Increased expression of insulin-like growth factor-I in serum and liver after recombinant human growth hormone administration in thermally injured rats

Metabolic and Nutritional Support

Hypermetabolism is a hallmark of larger burn injuries. The hypermetabolic response is characterized by marked and sustained increases in catecholamines, glucocorticoids, and glucagon. There is an increasing body of literature for nutrition and metabolic treatment and supplementation to counter the hypermetabolic and catabolic response secondary to burn injury. Early and adequate nutrition is key in addition to adjunctive therapies, such as oxandrolone, insulin, metformin, and propranolol. The duration of administration of anabolic agents should be at minimum for the duration of hospitalization, and possibly up to 2 to 3 years postburn.

Modulation of Burn Hypermetabolism in Preclinical Models

Severe burns elicit a state of physiological stress and increased metabolism to help the body compensate for the changes associated with the traumatic injury. However, this hypermetabolic state is associated with increased insulin resistance, cardiovascular dysfunction, skeletal muscle catabolism, impaired wound healing, and delayed recovery. Several interventions were attempted to modulate burn hypermetabolism, including nutritional support, early excision and grafting, and growth hormone application. However, burn hypermetabolism still imposes significant morbidity and mortality in burn patients. Due to the limitations of in vitro models, animal models are indispensable in burn research. Animal models provide researchers with invaluable tools to test the safety and efficacy of novel treatments or advance our knowledge of previously utilized agents. Several animal studies evaluated novel therapies to modulate burn hypermetabolism in the last few years, including recombinant human growth hormone, erythropoietin, acipimox, apelin, anti-interleukin-6 monoclonal antibody, and ghrelin therapies. Results from these studies are promising and may be effectively translated into human studies. In addition, other studies revisited drugs previously used in clinical practice, such as insulin and metformin, to further investigate their underlying mechanisms as modulators of burn hypermetabolism. This review aims to update burn experts with the novel therapies under investigation in burn hypermetabolism with a focus on applicability and translation. Furthermore, we aim to guide researchers in selecting the correct animal model for their experiments by providing a summary of the methodology and the rationale of the latest studies.

Metabolic and Endocrine Considerations After Burn Injury

Severe burn injury is followed by a profound hypermetabolic response that persists up to 2 years after injury. It is mediated by up to 50-fold elevations in plasma catecholamines, cortisol, and glucagon that lead to whole-body catabolism, elevated resting energy expenditures, and multiorgan dysfunction. Modulation of the response by early excision and grafting of burn wounds, thermoregulation, control of infection, early and continuous enteral nutrition, and pharmacologic treatments aimed at mitigating physiologic derangements have markedly decreased morbidity.

Postburn Hypermetabolism: Past, Present, and Future

Hypermetabolism is the ubiquitous response to a severe burn injury, which was first described in the nineteenth century. Despite identification of important components of this complex response, hypermetabolism is still not well understood in its entirety. This article describes this incredibly fascinating response and the understanding we have gained over the past 100 years. Additionally, this article describes novel insights and delineates treatment options to modulate postburn hypermetabolism with the goal to improve outcomes of burn patients.

Recombinant human growth hormone for treating burns and donor sites

BACKGROUND

Recombinant human growth hormone (rhGH) increases protein synthesis, therefore it is used in burns with a total body surface area (TBSA) greater than 40%, where there is frequently an increase in protein breakdown and a decrease in protein synthesis. This change in protein metabolism correlates with poor wound healing of the burn and donor sites.

OBJECTIVES

To determine the effects of rhGH on the healing rate of burn wounds and donor sites in people with burns.

SEARCH METHODS

For this first update we searched the Cochrane Wounds Group Specialised Register (searched 04 September 2014); The Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2014, Issue 8); Database of Abstracts of Reviews of Effects (DARE) (The Cochrane Library 2014, Issue 3); Ovid MEDLINE (1950 to September Week 4 2014); Ovid MEDLINE (In-Process & Other Non-Indexed Citations September 8, 2014); Ovid EMBASE (1980 to 2014 Week 35); and EBSCO CINAHL (1982 to 8 September 2014).

