Circulating insulin-like growth factors (IGFs), IGF-binding proteins (IGFBPs) and tissue mRNA levels of IGFBP-2 and IGFBP-4 in the ovine fetus

Increasing the Understanding of Nutrient Transport Capacity of the Ovine Placentome

Placental nutrient transport capacity influences fetal growth and development; however, it is affected by environmental factors, which are poorly understood. The objective of this study was to understand the impact of the ovine placentome morphological subtype, tissue type, and maternal parenteral supplementation of arginine mono-hydrochloride (Arg) on nutrient transport capacity using a gene expression approach. Placentomal tissues of types A, B, and C morphologic placentome subtypes were derived from 20 twin-bearing ewes, which were infused thrice daily with Arg (n = 9) or saline (Ctrl, n = 11) from 100 to 140 days of gestation. Samples were collected at day 140 of gestation. Expression of 31 genes involved in placental nutrient transport and function was investigated. Differential expression of specific amino acid transporter genes was found in the subtypes, suggesting a potential adaptive response to increase the transport capacity. Placentomal tissues differed in gene expression, highlighting differential transport capacity. Supplementation with Arg was associated with differential expressions of genes involved in amino acid transport and angiogenesis, suggesting a greater nutrient transport capacity. Collectively, these results indicate that the morphological subtype, tissue type, and maternal Arg supplementation can influence placental gene expression, which may be an adaptive response to alter the transport capacity to support fetal growth in sheep.

Asymmetric growth-limiting development of the female conceptus

Introduction

Sex differences in prenatal growth may contribute to sex-dependent programming effects on postnatal phenotype.

Methods

We integrated for the first time phenotypic, histomorphological, clinico-chemical, endocrine and gene expression analyses in a single species, the bovine conceptus at mid-gestation.

Results

We demonstrate that by mid-gestation, before the onset of accelerated growth, the female conceptus displays asymmetric lower growth compared to males. Female fetuses were smaller with lower ponderal index and organ weights than males. However, their brain:body weight, brain:liver weight and heart:body weight ratios were higher than in males, indicating brain and heart 'sparing'. The female placenta weighed less and had lower volumes of trophoblast and fetal connective tissue than the male placenta. Female umbilical cord vessel diameters were smaller, and female-specific relationships of body weight and brain:liver weight ratios with cord vessel diameters indicated that the umbilico-placental vascular system creates a growth-limiting environment where blood flow is redistributed to protect brain and heart growth. Clinico-chemical indicators of liver perfusion support this female-specific growth-limiting phenotype, while lower insulin-like growth factor 2 (IGF2) gene expression in brain and heart, and lower circulating IGF2, implicate female-specific modulation of key endocrine mediators by nutrient supply.

Conclusion

This mode of female development may increase resilience to environmental perturbations in utero and contribute to sex-bias in programming outcomes including susceptibility to non-communicable diseases.

Ruminant Placental Adaptation in Early Maternal Undernutrition: An Overview

Correct placental development during early gestation is considered the main determinant of fetal growth in late pregnancy. A reduction in maternal nourishment occurring across the early developmental window has been linked to a wide range of pregnancy disorders affecting placental transport capacity and consequently the fetal nutrient supply line, with long-term implications for offspring health and productivity. In livestock, ruminant species specifically experience maternal undernutrition in extensive systems due to seasonal changes in food availability, with significant economic losses for the farmer in some situations. In this review, we aim to discuss the effects of reduced maternal nutrition during early pregnancy on placental development with a specific focus on ruminant placenta physiology. Different types of placental adaptation strategies were examined, also considering the potential effects on the epigenetic landscape, which is known to undergo extensive reprogramming during early mammalian development. We also discussed the involvement of autophagy as a cellular degradation mechanism that may play a key role in the placental response to nutrient deficiency mediated by mammalian target of rapamycin, named the mTOR intracellular pathway.

Components of the insulin-like growth factor system in in vivo - and in vitro-derived fetuses of cattle, and the association with growth and development

This experiment was designed to study mechanisms affecting growth of in vivo-derived (IVD) and in vitro-produced (IVP) fetuses of cattle. Day-7 IVD or IVP cattle blastocysts were transferred to recipients, with pregnant females being slaughtered on Days 90 or 180 of gestation or allowed to undergo parturition. Uteri and contents were dissected and physically measured, and maternal and fetal plasma and amniotic and allantoic fluids were collected for IGF-1 and IGF-2 determinations, and IGFBP profile characterization. Transcripts for IGF-1 and IGF-2 mRNA in placental and fetal tissues, and IGF-1r and IGF-2r in placentomes were determined. There was a greater fetal weight in the IVP group, which was associated with greater IGF-1 and IGF-2 concentrations in maternal circulation, and changes in IGFBP profiles within fetal fluids. Day-90 IVP-derived fetuses were longer, had greater organ weights, larger placentomes, less placentome IGF-2r mRNA transcript, and greater maternal IGF-1 and IGF-2 concentrations than controls. On Day 180 and at parturition tissues from IVP-derived fetuses/calves were from larger uteri, with larger placentomes/fetal membranes, fetuses/calves weighed more, had greater fetal hepatic IGF-2 mRNA transcript, had less fetal plasma IGF-1 and greater allantoic IGF-2 concentrations, greater and lesser IGFBP activities in the allantoic and amniotic fluids, respectively, and greater glucose and fructose accumulation in fetal fluids. Components of the IGF system were differentially regulated not only according to the gestation period (Days 90 or 180) and fluid type (maternal or fetal plasma, amniotic or allantoic fluids), but also based on conceptus origin (IVP or IVD) in cattle.

The tammar wallaby: a non-traditional animal model to study growth axis maturation

Maturation of the growth hormone (GH)/insulin-like growth factor 1 (IGF1) axis is a critical developmental event that becomes functional over the peripartum period in precocial eutherian mammals such as sheep. In mice and marsupials that give birth to altricial young, the GH/IGF1 axis matures well after birth, suggesting that functional maturation is associated with developmental stage, not parturition. Recent foster-forward studies in one marsupial, the tammar wallaby (Macropus eugenii), have corroborated this hypothesis. 'Fostering' tammar young not only markedly accelerates their development and growth rates, but also affects the timing of maturation of the growth axis compared with normal growing young, providing a novel non-traditional animal model for nutritional manipulation. This review discusses how nutrition affects the maturation of the growth axis in marsupials compared with traditional eutherian animal models.

Atlas of tissue- and developmental stage specific gene expression for the bovine insulin-like growth factor (IGF) system

The insulin-like growth factor (IGF) axis is fundamental for mammalian growth and development. However, no comprehensive reference data on gene expression across tissues and pre- and postnatal developmental stages are available for any given species. Here we provide systematic promoter- and splice variant specific information on expression of IGF system components in embryonic (Day 48), fetal (Day 153), term (Day 277, placenta) and juvenile (Day 365–396) tissues of domestic cow, a major agricultural species and biomedical model. Analysis of spatiotemporal changes in expression of IGF1, IGF2, IGF1R, IGF2R, IGFBP1-8 and IR genes, as well as lncRNAs H19 and AIRN, by qPCR, indicated an overall increase in expression from embryo to fetal stage, and decrease in expression from fetal to juvenile stage. The stronger decrease in expression of lncRNAs (average ―16-fold) and ligands (average ―12.1-fold) compared to receptors (average ―5.7-fold) and binding proteins (average ―4.3-fold) is consistent with known functions of IGF peptides and supports important roles of lncRNAs in prenatal development. Pronounced overall reduction in postnatal expression of IGF system components in lung (―12.9-fold) and kidney (―13.2-fold) are signatures of major changes in organ function while more similar hepatic expression levels (―2.2-fold) are evidence of the endocrine rather than autocrine/paracrine role of IGFs in postnatal growth regulation. Despite its rapid growth, placenta displayed a more stable expression pattern than other organs during prenatal development. Quantitative analyses of contributions of promoters P0-P4 to global IGF2 transcript in fetal tissues revealed that P4 accounted for the bulk of transcript in all tissues but skeletal muscle. Demonstration of IGF2 expression in fetal muscle and postnatal liver from a promoter orthologous to mouse and human promoter P0 provides further evidence for an evolutionary and developmental shift from placenta-specific P0-expression in rodents and suggests that some aspects of bovine IGF expression may be closer to human than mouse.

