Insulin-like Growth factor-I Production Research Articles

Suppression of uterine insulin-like growth factor binding protein 5 by estrogen is mediated in part by insulin-like growth factor I.

Insulin-like growth factor I (IGF-I) is an important mediator of estradiol-induced uterine growth in vivo. Insulin-like growth factor binding proteins (IGFBPs) are known to regulate access of insulin-like growth factors to IGF receptors. In this report we demonstrate that the positive uterotrophic agent estradiol, suppresses expression of the IGFBP-5 gene in the uterus to less than 15% of control values, while oophorectomy results in uterine involution and is associated with a greater than 3-fold stimulation of uterine IGFBP-5 gene expression. Immunohistochemical studies show that in intact rat uterus, the luminal epithelial cells are weakly stained with IGFBP-5 antibodies. Following ovariectomy, IGFBP-5 is confined in the luminal epithelial layer and longidinal smooth muscle cells. Administration of estradiol to ovariectomized rats increases uterine weight and uterine IGF-I gene expression, while immunostaining of IGFBP-5 in the luminal epithelial cells and longidinal smooth muscle cells is almost extinguished. In vitro studies using primary uterine cells reveal that IGF-I increases thymidine incorporation and inhibits IGFBP-5 gene expression, whereas estradiol has no effect suggesting that in vivo estradiol-induced IGFBP-5 suppression is mediated through increased IGF-I production. Our results suggest that in vivo, the uterotrophic effects of estradiol are mediated at least in part by estradiol-stimulated uterine IGF-I expression which in turn inhibits IGFBP-5 expression, an action which would be expected to increase IGF bioactivity.

Recombinant insulin-like growth factor-I (IGF-I) production in Super-CHO results in the expression of IGF-I receptor and IGF binding protein 3.

Previously, we described the genetic construction Super- CHO, a cell line capable of autocrine growth under fully defined protein-free conditions. Super-CHO cells constitutively express insulin growth factor-I (IGF-I) and transferrin in sufficient amounts to support long-term, stable growth without the addition of exogenous growth factors, thus making it an ideal host for the production of recombinant biopharmaceuticals. although IGF-I has been successfully expressed in Chinese Hamster Ovary (CHO) cells, the long term effects of recombinant IGF-I expression have not been explored. In particular, the expression of the endogenous IGF-I receptor in response to IGF-I production has not been reported. We report here the transcriptional induction of the type I IGF receptor gene in Super-CHO. In addition, we examined the conditioned medium for the presence of IGF-I binding proteins. Ligand blot analysis reveals the presence of IGF binding proteins present in the medium conditioned by Super-CHO cells as well as CHO cells incubated in the presence of IGF-I. Furthermore, immunoaffinity reveals that Super-CHO expresses IGF binding protein-3 in response to IGF-I production. These results suggest the autocrine growth of Super-CHO involves a complex interaction of cell type specific factors which regulate its utility of IGF-I.

Programming of growth hormone secretion and bone mineral density in elderly men: a hypothesis.

Epidemiological studies suggest that retarded growth in infancy is associated with low adult bone mass. The mechanism underlying this association is unknown, but the programming of GH secretion or sensitivity by environmental influences during early development may play a role. We examined this issue in a sample of 37 healthy men, aged 63-73 yr, whose weight gain in infancy had been recorded. Venous blood samples were obtained under standard conditions every 20 min over a 24-h period. Measurements were made of the GH secretory profile, insulin-like growth factor I (IGF-I), IGF-binding protein-1 and -3, and GH-binding protein. Bone mineral density was measured at the lumbar spine and femoral neck using dual energy x-ray absortiometry. There was a statistically significant association between peak GH concentration (r = 0.46; P < 0.01) and fasting IGF-I concentration (r = 0.46; P < 0.01) with femoral neck bone density. After allowing for the peak GH concentration, median GH was negatively (P < 0.05) associated with bone mineral density. Weight at 1 yr was not related to peak GH, but was strongly related to the median GH concentration (r = 0.42; P = 0.01). These observations are consistent with a dual effect of GH secretion on bone density. High peak GH values drive IGF-I production and maintain bone mineralization in adult life. However, integrated GH secretion, after adjusting for the effect of pulse amplitude, is negatively associated with bone density in adult life. This particular characteristic of the GH secretory profile correlates with growth during infancy and might be programmed by environmental factors during intrauterine or early postnatal life.

