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.

Effects of recombinant insulin-like growth factor I on insulin secretion and renal function in normal human subjects

Insulin-like growth factor I (IGF-I) is an important mediator of growth hormone (GH) action and it appeared tempting to evaluate possible clinical applications. Recombinant IGF-I was infused s.c. at a dose of 20 micrograms/kg of body weight per hour during 6 days in two healthy adult subjects. Blood glucose and fasting insulin levels remained within normal limits and IGF-II levels were suppressed. In contrast to insulin, fasting C peptide levels were decreased. GH secretion was also suppressed by IGF-I. Our preliminary data allow us to distinguish between the effects of GH per se and those of IGF-I: GH causes hyperinsulinism, whereas IGF-I leads to decreased insulin secretion. Glomerular filtration rate, as estimated by creatinine clearance, increased to 130% of preinfusion values during the IGF-I infusion. Total creatinine and urea excretion remained unchanged. We conclude that IGF-I influences kidney function and, in contrast to GH, exerts an insulin-sparing effect. It may be speculated that the therapeutic spectrum of IGF-I is quite different from that of GH.

Insulin-like growth factors I and II in evaluation of growth retardation

Plasma samples from 68 growth hormone (GH)-deficient children (provocative serum GH level less than 7 ng/ml), 44 normal short children, and 197 children with normal height were assayed by specific radioimmunoassays for the somatomedin peptides, insulin-like growth factors (IGF)-I and -II. Eighteen percent of the GH-deficient children had IGF-I levels within the normal range for age, whereas 32% of normal short children had low IGF-I levels. Low IGF-II levels were found in 52% of GH-deficient children, but also in 35% of normal short children. However, only 4% of GH-deficient children had normal plasma levels of both IGF-I and IGF-II. Furthermore, only 0.5% of normal children and 11% of normal short children had low plasma levels of both IGF-I and IGF-II. We conclude that plasma levels of either IGF-I or IGF-II overlap in GH-deficient and normal short children, but that the combination of radioimmunoassays may permit better discrimination among normal, normal short, and GH-deficient children.

Serum insulin-like growth factors I and II concentrations and growth hormone and insulin responses to arginine infusion in children with protein-energy malnutrition before and after nutritional rehabilitation

Serum insulin, growth hormone (GH), insulin-like growth factors (IGFs) I and II, cortisol, and albumin concentrations were measured in 15 children with kwashiorkor, 15 with marasmic-kwashiorkor, and 21 with marasmus, before and in the survivors, after nutritional rehabilitation, as well as in 10 underweight and eight normal Egyptian children. We also evaluated arginine-induced insulin and GH secretion. IGF-I concentrations were reduced in the three severely malnourished groups (0.07 +/- 0.03, 0.05 +/- 0.03, and 0.09 +/- 0.09 U/ml, respectively) but returned to normal after refeeding. IGF-II concentrations were low in the kwashiorkor (175 +/- 79 ng/ml), marasmic-kwashiorkor (111 +/- 57 ng/ml), and marasmic children (128 +/- 70.9 ng/ml) and returned to normal after nutritional rehabilitation. Basal GH levels were high in the three severely malnourished groups (21.9, 28.8, and 16.6 ng/ml, respectively) and returned to normal after refeeding (8.1, 6.5, and 6.0 ng/ml, respectively). GH responses to arginine were depressed in the three malnourished groups and improved significantly in marasmic-kwashiorkor and marasmic children after nutritional rehabilitation. Insulin responses to arginine were impaired in kwashiorkor, and marasmic-kwashiorkor children and improved significantly after refeeding. IGF-I levels correlated significantly with percent of expected weight (r = 0.52, p less than 0.001), percent of expected height (r = 0.42, p less than 0.001), and weight/(height)2 index (r = 0.34, p less than 0.01). IGF-I levels correlated positively with insulin levels (r = 0.421, p less than 0.001) and negatively with cortisol concentrations (r = -0.400, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factors in vitreous. Studies in control and diabetic subjects with neovascularization