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing rhGH with any comparator intervention, e.g. oxandrolone or placebo, in adults or children with burns.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies, assessed trial quality and extracted data. The primary outcomes were the healing of the burn wound and donor sites and the occurrence of wound infections. The secondary outcomes were mortality rate, length of hospital stay, scar assessment, and adverse events: hyperglycaemia and septicaemia.

MAIN RESULTS

We included 13 RCTs (701 people). Six of the RCTs included only children aged 1 to 18 years and seven involved only adults (from 18 to 65 years of age). The mean TBSA of the included participants was greater than 49%. Twelve studies compared rhGH with placebo and one study compared rhGH with oxandrolone. Two trials found that compared with placebo, burn wounds in adults treated with rhGH healed more quickly (by 9.07 days; 95% confidence interval (CI) 4.39 to 13.76, I² = 0%). The donor site healing time was significantly shorter in rhGH-treated adults compared with placebo-treated participants (by 3.15 days; 95% CI 1.54 to 4.75, I² = 0%). Two studies in children with the outcome of donor site healing time could be pooled and the donor site healing time was shorter in the rhGH-treated children (by 1.70 days; 95% CI 0.87 to 2.53, I² = 0%). No studies reporting the outcome of wound infection were found. The incidence of hyperglycaemia was higher in adults during rhGH treatment compared with placebo (risk ratio (RR) 2.43; 95% CI 1.54 to 3.85), but not in children. Pooling the studies of adults and children yielded a significantly higher incidence of hyperglycaemia in the rhGH-treated participants (RR 2.65; 95% CI 1.68 to 4.16).

AUTHORS' CONCLUSIONS

There is some evidence that using rhGH in people with large burns (more than 40% of the total body surface area) could result in more rapid healing of the burn wound and donor sites in adults and children, and in reduced length of hospital stay, without increased mortality or scarring, but with an increased risk of hyperglycaemia. This evidence is based on studies with small sample sizes and risk of bias and requires confirmation in higher quality, adequately powered trials.

Burns in children: standard and new treatments

Outcomes of patients with burns have improved substantially over the past two decades. Findings from a 2012 study in The Lancet showed that a burn size of more than 60% total body surface area burned (an increase from 40% a decade ago) is associated with risks and mortality. Similar data have been obtained in adults and elderly people who have been severely burned. We discuss recent and future developments in burn care to improve outcomes of children.

Recombinant human growth hormone for treating burns and donor sites

BACKGROUND

Recombinant human growth hormone (rhGH) increases protein synthesis, therefore it is used in burns with a total body surface area (TBSA) greater than 40%, where there is frequently an increase in protein breakdown and a decrease in protein synthesis. This change in protein metabolism correlates with poor wound healing of the burn and donor sites.

OBJECTIVES

To determine the effects of rhGH on the healing rate of burn wounds and donor sites in people with burns.

SEARCH METHODS

We searched the Cochrane Wounds Group Specialised Register (searched 28 June 2012); The Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2012, Issue 6); Database of Abstracts of Reviews of Effects (DARE) (The Cochrane Library 2011, Issue 3); Ovid MEDLINE (1950 to June Week 3 2012); Ovid MEDLINE (In-Process & Other Non-Indexed Citations June 27, 2012); Ovid EMBASE (1980 to 2012 Week 25); and EBSCO CINAHL (1982 to 21 June 2012).

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing rhGH with any comparator intervention, e.g. oxandrolone or placebo, in adults or children with burns.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies, assessed trial quality and extracted data. The primary outcomes were the healing of the burn wound and donor sites and the occurrence of wound infections. The secondary outcomes were mortality rate, length of hospital stay, scar assessment, and adverse events: hyperglycaemia and septicaemia.