Insulin-like growth factor I (IGF-I) serum level modifications during transdermal estradiol treatment in postmenopausal women: A possible bimodal effect depending on basal IGF-I values

The objective of this study was to determine the influence of transdermal estradiol administration on insulin-like growth factor I (IGF-I) serum level in a series larger than those published to date. Thirty-nine postmenopausal women with vasomotor symptoms were studied; blood samples (after overnight fast) were obtained just before and at the 6th month of treatment with transdermal estradiol 0.05 mg/day, and serum levels of IGF-I, growth hormone and sex hormone binding globulin (SHBG) were evaluated.Sixteen of the 39 women did not show variations of IGF-I values (group A), while 11 showed an increase (group B) and 12 showed a decrease (group C) by at least 20% with transdermal estradiol treatment. IGF-I basal levels were higher in group C as compared to group A (p < 0.05) and to group B (p < 0.01), intermediate in group A, and lower in group B. Group C showed a significant increase of SHBG values with transdermal estradiol treatment.Transdermal estradiol seems to induce a bimodal effect on IGF-I serum levels, depending on IGF-I basal values. This could be caused by a different responsivity to estrogen action on the liver (the major site of circidating IGF-I production) and also, possibly, by a different degree in insulin sensitivity changes caused by estrogen.

Serum levels of GH, IGF-I, LH and ovarian steroids in cyclic and RU486-treated rats.

Rats lacking progesterone action due to RU486 treatment have been reported to show numerous endocrine and morphological similarities with respect to human polycystic ovary syndrome (PCO). Nevertheless, abnormalities on insulin or insulin-like growth factor I (IGF-I) production, a frequent finding in the polycystic disease, have not been studied in such rats yet. The aim of these experiments was to evaluate the serum concentrations of IGF-I in rats treated with 4 mg of the antiprogestagen RU486 over 4 or 8 consecutive days starting on estrus (day 1) and decapitated on the morning of day 5 and 9. Serum levels of growth hormone (GH), luteinizing hormone (LH), testosterone (T) and 17 beta estradiol (E2) were determined and correlated with those of IGF-I. Controls were rats injected with oil and killed in the morning of metestrus, diestrus, proestrus and estrus. Rats treated with RU486 had increased serum concentrations of IGF-I, LH, T and E2 with respect to control rats on estrus, while no differences were found in the serum concentrations of GH. Parallel estrous cycle related changes were observed in the serum concentrations of IGF-I, T and E2 with the highest values at proestrus. However, changes on serum concentrations of GH were not associated with those of IGF-I in control rats through the estrous cycle. The present results are consistent with the idea that beside on GH, serum concentrations of IGF-I in the rat depend also on LH or LH-dependent ovarian steroid production. Moreover, the results indicate that IGF-I production increased in RU486-treated rats, which may have a role in the ovarian abnormalities induced by RU486 treatment in the rat.

Growrth hormone secretion and circulating insulin-like growth factor-I (IGF-I) and IGF binding protein-3 concentrations in children with sickle cell disease

Impaired growth involving both height and weight accompanying sickle cell disease (SCD) poses diagnostic and therapeutic problems. We undertook this study to test the hypothesis that this impaired growth is associated with abnormalities of the growth hormone (GH)/insulin-like growth factor-I (IGF-I)/IGF binding protein-3 (IGFBP-3)axis in 21 children with SCD and that SCD is associated with GH resistance. Nine of 21 children with SCD had a defective GH response to both clonidine and glucagon provosation (peak, < 10 μg/L); these children differed from the 12 others in having slower linear growth velocity (GV and GVSDS), lower circulating concentrations of IGF-I and IGFBP-3, and either partial or complete empty sellae in computed tomographic scans of the hypothalamic-pituitary area. In this group of patients with SCD, it appears that defective GH secretion and consequent low IGF-I production are the major etiological factors causing the slow growth. The two groups with SCD did not differ significantly in dietary intake, body mass index (BMI), midarm circumference, skinfold thickness, serum albumin concentration, or intestinal absorption of d-xylose. A single injection of GH produced a smaller increase in circulating IGF-I in children with SCD with or without defective GH secretion versus 10 age-matched children with idiopathic short stature (ISS) and 11 children with isolated GH deficiency (GHD), suggesting partial GH resistance in the SCD group. The presence of defective GH secretion, decreased IGF-I synthesis, and partial resistance to GH in short children with SCD suggests that treatment with IGF-I may be superior to GH therapy for improving growth.