Vitreous and serum were obtained at the time of vitrectomy from 23 diabetic subjects with proliferative retinopathy and from 8 nondiabetic subjects. The mean concentration of IGF-I in vitreous from diabetic patients with neovascularization was 6.3 +/- 0.93 versus 2.7 +/- 0.96 ng/ml. Chi-square and rank analysis indicated that higher concentrations of IGF-I occurred in diabetic vitreous (P less than 0.01 by both analyses). IGF-II concentrations in vitreous of control and diabetic subjects were not significantly different. A positive correlation existed between the concentrations of IGF-I and IGF-II in vitreous and their concentrations in serum in diabetic subjects, but not in control subjects. When vitreous concentrations of IGF-I were calculated for diabetic subjects studied previously with rapid acceleration of retinal disease, these concentrations varied from 20 to 30 ng/ml. The concentrations of IGF-I in the vitreous of most diabetic subjects with severe neovascularization are thus in the range known to stimulate cellular differentiation and growth in several systems. Whether they do so in the eye, and thus contribute to the development of retinopathy, remains to be determined.

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)

Serum somatomedin levels in adults with chronic renal failure: the importance of measuring insulin-like growth factor I (IGF-I) and IGF-II in acid-chromatographed uremic serum

Somatomedin levels measured by radioreceptor assay (RRA) or RIA on acid-ethanol-extracted or unextracted serum from patients with uremia are quite variable relative to normal values. We have investigated whether compounds accumulating in uremic serum were interfering with these RRA and RIA measurements. Insulin-like growth factor I (IGF-I) and IGF-II were separated from carrier proteins by either Sephadex G-50 acid chromatography or acid-ethanol extraction. IGF-I was measured by RIA, and IGF-II was determined by rat placental membrane RRA. IGF-I levels in the acid-ethanol extracts of serum from eight uremic adults were only 50% of the levels found in seven normal subjects, and IGF-II levels in these uremic patients were 350% of normal values. However, these significant differences were not found when comparable serum samples were acid chromatographed rather than acid-ethanol extracted; instead, IGF-I levels were 343 +/- 168 (mean +/- SD) ng/ml in uremic patients and 325 +/- 54 ng/ml in normal subjects, while IGF-II levels were 780 +/- 215 ng/ml in uremic patients and 588 +/- 46 ng/ml in normal subjects. To determine whether compounds that interfere with somatomedin assays were present in the acid-ethanol extracts of uremic serum, we acid chromatographed these extracts and found that a compound eluting in the carrier protein fraction of the uremic extract artifactually decreased IGF-I levels measured by RIA and increased IGF-II levels measured by RRA. We also found that unsaturated carrier protein binding of IGF-I and IGF-II was significantly increased in the carrier protein fraction of uremic acid-ethanol extracts at the dilutions used for somatomedin assays. We conclude that acid chromatography of unextracted or acid-ethanol-extracted uremic serum is necessary to remove a compound, probably unsaturated carrier protein, which interferes with RIA of IGF-I and RRA of IGF-II. Once this compound is removed, serum IGF-I levels (RIA) in uremic patients are not different from normal, and serum IGF-II levels (RRA) are not lower than normal.

Influence of nutritional status and oestradiol-17 beta on plasma growth hormone, insulin-like growth factors-I and -II and the response to exogenous growth hormone in young steers