A Novel igf3 Gene in Common Carp (Cyprinus carpio): Evidence for Its Role in Regulating Gonadal Development

Since the insulin-like growth factor 3 (igf3) gene was recently discovered in fish ovary, its function in the gonads has received much attention. In this study, we isolated two igf3 subtypes from common carp (Cyprinus carpio), which comprised full-length cDNA of 707 and 1153 nucleotides encoding 205 and 198 amino acids (aa), respectively. The Igf3 aa sequence had the highest gene homology of 72% with the corresponding sequence in zebrafish (Danio rerio). Phylogenetic tree construction revealed that the C. carpio igf3 gene was first clustered with D. rerio and then with other teleost species. Igf3 mRNA was widely expressed, with expression being highest in the gonads and blood. In the gonad development stage, igf3a mRNA expression was highest in the maturity and recession stage of the ovary, and decline phase of the testis, while igf3b was highest in the recession and fully mature periods of the ovaries and testes, respectively. Western blotting of testis protein samples showed two bands of approximately 21 kDa and 34 kDa corresponding to the calculated molecular mass of the two Igf3 subtypes; no signal was detected in the ovary. The Igf3 protein was localized in the ovary granulosa cells and testis spermatogonium and spermatids. 17β-Ethinylestradiol treatment increased both ovary and testis igf3 mRNA expression. These findings suggest that Igf3 may play an important role in C. carpio gonadal development.

Endocrine and other physiologic modulators of perinatal cardiomyocyte endowment

Immature contractile cardiomyocytes proliferate to rapidly increase cell number, establishing cardiomyocyte endowment in the perinatal period. Developmental changes in cellular maturation, size and attrition further contribute to cardiac anatomy. These physiological processes occur concomitant with a changing hormonal environment as the fetus prepares itself for the transition to extrauterine life. There are complex interactions between endocrine, hemodynamic and nutritional regulators of cardiac development. Birth has been long assumed to be the trigger for major differences between the fetal and postnatal cardiomyocyte growth patterns, but investigations in normally growing sheep and rodents suggest this may not be entirely true; in sheep, these differences are initiated before birth, while in rodents they occur after birth. The aim of this review is to draw together our understanding of the temporal regulation of these signals and cardiomyocyte responses relative to birth. Further, we consider how these dynamics are altered in stressed and suboptimal intrauterine environments.

Circulating IGF1 and IGF2 and SNP genotypes in men and pregnant and non-pregnant women

Circulating IGFs are important regulators of prenatal and postnatal growth, and of metabolism and pregnancy, and change with sex, age and pregnancy. Single-nucleotide polymorphisms (SNPs) in genes coding for these hormones associate with circulating abundance of IGF1 and IGF2 in non-pregnant adults and children, but whether this occurs in pregnancy is unknown. We therefore investigated associations of plasma IGF1 and IGF2 with age and genotype at candidate SNPs previously associated with circulating IGF1, IGF2 or methylation of the INS-IGF2-H19 locus in men (n=134), non-pregnant women (n=74) and women at 15 weeks of gestation (n=98). Plasma IGF1 concentrations decreased with age (P<0.001) and plasma IGF1 and IGF2 concentrations were lower in pregnant women than in non-pregnant women or men (each P<0.001). SNP genotypes in the INS-IGF2-H19 locus were associated with plasma IGF1 (IGF2 rs680, IGF2 rs1004446 and IGF2 rs3741204) and IGF2 (IGF2 rs1004446, IGF2 rs3741204 and H19 rs217727). In single SNP models, effects of IGF2 rs680 were similar between groups, with higher plasma IGF1 concentrations in individuals with the GG genotype when compared with GA (P=0.016), or combined GA and AA genotypes (P=0.003). SNPs in the IGF2 gene associated with IGF1 or IGF2 were in linkage disequilibrium, hence these associations could reflect other genotype variations within this region or be due to changes in INS-IGF2-H19 methylation previously associated with some of these variants. As IGF1 in early pregnancy promotes placental differentiation and function, lower IGF1 concentrations in pregnant women carrying IGF2 rs680 A alleles may affect placental development and/or risk of pregnancy complications.

Loss of the pregnancy-induced rise in cortisol concentrations in the ewe impairs the fetal insulin-like growth factor axis

Maternal cortisol levels increase during pregnancy. Although this change is important for optimal fetal growth, the mechanisms of the changes in growth remain unclear. The hypothesis examined was that alterations in maternal plasma cortisol concentrations are associated with changes in the fetal insulin-like growth factor (IGF) axis. Pregnant ewes in late gestation (115 ± 0.4 days) were studied: six control animals, five ewes given 1 mg kg(-1) day(-1) cortisol (high cortisol) and five adrenalectomised ewes given 0.5-0.6 mg kg(-1) day(-1) cortisol (low cortisol). Blood samples were taken throughout the experiment and at necropsy (130 ± 0.2 days) and fetal liver was frozen for mRNA analysis. Fetal IGF-I and insulin plasma concentrations were lower and insulin-like growth factor-binding protein-1 (IGFBP-1) concentrations were higher in the low cortisol group compared with those in the control group (P < 0.05). Fetal liver IGF-II and IGFBP-3 mRNA were decreased in low cortisol animals compared with controls (P < 0.05). There were no significant changes in these parameters in the high cortisol group, and there were no changes in fetal liver IGF-I, growth hormone receptor, IGF-I receptor, IGF-II receptor, IGFBP-1 or IGFBP-2 mRNA levels between the groups. These data suggest that reduced fetal IGF availability contributes to reduced fetal growth when maternal cortisol secretion is impaired, but not during exposure to moderate increases in cortisol.

Heifer nutrient intake during early- and mid-gestation programs adult offspring adiposity and mRNA expression of growth-related genes in adipose depots

Changes in maternal nutrient intake during gestation alter IGF receptor abundance and leptin (LEP) mRNA expression in fetal adipose tissue. It is not known whether such changes persist into adult life and whether they are associated with an effect on phenotype. We investigated the effect of high (240%) and low (70%) levels of recommended daily crude protein intake for beef heifers during the first and second trimesters of gestation on singleton progeny (n=68): subcutaneous (SC) adipose tissue depth at rump (P8) and rib (RF) sites from 65 until 657 days of age; plasma leptin concentrations from birth until 657 days and expression of IGF1 and IGF2, their receptors (IGF1R and IGF2R) and LEP mRNA in perirenal (PR), omental (OM) and SC adipose tissue at 680 days of age. High-protein diets during the first trimester increased LEP and IGF1 mRNA in PR of males and females, respectively, compared with low-protein diets, and decreased IGF1R mRNA in SC of all progeny but increased RF depth of males between 552 and 657 days. High-protein diets compared with low-protein diets during the second trimester increased IGF1R mRNA in PR and OM of all progeny; LEP mRNA in PR of males; and IGF2 and IGF2R mRNA in OM of all progeny. Conversely, LEP mRNA in OM and IGF2 mRNA in PR of all progeny were decreased following exposure to high- compared with low-protein diets during the second trimester. Heifer diet during gestation has permanent sex- and depot-specific effects on the expression of adipogenic and adipocytokine genes and offspring adiposity.

Protein intake during gestation affects postnatal bovine skeletal muscle growth and relative expression of IGF1, IGF1R, IGF2 and IGF2R

Expression of insulin-like growth factor (IGF)1 and IGF2 and their receptor (IGF1R and IGF2R) mRNA in fetal skeletal muscle are changed by variations in maternal nutrient intake. The persistence of these effects into postnatal life and their association with phenotype in beef cattle is unknown. Here we report that the cross-sectional areas of longissimus dorsi and semitendinosus (ST) muscles were greater for mature male progeny born to heifers fed low protein diets (70% vs. 240% of recommended) during the first trimester. In ST, this was accompanied by greater IGF1, IGF2 and IGF2R mRNA at 680 d. Females exposed to low protein diets during the first trimester had decreased IGF2 mRNA in ST at 680 d, however this did not result in an effect to phenotype. Exposure to low protein diets during the second trimester increased IGF1R mRNA in ST of all progeny at 680 d. Changes to expression of IGF genes in progeny skeletal muscle resulting from variations to maternal protein intake during gestation may have permanent and sex-specific effect on postnatal skeletal muscle growth.