Effects of calcitonin gene-related peptide on bone turnover in ovariectomized rats

Calcitonin gene-related peptide (CGRP) is a neuropeptide abundantly concentrated in sensory nerve endings innervating bone metaphysis and periosteum, which indicates that it plays a local role in bone metabolism. CGRP-α and -β share structural and functional homology with calcitonin (CT) and have been shown to inhibit bone resorption in vitro and to induce hypocalcemia in vivo. We recently reported that CGRP stimulates the production of the growth factor insulin-like growth factor-I and inhibits that of the cytokine tumor necrosis factor-α by osteoblasts, suggesting that CGRP may control bone cell activity. To investigate this possibility, we used ovariectomized (ovx) rats as a high bone turnover model and compared the effects of CGRP to those of CT. ovx young female rats were injected daily starting the day after surgery with either phosphate-buffered saline, CGRP-α (1.15 mg/kg per day), or CT (3 μg/kg per day) for 28 days. Ovariectomy induced an increase in bone turnover associated with a 60% loss in trabecular bone volume of the proximal tibia. CGRP inhibited bone resorption but not bone formation, and was nevertheless less efficient than CT in preventing bone loss, since CGRP-treated rats had a loss of 46% of cancellous bone, whereas CT-treated rats had a loss of 21%. This suggests that CGRP is either less potent than CT at inhibiting bone resorption or else very rapidly degraded. These data indicate that CGRP can control bone cells through a mechanism that is in part different from that of CT, and further suggest that CGRP may play a local role in bone metabolism. (Bone 21:269–274; 1997)

Molecular mechanisms involved in the nutritional and hormonal regulation of growth in pigs.

Nutritional and hormonal factors are major determinants of animal growth and, postnatally at least, pituitary-derived growth hormone (GH), via its stimulatory effects on insulin-like growth factor-I (IGF-I) production, is one of the major regulators of growth. The production of GH by the pituitary is under the local control of growth-hormone-releasing factor (GRF) and growth-hormone-release-inhibiting factor (somatostatin). However, diet also has a major effect on circulating GH concentrations, such that nutritional restriction leading to growth arrest is associated with a decrease in plasma IGF-I concentration, but an increase in plasma GH concentration in most species, including the pig (Buonomo & Baile, 1991), the rat being the exception. The molecular mechanisms for this growth arrest, in the presence of high concentrations of this positive regulator of growth (GH), are proposed to be via dietary effects on the components of the GH-IGF axis, and in particular IGF-I, and form the subject for the present review.

Somatic and renal effects of growth hormone in rats with chronic renal failure.

Recombinant human growth hormone (rhGH) has been widely used to improve growth in children with chronic renal failure (CRF). However, there has been great concern that GH may aggravate renal disease and hasten the progression to end-stage renal failure. We therefore investigated the effect of prolonged administration of rhGH at various doses on somatic growth and renal function and structure in rats with CRF, divided into four groups based on rhGH dose (vehicle, 0.4, 2.0, and 10.0 IU/day). rhGH was administered subcutaneously daily for 8 weeks. The mean growth was significantly greater in rats treated with high-dose rhGH (10.0 IU) than those treated with low-dose rhGH (P = 0.0089) or vehicle (P = 0.0011). Body weight gain increased in parallel with body length (Creatinine clearance at the end of the experiment was significantly lower in rats on high or medium-dose rhGH than those on low-dose rhGH and controls (P < 0.05). The glomerular sclerosing index was greater in rats treated with higher doses of rhGH. There were significant differences between rats treated with high-dose rhGH and controls (P = 0.0144) and also between rats on medium-dose rhGH and controls (P = 0.0065). Although there was no significant difference, rats treated with higher doses of rhGH tended to excrete more protein. Renal insulin-like growth factor-I (IGF-I) content and circulating IGF-I and IGF-II levels did not significantly differ among groups. We conclude that: (1) GH improves somatic growth failure in rats with CRF, but prolonged administration of GH dose-dependently induces deterioration in renal function and structure and (2) this effect was induced neither via circulating IGF-I and IGF-II nor by local production of IGF-I, but seems to be direct.

Insulin-like growth factor-I (IGF-I) production by bovine granulosa cells in vitro and peripheral IGF-I measurement in cattle serum: an evaluation of IGF-binding protein extraction protocols.

