Relationships of serum insulin-like growth factor I concentrations to growth, composition, and reproductive traits of swine

Insulin-like growth factor I (IGF-I) is a peptide hormone that has been shown to be involved in metabolic regulation of growth and reproduction in livestock species. The objectives of this study were to quantify concentrations of IGF-I in growing pigs and determine whether IGF-I concentration can be used as a predictor of growth, composition, and reproductive traits. Forty male and 60 female pigs, divided equally between two locations, were weighed and bled at 3-wk intervals from 6 to 21 wk of age. At each sampling, two blood samples were collected via jugular venipuncture at an interval of at least 1 h. Serum was separated and IGF-I concentration determined via RIA. Pigs were weighed at each sampling date. Backfat and longissimus muscle area were measured with the use of B-mode ultrasound and adjusted to 100 kg. Age at puberty and first-parity litter size were measured on gilts. Effects of age, sex, location, and pig within sex x location on log-transformed IGF-I concentrations were determined by analyzing data as a split-plot. Performance traits were fitted to a model including the effects of IGF-I concentration, sex, location, and interactions. The IGF-I concentrations increased (P < .05) from 3 to 18 wk of age before dropping at 21 wk of age. Concentrations increased more rapidly in males than in females and differed significantly between sexes from 12 to 21 wk of age. Repeatability of IGF-I concentration was .29 +/- .02; IGF-I concentrations of samples collected at 6 wk were not correlated with those at later ages. Correlations between IGF-I concentrations of samples at later ages ranged from .27 to .51. Heritability of IGF-I concentration was .27 +/- .07. There was a tendency for weight to be affected by a sex x age interaction (P = .09). Weight of boars exceeded weight of gilts only at 21 wk (111.4 +/- 1.1 vs 107.1 +/- .8 kg). Regressions of weight on IGF-I concentrations were positive at all ages but greatest at 6 wk. The IGF-I concentration did not affect backfat thickness, longissimus area, percentage of lean, age at puberty, or litter size.     

Sexual dimorphism of circulating somatotropin, insulin-like growth factor I and II, insulin-like growth factor binding proteins, and insulin: relationships to growth rate and carcass characteristics in growing lambs

The effects of sex and age on patterns of circulating somatotropin (ST) concentration and plasma IGF-I, IGF-II, insulin, and IGF binding protein-3 (IGFBP-3) were studied in ram, wether, and ewe lambs (n = 7 or 8) sampled at mean ages of 81 (I1) and 158 d (I2). Between 81 and 158 d of age, rams grew more rapidly than wethers (P < .01), and wethers grew more rapidly than ewes (P < .01). The sex differences in growth were reflected in empty body weight at slaughter: rams > wethers > ewes (P < .05). Mean plasma ST concentrations, ST pulse amplitude, and integrated plasma ST concentrations were greater (P < .05) in rams than in ewes at I1 and I2. Characteristics of the ST plasma profile in wethers were generally intermediate between those of rams and ewes. The interpulse interval was greater in ewes than in wethers at I2. The IGF-I and IGFBP-3 concentrations were greater in rams than in ewes at both sampling times. Plasma IGF-II was greater in ewes than in rams at I2. Mean plasma ST was approximately two thirds less at I2 than at I1 regardless of sex. Mean plasma ST and IGF-I at both ages were positively correlated with growth. Mean plasma ST at I2 was negatively correlated with fatness at slaughter. Sex and age significantly affected patterns of circulating ST and concentrations of IGF-I and IGFBP-3 in prepubertal growing lambs, under conditions for which growth rates and composition were also sexually dimorphic.     

Serum insulin-like growth factor-I, insulin-like growth factor binding protein-3, sex steroids, osteocalcin and bone mineral density in male and female rats

