Changes in Plasma Somatomedin-C in Response to Ingestion of Diets with Variable Protein and Energy Content

We have attempted to determine the relative importance of dietary intake of protein and energy in restoring plasma immunoreactive somatomedin-C (Sm-C) concentrations after fasting. Ten healthy human volunteers were fasted for 5 days, then divided into two refeeding groups. One group (variable energy) was refed 1.0 g protein/kg ideal body weight, and in 9-day sequences, 11, 18 and 25 kcal of energy/kg. The other group (variable protein) was given 35 kcal energy/kg, and in 9-day sequences, 0.2, 0.4, and 1.0 g protein/kg. When subjects were refed the variable energy diets there was no significant increase in Sm-C at 11 kcal/kg (0.47 +/- 0.13 to 0.45 +/- 0.12 U/ml), suggesting that there is a threshold energy requirement below which optimal protein intake is not sufficient to raise the Sm-C. When subjects were refed 18 and 25 kcal/kg, it became apparent that the more energy added to the diet, the greater the absolute concentration of Sm-C attained (0.66 U/ml on 18 kcal/kg and 0.97 U/ml on 25 kcal/kg). Sm-C correlated with nitrogen balance (r = 0.58) during refeeding with the variable energy diets and was a good indicator of acute directional change in nitrogen balance. However, Sm-C was not a reliable indicator of nitrogen repletion, since it rose almost to control levels on the 25 kcal/kg diet while nitrogen balance remained slightly negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of 24-hour somatostatin infusion on glucose homeostasis and on the levels of somatomedin A and pancreatic and thyroid hormones in man

In order to investigate whether somatostatin plays a role in the regulation of thyroid hormone secretion we have compared the effects of a prolonged somatostatin infusion on insulin and glucagon levels, on the one hand, with its effect on T4, T3, rT3 and TSH, on the other. Furthermore, the serum levels of somatomedin A were determined. Saline was infused in control experiments. Cyclic somatostatin was given as an i.v. bolus of 200 micrograms followed by a constant rate infusion of 50 micrograms/h during 24 hours. Somatostatin suppressed basal insulin and glucagon levels as well as insulin responses to meals but did not influence somatomedin A levels. T4 and T3 decreased during the first hour, whether somatostatin was given or not. Thereafter, T4 and T3 remained stable in the control experiments, while they continued to decrease slowly when somatostatin was added. The suppressive effect of somatostatin was significant 11 hours (p less than 0.05) and 24 hours (p less than 0.005) after the onset of the infusion. In contrast, rT3 and TSH were not suppressed by somatostatin. The fact that basal TSH did not decrease, favors the idea that the suppression of T4 and T3 was mainly due to a direct inhibitory effect of somatostatin on the thyroid gland. Our observation that a low dose of somatostatin decreases peripheral T4 and T3 levels supports the idea that somatostatin plays a role in the regulation of thyroid hormone secretion.

Molecular forms of serum insulin-like growth factor (IGF)-binding proteins in man: relationships with growth hormone and IGFs and physiological significance

Insulin-like growth factor-I (IGF-I) and IGF-II are associated in the blood with specific binding proteins (BPs), forming complexes that elute in gel filtration with estimated mol wt around 40 and 150 kD. The latter appears to be under GH control. Five molecular forms of BP (41.5, 38.5, 34, 30, and 24 kD) have been identified by Western blotting using 125I-labeled IGF. All five forms are present in the smaller complexes, but only the 41.5- and 38.5-kD forms are found in the larger complexes. In this study immunoblotting showed that the 41.5- and 38.5-kD forms were recognized by antibodies directed against the GH-dependent BP purified from human plasma, and the 30-kD form was recognized by antibodies directed against the BP purified from amniotic fluid. The 34- and 24-kD forms proved to be immunologically unrelated to the other three. In sera with large quantities of the 41.5- and 38.5-kD forms, an additional band was often observed immediately ahead of the migration front of the 30 kD band. This was recognized by the anti-GH-dependent BP antibody and probably corresponds to a degradation product of the 41.5- and 38.5-kD BPs. Serum 41.5- and 38.5-kD BPs have been found to be elevated in acromegaly, where GH hypersecretion causes increased IGF-I levels, and diminished in cases of genetic or idiopathic GH deficiency and defects of the GH receptor (Laron's syndrome), where both IGF-I and IGF-II are decreased, as well as in Pygmy adults and children who have isolated IGF-I deficiency. In all of these conditions, the proportions of the 34- and 30-kD forms were inversely related to those of the 41.5- and 38.5-forms. Under treatment, the BP profiles tended to return to normal. In cases of GH deficiency caused by a tumor, the BP profiles resembled those of hypopituitary or normal serum, depending on whether IGF levels were diminished or normal. It, therefore, seems that BP synthesis is coordinated with IGF-I synthesis and may not be directly GH dependent. The results of neutral pH gel filtration analysis of hypopituitary (idiopathic and tumoral) and normal sera point to a relationship between the levels of circulating IGFs and those of the 150-kD IGF-BP complex whose binding units are the 41.5- and 38.5-kD BPs. It, therefore, seems that the 150-kD complex controls the bioavailability of IGF-I and IGF-II.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of insulin-like growth factor I in growth of diabetic rats

Insulin-deficient, streptozotocin-diabetic rats show severe metabolic disturbances and stop growing. Besides insulin, these animals also lack growth hormone and insulin-like growth factor-I. We examined whether or not growth parameters correlate with IGF-I serum levels in young rats with streptozotocin-diabetes of different severity. In the diabetic rats, blood glucose varied between 18.4 and 38.6 mmol/l (healthy controls between 6.1 and 9.3), IGF-I serum levels between 2.6 and 15.6 nmol/l (controls between 19.6 and 26.5), and serum insulin levels between 0.05 and 0.14 nmol/l (controls between 0.36 and 0.55). We found a highly significant linear correlation between IGF-I serum levels and the two investigated growth parameters, tibial epiphyseal width and longitudinal tibial bone growth. The finding that these indices of growth are strongly correlated with IGF-I serum levels in young rats with diabetes of different severity, suggests that IGF-I is a major determinant of growth. This is in keeping with our earlier demonstration that exogenously infused IGF-I promotes growth in diabetic rats.

Dietary carbohydrate content determines responsiveness to growth hormone in energy-restricted humans

To determine if diet composition influences responses to GH, we fed 11 obese women diets containing 12 Cal/kg ideal BW (IBW) for 2 5-week study intervals. Nonprotein calories were supplied to 6 subjects as 72% carbohydrate (high carbohydrate diet), and 5 subjects received 80% of their nonprotein calories as lipid (high lipid diet). Protein intake was constant (1.0 g/kg IBW) in both groups. During 1 study interval we gave injections of GH (0.1 mg/kg IBW) every other day for 3 weeks (weeks 2-4), and in the other interval injections of vehicle were given. Subjects ingesting the high carbohydrate diet excreted significantly less urinary nitrogen [660.2 +/- 124.1 mmol/day (mean +/- SD)] than those who received high lipid (794.2 +/- 198.5 mmol/day; P less than 0.001), and GH injections reduced nitrogen excretion in the high carbohydrate subjects (532.8 +/- 123.8 mmol/day), but not in the high lipid subjects (743.7 +/- 126.6 mmol/day). The subjects receiving the high carbohydrate diet had a significant increase in serum insulin-like growth factor-I (IGF-I; from 36.2 +/- 9.7 to 55.9 +/- 6.6 nmol/L) and urinary C-peptide excretion (from 43.9 +/- 25.6 to 60.8 +/- 29.4 nmol/day) in response to GH. The IGF-I response attenuated slowly over the 3-week treatment interval. On the other hand, the high lipid group had lesser increases in IGF-I (from 31.0 +/- 6.5 to 41.7 +/- 8.8 nmol/L) and C-peptide excretion (from 24.3 +/- 28.9 to 29.8 +/- 32.8 nmol/day), and IGF-I concentrations declined to control values after only 5 days of GH injection. We believe that this initial IGF-I response was due to an antecedent 35-Cal balanced diet. The mean increment in serum FFA 4 h after GH injection was significantly less in subjects fed the high lipid diet (0.53 +/- 0.40 meq/L) than in those fed the high carbohydrate diet (0.83 +/- 0.43 meq/L). GH injections produced more body fat loss than injections of vehicle whether expressed as percent body fat lost (GH, 3.7 +/- 1.0%; vehicle, 2.8 +/- 0.7%, P less than 0.05) or as the fraction of weight lost as fat (fat loss/weight loss; GH, 0.81 +/- 0.13; vehicle, 0.64 +/- 0.08; P less than 0.005). There was an inverse correlation between the percentage of body fat lost and mean urinary C-peptide excretion during GH injections (r = -0.70; P less than 0.05), suggesting that stimulation of insulin secretion by GH might antagonize the tendency of GH to promote fat loss.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of a type 1 insulin-like growth factor binding protein (IGF BP) in serum from rats with diabetes mellitus

Circulating insulin-like growth factor binding protein (IGF BP) activity is increased in animals with streptozotocin-induced diabetes. Separation of BPs by SDS/PAGE for ligand and immunoblot analysis revealed that a 32,000 molecular weight BP is present and increased in diabetic serum. This BP is immunologically distinct from the low molecular weight fetal rat BP (rBP2) and is related to the human amniotic fluid BP (hBP1) that is increased in patients with insulin dependent diabetes mellitus.