Plasma GH profiles and circulating concentrations of plasma insulin-like growth factors-I and -II (IGF-I and -II) were examined in 20 steers on either high (3% dry matter of body weight per day) or low (1% dry matter of body weight per day) planes of nutrition with or without an implant of oestradiol-17 beta. The response of plasma IGF-I and -II to a bolus injection of bovine GH (bGH) was also investigated. Reduced feeding significantly (P less than 0.01) increased the mean concentration, peak height and integrated area of plasma GH. Treatment of steers with oestradiol at low nutrition significantly increased baseline GH concentrations. Treatment of steers with oestradiol at high nutrition significantly (P less than 0.05) increased mean, baseline, peak height, and integrated area of plasma GH. GH pulse frequency was not changed by either nutritional plane or oestradiol treatment. Basal concentrations of plasma IGF-I were significantly (P less than 0.01) decreased by reduced feeding in both the oestradiol-treated and the control group. Treatment with oestradiol increased (P less than 0.01) basal plasma concentrations of IGF-I at both high and low levels of nutrition. After i.v. injection of bGH (0.1 mg/kg body weight), an increase in plasma IGF-I was observed only in steers at high nutrition. Basal concentrations of plasma IGF-II were not altered by nutritional manipulations but were significantly (P less than 0.001) increased by oestradiol treatment. After bGH infusion only steers at high nutrition showed an increase in plasma IGF-II.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterogeneity of insulin-like growth factor binding proteins and relationships between structure and affinity. 1. Circulating forms in man

Circulating insulin-like growth factors (IGFs) are bound to specific, high-affinity binding proteins (BPs), and form complexes with relative molecular masses of about 150,000 ('large' complex) and 40,000 ('small' complex). The large complex appears to be under growth-hormone control and its proportions vary with those of the IGFs. Molecular heterogeneity among the binding proteins was revealed by polyacrylamide gel electrophoresis (SDS-PAGE) of serum in which they were cross-linked to 125I-labelled IGF I or II. Out of the six specific bands observed, of 150,000, 120,000, 49,000, 40,000 and 37,000 Mr, the last three appeared in both complexes, whereas the first three were visible only in the large complex. Some or all of the 49,000-37,000-Mr species may constitute the subunits of 150,000-Mr and/or 120,000-Mr IGF-BP complexes. With electrophoresis followed by transfer onto nitrocellulose and incubation with either 125I-labelled IGF I or II (western blot), the different binding proteins were identified per se. There were five molecular forms with Mr of 41,500, 38,500, 34,000, 30,000 and 24,000. In normal serum the 41,500 and 38,500-Mr forms were the major binding proteins. They appeared in both complexes, but were predominant in the large complex where they constitute the elementary binding units. These two proteins therefore bind to IGFs to form both 'monomeric' IGF-BP and 'oligomeric' (IGF-BP)n complexes. The 34,000, 30,000 and 24,000-Mr forms, by contrast, were visible only in the small complex. Different mechanisms appear to regulate the different binding proteins: in acromegalic serum the 41,500 and 38,500-Mr forms were augmented and the 34,000-Mr form diminished, whereas in hypopituitary serum the reverse was true and, in addition, the 30,000-Mr form was augmented. With chromatofocusing, the 34,000, 30,000 and 24,000-Mr forms eluted in three peaks between pH 6.0 and 4.0, whereas the 41,500 and 38,500-Mr forms eluted throughout the gradient, principally at pH 7.5 and 7.0. Competitive binding studies, done on binding proteins separated either by chromatofocusing or by SDS-PAGE and transfer onto nitrocellulose, revealed different affinities for the IGFs among the different molecular forms. The 41,500 and 24,000-Mr binding proteins preferentially bound IGF I and the 38,500, 34,000 and 30,000-Mr proteins preferentially bound IGF II. Our findings demonstrate the molecular heterogeneity of the binding proteins and the existence of a relationship between their structure and their affinities for the IGFs.(ABSTRACT TRUNCATED AT 400 WORDS)

A specific radioimmunoassay for insulin-like growth factor II: the interference of IGF binding proteins can be blocked by excess IGF-I