Insulin-like growth factor-binding protein (IGFBP) extraction protocols were tested for their efficacy in removing IGFBPs from bovine plasma and bovine granulosa cell culture medium compared with standard acid exclusion chromatography. Traditional extraction methods, acidification, Sep-Pak, ethanol:acetone:acetic acid (EAA) and EAA-cryoprecipitation (EAA-C), failed to remove all the IGFBPs from both granulosa cell culture medium and plasma. However, EAA and EAA-C treatment of plasma samples did give values similar to those obtained by acid exclusion HPLC, when corrected for extraction efficiency. There was an inverse relationship between insulin-like growth factor-I (IGF-I) concentration in plasma samples, as measured using HPLC chromatography, and IGF-I concentration after EAA extraction. Furthermore, the interference caused by residual IGFBPs differed between samples taken from animals given various treatment that altered peripheral IGF-I concentrations. As for plasma samples, EAA was the most effective extraction method for culture media, but residual IGFBPs caused an overestimation of IGF-I concentrations. In culture media, but not plasma, it was possible to block the interference of IGFBPs in the IGF-I assay, in both extracted and non-extracted culture samples, by the addition of excess IGF-II. Using this assay procedure, no IGF-I production by bovine granulosa cells was detected. This was confirmed by HPLC acid chromatography. It is concluded that HPLC extraction is needed for the accurate measurement of peripheral IGF-I concentrations. For granulosa cell culture media it is possible to measure IGF-I concentration in non-extracted samples if the IGFBPs are blocked by adding IGF-II. Using either this assay, or after HPLC acid chromatography, no IGF-I was detected in culture media, suggesting that IGF-I is not produced by non-luteinised bovine granulosa cells.

Is Milk-Borne Insulin-Like Growth Factor-I Essential for Neonatal Development?

Insulin-like growth factor-I (IGF-I), a polypeptide growth factor found in milk, is hypothesized to play a functional role in the growth and development of neonates, particularly the gastrointestinal tract. Considerable evidence, based on direct tracer studies with 125I-labeled IGF-I and measurements of circulating IGF-I concentrations in neonatal animals fed a range of IGF-I doses, indicates that the intestinal absorption of IGF-I and the possible effect on metabolism and somatic growth are negligible. However, studies in neonatal animals indicate that oral administration of pharmacological doses of IGF-I increases small intestinal mucosal growth, whereas oral IGF-I provided within the physiological range may enhance the development of intestinal lactase. Therefore, clinical trials exploring the therapeutic use of oral IGF-I as an intervention for preterm neonates and those with compromised intestinal function seem warranted. However, milk-borne IGF-I may not be essential for normal healthy infants, perhaps because endogenous IGF-I provides a sufficient stimulus for maintenance of gastrointestinal structure and function. Future studies should explore the significance of endogenous IGF-I and whether milk-borne IGF-I may be important under pathological conditions in which the endogenous IGF-I production may be compromised.

Inhibition by Interleukin-1β and Tumor Necrosis Factor-α of the Insulin-Like Growth Factor I Messenger Ribonucleic Acid Response to Growth Hormone in Rat Hepatocyte Primary Culture*

The cytokines are the putative mediators of the catabolic reaction that accompanies infection and trauma. Evidence suggests that their catabolic actions are indirect and potentially mediated through changes in hormonal axis such as the hypothalamo-pituitary-adrenal axis. Insulin-like growth factor I (IGF-I) is a GH-dependent growth factor that regulates the protein metabolism. To determine whether cytokines can directly inhibit the production of IGF-I by the liver, we investigated the regulation of IGF-I gene expression by interleukin (IL)-1 beta, IL-6, and tumor necrosis factor (TNF)-alpha (10 ng/ml) in a model of rat primary cultured hepatocytes. Hepatocytes were isolated by liver collagenase perfusion and cultured on Matrigel 48 h before experiments. Each experiment was performed in at least three different animals. In the absence of GH, IL-1 beta and TNF-alpha did not affect the IGF-I messenger RNA (mRNA) basal levels, whereas IL-6 increased it by a factor of 2.5 after 24 h (P < 0.05). GH (500 ng/ml) alone stimulated the IGF-I gene expression markedly (5-to 10-fold increase) after 24 h (P < 0.001). IL-1 beta, and TNF-alpha to a lesser extent, dramatically inhibited the IGF-I mRNA response to GH (IL-1 beta: -82%, P < 0.001 and TNF-alpha: -47%, P < 0.01). The half-maximal inhibition of the IGF-I mRNA response to GH was observed for a concentration of IL-1 beta between 0.1 and 1 ng/ml. Moreover, IL-1 beta abolished the IL-6-induced IGF-I mRNA response. In contrast, IL-6 did not impair the IGF-I mRNA response to GH. To determine the potential role of the GH receptor (GHR) and the GH-binding protein (GHBP) in this GH resistance, we assessed the GHR and GHBP mRNAs response to these cytokines. GH alone did not affect the GHR/GHBP mRNA levels. IL-1 beta markedly decreased the GHR and GHBP mRNA levels (respectively, -68% and -60%, P < 0.05). Neither TNF-alpha nor IL-6 affected the GHR/GHBP gene expression. In conclusion, our results show that IL-1 beta, and TNF-alpha to a lesser extent, blunt the IGF-I mRNA response to GH. The resistance to GH induced by IL-1 beta might be mediated by a decrease of GH receptors, as suggested by the marked reduction of GHR mRNA. These findings suggest that decreased circulating IGF-I, in response to infection and trauma, may be caused by a direct effect of cytokines at the hepatocyte level.