Repeated betamethasone treatment of pregnant sheep programs persistent reductions in circulating IGF-I and IGF-binding proteins in progeny

Exposure to synthetic glucocorticoids in utero markedly improves survival after preterm birth, but repeated exposures impair fetal and postnatal growth and are associated with evidence of insulin resistance in later life. The insulin-like growth factor (IGF) axis is an important regulator of growth and metabolism before and after birth. We have therefore investigated the effects of repeated maternal betamethasone injections on plasma IGF-I, IGF-II, and IGF-binding proteins (IGFBP) in fetal and postnatal progeny in the sheep. Pregnant sheep carrying male fetuses were injected with saline or betamethasone at 104, 111, and 118 days of gestation (dG, term approximately 150 dG). Plasma samples were collected postmortem from fetuses before (75, 84, 101 dG) or after one (109 dG), two (116 dG), or three (121-122, 132-133, 145-147 dG) doses of saline or betamethasone and from progeny at 42 and 84 days of age. Fetal weight was reduced after two or more maternal betamethasone injections, and this effect persisted to term. Repeated betamethasone exposures reduced plasma IGF-I and total IGFBP in fetuses at 133 dG and progeny at 84 days, and reduced plasma IGFBP-3 at 84 days. Fetal plasma IGF-II tended to increase transiently at 109 dG following the first betamethasone injection. Fetal, placental, and/or postnatal weights correlated positively with concomitant plasma IGF-I, IGF-II, and total IGFBP. We conclude that repeated exposure to synthetic glucocorticoids in utero programs the IGF axis before and after birth, which may contribute to the adverse effects of betamethasone exposure on growth and metabolism.

Placental restriction of fetal growth decreases IGF1 and leptin mRNA expression in the perirenal adipose tissue of late gestation fetal sheep

Placental restriction (PR) of fetal growth results in a low birth weight and an increased visceral fat mass in postnatal life. We investigated whether PR alters expression of genes that regulate adipogenesis [IGF1, IGF1 receptor (IGF1R), IGF2, IGF2R, proliferator-activated receptor-γ, retinoid-X-receptor-α], adipocyte metabolism (lipoprotein lipase, G3PDH, GAPDH) and adipokine signaling (leptin, adiponectin) in visceral adipose tissue before birth. PR was induced by removal of the majority of endometrial caruncles in nonpregnant ewes before mating. Fetal blood samples were collected from 116 days gestation, and perirenal visceral adipose tissue (PAT) was collected from PR and control fetuses at 145 days. PAT gene expression was measured by quantitative RT-PCR. PR fetuses had a lower weight (PR 2.90 ± 0.32 kg; control, 5.12 ± 0.24 kg; P < 0.0001), mean gestational arterial Po2 ( P < 0.0001), plasma glucose ( P < 0.01), and insulin concentrations ( P < 0.02), than controls. The expression of IGF1 mRNA in PAT was lower in the PR fetuses (PR, 0.332 ± 0.063; control, 0.741 ± 0.083; P < 0.01). Leptin mRNA expression in PAT was also lower in PR fetuses (PR, 0.077 ± 0.009; control, 0.115 ± 0.013; P < 0.05), although there was no difference in the expression of other adipokine or adipogenic genes in PAT between PR and control fetuses. Thus, restriction of placental and hence, fetal substrate supply results in decreased IGF1 and leptin expression in fetal visceral adipose tissue, which may alter the functional development of the perirenal fat depot and contribute to altered leptin signaling in the growth-restricted newborn and the subsequent emergence of an increased visceral adiposity.

The kidney is resistant to chronic hypoglycaemia in late-gestation fetal sheep

We imposed a sustained reduction in glucose supply to late-gestation fetal sheep to see whether the reduction in glucose and insulin levels affected renal growth, renin expression and synthesis, and renal function. Maternal glucose concentrations were lowered to 1.7-1.9 mmol/L for 12-13 days by i.v. insulin infusion (n = 9, 121 days gestation, term = 150 days). Control ewes (n = 7) received vehicle. Maternal and fetal glucose concentrations were 40% and 31% lower than in controls (p < 0.001), respectively. Fetal plasma insulin levels fell 36% +/- 7% by day 7 (p < 0.05); IGF-I levels were unchanged. Arterial PO2 and pH increased and PCO2 fell (p < 0.05). Renal function was largely unaffected. Longitudinal growth was 28% slower and spleen weights were 36% smaller (p < 0.05); body and kidney weights were not affected. Renal renin levels and renin, angiotensinogen, and angiotensin receptor mRNA levels were similar to those of controls. Plasma renin levels increased from 2.1 +/- 0.6 to 7.6 +/- 2.8 ng angiotensin I.mL-1.h-1 (p = 0.01). Thus reductions in fetal glucose and insulin levels in late gestation that were sufficient to retard skeletal growth had no effect on kidney growth or function or the renal renin-angiotensin system, possibly because IGF-I levels were not reduced. There was, however, increased activity of the circulating renin-angiotensin system similar to that seen during insulin-induced hypoglycaemia.

Dermal fibroblasts derived from fetal and postnatal humans exhibit distinct responses to insulin like growth factors

Background

It has been well established that human fetuses will heal cutaneous wounds with perfect regeneration. Insulin-like growth factors are pro-fibrotic fibroblast mitogens that have important roles in both adult wound healing and during development, although their relative contribution towards fetal wound healing is currently unknown. We have compared responses to IGF-I and -II in human dermal fibroblast strains derived from early gestational age fetal (<14 weeks) and developmentally mature postnatal skin to identify any differences that might relate to their respective wound healing responses of regeneration or fibrosis.

Results

We have established that the mitogenic response of fetal cells to both IGF-I and -II is much lower than that seen in postnatal dermal fibroblasts. Further, unlike postnatal cells, fetal cells fail to synthesise collagen in response to IGF-I, whereas they do increase synthesis in response to IGF-II. This apparent developmentally regulated difference in response to these related growth factors is also reflected in changes in the tyrosine phosphorylation pattern of a number of proteins. Postnatal cells exhibit a significant increase in phosphorylation of ERK 1 (p44) in response to IGF-I and conversely the p46 isoform of Shc on IGF-II stimulation. Fetal cells however only show a significant increase in an unidentified 100 kDa tyrosine-phosphorylated protein on stimulation with IGF-II.

Conclusion

Dermal fibroblasts exhibit different responses to the two forms of IGF depending on their developmental maturity. This may relate to the developmental transition in cutaneous wound healing from regeneration to fibrosis.

Intrafetal insulin-like growth factor-I infusion stimulates adrenal growth but not steroidogenesis in the sheep fetus during late gestation

We investigated the effects of an intrafetal infusion of IGF-I on adrenal growth and expression of the adrenal steroidogenic and catecholamine-synthetic enzyme mRNAs in the sheep fetus during late gestation. Fetal sheep were infused for 10 d with either IGF-I (26 microg/kg.h; n = 14) or saline (n = 10) between 120 and 130 d gestation, and adrenal glands were collected for morphological analysis and determination of the mRNA expression of steroidogenic and catecholamine-synthetic enzymes. Fetal body weight was not altered by IGF-I infusion; however, adrenal weight was significantly increased by 145% after IGF-I infusion. The density of cell nuclei within the fetal adrenal cortex (the zona glomerulosa and zona fasciculata), and within the adrenaline synthesizing zone of the adrenal medulla, was significantly less in the IGF-I-infused fetuses compared with the saline-infused group. Thus, based on cell-density measurements, there was a significant increase in cell size in the zona glomerulosa and zona fasciculata of the adrenal cortex and in the adrenaline-synthesizing zone of the adrenal medulla. There was no effect of IGF-I infusion on the adrenal mRNA expression of the steroidogenic or catecholamine-synthetic enzymes or on fetal plasma cortisol concentrations. In summary, infusion of IGF-I in late gestation resulted in a marked hypertrophy of the steroidogenic and adrenaline-containing cells of the fetal adrenal in the absence of changes in the mRNA levels of adrenal steroidogenic or catecholamine-synthetic enzymes or in fetal plasma cortisol concentrations. Thus, IGF-I infusion results in a dissociation of adrenal growth and function during late gestation.