Although it has been reported that the rate of weight gain and linear growth increases markedly during puberty in rats, little is known about the relationship between endocrine changes and bone mineral density (BMD) changes upon sexual maturation in these animals. The aim of this study was to examine the levels of serum insulin-like growth factor-I (IGF-I), IGF binding protein (IGFBP)-3, sex steroids and osteocalcin, and the changes in BMD in normal aging male and female rats. Male rats exhibited increases in serum IGF-I and IGFBP-3 concentrations before increases in serum testosterone levels. IGF-I and testosterone peaked at 9 weeks of age, and thereafter remained in a steady state, whereas IGFBP-3 reached a peak at 7 weeks of age, and then gradually declined. A strong correlation between serum IGF-I and IGFBP-3 levels was found in subjects 3-9 weeks old. A highly significant correlation between serum IGF-I and testosterone levels was also found. In females, serum 17 beta-estradiol, IGF-I and IGFBP-3 levels increased gradually from 3 to 5 weeks old, peaked at 9 weeks, and then decreased slowly thereafter. The correlation coefficient between serum IGF-I and IGFBP-3 was highly significant. The correlation coefficient between serum IGF-I and 17 beta-estradiol levels was weak, although it was strongest when the subjects were 3-9 weeks old. Serum osteocalcin is a marker of bone formation; its level remained relatively high from 3 to 9 and from 3 to 7 weeks of age in males and females, respectively, although osteocalcin in both sexes declined gradually with age. As for bone mass, sharp increases in BMD in the tibia, femur and lumbar vertebrae appeared earlier in female than in male rats, and the BMD in females tended to be higher than in males between 5 and 9 weeks old. After 9 weeks of age, BMD in males was higher than that in females, as BMD in males continued to increase whereas females tended to remain in a steady state after this stage. The correlation coefficients between tibial BMD and serum IGF-I or IGFBP-3 levels were highly significant when the subjects were from 3 to 9 weeks old. Taken together, these results suggest that BMD development occurs earlier in female than in male rats. This sex-related difference in changes in the BMD pattern may result from the earlier onset of puberty in females, and from sex-specific differences in concentrations of IGF-I, IGFBP-3 and sex steroids during maturation.     

Effects of growth rate on carcass composition and lipid partitioning at puberty and growth hormone, insulin-like growth factor I, insulin, and metabolites before puberty in beef heifers

The effect of three rates of gain on carcass composition, lipid partitioning, age and BW at puberty, and concentrations of growth hormone (GH), IGF-I, insulin, glucose, and NEFA in plasma were evaluated in 38 Angus x Hereford heifers. Heifers were allotted by BW and age to three treatments with a replication in each of 2 yr: full-fed (n = 13; FF) to gain 1.36 kg/d; limit-fed (n = 12; LF) to gain .68 kg/d; maintenance-full-fed (n = 13; MFF) to gain .23 kg/d for 16 wk, then full-fed to gain 1.36 kg/d. Heifers were slaughtered within 10 d after the onset of puberty. At slaughter, kidney, pelvic, and heart fat (KPH) and udder (UDDER) were separated from carcass, as was fat surrounding viscera (OM). After 48 h at 4 degrees C a carcass side was dissected into subcutaneous fat (SC), intermuscular fat (SEAM), soft tissue (SFT = inseparable lean and fat), LEAN, and BONE. In yr 1, LF heifers (431 d) were older (P < .05) than MFF heifers (371 d) at puberty, but age of FF heifers (389 d) did not differ (P > .10) from that of LF and MFF heifers. In yr 2, FF heifers (351 d) were younger (P < .05) than LF and MFF heifers (398 and 434 d, respectively). The FF heifers had greater (P < .05) BW and a greater (P < .01) percentage of lipid in the carcass at puberty than LF and MFF heifers. During the first 16 wk of treatment, concentrations of NEFA were greater in heifers with slower daily gains (MFF > LF > FF; P < .01). Concentrations of NEFA were lesser and concentrations of IGF-I and insulin were greater in plasma of FF than in that of MFF heifers during the 10 wk before puberty. Treatment significantly altered age, BW, carcass composition, and lipid partitioning at puberty in beef heifers. We conclude that the percentage of body fat is not the sole regulator of puberty, and age may be an important modulator in determining the onset of puberty in beef heifers.     

Skeletal muscle growth and expression of skeletal muscle alpha-actin mRNA and insulin-like growth factor I mRNA in pigs during feeding and withdrawal of ractopamine