Effect of 1,25(OH)2 vitamin D3 on circulating insulin-like growth factor-I and beta 2 microglobulin in patients with osteoporosis.

To test the hypothesis that growth factors mediate the stimulatory effect of 1,25(OH)2 vitamin D3 [1,25(OH)2D3] on bone remodeling in osteoporosis, the authors studied the effect of the secosteroid administration in two doses (1 microgram/day and 2 micrograms/day) for 14 days on circulating insulin-like growth factor-I (IGF-I), beta 2 microglobulin, and osteocalcin in 18 osteoporotic women. The biological effectiveness of the treatment was controlled by a decline of serum intact parathyroid hormone. Compared with the values before treatment, 1,25(OH)2D3 increased means of plasma IGF-I, beta 2 microglobulin, and serum osteocalcin significantly; however, the effects were only apparent after the higher dose of the drug (169 +/- 26 versus 134 +/- 28 ng/ml, P < 0.01; 2.08 +/- 0.1 versus 1.92 +/- 0.1 micrograms/ml, P < 0.05; and 8.5 +/- 1.3 versus 5.4 +/- 1.1 ng/ml, P < 0.01, respectively). The authors conclude that exogenous 1,25(OH)2D3 promotes the production of IGF-I and beta 2 microglobulin in osteoporotic patients in parallel to the marker of osteoblastic function, osteocalcin, which supports the tested hypothesis.

Basal and growth hormone-induced hepatic messenger ribonucleic acid expression of insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 is independent of hyperinsulinemia and increased energy status in the genetically obese Zucker rat.

Genetically obese Zucker rats, like obese humans, have normal or elevated circulating insulin-like growth factor-I (IGF-I) levels in the presence of low GH secretion. Hyperinsulinemia, increased energy status, or other nutritional factors associated with obesity could be responsible for these findings directly by increasing hepatic IGF-I production at the transcriptional or posttranscriptional level. Alternatively, circulating IGF-I could be modulated indirectly by affecting its binding proteins. To further elucidate this point, we quantitated hepatic IGF-I, IGF-binding protein-3 (IGFBP-3), and GH receptor messenger RNAs (mRNAs) expression in obese Zucker rats under different serum GH and insulin conditions using lean rats as controls. Eleven-week-old male rats were studied basally (intact) or after hypophysectomy (hx) at 9 weeks. In each condition, animals were killed before or 6 h after one dose of recombinant human GH (1.5 micrograms/g body weight ip). At this time, in addition to the mRNA expression of the above-mentioned genes, body weight, glycemia, insulinemia, serum GH (rat and human), and serum IGF-I levels were determined. Obese Zucker rats were significantly heavier than controls in all the conditions studied and did not show differences in glycemia. Severely hyperinsulinemic intact obese rats (146.9 +/- 14 vs. 46.3 +/- 3 microU/ml, P < 0.001) showed compared with intact lean rats significantly lower serum GH (2.39 +/- 0.9 vs. 4.98 +/- 0.68 ng/ml, P < 0.01), decreased hepatic IGF-I mRNA and IGFBP-3 mRNA accumulation (IGF-Ia: 79 +/- 5.9% vs. 100 +/- 0.9%, P < 0.05; IGF-Ib: 67 +/- 5.5% vs. 100.1 +/- 1.9%, P < 0.001; IGFBP-3: 54.7 +/- 2.75% vs. 100.5 +/- 1.55%, P < 0.001), and similar circulating IGF-I levels (1439 +/- 182 vs. 1516 +/- 121 ng/ml). Under comparable serum GH levels in GH-treated intact, hx, and GH-treated hx animals, hyperinsulinemia and/or increased body weight present in obese rats were not associated with increased hepatic IGF-I and IGFBP-3 mRNA amount. No differences in GH receptor/GH-binding protein mRNAs were found in any experimental condition. These results suggest that in vivo the imbalance of the serum GH/IGF-I axis present in obesity is primarily due to events distal to the hepatic IGF-I and IGFBP-3 mRNAs expression, which is tightly correlated to GH levels.

Decreased hepatic insulin-like growth factor (IGF)-I and increased IGF binding protein-1 and -2 gene expression in experimental uremia.