Structure, specificity, and regulation of the insulin-like growth factor-binding proteins in adult rat serum

Insulin-like growth factor-I (IGF-I), the principal IGF in adult rat serum, occurs complexed to specific binding proteins. After fractionation of serum on Sephadex G-200 at neutral pH, 62% of the immunoreactive IGF-I is recovered in the 150K region, 38% in the 40K region, and none is present as free 7.5K IGF-I. Adult rat serum also contains unoccupied binding sites for IGFs that also are predominantly (77%) located in the 150K region and have preferential binding affinity for IGF-II. IGF-binding protein components in the 150K and 40K regions were evaluated by affinity cross-linking to 125I-labeled IGFs and by ligand blotting (i.e. incubation of nitrocellulose blots of sodium dodecyl sulfate (SDS)-gels with [125I]IGFs). Affinity cross-linking of the 150K region revealed a major 43K binding protein complex and several minor covalent complexes of 97-210K that are formed during the cross-linking reaction. The 40K region of the gel filtration column contains a predominant 32K complex and smaller amounts of the 43K complex. Ligand blotting of the 150K region identifies a predominant cluster of binding components of about 40K and a smaller 29K protein. The apparent molecular masses of the 40K and 29K proteins are decreased by incubation with N-glycanase, indicating that they contain N-linked oligosaccharides. These glycoprotein components, designated gp40 and gp29, presumably combine with an acid-labile nonbinding subunit of about 100K to generate the 150K complex. The gp40 cluster represents glycosylation variants of a 34K protein; gp29 has been shown to correspond to an amino-terminal fragment of gp40. Ligand blotting of the 40K region indicates that it contains smaller amounts of gp40 and gp29, possibly representing free subunits not combined with the nonbinding subunit, as well as two proteins of apparent molecular mass 24K and 30K (p24 and p30) that are not glycosylated. Although p30 is similar in size to the binding protein from BRL-3A cells (BP-3A) that is present in fetal rat serum, immunoprecipitation and immunoblotting of whole and fractionated adult serum with an antiserum to BP-3A indicate that p30 in adult rat serum is an antigenically distinct protein. Serum levels of gp40 and gp29 are decreased by hypophysectomy and are restored by GH treatment; p24 and p30 show similar but smaller changes.

Significance of abnormal serum binding of insulin-like growth factor II in the development of hypoglycemia in patients with non-islet-cell tumors

We reported that serum and tumor from a hypoglycemic patient with a fibrosarcoma contained insulin-like growth factor II (IGF-II), mostly in a large molecular form designated "big IGF-II." We now describe two additional patients with non-islet-cell tumor with hypoglycemia (NICTH) whose sera contained big IGF-II. Removal of the tumor eliminated most of the big IGF-II from the sera of two patients. Because specific IGF-binding proteins modify the bioactivity of IGFs, the sizes of the endogenous IGF-binding protein complexes were determined after neutral gel filtration through Saphadex G-200. Normally about 75% of IGFs are carried as a ternary complex of 150 kDa consisting of IGF, a growth hormone (GH)-dependent IGF-binding protein, and an acid-labile complexing component. The three patients with NICTH completely lacked the 150-kDa complex. IGF-II was present as a 60-kDa complex with variable contributions of smaller complexes. In the immediate postoperative period, a 110-kDa complex appeared rather than the expected 150-kDa complex. Abnormal IGF-II binding may be important in NICTH because the 150-kDa complexes cross the capillary membrane poorly. The smaller complexes present in our patients' sera would be expected to enter interstitial fluid readily, and a 4- to 5-fold increase in the fraction of IGFs reaching the target cells would result.

Low somatomedin C and high growth hormone levels in newborns damaged by maternal alcohol abuse

To study the mechanism of alcohol-induced fetal damage, we determined the somatomedin C and growth hormone (GH) concentrations of umbilical cord blood samples in 56 infants of alcohol-abusing women and in 20 infants of alcohol-abstinent women. In addition, maternal serum somatomedin C concentrations were determined 1-7 days before delivery. Twenty-five infants born to alcohol-abusing mothers were growth-retarded and also had other signs of fetal alcohol effects, but the remaining 31 infants born to the drinkers and all infants of abstinent mothers were healthy. The somatomedin C levels of infants with fetal alcohol effects (mean +/- SD 4.6 +/- 1.5 nmol/L) were lower (P less than .005) than the levels of healthy infants of drinking (6.8 +/- 4.0 nmol/L) or abstinent (7.1 +/- 3.3 nmol/L) mothers, but the levels did not correlate with infant birth weight, placental weight, or fetal GH or maternal somatomedin C levels. Alcohol drinking was not associated with any changes in maternal somatomedin C levels. The GH levels of infants with fetal alcohol effects (25.4 +/- 22.6 ng/mL) were elevated (P less than .01) when compared with those of infants of abstinent mothers (13.1 +/- 5.3 ng/mL), but did not differ from those of healthy infants of drinking mothers (19.9 +/- 15.1 ng/mL). Low somatomedin C levels and high GH levels in infants born to the drinkers suggest a disharmony in the regulation of the synthesis and/or release of these growth factors, which may be of importance in alcohol-induced fetal damage.

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)

Caloric restriction and 7,12-dimethylbenz(a)anthracene-induced mammary tumor growth in rats: alterations in circulating insulin, insulin-like growth factors I and II, and epidermal growth factor

Caloric restriction (CR) inhibits many neoplastic diseases in rodents, yet the biochemical mechanism(s) for these effects are poorly understood. We have examined the effects of ad libitum (AL) feeding with 25 or 40% CR on the promotion of 7,12-dimethylbenz(a)anthracene-induced mammary tumorigenesis in virgin female Sprague-Dawley rats. Further, we have also studied the influence of chronic CR on temporal alterations in circulating insulin, insulin-like growth factor I/somatomedin C, insulin-like growth factor II/multiplication-stimulating activity, and epidermal growth factor levels at 0, 1, 3, 5, 11, and 20 weeks in carcinogen- and vehicle-treated animals. Tumor incidence and multiplicity were markedly inhibited (P less than 0.05) with increasing CR. Fasting serum insulin-like growth factor I/somatomedin C levels exhibited a significant acute decline with CR at 1 and 3 weeks, but were comparable to AL-fed controls throughout the remainder of the 5-month study, despite continued differences in weight gain between AL and CR rats. Levels of insulin-like growth factor II/multiplication-stimulating activity exhibited no discernible pattern in relation to CR. Serum insulin levels showed age-dependent increases, but were affected by increasing CR at all time points. Insulin levels were significantly (P less than 0.05) reduced in 40% CR rats from 3 weeks onward compared to controls, while 25% CR resulted in nonsignificant (P less than 0.07) reductions throughout the study. No significant differences in growth factor levels were observed between 7,12-dimethylbenz(a)anthracene- and vehicle-treated rats. Circulating epidermal growth factor was not detectable in any treatment group regardless of the nature or duration of the dietary regimen, time of blood collection, or subsequent tumor-bearing status. These data suggest that decreased serum insulin-like growth factor I/somatomedin C and insulin levels with CR and their complex interactions in vivo may play a role in the inhibition of mammary tumor promotion by CR.