Sixty crossbred barrows were used to study the effect of ractopamine (a phenethanolamine/beta-adrenergic agonist) treatment and its withdrawal on muscle growth and on the relative abundance of skeletal muscle alpha-actin (sk-alpha-actin) mRNA and of liver and longissimus muscle IGF-I mRNA at 4 wk. Ractopamine was fed (20 ppm) for periods of 2, 4, and 6 wk (six pigs per group). Additional pigs (four per group) were fed ractopamine (20 ppm) for 6 wk and then slaughtered 1, 3, and 7 d after withdrawal of ractopamine. Ractopamine increased (P < .05) longisimus muscle weight and protein content, although protein concentrations were not different. The increased muscle weight and protein content attained by feeding ractopamine for 6 wk was retained when ractopamine was withdrawn. The RNA and DNA concentrations did not change, whereas total DNA and RNA content per muscle was 18 and 26.7% greater, respectively, in ractopamine-treated pigs at 4 wk, but there were no differences at 2 or 6 wk or among the withdrawal groups. The relative abundance of sk-alpha-actin mRNA in the longissimus muscle was 41 and 62% greater (P < .05) in treated animals at 2 and 4 wk but was similar to that in controls at 6 wk and during the withdrawal period. The relative abundance of IGF-I mRNA in liver and longissimus muscle was not altered with ractopamine treatment for 4 wk. These results indicate that the ractopamine-enhanced muscle growth may result from increased myofibrillar gene expression at the pretranslational level, which is maximal with short-term treatment of ractopamine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ontogeny of insulin-like growth factors (IGF), IGF binding proteins, IGF receptors, and growth hormone receptor mRNA levels in porcine pancreas

We examined the ontogeny of mRNA levels of IGF-I and -II, IGF type 1 (IGFI-R) and type II receptors (IGFII-R), IGF binding protein-1 and -3 (IGFBP-1 and -3), GH receptor (GHR), and tissue concentrations of IGF and IGFBP in the pancreas of pigs. Tissues were collected from fetuses at 90 and 110 d of gestation and from pigs at 1, 21, 90 and 180 d of age. Northern blots were performed using total RNA hybridized with 32P-labeled cDNA probes (human IGF-I and human IGFI-R) and cRNA probes (rat IGF-II, human IGFII-R, human IGFBP-1, pig IGFBP-3, and pig GHR). There were two accelerated growth stages of the pancreas: the first one at 90 d of fetal life, which is characterized by cell hyperplasia (high ratio of DNA to body weight), and the second one at postnatal 90 d, which is attributed to cell hypertrophy (high ratios of pancreatic weight, RNA, and protein to DNA). The level of IGF-II mRNA and its tissue concentration were predominant during fetal life and low thereafter. The IGF-I mRNA level was high during fetal and early postnatal life and decreased thereafter. Messenger RNA levels of IGFI-R, IGFBP-3, and GHR and concentrations of IGFBP-1 and -2 were abundant during fetal and early postnatal life. In conclusion, IGF may be involved in various physiological periods of pancreatic development in pigs.     

Effects of prenatal androgenization and postnatal steroid treatment on growth hormone, insulin-like growth factor I and II, insulin, thyroxine, and triidothyronine concentrations in beef heifers

A 2 x 3 factorial arrangement of treatments was used to elucidate the mechanism(s) by which prenatal androgenization improves postnatal rate and efficiency of growth and composition of gain in beef heifers. Fifteen control (C) and 15 prenatally androgenized (PA) Angus x Simmental heifers (prenatal treatment, Pretrt) received no (N), estrogen (E), or estrogen and testosterone (ET) implants postnatally (postnatal treatment, Posttrt) to evaluate whether the postpubertal growth response after prenatal androgenization could be induced in prepubertal heifers. Blood was collected from the heifers at 6 +/- 1, 9 +/- 1, and 12 +/- 1 mo of age and analyzed from serum concentrations of growth hormone (GH), IGF-I, IGF-II, insulin, thyroxine (T4), and triiodothyronine (T3). Season of the year had a greater effect on hormone concentrations than either Pretrt or Posttrt, and there were no Pretrt x Posttrt interactions. Prenatal treatment, PA, had no effect on GH; however, Posttrt E and ET increased (P < .001) GH concentrations. Prenatal treatment, PA, increased (P < .05) IGF-I concentrations, and there was a nonsignificant increase (P = .11) in IGF-I concentrations with Posttrt E and ET. Concentrations of IGF-II were unaffected by Pretrt PA; however, they were lower (P < .01) in the Posttrt E and ET groups. Insulin, T4, T3, BW, and ADG were not affected by Pretrt and Posttrt. Concentrations of GH and IGF-I were increased in heifers that received Pretrt PA and(or) Posttrt E and ET in a manner to support improved growth performance; however, BW and ADG were similar. In prepubertal beef heifers, factors in addition to increased GH and IGF-I seem to be necessary for improved growth performance.     