Insulin-like growth factor-I and analogues increase growth in artificially-reared neonatal pigs

Exogenous insulin-like growth factor (IGF)-I has been shown to increase growth rate in neonatal pigs while an analogue of IGF-I, long arginine (LR3) IGF-I, has been shown to be more potent than IGF-I in the rat. Therefore, two studies were conducted to determine whether IGF-I and LR3IGF-I increase growth in the artificially-reared neonatal pig. Expt 1 involved forty-two (2 kg initial weight) pigs infused with either control, IGF-I (2, 4 or 8 μg/h) or LR3IGF-I (2, 4 or 8 μg/h) infusions for 8 d. Pigs were weighed and then offered 1·7 MJ (gross energy) milk replacer/kg0·75 per d. Expt 2 involved eighteen pigs (2 kg initial weight) treated with control saline, IGF-I (8 μg/h) or LR3IGF-I (8 μg/h) infusions. After 9 d an additional pump was inserted to increase the infusion rates of each of the growth factors (16 μg/h) for a further 9 d. Cows' milk was provided ad libitum. In Expt 1 there was no overall effect of growth factors on daily weight gain or slaughter weight. However, milk intake was greater in pigs infused with growth factors (909 v. 867 g/d, P=0·027), with an apparently greater milk intake by the pigs infused with IGF-I compared with LR3IGF-I (920 v. 898 g/d, P=0·12). Infusion of LR3IGF-I decreased plasma IGF-I concentrations, but had no effect on plasma IGF-II concentrations. In Expt 2, neither IGF-I nor LR3IGF-I infusion had any effect upon daily weight gain over the first 9 d of the study. However, over the second 9 d of the study, daily weight gain was increased in LR3IGF-I-infused pigs (457 v. 386 g/d, P<0·01), but not in pigs infused with IGF-I (413 v. 386 g/d, P=0·15). Milk intake was not different during the first 9 d of the study but was significantly greater in pigs infused with growth factors over the second half of the study (3407 v. 2905 g/d, P<0·01). Plasma IGF-binding protein-3 concentrations were highly correlated (R=0·85) with average daily gain over the 3 d preceding blood sampling. In conclusion, exogenous IGF-I and particularly LR3IGF-I can increase growth rate and milk intake in artificially-reared pigs fed ad libitum but not in limit-fed piglets.

Effects of sow nutrition on maternal and foetal serum growth factors and on foetal myogenesis

The objective of this study was to examine the effect of increased maternal nutrition in early to mid gestation on changes in serum growth factors of the sow and foetuses. Furthermore, the effect of the foetal sera on in vitro proliferation and differentiation of porcine primary myoblasts was examined. Pregnant sows were either given food either in accordance to requirements (2 kg/day; C) until day 50 or 70 of gestation or given food in accordance to requirements until day 25 and then ad libitum (A) until day 50 or 70. Sows were slaughtered at the Institute's veterinary controlled slaughterhouse at day 50 or 70, respectively. Serum from sows and pools of cord-blood serum from each litter were analysed for glucose, lactate, insulin, insulin-like growth factor (IGF; IGF-1 and -2) and IGF binding proteins (IGFBPs). IGF-1 (P < 0·001) was higher in A compared with C sows, and a 28-kDa IGFBP (P < 0·05) and a 24-kDa IGFBP (P < 0·05) was higher in serum from day 70 compared with day 50 sows. There was no significant effect of food intake on growth factor concentrations in foetal serum or on serum-induced proliferation and differentiation of myoblasts. A 28 kDa IGFBP, IGFBP-2 and -3 were all higher (P < 0·06) and serum-induced proliferation (P < 0·001) and differentiation (P < 0·1) lower at day 70 than day 50. Maternal food intake did not influence the DNA and RNA concentrations and the CPK activity in the foetal longissimus dorsi muscle. The glucose concentration in the liver was higher in C than A foetuses at day 70 of gestation, but not at day 50.

In conclusion, no significant effects of maternal nutrition were found on serum growth factor concentrations in the foetuses or on serum-induced proliferation and differentiation of primary myoblasts.

Acute ethanol exposure in pregnancy alters the insulin-like growth factor axis of fetal and maternal sheep

Maternal ethanol intake during pregnancy impairs fetal growth, but mechanisms are not clearly defined. Reduced IGF abundance or bioavailability in the fetus and/or mother may contribute to this growth restriction. We hypothesized that an episode of acute ethanol exposure, mimicking binge drinking would restrict fetal growth and perturb the maternal and fetal IGF axes. Pregnant sheep were infused intravenously with saline or ethanol (1 g/kg maternal wt) over 1 h, on days 116, 117, and 118 of gestation (start of 1st infusion = time 0, term is 147 days). Maternal and fetal plasma IGF and IGF-binding protein (IGFBP) concentrations were measured before and after each infusion. Compared with controls, ethanol exposure reduced fetal weight at day 120 by 19%, transiently reduced maternal plasma IGF-I (-35%) at 30 h, and decreased fetal plasma IGF-II (-28%) from 24 to 54 h after the first infusion. Ethanol exposure did not alter maternal or fetal plasma concentrations of IGFBP-2 and IGFBP-3, measured by Western ligand blotting. We conclude that suppression of maternal and fetal IGF abundance may contribute to fetal growth restriction induced by acute or binge ethanol exposure.

Altered placental and fetal expression of IGFs and IGF-binding proteins associated with intrauterine growth restriction in fetal sheep during early and mid-pregnancy

The insulin-like growth factors (IGFs) are postulated to be altered in association with the development of intrauterine growth restriction (IUGR). The present studies examined placental and fetal hepatic mRNA concentration of components of the IGF system at two time points (55 and 90 d gestational age, dGA; Term 147 dGA) in a hyperthermia (HT)-induced sheep model of placental insufficiency-IUGR. Maternal plasma insulin and IGF-I were constant at 55 and 90 dGA and were unaffected by treatment. Umbilical vein insulin concentrations tended to be reduced at 90 dGA following HT exposure. Caruncle IGF-I mRNA was increased at 90 dGA in HT placentae (p < 0.05), while cotyledon concentrations were constant over gestation and unaltered by treatment. In control cotyledons, IGF-II mRNA concentration increased (p < 0.01) and IGFBP-3 decreased between 55 and 90 dGA (p < 0.01). Cotyledon IGF-II and caruncle IGFBP-4 mRNA were elevated at 55 dGA in HT placentae compared with control (p < 0.01 and p < 0.05 respectively). Fetal hepatic IGF-I, IGFBP-2, -3 and -4 concentrations rose over gestation (p < 0.05), but there were no treatment effects. These data suggest that changes in placental IGF expression in early and mid gestation may predispose the pregnancy to placental insufficiency, resulting in inadequate substrate supply to the developing fetus later in gestation.

Maternal insulin-like growth factors-I and -II act via different pathways to promote fetal growth

The placenta transports substrates and wastes between the maternal and fetal circulations. In mice, placental IGF-II is essential for normal placental development and function but, in other mammalian species, maternal circulating IGF-II is substantial and may contribute. Maternal circulating IGFs increase in early pregnancy, and early treatment of guinea pigs with either IGF-I or IGF-II increases placental and fetal weights by mid-gestation. We now show that these effects persist to enhance placental development and fetal growth and survival near term. Pregnant guinea pigs were infused with IGF-I, IGF-II (both 1 mg/kg.d), or vehicle sc from d 20-38 of pregnancy and killed on d 62 (term = 69 d). IGF-II, but not IGF-I, increased the mid-sagittal area and volume of placenta devoted to exchange by approximately 30%, the total volume of trophoblast and maternal blood spaces within the placental exchange region (+29% and +46%, respectively), and the total surface area of placenta for exchange by 39%. Both IGFs reduced resorptions, and IGF-II increased the number of viable fetuses by 26%. Both IGFs increased fetal weight by 11-17% and fetal circulating amino acid concentrations. IGF-I, but not IGF-II, reduced maternal adipose depot weights by approximately 30%. In conclusion, increased maternal IGF-II abundance in early pregnancy promotes fetal growth and viability near term by increasing placental structural and functional capacity, whereas IGF-I appears to divert nutrients from the mother to the conceptus. This suggests major and complementary roles in placental and fetal growth for increased circulating IGFs in early to mid-pregnancy.