The effects of altered nutritional status upon insulin-like growth factors and their binding proteins in neonatal rats

To investigate the role of nutrition in the regulation of IGFs during the perinatal period, 10-d-old rats were infused intravenously with various concentrations of nutrients for 24 h. Breast-fed litter mates served as controls. The effect of caloric intake on concentrations of IGF-I and IGF-II as well as IGF-binding proteins in serum, liver, and brain of neonatal rats was studied. A total of 45 rats from 10 litters was infused with solutions ranging from a caloric intake of 0 (saline) to 75% (glucose, amino acids, and lipids) of the estimated intake of control rats. In serum, both IGF-I and -II concentrations fell markedly in response to fasting. Serum IGF-II levels were linearly related to caloric intake in the pooled data from all groups. Concentrations of IGF-II, but not IGF-I, in liver and brain were depressed by caloric restriction. In contrast to the fall in IGF concentrations, activity of IGF-associated binding proteins rose in serum and in liver cytosol 2- to 4-fold in response to decreased nutrient intake. In serum, but not liver, the rise in binding protein activity was inversely related to to caloric intake. In liver, cytosol, but not serum, the rise in binding protein activity was inversely related to total serum amino acid concentration. Thus, IGF concentrations in preweanling rats change in response to alterations of nutrient intake. The fasting induced decrements in IGF levels, as well as the elevations in IGF-associated binding protein activity, may serve as a protective mechanism to depress growth in times of caloric restriction.

Insulin-like growth factor-I in human malnutrition: relationship with some body composition and nutritional parameters

The insulin-like growth factor-I (IGF-I) plasma concentration was evaluated as a nutritional parameter in 18 patients affected with chronic malnutrition secondary to biliopancreatic bypass and compared with albumin, transferrin, and with body composition parameters: total body water (TBW), total body sodium (TBNa), total body potassium (TBK). Subjects were studied in malnutritional conditions and after 20 to 30 days of parenteral and enteral refeeding treatment. Immunoreactive IGF-I concentration was 0.35 U/ml +/- 0.07 (mean +/- SEM), significantly lower (p less than 0.01) than in age-matched controls (1.14 +/- 0.07 U/ml, n = 29) and rose significantly (0.84 +/- 0.12 U/ml; p less than 0.01) in parallel with the improvement of nutritional status. The ratios TBNa/TBW, TBNa/TBK, and TBK/TBW were then considered as reference parameters for definition of malnutritional state, and compared with IGF-I as well as with the most commonly used parameters, albumin and transferrin. Before treatment, IGF-I evidenced higher specificity (true negative ratios 0.63, 0.43, and 0.40 with regard to TBNa/TBW, TBNa/TBK, and TBK/TBW, respectively) than albumin (0.13, 0.14, and 0.10) and transferrin (0 in all cases), and slightly less sensitivity (true positive ratios for IGF-I 0.80, 0.67, and 0.67; always one for albumin and transferrin). Moreover, IGF-I resulted definitely more sensitive in assessing the effectiveness of the refeeding treatment and, on the basis of the likelihood ratio, it appeared a good discriminator of the nutritional status. The data indicate that different nutritional factors regulate IGF-I, albumin, and transferrin, and suggest that IGF-I can be used as a reliable and specific nutritional parameter, complementary to the others currently used.

Effects of breed and wintering diet on growth, puberty and plasma concentrations of growth hormone and insulin-like growth factor 1 in heifers

Twenty-five Brangus (BR) and 15 Angus (AN) heifers were used to study the effects of breed and wintering diet on average daily gain (ADG), onset of puberty and plasma concentrations of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). Wintering diets (fed for 107 days beginning November 15) consisted of the following: 1) native grass hay (NGH), 2) ammoniated NGH, 3) NGH plus cottonseed meal, 4) Diet 3 plus corn and 5) Diet 4 plus monensin. After wintering, heifers were transferred to ryegrass pasture for 70 days. Mean ADG during the wintering phase were -.20, -.10, .17, .29 and .39 kg for heifers fed Diets 1 through 5, respectively (P less than .01). ADG was greater (P less than .05) for BR than for AN heifers. Plasma concentrations of GH were higher (P less than .05) in heifers fed Diets 1 and 2 than in heifers fed Diets 3, 4 or 5. Plasma concentrations of IGF-1 were lowest in heifers fed Diet 1 and highest in heifers fed Diets 4 and 5. During ryegrass grazing, GH concentrations were similar for all groups. However, concentrations of IGF-1 were higher (P less than .05) in heifers fed Diets 3, 4 and 5 than in heifers fed Diets 1 and 2. Age at puberty (onset of cyclic progesterone concentrations) was greatest in heifers fed Diet 1 and lowest in heifers fed Diet 5. Weight at puberty was not affected (P greater than .10) by wintering diet but was greater (P less than .01) in BR than in AN heifers. Therefore, negative ADG appears to be associated with elevated plasma GH concentrations in heifers, and plasma IGF-1 concentration appears to be a more accurate indication of nutritional status than plasma concentrations of GH.

Insulinlike growth factors in patients with active nephrotic syndrome

The serum concentrations of insulinlike growth factors 1 and 2 (IGF-1 and IGF-2) were measured by specific radioimmunoassays in 25 nephrotic patients. The serum concentration of IGF-1 in nephrotic patients (mean +/- SEM, 169 +/- 17 ng/mL) was significantly lower than that observed in 20 control subjects matched for sex and age (338 +/- 36 ng/mL). The IGF-2 serum concentration was significantly lower in nephrotic patients (343 +/- 22 ng/mL) than in control subjects (898 +/- 80 ng/mL). The IGF-1 and IGF-2 150-kd and 45-kd carrier protein complexes were found in the urine of nephrotic patients, whereas there was no binding of radiolabeled IGF-1 or IGF-2 to IGF carrier proteins in the urine of control subjects. The low serum IGF-1 and IGF-2 levels observed in nephrotic patients could be partially due to the increased urinary losses of the IGF carrier proteins.

Effects of glucocorticoids on the regulation of the hypothalamic-pituitary-somatotropic system in depression

In order to evaluate the possible effect of glucocorticoids as neuromodulators of the hypothalamic-pituitary-somatotropic system in depression, cortisol, growth hormone (GH), and insulin-like growth factor I (IGF-I) concentrations were studied before and after oral administration of 1 mg dexamethasone at 11 p.m. in 16 patients during depression and after recovery and in 28 healthy controls. While there were no significant differences in GH and IGF-I levels between depressed, recovered and control subjects, GH and IGF-I concentrations of cortisol non-suppressors were significantly elevated compared to suppressors. Moreover, post-dexamethasone cortisol, GH, and IGF-I levels were positively correlated. Dexamethasone had a stimulating effect on GH and IGF-I values in patients during depression and in cortisol non-suppressors only; this effect was absent in recovered and in control subjects and in cortisol suppressors. Thus, hypercortisolemia may be of great importance for the dysregulation of the hypothalamic-pituitary-somatotropic system reported in depression.

Growth hormone deficiency impedes the rise in plasma insulin-like growth factor I levels associated with precocious puberty

We tested the hypothesis that growth hormone (GH) mediates the rise in insulin-like growth factor I (IGF-I) concentrations in children with precocious puberty. We studied three groups of patients. Group 1 included six children with GH deficiency and precocious puberty (precocious GH-deficient); group 2 included 10 GH-sufficient patients with idiopathic true precocious puberty (precocious GH-sufficient); and group 3 included 9 prepubertal children with GH deficiency (prepubertal GH-deficient). Growth rates, pubertal status, and plasma IGF-I concentrations were determined at regular intervals. The precocious children with GH deficiency had a mean (+/- SD) growth rate of 7.2 +/- 2.1 significantly below that of the precocious GH-sufficient patients (10.5 +/- 2.5 cm/yr, p less than 0.05) but above that of the prepubertal GH-deficient children (3.9 +/- 1.4 cm/yr, p less than 0.05). The mean IGF-I concentration in the precocious GH-deficient children was 0.77 +/- 0.39 U/ml, significantly lower than the mean level of 2.2 +/- 0.67 U/ml in the precocious GH-sufficient patients (p less than 0.01). However, precocious GH-deficient patients had significantly higher IGF-I values than the prepubertal GH-deficient children (0.24 +/- 0.10 U/ml, p less than 0.05). IGF-I values did not rise with the onset of precocious puberty in four of the precocious GH-deficient children evaluated before and after the development of precocious puberty. However, three patients who began GH treatment did have a rise in plasma IGF-I concentrations to levels of 1.2, 3.4, and 3.7 U/ml, respectively. These findings are compatible with the concept that sex steroids increase IGF-I levels in precocious puberty primarily by increasing GH production. A small but direct effect of sex steroids on IGF-I production may also exist. The onset of precocious puberty in children with organic GH deficiency may mask the abnormal growth pattern of these children and delay diagnosis; determinations of plasma IGF-I concentrations may be helpful in assessing the GH status of these patients.