Maternal and fetal insulin-like growth factor system and embryonic survival during pregnancy in rats: interaction between dietary chromium and diabetes

Chromium (Cr) depletion may exacerbate hyperglycemia and negative outcomes of pregnancy in the streptozotocin (STZ) diabetic pregnant rat model through the regulation of the insulin-like growth factor (IGF) system. To test this hypothesis, 40 female rats, all fed a low Cr diet (i.e., 70 microgram Cr/kg diet ) from 21 d of age, were randomly assigned one of four treatments, applied on Day 1 of pregnancy, in a 2 x 2 factorial design: 1) very low Cr diet (40 microgram Cr/kg diet) + citrate buffer injection, 2) very low Cr diet + STZ injection (30 mg STZ/kg body wt in citrate buffer), 3) adequate Cr diet (2 mg Cr [from added CrK(SO4)2]/kg diet) + citrate buffer injectionand 4) adequate Cr diet + STZ injection. Blood and tissues were collected on Day 20 of pregnancy. Chromium depletion increased (P < 0.05) urinary hydroxyproline excretion, 22-kDa IGF binding protein (IGFBP) concentration and litter size but decreased (P < 0. 05) placental wt, percentage of protein per fetus, and fetal IGF-I and -II concentrations. Chromium had no effect (P > 0.10) on maternal hormones, 32-kDa IGFBP, glucose, or placental and fetal hydroxyproline concentrations. Diabetes decreased (P < 0.05) maternal wt gain, embryonic survival, litter size, mean pup wt and maternal insulin concentrations, increased (P < 0.05) maternal blood glucose, IGF-I concentrations and maternal hydroxyproline excretion but did not affect fetal concentrations of hormones, IGFBP, glucose or hydroxyproline. Interaction between chromium and diabetes tended (P < 0.10) to affect maternal IGF-II concentrations, but had no effect on other maternal or fetal variables. In conclusion, maternal chromium depletion did not exacerbate hyperglycemia or pregnancy outcome in STZ-induced diabetic rats, but may negatively affect fetal protein content by decreasing fetal IGF-II concentrations. Diabetes may negatively affect fetal growth through its effect on maternal glucose, insulin and IGF-I.     

Effects of growth hormone, prolactin, insulin-like growth factors, and gonadotropins on progesterone secretion by porcine luteal cells

Growth hormone (GH) and IGF-I have receptors within the corpus luteum (CL) and stimulate CL function. Our objective was to investigate the effects of GH, prolactin (PRL), IGF-I, IGF-II, LH, and FSH on progesterone secretion by porcine luteal cells during mid-pregnancy. Gilts (crossbred Yorkshire/Landrace) were slaughtered on d 44 of pregnancy and CL were collected. Large and small luteal cells (LLC and SLC, respectively) were obtained from dissociated CL and separated by elutriation. Luteal cells were incubated with 0, 1, 10, or 100 ng/mL of GH, PRL, IGF-I, IGF-II, LH, and FSH or combinations of 10 ng/mL of these reagents for 24 or 48 h. Culture media were harvested and concentrations of progesterone analyzed by radioimmunoassay. Growth hormone, PRL, and IGF-I increased (P < .05; 100 ng/mL dose) concentrations of progesterone in media of LLC. Insulin-like growth factor-II, LH, and FSH had no effect on progesterone in LLC cultures. In SLC cultures, GH, PRL, IGF-I, IGF-II, and FSH failed to stimulate progesterone secretion, whereas LH increased progesterone secretion (linear effect of dose; P < .05). Combinations (10 ng/mL each hormone) of GH and IGF-I or PRL and IGF-I increased progesterone secretion by LLC compared with control, GH, PRL, or IGF-I alone (P < .05). Similar combinations of GH or PRL with IGF-I had no effect on SLC. Conclusions are that GH and PRL are stimulatory to progesterone secretion by LLC (location of GH receptor) and SLC are responsive to LH during mid-pregnancy. Both GH and PRL are synergistic with IGF-I for increased progesterone secretion.     