MAIN RESULTS

We included 13 RCTs (701 people). Six of the RCTs included only children aged 1 to 18 years and seven involved only adults (from 18 to 65 years of age). The mean TBSA of the included participants was greater than 49%. Twelve studies compared rhGH with placebo and one study compared rhGH with oxandrolone. Two trials found that compared with placebo, burn wounds in adults treated with rhGH healed more quickly (by 9.07 days; 95% confidence interval (CI) 4.39 to 13.76, I² = 0%). The donor site healing time was significantly shorter in rhGH-treated adults compared with placebo-treated participants (by 3.15 days; 95% CI 1.54 to 4.75, I² = 0%). Two studies in children with the outcome of donor site healing time could be pooled and the donor site healing time was shorter in the rhGH-treated children (by 1.70 days; 95% CI 0.87 to 2.53, I² = 0%). No studies reporting the outcome of wound infection were found. The incidence of hyperglycaemia was higher in adults during rhGH treatment compared with placebo (risk ratio (RR) 2.43; 95% CI 1.54 to 3.85), but not in children. Pooling the studies of adults and children yielded a significantly higher incidence of hyperglycaemia in the rhGH-treated participants (RR 2.65; 95% CI 1.68 to 4.16).

AUTHORS' CONCLUSIONS

There is some evidence that using rhGH in people with large burns (more than 40% of the total body surface area) could result in more rapid healing of the burn wound and donor sites in adults and children, and in reduced length of hospital stay, without increased mortality or scarring, but with an increased risk of hyperglycaemia. This evidence is based on studies with small sample sizes and risk of bias and requires confirmation in higher quality, adequately powered trials.

The GH/IGF-1 system in critical illness

The Growth Hormone and Insulin-like Growth Factor-1 (IGF-1) axis plays a pivotal role in critical illness, with a derangement leading to profound changes in metabolism. Protein wasting with skeletal muscle loss, delayed wound healing, and impaired recovery of organ systems are some of the most feared consequences. The use of human recombinant Growth Hormone (rhGH) and Insulin-like Growth Factor-1 (IGF-1) - alone and in combination - has been studied extensively in preclinical and clinical trials. This article reviews the current knowlegde and clinical practice of the use of rhGh and IGF-1 in critically ill patients, with a special focus on the trauma and burns patient population.

What, how, and how much should patients with burns be fed?

The hypermetabolic response to severe burn injury is characterized by hyperdynamic circulation and profound metabolic, physiologic, catabolic, and immune system derangements. Failure to satisfy overwhelming energy and protein requirements after, and during, severe burn injury results in multiorgan dysfunction, increased susceptibility to infection, and death. Attenuation of the hypermetabolic response by various pharmacologic modalities is emerging as an essential component of the management of patients with severe burn injury. This review focuses on the more recent advances in therapeutic strategies to attenuate the hypermetabolic response and its postburn-associated insulin resistance.

The hypermetabolic response to burn injury and interventions to modify this response

Severe burn injury is followed by a profound hypermetabolic response that persists up to 24 months after injury. It is mediated by up to 50-fold elevations in plasma catecholamines, cortisol, and inflammatory cells that lead to whole-body catabolism, elevated resting energy expenditures, and multiorgan dysfunction. All of these metabolic and physiologic derangements prevent full rehabilitation and acclimatization of burn survivors back into society. Modulation of the response by early excision and grafting of burn wounds, thermoregulation, early and continuous enteral feeding with high-protein high-carbohydrate feedings, and pharmacologic treatments have markedly decreased morbidity.

The hepatic response to thermal injury: is the liver important for postburn outcomes?

Thermal injury produces a profound hypermetabolic and hypercatabolic stress response characterized by increased endogenous glucose production via gluconeogenesis and glycogenolysis, lipolysis, and proteolysis. The liver is the central body organ involved in these metabolic responses. It is suggested that the liver, with its metabolic, inflammatory, immune, and acute phase functions, plays a pivotal role in patient survival and recovery by modulating multiple pathways following thermal injury. Studies have evaluated the role and function of the liver during the postburn response and showed that liver integrity and function are essential for survival, and that hepatic acute phase proteins are strong predictors for postburn survival. This review discusses these studies and delineates the pivotal role of the liver in patients following severe thermal injury.