Inhibition of neonatal rat growth and circulating concentrations of insulin-like growth factor-I using an antiserum to rat growth hormone

Treatment of rats for 24 h on day 2, 10 or 20 of age with a specific antiserum to rGH (anti-(rGH], GH, bromocriptine (CB-154) or prolactin failed to influence body weight gain or serum concentrations of insulin-like growth factor-I (IGF-I). On day 28 of age, however, anti-(rGH) completely inhibited body weight gain and markedly reduced circulating IGF-I concentrations, effects which were completely prevented by exogenous ovine GH (oGH). When administered to control rats on day 28 oGH caused supranormal weight gain and serum IGF-I concentrations. These results suggested that GH does not play a significant role in growth or regulation of serum IGF-I until after day 20 of age. By contrast, when anti-(rGH) was given for 4 consecutive days beginning on day 2 of life, body weight gain was reduced within 48 h and remained so until at least 28 days of age. Tail length was also significantly reduced. The effect was due to inhibition of GH effects since serum GH concentrations were low and exogenous GH prevented the effect. Inhibition of growth during the first 14 days of life occurred in the absence of any effect on serum IGF-I although by 21 days of age serum IGF-I was considerably lower than in control rats. The prolonged reduction in growth after treatment has stopped appeared to be due to a cytotoxic effect on the pituitary gland since pituitary weight and GH but not prolactin content were significantly decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor I binding proteins in dairy cows, calves and bulls

Our objective was to measure relative amounts and distributions of serum IGF-I binding proteins and concentrations of hormones and metabolites in dairy cows during the dry period and during lactation, as well as in calves and in growing bulls. Concentrations of IGF-I were lower in cows during lactation than during the dry period. Concentrations of IGF-I, growth hormone, insulin, T3, T1 and glucose were higher in calves and bulls as compared with cows, whereas concentrations of non-esterified fatty acids, urea, protein and albumin were lower. Three different IGF-I binding protein fractions were found with apparent molecular weights of greater than 200, 140-160 and 45-65 kD. Relative amounts of IGF-I binding proteins were similar, although great differences in hormones and metabolites were found in cows, bulls and calves. accessible binding sites were higher in dairy cows than in calves and bulls, mainly owing to the fact that dairy cows had lower concentrations of IGF-I bound to these fractions. additionally, we found significant negative correlations between total accessible binding sites and total IGF-I concentrations. There were significant differences in the distribution of binding proteins. In particular, there was a shift of binding ability from the 140-160 to the 45-65 kD binding sites from the end of pregnancy to early lactation. Amounts of IGF-I bound to proteins increased from lactating to dry cows and calves and were highest in bulls. IGF-I levels in the greater than 200 kD fraction were lower in lactating than in dry cows, and lower in cows than in calves and bulls. IGF-I measured in the 140-160 kD fraction was lowest in lactating cows and comparable in dry cows, calves and bulls. Concentrations of IGF-I in the 45-65 kD fraction were lowest in cows and highest in bulls. In conclusion, there were marked differences in growing, pregnant and lactating cattle, particularly as concerns accessible protein binding and amounts of IGF-I bound to proteins.

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

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

Attenuation of spontaneous, nocturnal growth hormone secretion in children with hypothyroidism and its correlation with plasma insulin-like growth factor I concentrations

To define further the alterations in growth hormone (GH) secretion that occur in childhood hypothyroidism, we quantified spontaneous nocturnal secretion in seven patients with primary hypothyroidism. We examined the relationship between plasma insulin-like growth factor I (IGF-I) and GH secretory profile in each patient before and during therapy with L-thyroxine. In contrast to the results of previous studies that used pharmacologic tests of GH release, spontaneous GH secretion was consistently attenuated in the hypothyroid state. Mean nocturnal GH levels were reduced by 58% (1.48 +/- 0.38 ng/ml, mean +/- SEM) in comparison with values obtained during L-thyroxine therapy (3.54 +/- 0.71 ng/ml, p less than 0.01). Coincident with the reduced levels of GH, plasma IGF-I concentrations were lower in patients before therapy (0.46 +/- 0.20 U/ml) compared with concentrations during therapy (1.50 +/- 0.34 U/ml, p less than 0.01). In treated, euthyroid patients, GH and IGF-I levels were equivalent to those of normal children. The excellent correlation (r = 0.77) between plasma IGF-I and mean nocturnal GH concentrations indicates that reduced plasma IGF-I levels in hypothyroidism probably result from suppressed GH secretion.

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)

The insulin-like growth factor II/mannose-6-phosphate receptor is present in fetal and maternal sheep serum

A large mol wt binding protein for insulin-like growth factor II (IGF-II) has been described in fetal sheep serum. We now provide evidence to demonstrate that this binding protein is the IGF-II/mannose-6-phosphate (Man-6-P) receptor. Serum and plasma were gel filtered on Sephadex G-200, and the column fractions were assayed for binding of radiolabeled IGF-II. There was significant binding of [125I]IGF-II to the void volume fractions in addition to binding to the 150K and 40K carrier proteins. Binding to the void volume fractions was increased in fetal serum as well as maternal serum and dramatically decreased in the nonpregnant adult. Competitive binding studies with [125I]IGF-II and the void volume pools from fetal and maternal sheep serum demonstrated that IGF-I competed less potently than IGF-II, and insulin did not compete. There was no specific binding of [125I]IGF-I to the void volume pools of either fetal or maternal samples. Chemical cross-linking of [125I]IGF-II to aliquots of the void volume pools from fetal and maternal sheep serum samples and analysis with sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of dithiothreitol demonstrated a specific band at about 240K. Western blotting using a specific antiserum (no. 3637) against rat IGF-II/Man-6-P receptor was performed on aliquots of the Sephadex G-200 void volume pools of fetal, maternal, uterine vein, and adult sheep serum; a band of approximately 210K (without dithiothreitol) was seen. The IGF-II/Man-6-P receptor band was more intense in fetal serum than in either maternal or adult nonpregnant sheep serum. There was also increased binding of [125I]IGF-II in the 40K region of the Sephadex G-200 column fractions in the maternal serum compared to that in serum from nonpregnant adult ewes. When fetal, maternal, and adult nonpregnant sheep serum Sephadex G-200 pools were gel filtered on Sephadex G-50 in 1 mol/liter acetic acid to separate bound from free IGF, and IGF-II was measured by RRA, approximately 50% of the circulating IGF-II was associated with this IGF-II/Man-6-P receptor in fetal serum compared to 7% in maternal serum and 3% in adult nonpregnant serum. These data demonstrate that the IGF-II/Man-6-P receptor circulates in fetal sheep serum as well as maternal serum and appears to be a significant carrier for IGF-II in fetal sheep.

Decreased 34K insulin-like growth factor binding protein in polycystic ovarian disease

Insulin and insulin-like growth factor I (IGF-I) have been implicated in ovarian androgen production. Insulin is closely related to IGF-I and cross-reacts with its receptor. The 34K IGF-binding protein (34K IGF-BP) has been shown to inhibit the binding of IGF-I to its receptor. The authors evaluated the role of insulin in the regulation of serum levels of 34K IGF-BP in patients with polycystic ovarian disease (PCOD). 34K IGF-BP levels during an oral glucose tolerance test (OGTT) were measured in 15 PCOD (8 obese and 7 nonobese) patients and in 10 healthy control subjects. The fasting level of 34K IGF-BP was decreased in nonobese PCOD patients (2.4 +/- 0.3 micrograms/l) (mean +/- standard error) (P = 0.02) and obese PCOD patients (0.59 +/- 0.2 micrograms/l) (P less than 0.001) as compared with healthy controls (4.8 +/- 0.9 micrograms/l). Both nonobese PCOD patients and normal controls demonstrated a significant decrease in 34K IGF-BP following OGTT. An insulin-related decrease in 34K IGF-BP may allow an increased pool of IGF-I able to bind to its receptor. This would provide a mechanism for increased ovarian androgen production via IGF-I stimulation of its receptor.