The insulin-like growth factors (IGF) and IGF type I receptor during postnatal growth of the murine mammary gland: sites of messenger ribonucleic acid expression and potential functions

The goals of this study were to determine the cellular sites of insulin-like growth factor (IGF) and IGF type-I receptor (IGF-IR) expression and to begin to elucidate functional roles for the IGFs during postnatal development of the murine mammary gland. Using in situ hybridization analyses, we determined that IGF-I, IGF-II, and IGF-IR messenger RNAs were expressed in the highly proliferative terminal end buds during pubertal ductal growth. Consistent with these data, IGF-I (in combination with mammogenic hormones) promoted ductal growth in pubertal stage mammary glands cultured in vitro. During postpubertal and pregnancy stages, IGF-II and IGF-IR continued to be expressed in ductal epithelium. Expression of IGF-II in ductal and alveolar epithelium correlated with the pattern of rapidly proliferating cells, as determined by incorporation of 5-Bromo-2'-deoxyuridine, suggesting a potential autocrine or paracrine role for IGF-II as a mitogen for ductal epithelial cells. IGF-I expression was reinitiated in mammary epithelium in the differentiated alveoli at the end of pregnancy, suggesting an additional role for this factor in maintenance of the alveoli during lactation. Taken together, these data support an in vivo role for locally-produced IGFs in promoting ductal growth during puberty and suggest that IGF-I and IGF-II may have distinct functions during pregnancy-induced alveolar development.     

Insulin-like growth factor I and insulin-like growth factor binding protein 3 as determinants of blood hemoglobin concentration in healthy subjects

We studied the serum concentrations of IGF-I, IGF-binding protein 3 (IGFBP-3), and testosterone in relation to blood Hb in 60 healthy prepubertal or early pubertal boys twice, with a 9-mo interval. Serum IGF-I and testosterone levels were measured by RIA, and serum IGFBP-3 was measured by monoclonal immunofluorometric assay. Positive correlations were observed between the concentrations of blood Hb and serum IGF-I at the first examination (r = 0.36, p = 0.008) and Hb and IGFBP-3 at both examinations (r = 0.53, p < 0.001, and r = 0.39, p = 0.003). No association between Hb and testosterone concentrations was found. Our results show that blood Hb is positively correlated to serum IGF-I and IGFBP-3 levels, indicating indirectly the involvement of growth hormone in the regulation of physiologic Hb concentration. Because no association was found between Hb and testosterone concentrations, this may indicate that the role of androgens in erythropoiesis may be different at different stages of puberty. It is concluded that the IGF system may be involved in the rise of Hb level during early puberty.     

Assessment of developmental changes in chicken and turkey insulin-like growth factor-II by homologous radioimmunoassay

The development of a homologous RIA for chicken insulin-like growth factor-II (cIGF-II) and its application to investigate the developmental changes in IGF-II in the chicken and turkey are described. A double-antibody RIA has been developed using recombinantly derived cIGF-II as antigen, radiolabelled tracer and standard. Serial dilutions of chicken and turkey plasma were parallel to serial dilutions of cIGF-II standard. We have also established that acid/ethanol extraction of chicken and turkey plasma reduced possible interference of insulin-like growth factor-binding proteins in the RIA. Consumption of a low-protein diet by male chickens lowered plasma IGF-I twofold, whereas IGF-II levels were unchanged. Food withdrawal evoked an increase in circulating IGF-II, while IGF-I levels were reduced. Refeeding returned both growth factors to normal circulating concentrations. During chick embryo incubation, plasma IGF-II levels were tenfold higher than those of IGF-I. In the turkey embryo, plasma IGF-II concentrations were higher than those of IGF-I. During the post-hatch period. IGF-II levels declined with age in chickens. In the growing turkey, IGF-II levels were consistently higher than IGF-I levels. The application of the homologous RIA to monitor plasma levels during embryonic development and post-hatch growth in avian species will provide more accurate comparisons of results from studies on the role of IGF-II in growth and metabolism of domestic birds.     

Stimulation of statural growth by recombinant insulin-like growth factor I in a child with growth hormone insensitivity syndrome (Laron type)

We studied the effects of 9 months of treatment with twice-daily subcutaneous injections of insulin-like growth factor I (IGF-I), 120 micrograms/kg per dose, in a 9.7-year-old child with growth hormone insensitivity syndrome, in whom short-term studies had suggested that IGF-I might promote linear growth. Height velocity increased from 6.5 cm/yr (+1.7 SD score) to 11.4 cm/yr (+8.8 SD score). Serum concentrations of IGF-I increased from pretreatment values of 9 +/- 2 micrograms/L to a peak of 347 +/- 26 micrograms/L after 2 hours. Serum concentrations of IGF-II were unchanged. Basal but not stimulated growth hormone concentrations were decreased. During the first 12 days of treatment, serum concentrations and the 24-hour urinary excretion of urea nitrogen were decreased by 28% and 10%, respectively (p < 0.05), there was a 2.4-fold increase in urinary excretion of calcium (p < 0.001), and creatinine clearance and urine volume increased by 22% and 55%, respectively (p < 0.02). The changes in serum levels of urea nitrogen and in urinary calcium and creatinine clearance were still evident at 10 weeks. Fasting and postprandial serum glucose concentrations remained normal. We conclude that IGF-I given as twice-daily subcutaneous injections is effective in stimulating statural growth without producing the hypoglycemia and hyperglycemia observed when IGF-I is infused continuously.     