Ghrelin inhibits skeletal muscle protein breakdown in rats with thermal injury through normalizing elevated expression of E3 ubiquitin ligases MuRF1 and MAFbx

We previously determined that ghrelin synthesis was downregulated after burn injury and that exogenous ghrelin retained its ability both to stimulate food intake and to restore plasma growth hormone levels in burned rats. These observations and the finding that anabolic hormones can attenuate skeletal muscle catabolism led us to investigate whether ghrelin could attenuate burn-induced skeletal muscle protein breakdown in rats. These studies were performed in young rats (50-60 g) 24 h after approximately 30% total body surface area burn injury. Burn injury increased total and myofibrillar protein breakdown in extensor digitorum longus (EDL) muscles assessed by in vitro tyrosine and 3-methyl-histidine release, respectively. Continuous 24-h administration of ghrelin (0.2 mg.kg(-1).h(-1)) significantly inhibited both total and myofibrillar protein breakdown in burned rats. Ghrelin significantly attenuated burn-induced changes in mRNA expression of IGFBP-1 and IGFBP-3 in liver. In EDL, ghrelin attenuated the increases in mRNA expression of the binding proteins, but had no significant effect on reduced expression of IGF-I. Ghrelin markedly reduced the elevated mRNA expression of TNF-alpha and IL-6 in EDL muscle that occurred after burn. Moreover, ghrelin normalized plasma glucocorticoid levels, which were elevated after burn. Expression of the muscle-specific ubiquitin-ligating enzyme (E3) ubiquitin ligases MuRF1 and MAFbx were markedly elevated in both EDL and gastrocnemius and were normalized by ghrelin. These results suggest that ghrelin is a powerful anticatabolic compound that reduces skeletal muscle protein breakdown through attenuating multiple burn-induced abnormalities.

Combination of recombinant human growth hormone and propranolol decreases hypermetabolism and inflammation in severely burned children

OBJECTIVE

Recombinant human growth hormone (rhGH) is a salutary modulator of posttraumatic metabolic responses. However, rhGH administration is associated with deleterious side effects, such as hyperglycemia, increased free fatty acids, and triglycerides, which limit its use. Administration of beta-blocker attenuates cardiac work and resting energy expenditure after severe thermal injury and improves fat metabolism and insulin sensitivity. Therefore, the combination of rhGH plus propranolol appears ideal. The aim of the present study was to determine whether rhGH plus propranolol improves hypermetabolism and the inflammatory and acute phase response after severe burn without causing adverse side effects.

DESIGN

Prospective randomized control trial.

SETTING

Shriners Hospitals for Children.

PATIENTS

Fifteen pediatric patients with burns > 40% total body surface area, 0.1-16 yrs of age, admitted within 7 days after burn. Fifteen children were matched for burn size, age, gender, inhalation injury, and infection and served as controls.

INTERVENTIONS

Patients in the experimental group received rhGH (0.2 mg/kg/day) and propranolol (to decrease heart rate by 15%) for > or = 15 days.

MEASUREMENTS AND MAIN RESULTS

Outcome measurements included resting energy expenditure, body composition, acute phase proteins, and cytokines. Both cohorts were similar in age, burn size, gender, and accompanying injuries. Percent predicted resting energy expenditure significantly decreased in patients receiving rhGH/propranolol (Delta -5% +/- 8%) compared with controls (Delta +35% +/- 20%) (p < .05). rhGH/propranolol administration significantly decreased serum C-reactive protein, cortisone, aspartate aminotransferase, alanine aminotransferase, free fatty acids, interleukin-6, interleukin-8, and macrophage inflammatory protein-1beta when compared with controls, while growth hormone/propranolol increased serum insulin-like growth factor-I, insulin-like growth factor binding protein-3, growth hormone, prealbumin, and interleukin-7 when compared with placebo (p < .05).

CONCLUSIONS

rhGH in combination with propranolol attenuates hypermetabolism and inflammation without the adverse side effects found with rhGH therapy alone.