Fetal intestinal fibroblasts respond to insulin-like growth factor (IGF)-II better than adult intestinal fibroblasts

Background

We compared IGF responses of fetal and adult intestinal fibroblasts to identify a developmental difference in the IGF-axis. Intestinal fibroblasts were isolated from maternal and fetal jejunum. Media was conditioned at confluence and one week afterwards. The proliferative response at confluence to 5 nM IGF-I or -II was compared.

Results

There were no significant differences in IGFBP expression at confluence. Post-confluence, fetal fibroblasts had no significant changes in IGFBP-2 and IGFBP-3 expression. Post-confluent maternal fibroblasts had increased IGFBP-3 levels that were significant compared to the fetal fibroblasts. IGF-I increased in post-confluent fetal fibroblasts, while in maternal fibroblasts it decreased (p < 0.001). IGF-II secretion decreased significantly in post-confluent maternal fibroblasts (p < 0.05). Maternal fibroblasts proliferated more with IGF-I than IGF-II (p < 0.001). Fetal fibroblasts responded to IGF-II slightly better than IGF-I and significantly greater than maternal cells (p < 0.001).

Conclusion

Fetal intestinal fibroblasts respond to IGF-II with greater proliferation and do not have the increased IGFBPs seen post-confluence in adult intestinal fibroblasts.

Growth factors in lung development

Organized and coordinated lung development follows transcriptional regulation of a complex set of cell-cell and cell-matrix interactions resulting in a blood-gas interface ready for physiologic gas exchange at birth. Transcription factors, growth factors, and various other signaling molecules regulate epithelial-mesenchymal interactions by paracrine and autocrine mechanisms. Transcriptional control at the earliest stages of lung development results in cell differentiation and cell commitment in the primitive lung bud, in essence setting up a framework for pattern formation and branching morphogenesis. Branching morphogenesis results in the formation of the conductive airway system, which is critical for alveolization. Lung development is influenced at all stages by spatial and temporal distribution of various signaling molecules and their receptors and also by the positive and negative control of signaling by paracrine, autocrine, and endocrine mechanisms. Lung bud formation, cell differentiation, and its interaction with the splanchnic mesoderm are regulated by HNF-3beta, Shh, Nkx2.1, HNF-3/Forkhead homolog-8 (HFH-8), Gli, and GATA transcription factors. HNF-3beta regulates Nkx2.1, a transcription factor critical to the formation of distal pulmonary structures. Nkx2.1 regulates surfactant protein genes that are important for the development of alveolar stability at birth. Shh, produced by the foregut endoderm, regulates lung morphogenesis signaling through Gli genes expressed in the mesenchyme. FGF10, produced by the mesoderm, regulates branching morphogenesis via its receptors on the lung epithelium. Alveolization and formation of the capillary network are influenced by various factors that include PDGF, vascular endothelial growth factor (VEGF), and retinoic acid. Epithelial-endothelial interactions during lung development are important in establishing a functional blood-gas interface. The effects of various growth factors on lung development have been demonstrated by gain- or loss-of-function studies in null mutant and transgenic mice models. Understanding the role of growth factors and various other signaling molecules and their cellular interactions in lung development will provide us with new insights into the pathogenesis of bronchopulmonary dysplasia and disorders of lung morphogenesis.

Variable maternal nutrition and growth hormone treatment in the second quarter of pregnancy in pigs alter semitendinosus muscle in adolescent progeny

Maternal nutrition and growth hormone (GH) treatment during early- to mid-pregnancy can each alter the subsequent growth and differentiation of muscle in progeny. We have investigated the effects of varying maternal nutrition and maternal treatment with porcine (p) GH during the second quarter of pregnancy in gilts on semitendinosus muscle cross-sectional area and fibre composition of progeny, and relationships between maternal and progeny measures and progeny muscularity. Fifty-three Large White x Landrace gilts, pregnant to Large White x Duroc boars, were fed either 2.2 kg (about 35 % ad libitum intake) or 3.0 kg commercial ration (13.5 MJ digestible energy, 150 g crude protein (N x 6.25)/kg DM)/d and injected with 0, 4 or 8 mg pGH/d from day 25 to 50 of pregnancy, then all were fed 2.2 kg/d for the remainder of pregnancy. The higher maternal feed allowance from day 25 to 50 of pregnancy increased the densities of total and secondary fibres and the secondary:primary fibre ratio in semitendinosus muscles of their female progeny at 61 d of age postnatally. The densities of secondary and total muscle fibres in semitendinosus muscles of progeny were predicted by maternal weight before treatment and maternal plasma insulin-like growth factor-II during treatment. Maternal pGH treatment from day 25 to day 50 of pregnancy did not alter fibre densities, but increased the cross-sectional area of the semitendinosus muscle; this may be partially explained by increased maternal plasma glucose. Thus, maternal nutrition and pGH treatment during the second quarter of pregnancy in pigs independently alter muscle characteristics in progeny.

Effects of insulin and insulin-like growth factor-I on renin gene expression in the renal cortical cells of ovine fetuses

Renin gene expression and insulin-like growth factor-I (IGFI) gene expression are both developmentally upregulated in the renal cortex of ovine fetuses and decline after birth. The infusion of IGFI into ovine fetuses in late gestation increases plasma renin activity and concentration. In order to determine whether there are direct effects of IGFI or insulin on renin gene expression in the kidneys of ovine fetuses, we treated the renal cortical cells of ovine fetuses with IGFI or insulin. The results showed that the responses of renal renin mRNA to IGFI or insulin treatment in vitro were dependent on the culture conditions. Renin mRNA levels were significantly elevated by IGFI or insulin if the cells were cultured in medium devoid of serum (starved) for 16-18 h before treatment. In contrast, no obvious changes in renal renin mRNA expression were observed in the cells cultured in the presence of serum (non starved) before treatment with IGFI or insulin. IGFI and insulin also significantly enhanced cAMP concentrations in the medium of the cells starved in vitro. The data suggest that IGFI and insulin can act directly on the renal cortical cells from ovine fetuses to stimulate renin mRNA expression. It is possible that IGFI and insulin stimulate renin mRNA expression by increasing cAMP concentration in the cells.

Insulin-like growth factor levels during pregnancy in the cow are affected by protein supplementation in the maternal diet

To determine if dietary protein supplementation in early pregnancy alters total circulating insulin-like growth factor (IGF) levels, genetically similar heifers were fed diets containing different levels of protein in the first and second trimesters of gestation. The groups were: low/low (L/L), fed a diet containing 7% crude protein (CP) per kg/DM (low protein) in the first and second trimesters; high/high (H/H), fed a diet containing 14% CP per kg/DM (high protein) in the first and second trimesters; low/high (L/H), fed low protein in the first trimester and high in the second trimester and vice versa for the high/low (H/L) group. At day 62 of gestation, there was a significant difference (P<0.01) in IGF I concentrations between the high and low protein groups (149 versus 119 ng/ml, S.E. 5.9). There was a strong effect (P<0.001) of protein levels in the second trimester on IGF I levels on days 119, 153, and 183 of gestation but not at day 257. Mean IGF I levels for high and low nutrition in the second trimester were 157 and 97 (S.E. 6.6) for days 119, 191, and 88 (S.E. 12.6) for days 153 and 160, and 67 (S.E. 7.7) for day 183. At day 257, there was a significant interaction (P<0.01) between treatments with the means being 98(ab), 110(b), 116(b) and 79(a gamma) (means followed by a letter in common do not differ significantly, P<0.05) (S.E. 7.5) for H/H, H/L, L/H, and L/L, respectively. There was a significant (P<0.05) effect of protein supplementation in the first trimester on calf IGF I levels at birth with means being 42 and 25 (S.E. 5.2) for high and low protein supplementation, respectively. There was a significant (P<0.01) effect of protein supplementation in second trimester upon IGF II levels and a significant (P<0.05) negative correlation between calf birth weight and IGF II levels.