Determinants of growth in diabetic pubertal subjects

OBJECTIVE: To analyze the relationship among metabolic control, IGF-I, and growth in pubertal diabetic subjects. RESEARCH DESIGN AND METHODS: In 72 diabetic children, we have studied the pattern of change of IGF-I, IGF-I SD score, IGF binding protein (BP)-1, and growth rate in different pubertal stages and have analyzed their relation to age sex, weight/length index, HbA1c, insulin concentration, insulin dose, and dehydroepiandrosteronesulfate (DHEAS). RESULTS: The serum IGF-I values increased up to Tanner stage 4 and thereafter decreased, whereas IGFBP-1 showed the inverse pattern. When transforming the IGF-I values into SD scores, correcting for age, sex, and pubertal stage, it was shown that the deviation from normal values increased with increasing pubertal stage in boys, but was equal in stages 3-5 in girls. Using multiple regression analysis, HbA1c, insulin dose, and DHEAS were significantly correlated to IGF-I SD score (R2 = 0.253, P = 0.001). IGFBP-I levels in the afternoon were within normal range. LogIGFBP-1 showed an inverse correlation, to insulin concentration in single correlation (r = -0.26, P = 0.02). In single correlation, growth rate correlated significantly to insulin dose (r = 0.25, P = 0.03). In a multiple regression analysis, only DHEAS and IGF-I SD score were found to be significantly correlated to growth rate (R2 = 0.370, P < 0.001). The 18 adolescents who had reached their final height did not deviate from their target final height, according to their recorded growth since birth. CONCLUSIONS: In a group of fairly well-controlled diabetic children, the normal increase in IGF-I during puberty is blunted. Despite decreased IGF-I levels, target final height was attained, probably because of adequate insulin compensation leading to normal IGFBP-l, thus adequate bioavailability of IGF-I. Our results point out the importance of sufficient exogenous insulin in the period of rapid linear growth.     

Serum concentrations of free and total insulin-like growth factor-I, IGF binding proteins -1 and -3 and IGFBP-3 protease activity in boys with normal or precocious puberty

OBJECTIVE: Circulating IGF-I and IGF binding protein-3 (IGFBP-3) levels both increase in puberty where growth velocity is high. The amount of free IGF-I is dependent on the IGF-I level and on the concentrations of the specific IGFBPs. Furthermore, IGFBP-3 proteolysis regulates the bioavailability of IGF-I. However, the concentration of free IGF-I and possible IGFBP-3 proteolytic activity in puberty has not previously been studied. SUBJECTS AND MEASUREMENTS: We investigated serum levels of easily dissociable IGF-I concentrations and ultrafiltrated free IGF-I levels by specific assays in 60 healthy boys and in 5 boys with precocious puberty before and during GnRH agonist treatment. In addition, total serum IGF-I, IGFBP-1 and IGFBP-3 levels as well as IGFBP-3 protease activity were determined. RESULTS: Free (dissociable and ultrafiltrated) IGF-I concentrations were significantly higher in pubertal boys than in prepubertal children and correlated significantly with the molar ratio between IGF-I and IGFBP-3 (r = 0.69, P < 0.0001 and r = 0.54, P = 0.0008, respectively) and inversely with IGFBP-1 (r = -0.47, P < 0.0001 and r = -0.43, P = 0.0003, respectively). Multiple regression analysis suggested that IGFBP-3 level, and not IGFBP-1, was the major determinant of the free IGF-I serum level in normal boys. Free IGF-I levels were elevated in boys with precocious puberty and decreased during GnRH treatment. IGFBP-3 proteolysis was constant throughout puberty (mean 20%). CONCLUSIONS: We conclude that easily dissociable and ultrafiltrated free IGF-I serum levels are increased in boys with normal and precocious puberty and suggest that the increased free IGF-I serum concentration in puberty primarily reflects changes in total concentrations of IGF-I and IGFBPs secondary to increased GH secretion, but that it is not influenced by changes in IGFBP-3 proteolysis.     