The pharmacologic modulation of the hypermetabolic response to burns

Patients with burns less than 40% TBSA do not have catabolism unless sepsis develops. Those with burns more than 40% TBSA always experience catabolism, which causes metabolic derangements that persist for at least 1 year after the injury in most body tissues. The accomplishments of the past decade have placed us in the midst of an exciting paradigm shift from what used to be a primary concern (ie, mortality) to areas that are more likely to enhance the quality of life of burn survivors. Modulating postburn hypermetabolism for the burned patient is of overwhelming importance in both the immediate care stage and the rehabilitative stage. Postburn hypermetabolism cannot be completely reversed but may be manipulated by nonpharmacologic and pharmacologic means. Early burn wound excision and complete wound closure, prevention of sepsis, the maintenance of thermal neutrality for the patient by elevation of the ambient temperature, and graded resistance exercises during convalescence are simple, highly effective primary treatment goals. Although the initial burn injury and sepsis-related complications principally determine the extent of the metabolic response in burn victims, obligatory activity, background- and procedural-related pain, and anxiety also greatly increase metabolic rates. Judicious maximal narcotic support, appropriate sedation, and supportive psychotherapy are mandatory if their effects are to be minimized. Several anabolic and anticatabolic agents are available for use during immediate care and rehabilitation. Exogenous, continuous low-dose insulin infusion, beta-blockade with propranolol, and the use of the synthetic testosterone analogue oxandrolone are the most cost-effective and least toxic therapies to date. These greatly assist therapeutic minimization of the loss of lean body mass and linear growth delay and are effective in burned patients with and without sepsis. Adverse effects, cost benefits, and the ease of administration and monitoring must be examined when considering the possibility of their use.

Epidermal homeostasis: the role of the growth hormone and insulin-like growth factor systems

GH and IGF-I and -II were first identified by their endocrine activity. Specifically, IGF-I was found to mediate the linear growth-promoting actions of GH. It is now evident that these two growth factor systems also exert widespread activity throughout the body and that their actions are not always interconnected. The literature highlights the importance of the GH and IGF systems in normal skin homeostasis, including dermal/epidermal cross-talk. GH activity, sometimes mediated via IGF-I, is primarily evident in the dermis, particularly affecting collagen synthesis. In contrast, IGF action is an important feature of the dermal and epidermal compartments, predominantly enhancing cell proliferation, survival, and migration. The locally expressed IGF binding proteins play significant and complex roles, primarily via modulation of IGF actions. Disturbances in GH and IGF signaling pathways are implicated in the pathophysiology of several skin perturbations, particularly those exhibiting epidermal hyperplasia (e.g., psoriasis, carcinomas). Additionally, many studies emphasize the potential use of both growth factors in the treatment of skin wounds; for example, burn patients. This overview concerns the role and mechanisms of action of the GH and IGF systems in skin and maintenance of epidermal integrity in both health and disease.

Effect of bombesin on gut mucosal impairment after severe burn

Severe cutaneous bum alters gut epithelial homeostasis. In previous studies, treatment with bombesin decreased mucosal atrophy and improved maintenance of gut mucosal integrity after severe burn. Our current hypothesis is that bombesin reduces burn-induced gut impairment by decreasing gut epithelial cell death. Fifty-four adult male Fisher-344 rats were randomly assigned to three groups: control, sham burn (I), burn (II), and burn + bombesin (III). Animals in groups II and III received a 60% total body surface area full thickness scald burn, and the treatment group (III) received bombesin subcutaneously (10 microg/kg, every 8 h) beginning immediately before the experiment. The proximal small bowel was harvested at 12 and 72 h after burn with measurement of wet and dry weight, mucosal weight, and protein content, and a 1-cm length of proximal end was excised and fixed in fomalin for histological and immunohistochemical observation. Data are expressed as means +/- SEM. Statistical analysis was by done by analysis of variance (significance at P < 0.05). Bombesin treatment attenuated mucosal atrophy demonstrated by restoration of the mucosal weight, mucosal protein content, and maintenance of mucosal height and total mucosal epithelial cell count. Gut epithelial cell apoptosis was, at least in part, inhibited by bombesin compared with a significant increase of gut cell apoptosis at 12 h after burn. Gut epithelial proliferation was not affected. Bombesin diminished burn-induced gut mucosal atrophy and gut epithelial cell apoptosis, suggesting that bombesin treatment may play an important role in the recovery of gut impairment after severe burn.