Clinical, hormonal, and hematologic characteristics of bovine calves derived from nuclei from somatic cells

Although healthy animals are born after nuclear transfer with somatic cells nuclei, the success of this procedure is generally poor (2%-10%) with high perinatal losses. Apparently normal surviving animals may have undiagnosed pathologies that could develop later in life. The gross pathology of 16 abnormal bovine fetuses produced by nuclear transfer (NT) and the clinical, endocrinologic (insulin-like growth factors I and II [IGF-I and IGF-II], IGF binding proteins, post-ACTH stimulation cortisol, leptin, glucose, and insulin levels), and biochemical characteristics of a group of 21 apparently normal cloned calves were compared with those of in vitro-produced (IVP) controls and controls resulting from artificial insemination. Oocytes used for NT or IVP were matured in vitro. NT to enucleated oocytes was performed using cultured adult or fetal skin cells. After culture, Day 7, grade 1-2 embryos were transferred (one per recipient). All placentas and fetuses from clones undergoing an abnormal pregnancy showed some degree of edema due to hydrops. Mean placentome number was lower and mean placentome weight was higher in clones than in controls (69.9 +/- 9.2 placentomes with a mean weight of 144.3 +/- 21.4 g in clones vs. 99 and 137 placentomes with a mean individual weight of 34.8 and 32.4 g in two IVP controls). Erythrocyte mean cell volume was higher at birth (P < 0.01), and body temperature and plasma leptin concentrations were higher and T4 levels were lower during the first 50 days and the first week (P < 0.05), respectively, in clones. Plasma IGF-II concentrations were higher at birth and lower at Day 15 in clones (P < 0.05). Therefore, apparently healthy cloned calves cannot be considered as physiologically normal animals until at least 50 days of age.

Short-term infusion of LongR(3) insulin-like growth factor (IGF)-I decreases hepatic IGF-I mRNA but not IGF binding protein-3 mRNA expression in pigs

Infusion of pigs with an insulin-like growth factor-I (IGF-I) analogue (LongR(3)IGF-I) that does not bind to IGF-binding proteins decreases growth rate and the plasma concentration of growth hormone (GH), IGF-I, IGFBP-3, and insulin. This study was designed to determine whether the decrease is due to changes in IGF-I and IGFBP-3 gene expression. IGF-I or LongR(3)IGF-I (180 microg/kg/day) was infused into 55-kg finisher pigs for 4 days using Travenol infuser pumps. Plasma IGF-I concentration was measured by radioimmunoassay and plasma IGFBP-3 and IGFBP-2 were estimated by Western ligand blotting. Steady-state levels of IGF-I and IGFBP-3 mRNA were measured by RNase protection assay. Neither IGF-I nor LongR(3)IGF-I had a significant effect on hepatic IGF-I class 1 mRNA expression, whereas hepatic IGF-I class 2 mRNA expression was significantly reduced by both peptides. Plasma IGFBP-3 levels were unaffected by IGF-I treatment but were reduced by LongR(3)IGF-I treatment. The decrease in IGFBP-3 was not due to decreased gene expression in porcine liver or kidney, since neither IGF-I nor LongR(3)IGF-I treatment altered IGFBP-3 mRNA. This study infers a direct effect of the IGF analogue LongR(3)IGF-I on GH through its inhibition of plasma IGF-I concentration and class 2 IGF-I mRNA. The decrease in plasma IGFBP-3 was not accompanied by a decrease in hepatic or renal IGFBP-3 mRNA, suggesting that in this case, plasma IGFBP-3 protein levels are posttranslationally regulated or are derived from tissues other than liver or kidney.

Ontogeny of the H19 gene in sheep and effect of maternal fasting on its expression in the fetus

Mapped on the same chromosome as the Insulin-like Growth Factor II (IGF-II), an important factor regulating fetal growth, the H19 gene, is believed to play a role during embryogenesis and to share similar regulatory elements with IGF-II possibly by an enhancer competition system. This study was designed to characterize the ontogeny of H19 in sheep and the effect of maternal fasting on the expression of fetal IGF-II and H19 mRNA. A partial cDNA clone for the ovine H19 gene was isolated and used as a probe for RNase protection analysis. The ontogeny of H19 in liver, skeletal muscle and heart of ovine fetuses at 62,100 and 130 days, lambs at 1 month and adult sheep revealed high tissue levels of H19 mRNA during fetal life that decreased significantly after birth. Maternal fasting significantly decreased fetal liver H19 mRNA expression but did not alter fetal IGF-II mRNA expression. These results suggest that H19, like IGF-II, may play an important role in the regulation of fetal growth and define an environmental condition whereby these two genes are regulated independently.

Chronic effect of insulin-like growth factor I on renin synthesis, secretion, and renal function in fetal sheep

In the adult, insulin-like growth factor I (IGF-I) increases glomerular filtration rate (GFR) and renal blood flow (RBF) during both acute and chronic treatment. To study its effects on the developing kidney, chronically catheterized fetal sheep (120 +/- 1 days gestation) were infused intravenously for up to 10 days with 80 microgram/h IGF-I (n = 5) or vehicle (0.1% BSA in saline, n = 6). In contrast to previous acute studies in adult rats and humans, after 4 h of IGF-I fetal GFR and RBF were unchanged. Fractional sodium reabsorption increased (P < 0.05). However, by 4 days, GFR per kilogram had risen by 35 +/- 13% (P < 0.05), whereas RBF remained unchanged. Tubular growth and maturation may have occurred, as proximal tubular sodium reabsorption increased by ~35% (P < 0.005). Therefore, despite a marked increase in filtered sodium (~30%, P < 0.05), fractional sodium reabsorption did not change. Although the effects of IGF-I on renal function were delayed, plasma renin activity and concentration were both elevated after 4 h and remained high at 4 days (P < 0.05). Despite this, arterial pressure and heart rate did not change. Kidneys of IGF-I-infused fetuses weighed ~30% more (P = 0.05) and contained ~75% more renin than control fetuses (P < 0.005). Thus, in the fetus, the renal effects of long-term IGF-I infusion are very different from the adult, possibly because IGF-I stimulated kidney growth.

Differential changes in insulin-like growth factors and their binding proteins following asphyxia in the preterm fetal sheep

1. The purpose of this study was to examine the changes in circulating concentrations of insulin-like growth factor (IGF)-I, IGF-II, IGF-binding protein (IGFBP)-1, IGFBP-2 and insulin following asphyxia in utero. 2. Fetal sheep at 90-93 days gestation underwent either sham occlusion (n = 7) or asphyxia (n = 6) induced by complete umbilical cord occlusion for 30 min. Fetal blood samples were taken before occlusion and 4, 6, 24, 48 and 72 h post-occlusion. 3. During the early phase of recovery there was a substantial fall (80 %) in circulating plasma IGF-I concentrations by 6 h post-asphyxia (P < 0.001). This was associated with a rapid rise in IGFBP-1 (P < 0.001), but no change in IGF-II or IGFBP-2. Insulin was significantly reduced at 4 h (P < 0.001) and glucose slightly elevated (P < 0.05), but insulin values returned to baseline by 6 h. Between 24 and 72 h of recovery, IGF-I gradually increased, IGFBP-1 returned to control values, and there was an increase in IGFBP-2 after 24 h (P < 0.05) and in IGF-II by 72 h (P < 0.05) after asphyxia. 4. These data demonstrate a differential effect of asphyxia on the IGF axis of the premature fetal sheep. A key finding was the large fall in circulating IGF-I, but not IGF-II, during the early phase of recovery. IGF-I bioavailability was, in part, regulated by IGFBP-1, but maximal changes in IGF-I and IGFBP-1 were independent of plasma insulin and glucose.5. The impact of this substantial change in circulating IGF-I on the fetus is unknown. It may facilitate metabolic requirements by promoting catabolism. Alternatively, as IGFs play a role in wound repair, the acute changes in IGF-I and IGFBP-1 may reflect transport of IGF-I from the circulatory pool to injured tissues to promote wound repair.