The imbalance between normal insulin-like growth factor-I (IGF-I) and markedly increased IGF binding protein (IGFBP) plasma levels plays a pathogenic role for growth retardation and catabolism in children with chronic renal failure. To investigate the mechanism of these alterations, experiments were performed in an experimental model of uremia in rats (5/6 nephrectomy) and in pair-fed and ad libitum-fed sham-operated controls Using a specific solution hybridization/RNase protection assay, we observed a marked reduction of hepatic IGF-I messenger RNA (mRNA) abundance at steady state in uremic animals (37 +/- 5% of control) compared both with pair-fed (65 +/- 10%) and ad libitum-fed controls (100 +/- 11%) (P < 0.001). Reduced IGF-I gene expression was clearly organ-specific; it was most pronounced in liver (significant vs., pair-fed controls) and lung and muscle tissue (significant vs., ad libitum-fed controls); no change was observed in kidney and heart tissue. To determine a potential mechanism of reduced hepatic IGF-I gene expression in uremia, the hepatic GH receptor gene expression in the same experimental animals was analyzed by specific solution hybridization/RNase protection assay. Uremic animals had a 20-30% reduction of hepatic GH receptor mRNA abundance compared with controls. Hepatic GHBP expression in uremia was decreased in parallel. Despite the reduction of hepatic IGF-I mRNA abundance, plasma IGF-I levels in uremia were not different from ad libitum-fed controls. This discrepancy is explained by an increased concentration of IGFBPs in uremic plasma. By RIA, plasma IGFBP-1 levels in uremia were increased 4-fold; by Western immunoblot, plasma IGFBP-2 levels were increased 7-fold and plasma IGFBP-4 levels were increased 2-fold compared with both control groups. Intact IGFBP-3 (M(r), approximately 48 kDa) and low molecular IGFBP-3 fragments were not significantly different among the three groups. By Northern blot analysis, hepatic IGFBP-1 mRNA levels in uremia were 2-fold higher than in controls. IGFBP-2 mRNA abundance in liver tissue was increased 4-fold, whereas in kidney there was a significant reduction of IGFBP-2 mRNA (30% of control). IGFBP-4 mRNA was increased by 50% in kidney but not in liver. Plasma insulin and corticosterone levels were not different among the groups. Our study shows that hepatic IGF-I gene expression was specifically reduced in uremia, partially as the consequence of a reduced hepatic GH receptor gene expression. One of the mechanisms contributing to increased IGFBP levels in uremia is increased hepatic gene expression of IGFBP-1 and IGFBP-2. The imbalance between reduced hepatic IGF-I production and increased hepatic IGFBP-1 and 2 production is likely to play a pathogenic role for catabolism and growth failure in CRF.

Beneficial effects of growth hormone combined with parenteral nutrition in the management of inflammatory bowel disease: An experimental study

Background. Growth hormone (GH) improves net protein anabolism and stimulates wound healing. Although GH is also known to exert the trophic effect on the intestinal tract, its role in the healing of intestinal ulceration is not known. The aim of this study was to evaluate the effects of exogenous GH coinfused with parenteral nutrition (PN) in an experimental model of inflammatory bowel disease in rats. Methods. All rats underwent central venous cannulation and were randomized to two groups after induction of small intestinal ulceration with indomethacin. Both groups received the same PN formula. In addition, the GH group (n = 10) received subcutaneous injections of human GH at a dose of 1.0 IU/kg daily for 4 days, whereas the control group (n = 10) received injections of normal saline solution. Nitrogen balance, macroscopic inflammation score, intestinal myeloperoxidase activity, DNA content, and mucosal permeability were determined for each rat. Insulin-like growth factor-I (IGF-I) mRNA was detected by reverse transcription and polymerase chain reaction. Results. Administration of GH significantly improved the cumulative nitrogen balance, ameliorated the gross inflammation score, and decreased intestinal myeloperoxidase activity. Similarly, intestinal permeability was significantly decreased in the GH group as compared with the control group. GH treatment resulted in increased plasma concentration of IGF-I and IGF-I mRNA expressions in both the liver and the small intestine compared with those in the control group. Conclusions. Exogenous GH plays an important role in accelerating intestinal healing in an experimental model of small bowel ulceration in rats. The mechanisms may include the stimulated IGF-I production, which thereafter augments intestinal epithelial cell growth.