A specific antiserum for human IGF-II has been produced by immunizing rabbits against the synthetic peptide IGF-II(33-40). With this antiserum and IGF-II as tracer a radioimmunoassay for IGF-II has been developed. Cross-reactivity with IGF-I was 0.05% and half-maximal displacement occurred at 2.5 micrograms IGF-II per 1. It was demonstrated that residual IGF-binding protein (IGF-BP) in acid-ethanol extracts interferes with IGF-II measurements and may produce erroneously high values. This interference could be completely blocked by excess IGF-I (25 ng per tube). Utilizing this method IGF-II was measured in subjects at various developmental stages. In newborns, the mean serum level was 237 micrograms/l (N = 56) with a range of 132-430 micrograms/l (5- and 95-percentile, respectively). During the first year of life a considerable increase occurred. Thereafter IGF-II increased only slightly with age from 520 micrograms/l (range 368-735) to 647 micrograms/l (range 507-823) in adults. In patients with growth hormone deficiency (N = 57) IGF-II levels were significantly (P less than 0.001) lower than in controls (mean 261 micrograms/l, range 126-542). It is concluded 1) that residual IGF-binding proteins in acid-ethanol extracts may cause considerable error in IGF-II measurements, and 2) that this interference can be completely blocked by excess IGF-I, if highly specific antisera are used.

Insulin-like growth factors in pygmies. The role of puberty in determining final stature

We measured the serum concentrations of insulin-like growth factors (IGF) I and II and testosterone in pygmy children, adolescents, and adults, as well as in controls, to determine more precisely the role of these factors in controlling growth. We had previously shown that growth hormone levels were normal in pygmies. Prepubertal pygmy children and controls did not differ in linear growth or in serum concentrations of IGF I and II. In pygmy adolescent boys, the mean (+/- SEM) serum concentration of IGF I was only one third that in control adolescents, who were similar to the pygmies in age and Tanner stage of development (154 +/- 22 vs. 435 +/- 37 ng per milliliter; P less than 0.01). A similar difference in IGF I concentration was observed in girls (278 +/- 18 vs. 570 +/- 25 ng per milliliter; P less than 0.01). IGF II and testosterone levels were normal in all groups. There was a significant difference in growth between controls and pygmies only during puberty. There was a marked acceleration of growth in the controls during adolescence, but such an acceleration was absent or blunted in the pygmies. These findings suggest that the short stature of adult pygmies is due primarily to a failure of growth to accelerate during puberty. We postulate that IGF I is the principal factor responsible for normal pubertal growth and that testosterone does not accelerate growth appreciably in the absence of an increase in the level of IGF I.

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.

Insulin-like growth factors (IGF) 1 and 2 in human foetal plasma and relationship to gestational age and foetal size during midpregnancy

IGF-1 and IGF-2 were measured by specific radioimmunoassay after acid-ethanol extraction of plasma obtained by foetoscopy from 20 normal foetuses aged 15-23 weeks. IGF-1 and IGF-2 levels were 36 +/- 11 and 162 +/- 55 ng/ml, respectively. In comparison, levels in cord blood were 84 +/- 58 and 264 +/- 176 ng/ml, respectively, and in adult plasma were 410 +/- 106 and 818 +/- 272 ng/ml. Both IGF-1 and IGF-2 were in the normal foetal range in a further three foetuses with anencephaly and two foetuses with spina bifida. No sex difference was observed. IGF-1 was positively correlated with foetal body weight (P less than 0.001), placenta weight (P less than 0.02) and with body length measured crown-rump (P less than 0.01) or crown-heel (P less than 0.02). No correlation between IGF-2 and body weight, length, placenta weight or gestational age was found. Both IGF-1 and IGF-2 are present in the human foetal circulation earlier in gestation than has previously been demonstrated, the levels being low throughout this period of gestation in comparison with adult plasma.

IGF-2 stimulated growth mediated by the somatomedin type 2 receptor

Human Insulinlike Growth Factor 2 (IGF-2) can promote cell proliferation via the type 2 receptor in K562 cells, a human erythroleukemia cell line with IGF-2/type 2 receptors and insulin receptors but lacking IGF-1/type 1 receptors. Cells are grown in semi-solid agar in the absence and presence of increasing amounts of insulin, IGF-1 and IGF-2. Two strains of K562 cells have been studied, with different concentrations of insulin and IGF-2 receptors. The effect of IGF-2 is proportional to the IGF-2 receptor concentration.