Insulin-like growth factor I alters renal function and stimulates renin secretion in late gestation fetal sheep

While it is known that treatment with insulin-like growth factor I (IGF-I) stimulates growth of the fetal kidney, nothing is known about the short term or long term effects of IGF-I on fetal renal function. To investigate the acute effects of IGF-I on fetal renal function and on the activity of the fetal renin-angiotensin system, studies were carried out in 12 chronically catheterized fetal sheep aged 120 +/- 1 days, before and during a 4 h I.V. infusion of IGF-I at 80 ug h-1. Seven control fetuses were infused over the same period with vehicle (0.1% bovine serum albumin in 0.15 M saline). IGF-I infusion increased plasma IGF-I concentrations by about 80%. There was a small fall in arterial PO2 (P < 0.01), arterial PCO2 increased (P < 0.05), plasma lactate levels increased (P < 0.01) and arterial pH fell (P < 0.05). Fractional bicarbonate reabsorption increased and bicarbonate excretion decreased (P < 0.05). Infusions of IGF-I had no sustained effect on fetal arterial pressure. Glomerular filtration rate (GFR) did not change significantly during IGF-I infusion, but renal blood flow (RBF) fell (P < 0.05). Therefore filtration fraction relative to control values increased (P < 0.05), suggesting that efferent arteriolar vasoconstriction had occurred. IGF-I infusion led to an antidiuresis (P < 0.01), a rise in urinary osmolality (P < 0.05) and a fall in free water clearance (P < 0.01). Since fetal PO2 fell, it is probable that these effects were mediated by arginine vasopressin. The excretion rates of sodium, chloride and phosphate were all reduced by 4 h of infusion (P < 0.05), because their fractional reabsorption rates were all increased (sodium, P < 0.01; chloride, P < 0.01; and phosphate, P < 0.05). Plasma renin concentration increased by 275 +/- 52% during infusion of IGF-I (P < 0.005). Plasma renin activity also increased (P < 0.005), while circulating angiotensinogen concentrations fell (P < 0.05). In the adult, IGF-I increases both RBF and GFR, enhances tubular reabsorption and stimulates the renin-angiotensin system. In the fetus, however, it decreased RBF and had no effect on GFR, but was associated with enhanced tubular function and intense stimulation of renin secretion. Some of these effects of IGF-I on fetal renal function may be involved in maturation of the kidney in preparation for life after birth.

Interleukin-6 stimulates hepatic insulin-like growth factor binding protein-4 messenger ribonucleic acid and protein

Sepsis and bacterial lipopolysaccharide (LPS) injection decrease circulating concentrations of insulin-like growth factor (IGF)-I and induce an increase in IGFBP-1 and IGFBP-4 that may have impact upon IGF-I anabolic actions. Although the mechanisms responsible for the IGFBP-1 increase in response to LPS have already been unraveled, the cause for the IGFBP-4 elevation is still unknown. The aim of this study was to characterize the regulation of IGFBP-4 by proinflammatory cytokines and glucocorticoids. In rat primary cultured hepatocytes, interleukin (IL)-6 strongly stimulated IGFBP-4 messenger RNA (mRNA) and protein levels in a dose- and time-dependent way (mRNA levels: 9-fold, P: < 0.01 and protein levels: approximately 3-fold at 24 h, with IL-6 10 ng/ml). Interleukin (IL)-1ss and tumor necrosis factor (TNF)-alpha blunted the IL-6 stimulation of IGFBP-4 mRNA (66% and 46% decrease, respectively) and protein levels (82% and 68% decrease, respectively). In contrast, dexamethasone induced IGFBP-4 mRNA and protein and potentiated the effect of IL-6 on IGFBP-4 mRNA (2.5-fold, P: < 0.01 vs. IL-6 alone). Both actinomycin and cycloheximide prevented the IL-6 induction of IGFBP-4 mRNA suggesting that the IL-6 effect on IGFBP-4 gene occurs probably at the transcriptional level and needs an ongoing protein synthesis. Administration of IL-6 to rats caused a 3-fold increase in liver IGFBP-4 mRNA (P: < 0.001) reflected in serum levels of IGFBP-4 (P: < 0.05). In conclusion, our results show that IL-6 stimulates hepatic IGFBP-4 gene expression and production in vitro and in vivo, thereby suggesting another mechanism by which cytokines could control IGF-I action.

Ovine surfactant protein cDNAs: use in studies on fetal lung growth and maturation after prolonged hypoxemia

cDNAs for ovine surfactant-associated protein (SP) A, SP-B, and SP-C have been cloned and shown to possess strong similarity to cDNAs for surfactant apoproteins in other species. These reagents were employed to examine the effect of fetal hypoxia on the induction of surfactant apoprotein expression in the fetal lamb. Postnatal lung function is dependent on adequate growth and maturation during fetal development. Insulin-like growth factor (IGF) I and IGF-II, which are present in all fetal tissues studied, possess potent mitogenic and proliferative actions, and their effects can be modulated by IGF-specific binding proteins (IGFBPs). Hypoxia can lead to increases in circulating cortisol and catecholamines that can influence lung maturation. Therefore, the effects of mild hypoxia in chronically catheterized fetal lambs at gestational days 126-130 and 134-136 (term 145 days) on the expression of pulmonary surfactant apoproteins and IGFBPs were examined. Mild hypoxia for 48 h resulted in an increase in plasma cortisol that was more pronounced at later gestation, and in these animals, there was a twofold increase in SP-A mRNA. SP-B mRNA levels also increased twofold, but this was not significant. SP-C mRNA was not altered. No significant changes in apoprotein mRNA were observed with the younger fetuses. However, these younger animals selectively exhibited reduced IGFBP-5 mRNA levels. IGF-I mRNA was also reduced at 126-130 days, although this conclusion is tentative due to low abundance. IGF-II levels were not affected at either gestational age. We conclude that these data suggest that mild prolonged fetal hypoxia produces alterations that could affect fetal cellular differentiation early in gestation and can induce changes consistent with lung maturation closer to term.

Cellular localization and expression of insulin-like growth factors (IGFs) and IGF binding proteins within the epiphyseal growth plate of the ovine fetus: possible functional implications

The insulin-like growth factors (IGFs) are important in the regulation of normal fetal musculoskeletal growth and development, and their actions have been shown to be modulated by IGF binding proteins (IGFBPs). Because the anatomical distribution of IGFBPs is likely to dictate IGF bioavailability, we determined the cellular distribution and expression of IGF-I, IGF-II, and IGFBP-1 to IGFBP-6 in epiphyseal growth plates of the fetal sheep, using immunocytochemistry and in situ hybridization. Little mRNA for IGF-I was detectable within the growth plates, but mRNA for IGF-II was abundant in germinal and proliferative chondrocytes, although absent from some differentiating chondrocytes and hypertrophic cells. Immunohistochemistry for IGF-I and IGF-II showed a presence of both peptides in all chondrocyte zones, including hypertrophic cells. Immunoreactive IGFBP-2 to -5 were localized within the germinal and proliferative zones of chondrocytes, but little immunoreactivity was present within the columns of differentiating cells. IGFBP immunoreactivity again appeared in hypertrophic chondrocytes. IGFBP mRNA in chondrocytes of the epiphyseal growth plate was below the detectable limit of in situ hybridization. However, low levels of mRNAs for IGFBP-2 to -6 were detected by the reverse transcriptase polymerase chain reaction. A co-localization of IGFBPs with IGF peptides in intact cartilage suggests that they may regulate IGF bioavailability and action locally. To test this hypothesis, monolayer cultures of chondrocytes were established from the proliferative zone of the growth plate, and were found to release immunoreactive IGF-II and to express mRNAs encoding IGFBP-2 to -6. Exogenous IGFBP-3, -4, and -5 had an inhibitory action on IGF-II-dependent DNA synthesis. IGFBP-2 had a biphasic effect, potentiating IGF-II action at low concentrations but inhibiting DNA synthesis at equimolar or greater concentrations relative to IGF-II. Long R3 IGF-I, which has a reduced binding affinity for many IGFBPs, was more potent than native IGF-I in promoting DNA synthesis by chondrocytes. Our findings suggest that locally produced IGF-II and IGF-I derived from the circulation can influence fetal epiphyseal chondrogenesis, and that this may be modulated locally by multiple IGFBP expression.Key words: epiphyseal growth plate, insulin-like growth factor, insulin-like growth factor binding protein, chondrocyte, cartilage.