Tissue-Specific Alterations in Insulin-like Growth Factor-I Concentrations in Response to 3,3′,5-Triiodo-l-thyronine Supplementation in the Growth Hormone Receptor-Deficient Sex-Linked Dwarf Chicken

Insulin-like growth factor-I (IGF-I) mediates many of the effects of growth hormone (GH). The regulation of IGF-I, independent of GH, is methodologically difficult to assessin vivo,as hypophysectomy results in derangement of many pituitary hormone axes in addition to GH, and a gene knockout model is not available. The recessive sex-linked dwarfing (SLD) gene (dw) in chickens results in a lack of functional target tissue GH receptors due to a variety of molecular defects, which provides a unique model for evaluating GH-independent regulation of IGF-I. In the present study, the impact of 3,3′,5-triiodo-l-thyronine (T3) on circulating and tissue IGF-I was determined in normal versus SLD birds. Adult, nonovulatory female normal and SLD chickens were restrict-fed 40 g of feed/kg bw/day containing 0, 0.5, or 1.0 ppm T3, resulting in supplementation levels of 0 (control), 20 (low dose), or 40 (high dose) μg T3/kg bw/day for 10 days. Samples of GH target tissues including liver, abdominal fat pad, skeletal muscle (pectoralis major), and spleen were extracted and assayed for IGF-I. Plasma T3, T4, GH, and IGF-I were determined by homologous RIA. Tissue GH binding was determined for hepatic membranes by radioreceptor assay. Under control conditions, dwarf chickens were markedly hypersomatotropic (33.3±4.1 ng GH/ml plasma; mean±SEM) compared to normals (2.4±3.9 ng/ml), and T3supplementation reduced this to normal levels. Despite the high circulating level of GH in dwarfs, plasma IGF-I was low compared to normal controls (dwarfs 1.5±.9 ng/ml; normals 5.3±.9 ng/ml;P=0.004), but this difference was eliminated with low-dose T3. In this study, tissue IGF-I was undetectable in liver and pectoralis muscle in adults (55 weeks of age) of both genotypes, under all treatments. In contrast, adipose tissue IGF-I was relatively high and did not differ (P=0.84) between genotypes under control conditions (normals 776.5±236.7; dwarfs 844.6±236.7 pg/mg protein), but was increased in normals and decreased in dwarfs, resulting in higher levels (P=0.02) in the normal (1249.9±200.0 pg/mg protein) than in the dwarf genotype (558.4±200.0 pg/mg protein) at the higher level of T3supplementation. This relationship was somewhat reversed in spleen, where T3tended to decrease tissue IGF-I concentration in normals and increase it in dwarfs. The low level of plasma IGF-I despite nonmeasureable hepatic IGF-I tissue concentrations suggests that IGF-I synthesis by extrahepatic tissues contributes to the circulating pool of IGF-I. The relatively high control levels of adipose tissue IGF-I in the dwarf genotype further suggest that considerable IGF-I synthesis exists that is GH-independent in this extrahepatic tissue. The presence of GH action, however, may mediate the effects of other hormones that can influence local IGF-I production in this tissue, as reflected by the differential response to T3supplementation between genotypes. The tissue-specific nature of the effect of T3on IGF-I production supports an additional point of regulation of hormone action at the target tissue level.

Role of growth hormone in ovarian physiology and onset of puberty.

To review the role of growth hormone (GH) in the timing of puberty and to summarize the interactions between the somatotrophic and reproductive axes. The use of recombinant GH in patients with GH deficiency is outlined. A MEDLINE search was performed of English language manuscripts dealing with the role or use of GH in puberty and reproduction. Growth hormone appears to augment the rate of sexual maturation once a pubertal pattern of gonadotropin secretion is established. Growth hormone may modulate gonadal steroid production by increasing hepatic insulin-like growth factor-I production or by acting directly on GH receptors, localized recently in the granulosa cells and corpus luteum in the human ovary. Patients with isolated GH deficiency exhibit short stature, truncal adiposity, and delayed puberty. However, patients with isolated GH deficiency ultimately undergo spontaneous puberty, and women with GH receptor defects are fertile, suggesting that GH most likely acts as a co-gonadotropin to augment the actions of FSH and LH on estradiol and progesterone production. Growth hormone appears to increase the rate of sexual maturation once a pubertal pattern of pituitary gonadotropin secretion is established. The ovary is a site of GH reception and action, where it can potentiate steroidogenesis and gametogenesis either directly or through endocrine actions. Continued basic and clinical research is needed to characterize further the role of GH in reproductive physiology.