Endocrine and metabolic changes during altered growth rates in beef cattle

Eight steers from a group of 14 were fed ad libitum from 240 to 510 kg live weight, gaining at 1.4 +/- .2 kg/d. The six other steers were diet-restricted and grew at .37 +/- .09 kg/d from 240 to 307 kg, prior to ad libitum realimentation on the same diet to a final weight of 510 kg. Blood samples taken during the growth phases from both treatments were analyzed for insulin-like growth factor-I (IGF-I), triiodothyronine (T3), thyroxine (T4), glucose (GLU), nonesterified fatty acids (NEFA), and blood urea nitrogen (BUN) and (or) growth hormone (GH). During restricted growth, mean serum concentrations of GH were elevated (45.6 vs 23.4 ng/ml; P less than .05), serum concentrations of IGF-I decreased (108 vs 167 ng/ml; P less than .05) compared with control steers with ad libitum access to feed. Levels of T4 and GLU also were lower (P less than .05) during restricted than during normal growth. During early realimentation, levels of GLU (P less than .05), IGF-I (P less than .01), T4 and BUN (P less than .01) increased. Levels of T3 remained unchanged, whereas concentration of NEFA declined (P less than .001). Blood urea nitrogen decreased during early realimentation despite a large increase in diet protein intake and in protein storage, suggesting an increased efficiency of nitrogen use for protein synthesis. During realimentation, IGF-I levels rose above those of control steers and remained higher at the final weight of 510 kg (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor I responses to recombinant bovine growth hormone during feed restriction in heifers

Insulin-like growth factor I, other hormones and blood metabolites were measured in growing heifers before, during and after a 3-day period of normal feed intake and a corresponding period of reduced feed intake. In addition, 0.1 or 0.5 mg recombinant bovine GH/kg was injected daily for 5 days during normal or during and following reduced feed intake. During reduced feed intake blood concentrations of insulin-like growth factor I, insulin, T4, T3, glucose and urea-nitrogen decreased, whereas those of non-esterified fatty acids, albumin and protein increased (P less than 0.05). GH, insulin-like growth factor I and insulin increased, whereas urea-nitrogen decreased in response to exogenous GH when heifers were adequately fed (P less than 0.05). In contrast, insulin-like growth factor I did not change during GH injections while heifers received reduced amounts of feed. Therefore, during insufficient energy and (or) protein intake, characterized by low glucose, insulin and thyroid hormone levels and increased non-esterified fatty acid concentrations, insulin-like growth factor I concentrations and responses to GH administration were markedly reduced.

A two-year follow-up study of serum insulinlike growth factor-I in diabetics with retinopathy

Serum insulinlike growth factor-I (IGF-I) concentration was evaluated prospectively over two years in 35 diabetic patients with severe background or preproliferative retinopathy (group 1) and 24 diabetics with mild background retinopathy matched for age, sex, and glycemic control (group 2). In addition, 12 normal subjects were also studied to assess the variability of individual serum IGF-I levels over two years. Mean serum IGF-I (+/- SD) micrograms/l at entry, one year, and two years was not significantly different in the patient groups (157 +/- 71 v 168 +/- 77; 166 +/- 78 v 159 +/- 87; 143 +/- 58 v 159 +/- 67) or when compared with the normal subjects (181 +/- 47, 188 +/- 30; 221 +/- 56). Eight patients in the preproliferative group and none in the mild background group developed proliferative retinopathy. In this subgroup developing retinal neovascularization, serum IGF-I at the time of the first appearance of retinal new vessels was significantly higher than 3 months (1 to 4 months) before the onset of proliferation (271 +/- 94 v 196 +/- 58; P = .036). Values at the time of proliferation were not, however, significantly different from the mean serum IGF-I value of all patients in group 1 and by 4 months (3 to 6 m) had returned to their previous values. Although a transient elevation of IGF-I occurs at the time of retinal new vessel formation, the rise in serum concentration is not sufficiently great or early enough to be of clinical value as a predictor of retinal neovascularization.

Insulin-like growth factor I and daily growth hormone profile in the assessment of active acromegaly

A poor correlation exists between growth hormone levels and the severity of disease in patients with acromegaly. It has been suggested that insulin-like growth factor I correlates better with the clinical condition thaN GH itself, but the presence of a correlation between GH and IGF-I is still a matter of debate. We therefore studied the fasting concentration of acid-extracted IGF-I and the daily GH profile (at 08.00, 12.00, 16.00, 20.00 h) in 28 acromegalic patients, both in basal condition and at different times after treatment. All patients studied before treatment exhibited a GH mean daily concentration always above 5 micrograms/l (range 5.15-1.47 micrograms/l), and IGF-I values (1.99-6.85 U/l) always above the normal range (0.38-1.90 U/l). During the follow-up after medical, surgical or radiation therapy we did not observe normalization of the IGF-I concentration for a GH day curve value above 5 micrograms/l. Compared with the GH day curve, a single morning GH value was slightly less sensitive and definitely less specific. The analysis of covariance evidenced a good correlation (P less than 0.001) between the GH day curve and IGF-I concentration during the first 6 months of medical as well as during the first year of radiation therapy, and after surgical treatment. Our data indicate that a single determination of acid-extractable IGF-I is as reliable as GH multiple sampling to assess the acromegalic disease activity.

Pulsatile growth hormone, insulin-like growth factors and antler development in red deer (Cervus elaphus scoticus) stags

Plasma samples taken every 30 min over a 26-h period each month from six 4- to 15-month-old red deer stags were analysed for GH. In addition, two samples taken at 10.00 and 22.00 h were analysed for insulin-like growth factor-I (IGF-I) and insulin-like growth factor-II (IGF-II). A concentrate diet was available ad libitum. Food intake, body weight and antler status were recorded. Concentrations of GH were analysed using the PULSAR peak detection routine. Secretion of GH was pulsatile in every month of sampling, but the pattern of pulsatility differed seasonally. During the autumn and early winter (April-June in the Southern hemisphere) GH pulses were frequent and of low amplitude. In contrast, GH pulses in spring (August-September) were of high amplitude and high frequency resulting in a high mean level of GH circulating in the plasma. In early summer (November) the GH pulse amplitude was much lower and pulse frequency fell. There was a rise in GH pulse frequency not accompanied by an increase in GH pulse amplitude in summer (December-January). GH pulse amplitude seemed to be the main determinant of mean GH plasma level. Secretion of IGF-I was raised 1 month after peak monthly mean GH secretion. There was little consistent relationship between concentrations of IGF-II and mean daily GH. Concentrations of GH correlated positively and significantly with liveweight gain and antler growth rate with a delay of 1 month. Significantly positive correlations between concentrations of IGF-I, liveweight gain and antler growth rate were observed. It is considered that the spring and summer (September-December) seasonal acceleration of liveweight gain and antler development in stags could be a consequence of high winter/early spring (August-September) GH pulse frequency and amplitude resulting in increased concentrations of IGF-I, particularly in October.

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

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

Relationship between insulin, insulin-like growth factor I, and dehydroepiandrosterone sulfate concentrations during childhood, puberty, and adult life

The relationships between plasma insulin, insulin-like growth factor I (IGF-I) and dehydroepiandrosterone sulfate (DHEAS) concentrations in normal subjects have not been defined. We performed iv glucose tolerance tests on 102 normal subjects, aged 5-20 yr. The subjects were divided into 4 groups according to pubertal stage (Tanner): A, stage 1 (n = 22); B, stages 2 and 3 (n = 17); C, stages 4 and 5 (n = 20); and D, adult, greater than 17 yr (n = 43). The basal plasma IGF-I and insulin concentrations and incremental 0-60 min insulin areas in response to glucose rose significantly throughout puberty (P less than 0.001 for all parameters) and declined to prepubertal levels by the third decade of life. There was a strong positive correlation between log fasting plasma insulin vs. log plasma IGF-I (r = 0.625; P less than 0.001) and log incremental 0-60 min insulin areas vs. log plasma IGF-I (r = 0.572; P less than 0.001). Plasma DHEAS concentrations were measured in groups A-C (n = 59); these also rose throughout puberty. There was strong correlations between log plasma DHEAS and log basal or stimulated (incremental 0-60 min areas) insulin responses (P less than 0.001). To assess the relationship between plasma DHEAS and insulin before puberty, we analyzed the data from group A separately. Plasma DHEAS concentrations tended to be higher in children 9 yr of age or older than in those less than 9 yr old, whereas basal and stimulated plasma insulin levels were similar. We found no correlation between log plasma insulin (fasting or stimulated responses) and log plasma DHEAS concentrations in group A (P greater than 0.05). In conclusion, we found a strong relationship between plasma insulin and IGF-I throughout childhood and puberty and during adult life. This finding suggests that insulin may be important for normal growth during childhood. There was no correlation between plasma insulin and DHEAS concentrations in prepubertal children, which suggests that adrenarche does not influence insulin levels.