Concentration of insulin-like growth factor (IGF)-I and -II in iliac crest bone matrix from pre- and postmenopausal women: relationship to age, menopause, bone turnover, bone volume, and circulating IGFs

Insulin-like growth factor-I (IGF-I) and -II are important local regulators of bone metabolism, but their role as determinants of human bone mass is still unclear. In the present study, we analyzed the concentration of IGF-I and -II in the bone matrix of 533 human biopsies from the iliac crest that were obtained during surgery for early breast cancer. There was an inverse association of bone matrix IGF-I concentration with age that was unaffected by menopause. Bone matrix IGF-I was positively associated with histomorphometric and biochemical parameters of bone formation and bone resorption and with cancellous bone volume. Based on the estimates of the linear regression analysis, women with a bone matrix IGF-I concentration 2 SD above the mean had a 20% higher bone volume than women with a bone matrix IGF-I concentration 2 SD below the mean. In contrast, serum IGF-I was neither correlated with bone turnover nor with bone volume and was only weakly associated with bone matrix IGF-I when adjusted for the serum concentration of IGF binding protein-3. Bone matrix IGF-II was positively associated with the osteoblast surface, but in contrast to IGF-I, tended to be positively associated with age and was unrelated to cancellous bone volume. In summary, our study suggests the following. 1) The concentration of IGF-I in cancellous bone undergoes age-related decreases that are similar to those of circulating IGF-I. 2) Menopause has no effect on this age-related decline. 3) Physiological differences in bone matrix IGF-I are associated with differences in iliac crest cancellous bone volume. 4) Bone matrix IGF-I is a better predictor of cancellous bone volume than circulating IGF-I. 5) The role of IGF-II in human bone tissue is clearly distinct from that of IGF-I.     

Insulin-like growth factors-I and -II stimulate chemotaxis of osteoblasts isolated from fetal rat calvaria

Repair and regeneration of damaged bone is believed to be regulated in part by growth factors stored in the bone matrix. These growth factors are synthesized and secreted by osteoblasts and are incorporated into the developing bone. This pool of stored growth factors is then released into the immediate area following resorption of the matrix. One of the initial steps in bone repair is the recruitment of osteoblasts to the repair site. Growth factors, such as TGF-beta and PDGF, which are present in bone matrix, have been shown to be chemotactic for osteoblasts. In this study, primary cultures of osteoblasts isolated from fetal rat calvaria were examined for chemotaxis in response to IGF-I and IGF-II. IGF-I stimulated a dose-dependent increase in osteoblast chemotaxis, while IGF-II stimulated chemotaxis maximally at the lowest concentration studied (0.1 ng/ml), and had no effect at the highest concentration studied (100 ng/ml). IGF-I and -II had no effect on osteoblast proliferation at any of the concentrations examined. These results indicate that IGFs may be playing an important role in the early stages of bone repair by stimulating osteoblast chemotaxis to the repair site.     

Short stature associated with high circulating insulin-like growth factor (IGF)-binding protein-1 and low circulating IGF-II: effect of growth hormone therapy