Serum concentrations of insulin-like growth factor II are not changed by short-term fasting and refeeding

To determine the factors that regulate insulin-like growth factor II (IGF-II), we raised polyclonal antibodies to this peptide and developed a RIA that measures IGF-II in serum or plasma samples after extraction of IGF-binding proteins by C18 cartridge chromatography. The IGF-II antiserum was highly specific, exhibiting no cross-reactivity with IGF-I or insulin at the highest concentrations tested (10(-6) mol/L). As little as 0.43 micrograms/L IGF-II was detectable, and 50% displacement of tracer occurred at 1.7 microgram/L. The serum IGF-II concentrations of normal adults [mean, 634 +/- 170 (+/- SD) micrograms/L], patients with acromegaly (570 +/- 146 micrograms/L), and patients with hypopituitarism (156 +/- 58 micrograms/L) were similar to those reported by others. In eight obese subjects injected with GH (0.1 mg/kg ideal BW, im, every 48 h for 16 days), serum IGF-II concentrations did not rise significantly, whereas IGF-I concentrations increased 67%. Sixteen normal subjects, within 15% of ideal body weight, were fasted for 5 days on two to four occasions and refed diets of differing protein and calorie contents. Their mean serum IGF-II concentration before fasting (691 +/- 26 micrograms/L) was not significantly different from that after fasting (674 +/- 21 micrograms/L) or after refeeding (641 +/- 20 micrograms/L). In contrast, their mean IGF-I concentration decreased 42% with fasting and rose with refeeding. Unlike IGF-I, serum IGF-II concentrations do not appear to be regulated by short term changes in nutritional status. It is clear from this study and others that IGF-II and IGF-I are regulated differently despite their structural homology and the similarity of their actions in vitro.

Type II insulin-like growth factor receptor is present in rat serum

We previously identified in fetal rat serum a component capable of specifically binding radiolabeled insulin-like growth factor type II (IGF-II) that is considerably larger than both the fetal (40 kDa) and the adult (150 kDa) carrier proteins. We now present immunologic and affinity crosslinking data to show that this binding species is the type II IGF receptor. Rat serum was gel-filtered on a Sephadex G-200 column (0.05 M NH4HCO3, pH 8), and 125I-labeled IGF-II (125I-IGF-II) binding was measured in individual column fractions. 125I-IGF-II binding activity was found in the void volume of the column in addition to the carrier protein regions. Competitive binding studies using 125I-IGF-II and binding activity from the Sephadex G-200 void volume showed the characteristics of the type II receptor: IGF-II was more potent than IGF-I, and insulin did not compete. Moreover, a specific anti-type II IGF receptor antibody (no. 3637) completely blocked 125I-IGF-II binding. 125I-IGF-I did not bind to the void volume pool, demonstrating the absence of the type I IGF receptor in rat serum. Affinity crosslinking of 125I-IGF-II to the Sephadex G-200 void volume material demonstrated a specific band at 210 kDa without reduction and at 240 kDa after reduction of disulfide bonds. The serum type II IGF receptor size was confirmed by immunoblotting the void volume material with antiserum 3637, which revealed a band slightly smaller (approximately 10 kDa) than the type II IGF receptor from rat placental membranes. Immunoquantitation by immunoblotting using pure type II IGF receptor from rat placental membranes as standard showed a developmental pattern. In fetal rat serum (19-days gestation) and in sera from 3-, 10-, and 20-day-old rats, the concentrations of receptor protein were similar (1-5 micrograms/ml). The level of the type II IGF receptor in serum declined dramatically between age 20 and 40 days, but the receptor was still measurable at age 12 mo. We conclude that the type II IGF receptor is present in rat serum and is developmentally regulated.

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.

