29 children with idiopathic growth failure and normal GH stimulation tests (group 2), and 25 GH-deficient subjects (group 3). The mean (+/- SEM) urinary Sm-C/IGF-I excretion in group 1 (28.4 +/- 2.1 mU/kg) was significantly greater than that in group 2 (8.1 +/- 1.6 mU/kg) or group 3 (8.6 +/- 1.3 mU/kg). Twenty-two of the 29 subjects in group 2 had urinary Sm-C/IGF-I values less than 8 mU/kg. After the administration of biosynthetic GH to 12 GH-deficient subjects, urinary Sm-C/IGF-I excretion rose from 10.3 +/- 2.3 to 21.4 +/- 4.2 mU/kg within 12 h (P less than 0.05), indicating that renal excretion of Sm-C/IGF-I is GH dependent. One woman with acromegaly had markedly elevated urinary Sm-C/IGF-I excretion (420 mU/kg). The authenticity of urinary Sm-C/IGF-I was confirmed by high pressure liquid chromatography (HPLC). Assay of serial dilutions of urinary Sm-C/IGF-I demonstrated a direct proportionality between concentration and dilution. Although it is not possible to identify whether urinary Sm-C/IGF-I reflects local or generalized synthesis of the peptide, we hypothesize that quantitation of Sm-C/IGF-I in timed urine collections will yield additional information about GH production and action in children with normal and abnormal growth.

Impaired synergism between somatomedin C/insulin-like growth factor I and dexamethasone in the growth of fibroblasts from a patient with insulin resistance.

To explore a possible mechanism for the diminished growth potential in a patient with an unusual form of insulin resistance, somatomedin C/insulin-like growth factor I (SM-C/IGF-I) and insulin stimulation of [3H]thymidine incorporation and cell replication were compared in skin fibroblasts from the patient (DF) and normal controls. There appeared to be no generalized abnormality in cellular responsiveness to growth factors. In both DF and control cells, SM-C/IGF-I (50 ng/ml), insulin (100 ng/ml), and epidermal growth factor (5 ng/ml) stimulated [3H]thymidine incorporation 5-, 2-, and 6-fold, respectively. Low concentrations of human hypopituitary serum (0.25%) enhanced the effectiveness of SM-C/IGF-I and insulin to a similar extent in both DF and control cells. On the other hand, 10% calf serum stimulated [3H]thymidine incorporation 37-fold in control cells, while DF cells were only 50% as responsive. Preincubation of control cells with dexamethasone (10(-7) M) caused a marked synergistic increase in SM-C/IGF-I stimulated [3H]thymidine incorporation (15- to 20-fold in serum-free medium; 50- to 80-fold in 0.25% human hypopituitary serum). In contrast, preexposure to dexamethasone did not augment SM-C/IGF-I stimulation of thymidine incorporation into DNA of DF cells. Furthermore, the stimulation of cell replication by SM-C/IGF-I and insulin was potentiated by dexamethasone in control but not DF cultures. These data suggest that impairment of the synergistic action of glucocorticoids with SM-C/IGF-I and insulin regulation of fibroblast growth may be involved in the pathology of this insulin-resistant growth disorder.

Relationship of somatomedin-C/insulin-like growth factor I levels to conventional nutritional indices in critically ill patients.

Twenty ICU patients, with varying diagnoses and degrees of catabolism, were studied prospectively to determine whether somatomedin-C/insulin-like growth factor I (SMC/IGFI) is related to the conventional nutritional indices, plasma prealbumin, transferrin and albumin, and nitrogen balance (NB) in critical illness. Mean SMC/IGFI concentration in these critically ill patients was below the lower limit of the reference range. SMC/IGFI concentrations correlated with NB for the 24 h before measurement (r = .38, p less than .01) and with cumulative NB for the previous 2 (r = .50, p less than .01), 3 (r = .34, p less than .05), and 5 days (r = .46, p less than .05). Prealbumin correlated with cumulative 5-day NB (r = .39, p less than .05). Plasma albumin and transferrin concentrations did not correlate with NB for any of these time periods. SMC/IGFI concentrations correlated with cumulative protein (r = .59, p less than .01), carbohydrate (r = .63, p less than .01), and energy intake (r = .64, p less than .01). SMC/IGFI was the only index which consistently correlated with NB. We conclude it is a useful index of nutritional status in critically ill patients.