Recombinant human growth hormone modulates the hepatic acute-phase response and P-selectin in burned rats

The purpose of this study was to determine the effect of recombinant human growth hormone (rhGH) on serum constitutive proteins, cytokines, P-selectin, and insulin-like growth factor (IGF-1) in the thermally injured rats.Sprague-Dawley rats (64 males) were given 30% total body surface area full thickness scald burn. They were randomly divided to receive either 2.5mg/kg per day im rhGH or saline (control). Rats were sacrified on postburn days 1, 2, 5, and 7, and serum constitutive proteins, cytokines, P-selectin, and IGF-1 levels were measured.Serum IGF-1 levels were increased on days 2, 5, or 7 after burn in rhGH-treated rats compared with controls (P<0.001, <0.01 and <0.001, respectively). Serum transferrin and albumin levels were increased on days 7 after burn in rhGH-treated rats compared with controls (P<0.05). The cytokines increased after thermal injury. The rhGH decreased serum levels of tumor necrosis factor-alpha on postburn days 1 compared with controls (P<0.001). Serum levels of interleukin-1 were decreased on days 1 and 2 after burn in rhGH treated rats compared with controls (P<0.001, <0.01, respectively). Rats receiving rhGH showed significantly increased P-selectin levels at 5 and 7 postburn days compared with controls (P<0.001). Our data indicate that rhGH, given after thermal injury, increased albumin, transferrin, IGF-1, and P-selectin levels and decreased serum tumor necrosis factor-alpha and interleukin-1 levels.

Inhibition of growth hormone action in models of inflammation

Growth hormone (GH) action is attenuated during the hepatic acute-phase response (APR). To understand this attenuation, we asked whether GH and cytokine-signaling pathways intersect during an APR. In hypophysectomized rats treated with lipopolysaccharide (LPS), accumulation of activated signal transducer and transcription activator 5 (Stat5) in hepatic nuclei in response to GH and its binding to a GH response element (GHRE) from the serine protease inhibitor (Spi) 2.1 promoter are diminished in a time-dependent manner. Similarly, accumulation of activated Stat3 in hepatic nuclei in response to LPS and its binding to a high-affinity sis-inducible element (SIE) are also diminished by the simultaneous administration of GH. In functional assays with primary hepatocytes, LPS-stimulated monocyte-conditioned medium (MoCM) inhibits the GH response of Stat5-dependent Spi 2.1 reporter activity but induces Stat3-dependent Spi 2.2 reporter activity, as in an APR. Similar results are obtained when hepatocytes are treated with either tumor necrosis factor-alpha (TNF-alpha) or interleukin (IL)-1beta. TNF-alpha, IL-1beta, and IL-6 also inhibit GH-induced Spi 2.1 mRNA expression in hepatocytes. Thus inhibition of the GH signaling pathway during an APR results in reduced expression of GH-responsive genes.

Skeletal muscle apoptosis after burns is associated with activation of proapoptotic signals

Critical illness is associated with muscle wasting and muscle weakness. Using burn injury as a model of local and systemic inflammatory response, we tested the hypothesis that thermal injury causes apoptosis in muscle. After a 40% body surface area burn to rats, abdominal muscles beneath the burn and limb muscles distant from the burn were examined for apoptosis at varying times after burn. Ladder assay, ELISA, and histological methods showed evidence of apoptosis in the abdominal muscles within 4-12 h with peak changes occurring at 3-7 days. Maximal apoptosis was also evident at distant limb muscles at 3-7 days. Investigation of proapoptotic pathways indicated mitochondrial membrane potential to be altered by 1 h after burn. Starting at 15 min after burn, cytochrome c was released from the mitochondria into the cytosol, followed by increased activity of caspase-3, starting at 6 h after burn. These studies suggest that mitochondria and caspase-mediated apoptotic pathways may be an additional mechanism of muscle weight loss in burns and may be potential therapeutic targets for prevention of muscle wasting.