Growth hormone, somatomedin levels and growth regulation in Turner's syndrome

In a total of 56 children and adolescents with Turner's syndrome (41 with karyotype 45,X) basal serum levels of somatomedin bioactivity, Sm-C/IGF-I (RIA), IGF II (RIA), GH response to arginine and GHRH (GRF(1-29)NH2), and spontaneous GH secretion during 5.5 h of deep sleep were determined in a cross-sectional manner. GH responses to GRF and arginine as well as IGF-II levels were found to be in the normal range. Levels of somatomedin bioactivity were higher than normal before a bone age of 10 years, in the low-normal range thereafter, and below normal in some patients. Levels of Sm-C/IGF-I were found normal before and low-normal after a bone age of ten years. There was a trend towards increasing Sm-C/IGF-I levels with age. In contrast to the normal pattern, spontaneous sleep-related GH secretion was declining with age and did not show the puberty-associated rise. These findings suggest a normally functioning growth hormone-somatomedin axis in Turner's syndrome with alterations of its functioning level occurring secondarily as a result of absent gonadal activation. In single patients abnormally low growth hormone and/or somatomedin secretion may be present.

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.

Suppression of the growth hormone (GH) response to clonidine and GH-releasing hormone by exogenous GH

GH release in response to clonidine and human GH-releasing hormone-(1-44) (hGHRH-44) was assessed in 11 boys (aged 7-14 yr) with short stature, who had normal GH secretion. The response to these 2 provocative stimuli was repeated after, respectively, 2 and 3 days of treatment with human GH (0.1 U/kg, im). Exogenous GH significantly blunted the response to both clonidine [the mean 2-h integrated serum GH concentration falling from 1050 +/- 350 (+/- SEM) to 749 +/- 297 ng/ml X min; P = 0.03] and hGHRH-44, the 2-h integrated GH concentration falling from 1553 +/- 358 to 547 +/- 202 ng/ml X min; (P = 0.03). Plasma insulin-like growth factor (IGF-II) concentrations did not change after GH administration. In contrast, plasma IGF-I (somatomedin-C) concentrations increased from 97 +/- 16 ng/ml before administration of GH to 142 +/- 32 ng/ml (P = 0.05) after two days and 149 +/- 23 ng/ml (P less than 0.01) after the third treatment day. However, no correlation was found between the changes in response to clonidine or hGHRH-44 and changes in circulating levels of IGF-I. Our data confirm the existence of GH-dependent feedback inhibition of GH release during childhood and suggest that this inhibition operates, at least in part, at the level of the pituitary. While participation of the IGFs/somatomedins in this feedback loop cannot be excluded, the inhibitory effects of exogenous GH do not depend directly on circulating plasma IGF-I or IGF-II levels.

Effects of injecting growth hormone or thyroxine on milk production and blood plasma concentrations of insulin-like growth factors I and II in dairy cows

Three cows received injections of thyroxine (T4; 20 mg/day), four cows GH (40 mg/day) and three cows saline (control; 10 ml/day) on days 5-8 of a 16-day experimental period during peak lactation. Milk yield increased 13% in cows given GH (from 14.6 to 16.5 kg/day) and 15% in cows given T4 (from 15.8 to 18.2 kg/day) but did not change in control cows. Injection of T4 increased milkfat and lactose content but reduced milk protein content. Injection of GH was without effect on milk composition during the injection period but milk protein rose after injections ceased. Injection of T4 increased plasma concentrations of T4 and tri-iodothyronine six- to sevenfold, with maxima occurring on day 9. Injection of GH increased the plasma concentration of GH five- to tenfold 5 h after injection. The plasma concentration of insulin-like growth factor I (IGF-I) was increased in cows given GH in both morning (08.30 h) and afternoon (14.30 h) blood samples, the difference being greatest in afternoon samples in which plasma IGF-I content increased from 3.3 to 6.8 nmol/l. Injection of T4 reduced the plasma concentration of IGF-I in morning samples but the concentration in afternoon samples remained relatively constant throughout the 16-day experimental period. The plasma concentration of IGF-II rose in morning samples in all treatment groups to reach a maximum of 200-250 nmol/l by day 9. The galactopoietic response to injection of GH but not T4 was associated with an increase in plasma concentration of IGF-I. Changes in plasma concentration of IGF-II were not associated with changes in milk yield.