Insulin increases plasma somatomedin C (IGF-1) concentrations in adult type 1 diabetic patients

The role of insulin in the control of somatomedin release has been investigated in people with Type 1 diabetes. Six patients underwent insulin-induced hypoglycaemia of 20 min duration and 8 patients were studied using the hyperinsulinaemic euglycaemic clamp technique at insulin infusion rates of 0.25, 1.25, 2.5, and 0.25 mU kg-1 min-1 for 1 h at each rate. In the first study plasma insulin concentrations rose from (median, range) 23 (10-36) to 114(60-200) mU l-1 at the onset of hypoglycaemia, and fell to 53 (23-100) mU l-1 after 20 min hypoglycaemia and 30 (15-73) mU l-1 on return to normoglycaemia. Plasma IGF-1 rose from 140 (96-292) to 179 (127-352) micrograms l-1 (p less than 0.05) at the onset of hypoglycaemia and fell to 131 (125-173) micrograms l-1 after 20 min and to 154 (121-287) micrograms l-1 at the end of the study. During hyperinsulinaemia plasma insulin rose from 23 (19-40) mU l-1 at the lowest infusion rate to 61 (33-84) and 148 (68-200) mU l-1 at the two higher infusion rates. Over the same period, plasma IGF-1 increased from 91 (13-203) to 123 (98-182) micrograms l-1 (p less than 0.05) and 109 (84-160) micrograms l-1. There was no correlation between growth hormone levels and IGF-1 in either study. These results suggest that insulin produces short-term increases in IGF-1 levels in man in the absence of a growth hormone response.

The relationship of insulin-like growth factor-I to total thyroxine in normal and low birth weight infants

IGF-I concentrations were determined by RIA in eluates of dried blood collected on filter paper from infants who ranged in age from 3 to 21 d. The infants were separated into normal (greater than 2.5 kg) and low (less than 2.5 kg) birth wt groups and further subdivided on the basis of normal (greater than 83.7 nmol/liter) or low (less than 64.4 nmol/liter) levels of thyroxine. Both the normal and low birth wt groups whose blood thyroxine was in the normal range had similar mean IGF-I values during the 1st wk of life that were significantly higher (p less than 0.05) than those of either the normal or low birth wt groups whose thyroxine concentrations were below normal. Infants older than 1 wk of age with normal birth wt and normal thyroxine levels had significantly greater (p less than 0.05) mean IGF-I values than those of any of the other groups. Infants in the low birth wt-normal thyroxine group exhibited modest increases in IGF-I levels after the 1st wk of life that were significantly greater (p less than 0.05) than those found in the low birth wt-low thyroxine infants. These studies have demonstrated that IGF-I concentration is correlated positively with total thyroxine and with birth wt and that the latter is confounded by the former.

Effect of tamoxifen on plasma insulin-like growth factor I in patients with breast cancer

Human breast cancer cells secrete and have membrane receptors for insulin-like growth factor I (IGF-I), a growth hormone-dependent peptide that stimulates cell replication. However, little is known about plasma concentrations of IGF-I in breast cancer patients. Plasma IGF-I levels are decreased in malnutrition, decline with advancing age, and are influenced by estrogen. We evaluated the effect of the antiestrogen agent tamoxifen on plasma IGF-I in 32 ambulatory breast cancer patients. Treatment with tamoxifen was associated with lower concentrations of plasma IGF-I (0.48 +/- 0.3 unit/ml in treated versus 1.03 +/- 0.6 units/ml in nontreated patients, P less than 0.01). However, patients treated with tamoxifen did not differ from nontreated patients in age, menopause, duration since diagnosis, metastatic disease, recent weight loss, or measures of nutritional status. We conclude that tamoxifen therapy results in a reduction of plasma IGF-I concentration. We speculate that the antitumor action of tamoxifen in breast cancer is due in part to suppression of IGF-I.

Serum levels of insulin-like growth factor (IGF) I, II and IGF binding protein in diabetic adolescents treated with continuous subcutaneous insulin infusion

IGF-I and IGF-II as well as the low molecular type of IGF binding protein (IGFPB) were determined in serum from 11 adolescents with insulin-dependent diabetes mellitus (IDDM) during a cross-over study with conventional and continuous subcutaneous insulin infusion (CIT and CSII) therapy. At the onset of the study the mean IGF-I level, 127 +/- 15 ng ml-1, was significantly decreased (P less than 0.001) in comparison with age-matched controls, whereas the mean IGF-II level, 1024 +/- 48 ng ml-1, was increased. A significant correlation (r = 0.70, P less than 0.05) was found between IGF-II and HbA1c levels. The mean morning level of IGFBP, 75 +/- 17 ng ml-1, at the onset of the study, was increased threefold above that in age-matched controls (P less than 0.01). There was a significant correlation between IGFBP and blood glucose values (r = 0.66, P less than 0.05). During CSII therapy a significant decrease (P less than 0.05) of the IGFBP levels was seen in subjects with a decrease in glucose levels, whereas no change was observed in IGF levels. The findings of elevated IGF-II and IGFBP levels and correlations between IGFBP and blood glucose concentration as well as IGF-II and HbA1c levels in adolescents with IDDM indicate that both IGF-II and IGFBP reflect a deranged metabolism caused by inadequate insulin administration.

Evaluation of selective transsphenoidal adenomectomy by endocrinological testing and somatomedin-C measurement in acromegaly

A series of 29 previously untreated patients with acromegaly underwent transsphenoidal adenomectomy. Pre- and postoperative evaluation consisted of measuring growth hormone (GH) secretory dynamics during an oral glucose tolerance test (OGTT), the insulin hypoglycemia test, and the thyrotropin- and gonadotropin-releasing hormone (TRH/GnRH) test, and by obtaining the basal somatomedin-C level. After surgery, clinical and biochemical amelioration was achieved in all but two patients. In the whole group, basal GH and somatomedin-C levels decreased from a mean (+/- standard error of the mean) of 52.3 +/- 12.7 to 11.1 +/- 6.3 ng/ml and from 7.6 +/- 0.7 to 2.5 +/- 0.5 U/ml, respectively. Application of different criteria of cure revealed that 19 patients (66%) had basal GH levels below 5 ng/ml, 17 patients (59%) had normal somatomedin-C values, 16 patients (55%) had complete GH suppression (less than 1 ng/ml) during OGTT, and 13 patients (45%) met the above-mentioned criteria with disappearance of the paradoxical GH response to TRH/GnRH test. Evaluation of GH secretion by insulin hypoglycemia testing was useless in assessing the outcome after neurosurgery. When only patients with a normal somatomedin-C level and complete GH suppressibility during OGTT were considered "cured," the main favorable prognostic factor was intrasellar tumor localization, since 15 (75%) of 20 patients were "cured," as opposed to only one (11%) of nine with extrasellar extension of the adenoma. During the follow-up period, no tumor recurrence was detected in any of the "cured" patients. In these subjects somatomedin-C levels remained stable in all except two patients, who showed a slow increase within the normal range of somatomedin-C concentration. These data confirm that transsphenoidal surgery is the most effective form of treatment in previously untreated acromegalic patients and that normalization of somatomedin-C levels reflects normal GH secretion. Measurement of somatomedin-C could replace more extensive endocrinological testing during monitoring of treated acromegalic patients.