Conventional nutritional parameters, somatomedin-C/insulin-like growth factor-I (Sm-C/IGF-I) and body composition prior to and following biliopancreatic diversion (BPD) : Barreca A., [formula omitted], Fortini P., Castoagnola M., Scopinaro N., Minuto F. Patologia Chirurgica - Cattedra di Endocrinologia, Università di Genova

Conventional nutritional parameters, somatomedin-C/insulin-like growth factor-I (Sm-C/IGF-I) and body composition prior to and following biliopancreatic diversion (BPD) : Barreca A., [formula omitted], Fortini P., Castoagnola M., Scopinaro N., Minuto F. Patologia Chirurgica - Cattedra di Endocrinologia, Università di Genova

Expression of insulin-like growth factor-I and -II genes in rat medullary thyroid carcinoma

Several types of cancer cells produce polypeptide growth factors and often the same cells have functional receptors for the released growth factor (autocrine secretion). We have studied expression of genes encoding somatomedin-C/insulin-like growth factor-I (Sm-C/IGF-I) and IGF-II, in rat medullary thyroid carcinomas (MTCs) in different stages of tumour differentiation. RNAs hybridizing specifically to an IGF-I cDNA probe were detected in 6 out of 7 differentiated MTCs and IGF-II related RNAs were demonstrated in 5 out of these 7 differentiated MTCs. In 5 anaplastic MTCs no IGF RNAs were detected, except for a small amount of IGF-II related RNA in one tumour.

Alterations in the synthesis of a fibroblast surface associated 35 K protein modulates the binding of somatomedin-C/insulin-like growth factor I.

Human fibroblasts, a cell type that is used extensively to determine the pleiotypic effects of the insulin-like growth factors, have been shown to secrete a 35K protein that binds somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) but not insulin. This 35 K protein is associated with the fibroblast surface and following transfer to the surface of cell types that do not have this protein on their surfaces, it alters the binding of radiolabeled Sm-C/IGF-I. In this study human fibroblast monolayers that were incubated with cyclohexamide (50 micrograms/ml) for 14 h at 37 C had no detectable 35 K protein on their cell surface, but type I Sm-C/IGF-I receptors were still present. Loss of the 35 K protein was associated with 60-70% increase in binding of Sm-C/IGF-I to type I receptors. The relative affinity of the type I receptor for Sm-C/IGF-I was apparently increased because unlabeled Sm-C/IGF-I (12 ng/ml) competitively displaced 63% of radiolabeled Sm-C/IGF-I after cycloheximide exposure, whereas in cultures not exposed to cycloheximide [125I]Sm-C/IGF-I binding was increased by 11%. Coincubation of fibroblast conditioned media containing the 35 K protein with cycloheximide-treated fibroblast monolayers resulted in restoration of the paradoxical increase in Sm-C/IGF-I binding and loss of sensitivity to competition by unlabeled Sm-C/IGF-I. Exposure of suspended fibroblasts, which do not have 35 K on their cell surface, to media conditioned by fibroblast monolayers also induced both of these changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization and regulation of somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) receptors on cultured pig Leydig cells. Effects of Sm-C/IGF-I on luteotropin receptors and steroidogenesis.

We have characterized somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) receptors in cultured pig Leydig cells by binding and cross-linking affinity experiments. At equilibrium the dissociation constant and the number of binding sites per cell were 1.8 +/- 0.2 X 10(-9) M and 12,200 +/- 3200 respectively. Under reducing conditions, disuccinimidyl suberate cross-linked 125I-Sm-C to one receptor complex with apparent Mr = 120,000. Continuous treatment of Leydig cells with increasing concentrations of human chorionic gonadotropin (hCG) for 48 h resulted in a dose-dependent (ED50 0.05 nM) increment in IGF type I receptors (2.5-3-fold increase). Conversely, treatment of Leydig cells for 48 h with increasing concentrations of Sm-C/IGF-I produced a 3-4-fold increase in hCG receptors. This effect was dose-dependent (ED50 = 7 ng/ml). Sm-C/IGF-I treatment also enhanced Leydig cell responsiveness to hCG for both cAMP (6-fold) and testosterone (8-fold). Moreover the stimulatory effects of Sm-C/IGF-I on cells cultured either in the absence or presence of 5% human serum from an hypopituitary patient were inhibited by anti-(Sm-C/IGF-I) antibodies. Taken together these results not only show that Leydig cells must be considered as targets for Sm-C/IGF-I, but also lend support to the possibility that Sm-C/IGF-I plays a role in the regulation of Leydig cell function. Moreover, they suggest that Sm-C/IGF-I might be responsible for the delayed puberty observed in some patients with isolated growth hormone deficiency.