C-peptide, insulin-like growth factors I and II, and insulin-like growth factor binding protein-1 in cord serum of twins: Genetic versus environmental regulation

OBJECTIVE: Our purpose was to examine the regulation of fetal serum concentrations of insulin (C-peptide), insulin-like growth factor-I, insulin-like growth factor-II, and insulin-like growth factor binding protein-1, which are growth-regulating factors in the fetus, in monozygotic and dizygotic twin pairs. STUDY DESIGN: Cord serum samples were collected from 110 twin pairs and compared with 178 nonsibling singleton pairs with the same gestational age. Five twin pairs were excluded from the statistical analyses because of severe intrauterine growth restriction and placental abnormalities in one. Zygosity was assigned by histologic examination of the placenta and by a questionnaire sent to the mother when the twins were ≥6 months old. Analyses included the calculation of correlation coefficients, between-pair variation, and univariate genetic analysis. RESULTS: Cord serum C-peptide concentrations were highly correlated in monozygotic ( r = 0.94) and dizygotic twins ( r = 0.79) but not in singleton pairs ( r = -0.05); the between-pair variation was also smaller in twins than in singletons. Genetic analysis demonstrated a large contribution of the common environment to the variance in C-peptide concentrations (80%) and a smaller genetic contribution (12%). Insulin-like growth factor-I concentrations were better correlated in monozygotic ( r = 0.82) than in dizygotic twins ( r = 0.42), with a smaller between-pair variation in the former group (22% ± 4% vs 51% ± 5%). Univariate genetic analysis indicated that insulin-like growth factor-I levels were regulated predominantly by genetic mechanisms (93% in boys and 77% in girls). The regulation of insulin-like growth factor-II was more complex, with a gender-specific genetic contribution (50% for both sexes combined, 63% for girls but only 5% for boys). Insulin-like growth factor binding protein-1 was regulated by genetic mechanisms (41%) and the common environment (32%) but also by the specific or unique environment of each fetus (27%). In all five twins with intrauterine growth restriction of one member, insulin-like growth factor binding protein-1 concentrations were markedly higher in the growth-restricted fetus. CONCLUSIONS: Insulin secretion in twin fetuses is determined primarily by their common, probably maternal, environment, whereas insulin-like growth factor-I production is predominantly genetically regulated. Insulin-like growth factor-II and insulin-like growth factor binding protein-1 are regulated by both genetic and environmental factors. Of these growth-regulating factors, insulin-like growth factor binding protein-1 appears to be the best marker of intrauterine growth restriction in the individual case. (Am J Obstet Gynecol 1996;175:1180-8.)

Insulin-like growth factor I and insulin down-regulate growth hormone (GH) receptors in rat osteoblasts: evidence for a peripheral feedback loop regulating GH action.

The anabolic actions of GH are mediated by the production of insulin-like growth factor I (IGF-I) from the liver and by local production of IGF-I in extrahepatic tissues. Insulin facilitates the hepatic production of IGF-I by up-regulating GH receptors (GHRs) in the liver and augmenting the IGF-I response to GH. Although GHRs have also been identified in extrahepatic tissues that produce IGF-I, the possibility that IGF-I and insulin might partake in GHR regulation, thereby modulating the effects of GH locally has not received detailed study. The aim of this study was to investigate whether IGF-I and insulin are involved in the local regulation of GHRs, using osteoblasts as a model of GH-responsive extrahepatic tissues. We have used UMR106.06, a well differentiated rat osteoblast-like cell line that expresses GHRs and exhibits a mitogenic response to GH. IGF-I and insulin (0-10 nM) increased cell number and reduced [125I]GH binding in a concentration-dependent manner, with ED50 values of 0.8 and 0.3 nM, respectively. Although IGF-I increased cell number maximally by 36.9 +/- 1.2% (mean +/- SE) above the control value and insulin by 104.8 +/- 5.7% (P < 0.001), they decreased GH binding to 47.0 +/- 9.3% (P < 0.01) and 29.8 +/- 8.7% of the control value (P < 0.001), respectively. Scatchard analysis revealed that the down-regulation of GH binding was attributed to reduced receptor numbers and not binding affinity. The effects of IGF-I and insulin at submaximal concentrations were additive, although the combined effects did not exceed the maximal effect of either growth factor alone. Addition of an anti-IGF-I receptor antibody (alpha IR3) reversed the inhibition of GH binding induced by IGF-I, but not that caused by insulin; similarly, an antiinsulin receptor antibody (29B4) attenuated the inhibitory effect of insulin only. Addition of alpha IR3 alone or an ant-IGF-I antibody (Sm1.2) decreased cell number and increased GH binding in a concentration-dependent mode. GH at 1.5 nM significant increased cell number by 19.3 +/- 2.4% above the control level (P < 0.01), an increase that was reversed by alpha IR3. GH increased GH binding by 32.4 +/- 7.2% (P < 0.05) in cells treated with alpha IR3 to remove the secondary effect of IGF-I. In summary, IGF-I and insulin acted via specific receptors to stimulate cell proliferation and down-regulate GHRs in osteoblasts. GH stimulated cell proliferation, an action mediated by local production of IGF-I, and GH enhanced its own binding. The collective data suggest the presence of a peripheral negative feedback loop that allows IGF-I to limit locally the response of extrahepatic tissues to circulating GH.