[Circulating forms of insulin-like growth factor-I(IGF-I)/somatomedin C (SMC) in fetal life: relationship between changes in its binding proteins and growth delay during intrauterine and post-natal periods]

IGF-I/SMC shows mitogenic activities in a wide variety of cell types and stimulates cell growth in vitro and in vivo. Unlike most other peptide hormones, IGF-I/SMC circulates in the plasma as macromolecular complexes with specific plasma binding proteins, approximate molecular weight of 150K and 40K daltons. In order to elucidate the roles of IGF-I/SMC for fetal and postnatal development, the levels of plasma IGF-I/SMC, distribution of circulating IGF-I/SMC on its binding proteins, and profiles of unsaturated somatomedin binding proteins (USBP) were estimated in newborns and a growth-retarded infant (leprechaunism). The concentrations of IGF-I/SMC in cord plasma increased gradually after the 28th week of gestation and reached 37.3 +/- 14.6 ng/ml (Mean +/- S.D.) in full term infants. Although the levels of IGF-I/SMC in cord plasma were significantly lower than those in non-pregnant women (188 +/- 58), they showed a positive correlation with birth weight and relative birth weight (R.B.W.: percentage comparison to the average birth weight of normal infants in the same gestational week). In adult plasma, immunoreactive IGF-I/SMC was eluted predominantly in 150K dalton region (73.5%) and to a lesser extent (26.5%) in 40K dalton, and two apparent peaks of USBP could also be determined in both 150K and 40K dalton regions. On the other hand, in fetal plasma 84.4% of immunoreactive IGF-I/SMC was eluted in 40K region on the 20th week, but on the 26th week, 71.6% of IGF-I/SMC was eluted in 150K region and after the 35th week, more than 70% of IGF-I/SMC was determined in 150K region as observed in adult plasma. However, 150K.USBP could not be detected in cord plasma obtained from appropriate-for-date(AFD) infants until after the 35th week of gestation. Additionally, a positive correlation was demonstrated between 150K.USBP/40K.USBP ratio and birth weight. Some cases of small-for-date(SFD) infants whose IGF-I/SMC circulated mainly as 150K complex could catch up on their growth early in postnatal life. However, in the SFD newborns, if either 150K.USBP or 150Kcomplex of IGF-I/SMC could not be detected, their growth spurt was remarkably delayed until a year after birth. Furthermore, the similar disorders of IGF-I/SMC distribution and its USBP profile were also observed in the case of leprechaunism, who showed severe intrauterine and postnatal growth retardation.(ABSTRACT TRUNCATED AT 400 WORDS)

Serum insulin-like growth factor II in chronic liver disease

Insulin-like growth factor II is secreted primarily by the liver and is reported to be transcribed in many primary hepatocellular carcinoma (PHC) cell lines. We have studied diagnostic significance of serum IGF-II in chronic liver diseases using specific enzyme immunoassay. Serum IGF-II levels (mean +/- SE) were decreased in chronic hepatitis (538 +/- 51 ng/ml; N = 29), liver cirrhosis (427 +/- 45; 50) and PHC (260 +/- 41; 17) compared to controls (830 +/- 49; 57). Serum IGF-II was not different from controls in any of nonhepatic diseases such as diabetes (1032 +/- 97; 19) pancreatic cancer (1413 +/- 282; 8), chronic pancreatitis (999 +/- 126; 17), peptic ulcer (1186 +/- 43; 11), irritable bowel syndrome (1002 +/- 109; 12), gastrointestinal tract cancer (1250 +/- 216; 21) and chronic renal failure (733 +/- 135; 14). In liver diseases serum IGF-II showed a significant correlation with liver function test (negative with retention of indocyanine green and total bile acids; positive with albumin, thrombo-test, and cholinesterase). These results suggest that serum IGF-II reflects a reduced production of IGF-II in the liver and that it can be an index for the residual capacity of liver function.

Hypophysectomy of the fetal lamb leads to a fall in the plasma concentration of insulin-like growth factor I (IGF-I), but not IGF-II

The role of the pituitary gland in the regulation of the plasma concentrations of insulin-like growth factors (IGFs) in the late gestation sheep fetus has been examined. Singleton sheep fetuses were either hypophysectomized or sham-operated between days 110-120 of gestation. Blood samples were then collected via carotid cannulae at least three times weekly for the remainder of gestation. In some hypophysectomized fetuses T4 was administered (100 g/day) to overcome the hypothyroidism caused by hypophysectomy. Blood samples were also obtained from lambs during the perinatal period, neonatal lambs within 1-10 days after birth, and pregnant and nonpregnant adult ewes. All plasma samples were subjected to Sephadex G-50 gel filtration under acidic conditions (pH 2.3) to eliminate IGF-binding protein activity. The fractions containing the free IGF peptides were collected and assayed for IGF-I by heterologous RIA, and IGF-II by a homologous RRA. Plasma concentrations of IGF-I and IGF-II did not change with advancing gestational age in any fetal group and were not affected by the prolonged gestation that results from hypophysectomy. The mean plasma IGF-I and IGF-II concentrations in the sham fetuses were 112 +/- 8 and 1340 +/- 112 ng/ml, respectively. Hypophysectomy without thyroid hormone replacement resulted in a significant decrease in plasma IGF-I concentrations to 50 +/- 5 ng/ml, whereas IGF-II concentrations were not affected (1096 +/- 124 ng/ml). IGF-I concentrations in the hypophysectomized fetuses that received T4 were significantly increased (67 +/- 6.0 ng/ml) compared to those in the hypophysectomized fetuses that did not receive T4. The IGF-II concentrations in the hypophysectomized fetuses that received T4 were similar to those in the sham-operated fetuses (1120 +/- 112 ng/ml). At term IGF-I concentrations were increased (180 +/- 21 ng/ml) and IGF-II concentrations were decreased (264 +/- 25 ng/ml) compared to fetal values. Plasma IGF-I concentrations in the prepubertal lamb were similar to the fetal values. Pregnancy in the adult ewe was associated with a significant increase in IGF-II, but had no effect on IGF-I plasma concentrations. These data show that circulating IGF-I concentrations in the fetal lamb are under some pituitary and thyroid control, whereas IGF-II concentrations are independently of pituitary or thyroid status. We confirm, using a homologous assay, that fetal IGF-II concentrations are high and then decrease at term. These data also support the concept that a pregnancy-related factor may regulate plasma IGF-II concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin-like growth factor-I binding proteins in serum from the domestic fowl

This investigation describes the presence of insulin-like growth factor-I (IGF-I) binding proteins in chicken serum. Whole blood was collected from broiler chickens of 7-9 weeks of age and analysed for binding proteins after gel permeation chromatography under both neutral and acidic conditions, and by polyacrylamide gel electrophoresis in the presence of 12.5% sodium dodecyl sulphate (SDS-PAGE). When serum was chromatographed under neutral conditions, about 70% of the IGF-I immunoreactivity was associated with a large protein complex (Mr = 150,000) and 20-25% was associated with an intermediate-sized protein complex (Mr = 45,000). Up to 6% of the serum IGF-I immunoreactivity was eluted in a fraction which corresponded to an Mr of about 7500 and was presumably free IGF-I. Chromatography under acidic conditions dissociated the IGF-I/protein complexes and revealed the presence of an acid-stable binding protein (Mr = 50,000-60,000). After analysis of serum by SDS-PAGE, three monomeric IGF-I binding proteins (Mr = 28,800, 33,200 and 40,700) were detected. The largest monomer (Mr = 40,700) is probably the binding protein component of the intermediate-sized IGF-I/protein complex. The relationship between the other monomers and both the large IGF-I/protein complex and the acid-stable binding protein is not known. Although the pattern of binding proteins in chicken serum is similar to that observed in mammals, a major difference is the presence of up to 6% of the serum IGF-I immunoreactivity in an unbound form.