We report a case of short stature associated with high circulating levels of insulin-like growth factor (IGF)-binding protein-1 (IGFBP-10 and low levels of IGF-II responsive to pharmacological treatment with GH. Our patient suffered severe growth failure from birth (2.06 SD below the mean for normal full-term boys, and 5.2 and 7.3 SD below the mean at 5 and 10 months). Studies carried out before referral to our pediatric unit included normal 46,XY karyotype and normal encephalic imaging. Other endocrine and metabolic alterations and other systemic diseases were excluded. At 1.7 yr of age (length, 6.1 SD; weight, 4.6 SD; head circumference, 1.4 SD below the mean, respectively) the patient was referred to our pediatric unit. The baseline GH concentration was 31 microg/L, and the peak after an arginine load was 59.6 microg/L. In the same samples GH bioactivity was nearly superimposable (RIA/Nb2 bioactivity ratio = 0.9). Fasting insulin and glucose concentrations were 7.4 microU/mL and 65 mg/dL, respectively, both normally responsive to an oral glucose load. GH insensitivity was excluded by a basal IGF-I concentration (64 ng/mL) in the normal range for 0- to 5-yr-old boys and its increase after 2 IU/day hGH administration for 4 days. IGFBP-3 (0.5 microg/mL) was slightly reduced, whereas IGFBP-1 (2218 and 1515 ng/mL in two different basal samples) was well above the normal values for age and was suppressible by GH (maximum suppression, -77% at 84 h) and glucose load (maximum suppression, -46% at 150 min). The basal IGF-II concentration was below the normal range (86 ng/mL), whereas IGFBP-2 was normal (258 ng/mL). Analysis of the promoter region of IGFBP-1 and IGF-II failed to find major alterations. Neutral gel filtration of serum showed that almost all IGF-I activity was in the 35- to 45-kDa complex, coincident with IGFBP-1 peak, while the 150-kDa complex was absent, although the acid-labile subunit was normally represented. At 2.86 yr (height, 65.8 cm; height SD score, -7.3; height velocity SD score, -5) the patient underwent treatment with 7 IU/week human GH; after 4 months, the patient's height was 68.5 cm (height SD score, -6.9) corresponding to a growth velocity of 8.3 cm/yr (0.3 height velocity SD score). IGFBP-1 was reduced (216 ng/mL), although still in the high range, whereas IGF-I (71 ng/mL), IGFBP-3 (0.62 microg/mL), and IGF-II (111 ng/mL) were only slightly increased. The IGF-I profile showed activity in the 150-kDa region. In conclusion, we speculate that the increased IGFBP-1 values found in this patient produce 1) inhibition of IGF-I biological activity and, therefore, a resistance to IGF-I not due to a receptor defect for this hormone; 2) inhibition of formation of the circulating 150-kDa ternary complex and, therefore, an accelerated clearance rate of IGF peptides; 3) inhibition of the feedback action on GH, leading to increased GH levels, which could suggest the diagnosis of GH insensitivity syndrome; and 4) inhibition of body growth.     

Three cases of near-tetraploid acute myeloid leukemias originating in pluripotent myeloid progenitors

The kinetics of peritoneal transport of insulin-like growth factor (IGF) system-related proteins during dialysis is not well characterized. We studied temporal changes in dialysate and serum concentrations of IGF-I and IGF-II as well as IGF binding protein (BP)-1, -2, and -3 in ten children with end-stage renal disease (ESRD) undergoing continuous cycling peritoneal dialysis (CCPD) during a 4-h peritoneal equilibration test (PET). Dialysate concentrations of IGF-I, IGF-II, and all three IGFBPs demonstrated a time-dependent increase during PET. Despite their transport, the serum concentrations of these proteins did not change significantly during the PET. Dialysate/serum ratios for IGF-I, IGF-II, and IGFBP-1, -2, and -3 were significantly increased at 2 h and increased further at 4 h, at which time values averaged 1.3+/-0.2%, 3.1+/-0.5%, 6.2+/-1.0%, 2.4+/-0.2%, and 1.3+/-0.2% of serum levels, respectively. The transperitoneal clearance (microl/min per 1.73 m2) of the three IGFBPs was inversely related to both their molecular weight and plasma concentration. However, peritoneal clearance of IGF-I and -II was similar to that of the larger and more-abundant IGFBP-3. Mass transfer rates (microg/h per 1.73 m2) for the IGFs and their binding proteins were directly proportional to their prevailing plasma concentration. Based on estimates of mass transfer, only a small molar excess of IGFBPs was removed from the circulation relative to the combined molar concentration of IGF-I and IGF-II. Hence, it seems unlikely that any beneficial effect of CCPD on growth in children with ESRD is mediated via a preferential loss of IGFBPs into the dialysate fluid.     

Effect of growth factors on growth of bovine parathyroid cells in serum-free medium

Published work has suggested a possible role of the epidermal growth factor receptor (EGFr) in parathyroid disease. Bovine parathyroid cells (BPCs) are frequently used as a tissue model for studying parathyroid disorders. We have studied the effect of the EGFr ligands EGF and transforming growth factor alpha (TGFalpha), alone and with insulin-like growth factors IGF-I and IGF-II on BPC growth. Experiments were run in triplicate and repeated three times. Cell numbers were assessed on day 5 by colorimetric MTT assay as well as by tritiated thymidine uptake. Results show that TGFalpha alone (p < 0.05) and IGF-I and IGF-II alone (p < 0.05) significantly stimulated growth over controls (t-test). Furthermore, the combination of TGFalpha with IGF-I and IGF-II exhibited significant enhancement above that seen with IGF-I and IGF-II alone (p < 0.01). EGF did not stimulate growth over controls. EGFr may be expressed in BPCs, but TGFalpha exhibits a more potent growth stimulus than EGF. Addition of IGF-I or IGF-II to the growth medium further enhances this effect.