Age- and sodium-sensitive hypertension and sex-dependent renal changes in rats with a reduced nephron number

We have demonstrated that the reduction of angiotensin II effects during the nephrogenic period reduces the nephron number and induces the development of hypertension. The hypotheses examined are that this reduction of angiotensin effects leads to the development of an age-dependent sodium sensitive hypertension and that the hypertension is angiotensin II dependent. Newborn rats were treated with an angiotensin II type 1 receptor antagonist during the first 2 weeks of age. At 3 to 4 and 11 to 12 months of age, changes in systolic blood pressure, proteinuria, and renal function in response to a prolonged high sodium intake were examined. The basal blood pressure response to the administration of the angiotensin II receptor antagonist was also evaluated at both ages. Basal blood pressure was similarly elevated (P<0.05) in male and female treated rats, and the increment was age dependent. High sodium intake only elicited a blood pressure elevation (136+/-1 to 154+/-3 mm Hg; P<0.05) and a decrease in glomerular filtration rate (28%; P<0.05) at 11 to 12 months in treated rats. Blockade of angiotensin II receptors during renal development induced an increase (P<0.05) in proteinuria that was age and sex dependent, but high sodium intake only induced an elevation in proteinuria in the younger rats (50%; P<0.05). Hypertension was maintained by angiotensin II at both ages because blood pressure decreased to normal levels after treatment with an angiotensin II type 1 receptor antagonist. This study shows that the reduction of angiotensin II effects during the nephrogenic period modifies renal function and induces the development of an angiotensin II-dependent hypertension that becomes sodium sensitive during aging.     

Genetic selection for insulin-like growth factor-1 in growing mice is associated with altered growth

Substantial responses in the 6-week and mature body-weights of mice occurred after 7 generations of selection for or against plasma levels of Insulin-like Growth Factor-1 (IGF-1). Plasma levels of IGF-1 were also significantly different after 7 generations of selection (high line = 85 +/- 2 ng/ml, low line = 58 +/- 2 ng/ml). The average 6-week weight in the line selected for high plasma IGF-1 was 22.5 +/- .2 g compared with 18.5 +/- .2 g in the low plasma IGF-1 line, after 7 generations of selection. The difference between lines was maintained at 20 weeks of age. These data provide further evidence for the roles of IGF-1 in the regulation of somatic growth and as a mediator of a genetic component of growth.     

Wasting in the acquired immune deficiency syndrome is associated with multiple defects in the serum insulin-like growth factor system

OBJECTIVE The aim of this investigation was to characterize the GH–IGF axis of patients with AIDS associated wasting. A special emphasis was placed on determining whether IGF binding proteins (IGFBPs) of patients who have lost more than 10% of their ideal body mass are structurally different from the IGFBPs of patients with no weight loss. DESIGN AND PATIENTS A cross-sectional study of 11 AIDS patients was performed to determine whether the IGF system is abnormal in AIDS patients with wasting. Seven additional AIDS patients were followed longitudinally to determine whether AIDS patients experience long-term changes to their IGF system. MEASUREMENTS Serum levels of GH and IGF-I were measured by radioimmunoassay, IGF-II was measured by radioreceptor assay, and IGFBP-1 was measured by an enzyme linked immunoassay. IGFBP-3 and IGFBP-3 protease activity were measured by ligand blotting and a BP-3 protease assay, respectively. IGFBP-3 ternary complex formation and IGFBP-1 phosphovariants were analysed by non-denaturing PAGE. RESULTS AIDS patients who had lost more than 10% of their ideal body mass demonstrated a 55% reduction in serum IGF-I (81 vs 179 μg/l) and a 70% reduction in IGF-II (226 vs 776 μg/l), compared to healthy HIV negative subjects. IGF-I levels were depressed, in some patients, despite high serum levels of GH. AIDS patients who had lost more than 10% of their ideal body mass had low levels of IGFBP-3 and a reduced ability to form the IGFBP-3 ternary complex. The IGFBP-3 ternary complex could be restored only upon addition of pure IGFBP-3 and acid labile subunit to serum. Serum IGFBP-1 was increased more than threefold compared to control subjects (90 vs 24 μg/l). IGFBP-1 was present as a free phosphoprotein in AIDS patients with low levels of IGF-I and in a bound form when serum IGF-I levels were normal. Changes in the GH–IGF axis were sustained for up to 25 months in AIDS patients with wasting. CONCLUSIONS AIDS wasting is associated with a GH resistant state that results in low levels of serum IGF-I, IGF-II and IGFBP-3, elevated levels of phosphorylated IGFBP-1, and a reduced ability to form the IGFBP-3 ternary complex.     