Characterization of insulin-like growth factor binding proteins in ovine tissue fluids

Competitive tracer binding studies using radioiodinated insulin-like growth factor-I and -II (125I-labelled IGF-I and 125I-labelled IGF-II) together with size exclusion chromatography and IGF-I affinity chromatography have been used to characterize IGF binding protein activity in ovine tissue fluids. Binding proteins of greater than 200, 150 and 40-50 kDa were revealed in these studies and shown to be widely distributed in body fluids. Thus, the greater than 200 kDa binding protein, which is IGF-II specific, is present in plasma from mature sheep, colostrum and follicular fluid as well as fetal sheep plasma. This may be the ovine equivalent of the soluble type-2 IGF receptor recently identified in rat serum. The presence of a 150 kDa binding protein, of mixed specificity for IGF-I and IGF-II, in fetal and mature sheep plasma was confirmed in these studies. This protein, previously believed to be restricted to vascular fluids, was also identified in mammary lymph, follicular fluid and as a minor component in vitreous humor. Binding proteins of 40-50 kDa were revealed in every fluid tested and multiple variants with distinct specificities were also suggested. This was investigated by IGF-I affinity chromatography using mature sheep plasma. Following passage through the affinity adsorbent, binding of 125I-labelled IGF-I to proteins in the 40-50 kDa region was abolished but when 125I-labelled IGF-II was used as tracer, a binding protein of 40-50 kDa was still observed. Thus sheep plasma contains at least two 40-50 kDa binding proteins. The competitive tracer binding studies indicated that one such protein demonstrates mixed specificity for IGF-I and -II while the other strongly favours IGF-II.

Insulin stimulates skeletal growth in vivo and in vitro--comparison with growth hormone in rats

The effect of insulin on skeletal growth was examined by (1) systemic injection, (2) local administration into the tibia growth plate and (3) in vitro by use of chondrocytes in culture. (1) Male rats, body weight 60-75 g, were hypophysectomised. One week after the operation, the animals were divided into three groups. Group A received intraperitoneally saline, group B insulin (5-30 U.kg-1.day-1) and group C human growth hormone (250 micrograms/kg/day) for the following 10 days. In addition, on day 10 the rats were injected with 10 mu-Ci 35-S-sulfate intraperitoneally. Twenty-four h later in the non-fasting state plasma glucose, insulin, somatomedin activity (porcine assay), body weight, nose-rump length, width of the tibia growth plate, and the 35-S-sulfate incorporation into rib cartilage were determined. Compared to saline, growth hormone and insulin treatment significantly enhanced body weights, nose-rump lengths, the widths of the proximal tibia growth plates and the incorporation of sulfate into rib cartilage. For the three skeletal growth parameters, growth hormone was more effective than insulin, while body weights did not differ after insulin or growth hormone treatment. Somatomedin activity (U/ml) was low in group A (0.39 +/- 0.04, n = 9, Mean +/- SEM) and group B (0.34 +/- 0.08, n = 8) and high in the growth hormone treated group C (0.90 +/- 0.09, n = 7; p less than 0.002). (2) To test the possibility that insulin might directly augment skeletal growth, insulin (80 mU) was injected into the proximal tibia growth plate of one leg and saline into the cartilage zone of the other leg.(ABSTRACT TRUNCATED AT 250 WORDS)

Sheep insulin-like growth factors I and II: sequences, activities and assays

This report describes the purification, sequences, and activities of insulin-like growth factors (IGFs) from adult and fetal sheep plasma. IGF-1 from adult sheep is identical to human and bovine IGF-I, except for substitution in the sheep of Ala at residue 66 for Pro in the human and bovine polypeptides. IGF-II from adult sheep differs from bovine IGF-II also by a single amino acid, with residue 62 being Ala in ovine and Thr in bovine IGF-2. The first 10 amino-terminal residues of fetal sheep plasma IGF-I and 92% of the amino acids of fetal IGF-II were identified and found to be the same as those of the corresponding IGFs isolated from adult sheep. Ovine IGF-I was virtually equipotent with human IGF-I in growth-related bioassays and in a RIA for human and bovine IGF-I and inhibited the binding of radiolabeled human IGF-I to type I IGF receptors and to a pure IGF-binding protein. Ovine and bovine IGF-II were also found to be similar to each other in biological and immunochemical activities, and in their binding to type I and II IGF receptors and IGF-binding protein. As observed with human and bovine IGF-I and IGF-II, ovine IGF-I bound slightly better to type I IGF receptors than ovine IGF-II, but bound very poorly to type II IGF receptors. This study shows that IGFs from sheep are very similar to those of human and bovine in structure and activity and defines sensitive radioligand assays specific for ovine IGF-I and ovine IGF-II.

Serum form of the rat insulin-like growth factor II/mannose 6-phosphate receptor is truncated in the carboxyl-terminal domain

The insulin-like growth factor (IGF)-II/mannose 6-phosphate (Man-6-P) receptor present in mammalian tissues as an apparent molecular mass = 250 kDa glycoprotein has recently been detected in fetal rat serum in a lower molecular mass form (240 kDa). In the present studies the serum receptor was affinity labeled with 125I-IGF-II after its adsorption onto pentamannosyl 6-phosphate-Sepharose, demonstrating that it can also bind both ligands simultaneously. The receptors in both serum and fresh plasma exhibited the lower molecular mass compared to tissue receptors, indicating this form circulates in vivo. In order to probe the structural basis of the serum receptor's lower mass, we raised antipeptide antibodies against cytoplasmic and extracellular domains of the tissue form of the rat receptor deduced from complementary DNA clones (MacDonald, R. G., Pfeffer, S. R., Coussens, L., Tepper, M. A., Brocklebank, C. M., Mole, J. E., Anderson, J. K., Chen, E., Czech, M. P., and Ullrich, A. (1988) Science 239, 1134-1137). Peptide 22C, Glu-Glu-Glu-Thr-Asp-Glu-Asn-Glu-Thr-Glu-Trp-Leu-Met-Glu-Glu-Ile-Gln-Val- Pro-Ala - Pro-Arg, located in the cytoplasmic domain 32 residues carboxyl-terminal to the transmembrane region, and peptide 13D, Tyr-Tyr-Leu-Asn-Val-Cys-Arg-Pro-Leu-Asn-Pro-Val-Pro-Gly-Cys-Asp, located 1476 residues amino-terminal to the transmembrane domain were synthesized and used as immunogens in rabbits. IGF-II/Man-6-P receptors were first immunoprecipitated from either rat serum or a Triton X-100 extract of rat placental plasma membranes using a polyclonal antireceptor antibody. The immunoadsorbed receptors were then reduced, alkylated, electrophoresed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, blotted onto nitrocellulose, and probed with antipeptide antibodies. Anti-13D revealed the major receptor band in all the membrane and serum samples tested as well as several minor species of lower apparent mass in serum. Fetal and neonatal rat sera contained 3-4 times as much of the receptor as adult serum. In contrast, anti-22C recognized the membrane IGF-II/Man-6-P receptor but failed to recognize any of the serum receptor species. These results indicate that the serum IGF-II/Man-6-P receptor is truncated or altered in its cytoplasmic domain, consistent with the hypothesis that it is derived from cells by proteolytic cleavage.

Growth hormone increases plasma levels of insulin-like growth factor (IGF-I) in a teleost, the gilthead seabream (sparus aurata)

A heterologous radioimmunoassay (RIA) was applied for the determination of immunoreactive (IR)--insulin-like growth factor (IGF-I) in a teleost, the gilthead seabream (Sparus aurata). Serial dilutions of the fish plasma gave a linear curve when added to constant amounts of 125I-labelled human IGF-I(53-70) and antiserum prepared against this fragment. The RIA was used to study the effect of GH on plasma levels of IR-IGF-I in S. aurata. A single injection of human recombinant GH (1 micrograms/g) resulted in a significant increase in IR-IGF-I at 29, 48 and 72 h, when compared with saline-injected fish. This novel observation suggests that in fish, as in mammals, circulating IGF-I levels are modulated by GH.

Insulin-like growth factors I and II. Peptide, messenger ribonucleic acid and gene structures, serum, and tissue concentrations

There is currently widespread interest in the IGFs (IGF-I and IGF-II) and their roles in the regulation of growth and differentiation of an ever increasing number of tissues are being reported. This selective review focused on the current state of our knowledge about the structure of mammalian IGFs and the multiple forms of mRNAs which arise from alternative splicing and promoter sites which arise from gene transcription. Current progress in the immunological measurement of the IGF is reviewed including different strategies for avoiding binding protein interference. The results of measurements of serum IGF-I and IGF-II in fetus and mother and at various stages of postnatal life are described. Existing knowledge of the concentration of these peptides in body fluids and tissues are considered. Last, an attempt is made to indicate circumstances in which the IGFs are exerting their actions in an autocrine/paracrine mode and when endocrine actions predominate. In the latter context it was concluded that an important role for GH action on skeletal tissues via hepatic production of IGF-I and endocrine action of IGF-I on growth cartilage is likely.