Effect of hypophysectomy with and without thyroxine replacement on growth and circulating concentrations of insulin-like growth factors I and II in the fetal lamb

The role of the pituitary gland in the regulation of skeletal growth and plasma insulin-like growth factor (IGF)-I and IGF-II concentrations in the late gestation sheep fetus has been studied. Singleton fetuses were either hypophysectomized (n = 14) or sham operated (n = 8) between days 110 and 125. Fetal and maternal blood samples were collected three times weekly through the remainder of gestation. In some hypophysectomized fetuses (HXT4 group, n = 4), T4 was administered (100 micrograms L-T4/day) to overcome the hypothyroidism caused by hypophysectomy. The other hypophysectomized fetuses received no replacement therapy (HXNR group, n = 10). Six HXNR fetuses were allowed to remain in utero post term and were killed at day 163 of gestation. All other animals were killed at day 147. All values are group means +/- SE. Hypophysectomized fetuses had significantly shorter limbs and long bones and delayed osseous maturation at term compared to sham controls. Plasma free T4 concentrations in HXT4 fetuses were not significantly different from those measured in sham fetuses (P greater than 0.05). Bone maturation at term was normal in HXT4 fetuses although there was no improvement in limb or bone elongation. Retention of hypophysectomized fetuses in utero until 16 days past term yielded fetuses which were heavier than controls but whose limb and bone lengths were no greater than hypophysectomized fetuses killed at term. Osseous maturation was appropriate for term in five of the six postterm hypophysectomized fetuses. The plasma IGF-I and IGF-II concentrations were not significantly affected by hypophysectomy, hypophysectomy with T4 replacement, gestational age, or prolonged gestation. The plasma IGF-I concentrations in the sham, HXNR, and HXT4 fetuses were 35.4 +/- 6.6, 28.2 +/- 3.0, and 34.4 +/- 1.7 ngeq human (h)IGF-I/ml, and the IGF-II concentrations were 656.3 +/- 59.2, 635.3 +/- 56.3, and 645.5 +/- 71.9 ngeq hIGF-II/ml, respectively, and remained within these ranges throughout the experiment. Fetal IGF-I concentrations were significantly lower than mean maternal IGF-I concentrations (88.0 +/- 6.8 ngeq hIGF-I/ml, P less than 0.05), and fetal IGF-II concentrations were significantly higher than mean maternal IGF-II concentrations (362.4 +/- 24.0 ngeq hIGF-II/ml, P less than 0.05). We conclude that in the late gestation fetal sheep, elongation of the appendicular skeleton is under some direct pituitary control whereas appendicular maturation exhibits some dependence on circulating T4 concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth hormone treatment in short children: relationship between growth and serum insulin-like growth factor I and II levels

Thirty-one children who were short but not GH deficient, whose serum GH responses to provocative tests were normal, and whose spontaneous GH secretion was low received daily sc injections of human GH (Crescormon; 0.1 IU/kg BW) for 1 yr. Their initial serum insulin-like growth factor I (IGF-I) and IGF-II responses to GH were compared with their 1-yr growth response to therapy. In the prepubertal group (n = 18) the growth rate of all but two children increased 3.4 +/- 0.2 (+/- SEM) cm (from 4.1 +/- 0.2 to 7.5 +/- 0.3 cm/yr). The mean increment in the growth rate of the pubertal group was 5.2 +/- 0.5 cm. In both groups the growth increase was strongly correlated with both the percent increase in serum IGF-I and the percent increase in serum IGF-II during the first 10 days of treatment. No correlation was found between the basal growth rate and basal serum IGF-I or IGF-II levels. In the prepubertal group of children, both the percent increase in serum IGF-I levels in response to GH and the age at start of treatment were predictors of long term growth. We conclude that this subgroup of normal short children with low spontaneous GH secretion and high percent increase in serum IGF values benefits from GH treatment with an increased growth rate.

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)