Ontogeny of insulin-like growth factor 1 in a rabbit model of growth retardation

Many cases of intrauterine growth retardation (IUGR) result from placental insufficiency, but the molecular signals accompanying this event are unknown. Insulin-like growth factor 1 (IGF-1) is a potent mitogen for fetal tissues and is lowered in the serum of human infants with IUGR. The rabbit provides an optimal model for the study of IUGR based on fetal position. To determine if IGF-1 expression is altered in the growth-retarded fetus, this naturally occurring rabbit model of IUGR was used. Four fetal rabbit pairs were harvested on Days 21, 23, 25, 27, 29, and 31 of their normal 31-day gestation; they were identified based on uterine position as normal or growth retarded. Fetal weight was recorded and the serum, amniotic fluid, liver, kidney, and small intestine (SI) were collected. The SI was divided into three equal segments: proximal, middle, and distal. Reverse transcription polymerase chain reaction (RT-PCR) was used to measure IGF-1/beta-actin mRNA densitometric band ratios in all tissues. Radioimmunoassay (RIA) was used to measure IGF-1 protein levels in the serum and amniotic fluid. Statistical analysis was performed using ANOVA and the paired Student's t test. Weights were decreased in fetuses with IUGR at all time points (P < 0.05), further validating this rabbit model in the study of IUGR. Liver, proximal, and distal SI IGF-1 mRNA decreased during late gestation (P < 0.01). Kidney IGF-1 mRNA increased throughout late gestation (P < 0.01). Compared with their normal counterparts, fetuses with IUGR had a trend toward decreased IGF-1 mRNA in the kidney, liver, and SI at all time points, reaching significance in the liver on Day 27 (P = 0.002). Serum IGF-1 decreased throughout gestation in all fetuses (P < 0.05). Compared with normal fetuses, fetuses with IUGR had lower serum IGF-1 at all time points, reaching significance at Day 27 (P = 0.02). Amniotic fluid IGF-1 was lower in fetuses with IUGR than in normal fetuses, though not quite reaching significance. Compared with normal fetuses, growth-retarded fetal rabbits trend toward depressed liver, kidney, and intestinal expression of IGF-1 mRNA and lower serum and amniotic fluid IGF-1 protein. Serum IGF-1 levels correlate with fetal weight change. Further studies and potential manipulation of fetal IGF-1 are warranted to investigate potential prenatal intervention in the treatment of IUGR.

Acute response of IGF-I and IGF binding proteins induced by thermal injury

Previous studies demonstrate that thermal injury decreases circulating levels of insulin growth factor I (IGF-I) and alters the plasma concentration of several IGF binding proteins (IGFBP), but the mechanisms for these alterations have not been elucidated. In the current study, a 30% total body surface area full-thickness scald burn was produced in anesthetized rats, and animals were studied 24 h later. The plasma concentration of both total and free IGF-I was decreased (38 and 65%, respectively) in burn rats compared with values from time-matched control animals. Thermal injury decreased the IGF-I peptide content in liver approximately 40%, as well as in fast-twitch skeletal muscle (56-69%) and heart (28%). In contrast, IGF-I content in kidney was elevated by 36% in burn rats. Northern blot analysis of liver indicated that burn decreased the expression of small (1.7- and 0.9- to 1.2-kb) IGF-I mRNA transcripts but increased the expression of the 7.5-kb transcript. In contrast, there was a coordinate decrease in all IGF-I mRNA transcripts in muscle and kidney of approximately 30%. For liver, muscle, and kidney, there was no significant difference in the expression of growth hormone receptor mRNA between control and burn rats. Thermal injury increased plasma IGFBP-1 levels, and this change was associated with increased IGFBP-1 mRNA in both liver and kidney. IGFBP-3 levels in plasma were concomitantly decreased by burn injury. This change was associated with a reduction in IGFBP-3 mRNA in liver but an increased expression of IGFBP-3 in kidney and muscle. Thermal injury also decreased the concentration of the acid-labile subunit (ALS) in plasma and ALS mRNA expression in liver. Finally, hepatic expression of IGFBP-related peptide-1 was increased twofold in liver but was unchanged in kidney or muscle of burn rats. These results characterize burn-induced changes in various components of the IGF system in select tissues and thereby provide potential mechanisms for alterations in the circulating IGF system and for changes in tissue metabolism.