Moderate doses of porcine somatotropin do not increase plasma insulin-like growth factor-I (IGF-I) or IGF binding protein-3

The growth rate of the young pig is generally much less than its potential and may be constrained by endocrine status as well as by nutrient intake. The aim of this study was to determine whether porcine somatotropin (pST) could increase growth in the nursing pig. Fourteen sows nursing litters of 6 (n = 7) or 12 (n = 7) piglets were utilized to establish a high and low plane of nutrition for sucking pigs. On Day 4 of lactation, the median two male pigs from each litter were randomly allocated to one of two doses of pST (0 or 60 micrograms/kg/d) until weaning on Day 31. Pigs were bled on Days 4, 13, 22, and 31 of lactation and the plasma was analyzed for insulin-like growth factor (IGF)-I, IGF-II, and IGF binding protein-3 (IGFBP-3). Pigs were weaned into conventional accommodation and further weighed on Days 63, 91, and 119. Pigs from litters of 6 grew more quickly and weighed 2.2 kg (P = 0.01) and 3.5 kg (P = 0.04) more than pigs from litters of 12 at 31 and 63 d of age, respectively. There was no effect of pST on preweaning growth of sucking pigs (261 vs. 258 g/d, P = 0.68), although growth rate increased in the final 3 d before weaning at 31 d (241 vs. 294 g/d, P = 0.01). IGFBP-3 was greater (1.09 vs. 0.78 micrograms/ml, P < 0.001), whereas IGF-I tended to be greater (206 vs. 176 ng/ml, P = 0.14), in pigs from the small litters. There was no effect of pST on plasma IGF-I (182 vs. 195 ng/ml, P = 0.454) or IGFBP-3 (0.93 vs. 0.94 microgram/ml, P = 0.85) concentrations. Plasma IGF-I and IGFBP-3 were highly correlated with the growth rate of nursing pigs (R = 0.638 and 0.756, respectively). There were no effects of pST (340 vs. 328 ng/ml, P = 0.48) or litter size (336 vs. 333 ng/ml, P = 0.88) on IGF-II. In conclusion, pST had no little or no effect on growth performance or plasma IGF-I, IGF-II, or IGFBP-3 in sucking pigs on either a high or low plane of nutrition.

Role of the insulin-like growth factor system in uterine function and placental development in ruminants

Maternal nutrition during pregnancy influences fetal and placental weights. The insulin-like growth factors (IGF) are also important determinants of fetal size. Furthermore, the expression of several components of the IGF system is regulated by nutrition. Effects of nutrition on fetal growth could therefore be mediated by the IGF system in the uterus and placenta. The oviductal mucosa produces IGF-I, which may influence oviductal secretions or act directly on embryonic type 1 IGF receptors. In the uterus, IGF-I mRNA is localized to the stroma surrounding the endometrial glands, which contain high concentrations of IGF type 1 receptors. Uterine IGF-I concentrations fall during pregnancy; therefore, glandular activity is more likely influenced by systemic than local IGF-I production. The IGF-II mRNA is present in both caruncles and fetal placental mesoderm, but concentrations are much higher in the latter. The actions of IGF-I and IGF-II on the endometrium and placenta are influenced by IGF-binding proteins. In the ewe, mRNAs for IGF binding protein-1 and -5 are located in the luminal and glandular epithelia, IGF binding proteins-2 and -4 are produced in the subepithelial stroma, and IGF binding protein-4 is also in the placentome capsule; IGF binding protein-3 is more widely expressed in both maternal and fetal tissues. The IGF binding proteins, therefore, form a major barrier to the passage of IGF between the fetal and maternal circulatory systems.

Secretion in Escherichia coli and phage-display of recombinant insulin-like growth factor binding protein-2

Insulin-like growth factors (IGFs) promote cell growth and differentiation. Their actions are regulated by six different, but related, binding proteins (IGFBPs). To investigate the molecular interactions between IGFs and IGFBPs, an Escherichia coli based production method and a phage display system has been developed. The cDNA for bovine IGFBP-2 was inserted between regions coding for the pelB signal sequence and geneIII product, g3p, of bacteriophage fd in a phagemid vector to generate pGF14. The coding sequences of IGFBP-2 and g3p were separated by an amber stop codon and a flexible linker containing the cleavage recognition site for H64A subtilisin. Using this system in BL21, a non-supE strain lacking ompT, most product, approximately 4 mg 1(-1) of IGFBP-2, was obtained in the growth medium. The bacterially derived IGFBP-2 had a correct N-terminal sequence, molecular mass on SDS-PAGE and the same affinity for IGF-1 and IGF-II as IGFBP-2 from mammalian cells. In a supE strain of E. coli, IGFBP-2 was produced as an IGF-binding fusion to g3p. Procedures for display and approximately 10000 fold enrichment of IGFBP-2 bearing phage using adsorption to IGF-II coated microtitre plates were developed. Thus IGFBP-2 can be secreted in E. coli and displayed on filamentous phage. These can be selectively enriched by binding to immobilised IGF-II.

Gene expression of the insulin-like growth factor system during mouse kidney development

Expression of the insulin-like growth factor (IGF) system was investigated in mouse renal development and physiology, using non radioactive in situ hybridization and quantitative RT-PCR. IGF-I mRNA levels increased after birth and were confined to distal tubules and peritubular capillaries in the outer medulla. IGF-II mRNA levels were high in developing kidneys and peaked after birth. The type I receptor mRNA expression pattern mostly parallelled those of IGF-I and IGF-II. The IGF binding proteins (IGFBP's) showed weak mRNA expression for IGFBP-1 and -6. High fetal mRNA levels were measured for IGFBP-2, showing a similar profile in time as observed for IGF-II. Low fetal IGFBP-3 and -5 mRNA levels increased after birth. IGFBP-2, -4 and -5 mRNA expression was localized to differentiating cells. In the mature kidney predominant expression was confined to proximal tubules (IGFBP-4), thin limbs of Henle's Loop (IGFBP-2), glomerular mesangial cells (IGFBP-5) and peritubular capillaries of the medulla (IGFBP-5). IGFBP-3 mRNA was exclusively expressed in endothelial cells of the renal capillary system. Distinct mRNA expression for each member of the IGF system may point to specific roles in development and physiology of the mouse kidney.

Insulin-like growth factor I inhibits degradation and improves retention of protein in hindlimb muscle of lambs

We infused recombinant human insulin-like growth factor I (IGF-I) for 4 h at 12.3 micrograms.h-1.kg live weight-1 directly into the left femoral artery and measured the rates of synthesis, degradation, and gain of protein by the treated and contralateral limbs of well-fed (n = 8), feed-restricted (n = 10), and fasted (n = 9) castrated male lambs. Reducing feed intake decreased net protein gain of hindlimb muscle, reduced hindlimb glucose uptake, and lowered arterial plasma concentrations of IGF-I, insulin, glucose, phenylalanine, tyrosine, and isoleucine. The effect of nutrition on IGF-binding proteins (IGFBP) was generally small; IGFBP-2 was more abundant in fasted lambs. Infusion of IGF-I into the left femoral artery increased plasma levels of IGF-I 2- to 4-fold in the left femoral vein and by 1.5- to 3-fold in the artery and right femoral vein. In the treated limb, IGF-I reduced protein degradation, increased protein gain, and increased glucose uptake without altering blood flow or oxygen uptake, regardless of feed intake. Systemically, IGF-I reduced plasma insulin, phenylalanine, tyrosine, isoleucine, and leucine in all nutrition groups. Plasma IGFBP-3 was increased by 4 h of IGF-I treatment in fasted but not in fed lambs. In fed but not fasted lambs, IGF-I increased blood glucose concentration. Effects of IGF-I on protein metabolism in the contralateral limb were affected by nutrition, generally more so in fasted than in unrestricted fed lambs.