Nutrition and the insulin-like growth factor system

Nutritional status is a key regulator of the circulating and tissue insulin-like growth factor (IGF) system. IGF-I mRNA and protein levels decrease in tissues such as liver and intestine with fasting and are restored with refeeding. Additional studies suggest that the level of protein and calorie intake independently regulate plasma IGF-I concentrations in man. The level of nutrition effects the biological actions of recombinant growth hormone (GH) and IGF-I administration in humans. Limited data demonstrate that plasma and tissue levels of the insulin-like growth factor binding proteins (IGFBPs) are also sensitive to nutrient intake. Specific micronutrients, such as potassium, magnesium and zinc also appear to be important for optimal IGF-I synthesis and anabolic effects in animal models. Malnutrition is common in elderly patients, however, the interaction between specific nutrients, general nutritional status and the aging process on the IGF system is incompletely understood. Mechanisms of nutrient-IGF systeminteractions which may affect the biological actions of IGF-I, IGF-II, and the IGFBPs are increasingly being determined in basic studies. The effects of underlying nutritional status and responses to dietary intake will be important to evaluate in clinical studies of the IGF system and exogenous growth factor therapy.     

Intrauterine growth restriction in humans is associated with abnormalities in placental insulin-like growth factor signaling

The IGFs promote the growth and development of the feto-placental unit during gestation, and impairment of their placental actions may result in altered intrauterine growth of the fetus. In this study, proteins involved in IGF signaling were investigated in human placentas from pregnancies complicated by intrauterine growth restriction (IUGR) compared with those from normal pregnancies. IUGR placentas exhibited 33% reduction in the protein content of IGF-I receptors, but no changes in insulin receptor protein levels. In addition, insulin receptor substrate-2 (IRS-2) protein levels were reduced in IUGR placentas, with no changes in IRS-1 or Shc protein content, and this was associated with a parallel decrease in IRS-2-associated phosphatidyl inositol 3-kinase. Akt protein expression was also reduced in IUGR, whereas phosphorylation of Akt and its substrate glycogen synthase kinase-3 was unchanged. Finally, in IUGR placentas there was impaired activation of multiple members of the MAPK family, because phosphorylation of p38 and c-Jun N-terminal kinase was reduced 70%. In conclusion, human placentas from pregnancies complicated by IUGR are characterized by decreased IGF-I receptor content, selective impairment of the IRS-2/ phosphatidyl inositol 3-kinase pathway, and reduced p38 and c-Jun N-terminal kinase activation. The observed abnormalities in IGF-I signaling may contribute to altered fetal growth and development in human IUGR.     

The effect of growth hormone on the insulin-like growth factor system during fasting

The present study investigates the possible stimulatory effect of endogenous GH on IGF and IGF-binding protein (IGFBP) levels during fasting. Eight normal subjects were examined on four occasions: 1) in the basal postabsorptive state; 2) after 40 h of fasting; 3) after 40 h of fasting with somatostatin suppression of GH; and 4) after 40 h of fasting with suppression of GH and exogenous GH replacement. The two somatostatin experiments were identical in terms of hormone replacement (except for GH). Short-term fasting led to a 50% reduction in free IGF-I. The reduction in free IGF-I was paralleled by an increase in IGFBP-1, an increase in the complex formation of IGFBP-1 and IGF-I, and a modest reduction in IGFBP-3 proteolysis. GH deprivation during fasting led to a 35% reduction in total IGF-I and a 70% reduction in free IGF-I. GH replacement increased free and total IGF-I to levels similar to those observed during plain fasting and decreased IGFBP-1, however, without affecting IGFBP-1-bound IGF-I. Finally, IGFBP-3 proteolysis was slightly increased by GH replacement. In conclusion, the major new finding of the present study is that the GH hypersecretion seen during short-term fasting is not merely secondary to a reduction in IGF bioactivity.     

Altered growth of mice divergently selected for body weight is associated with complex changes in the growth hormone/insulin-like growth factor system.

Mice investigated in this study were generated by selecting a sub-population of the NMRI out-bred stock (C), for high (H) or low (L) 8-week body weight. After 58 generations of selection, 8-week body weights of the sub-populations were markedly different if compared to controls. To investigate endocrine changes causing the altered growth performance in the different lines of mice, we analysed several components of the growth hormone (GH)/insulin-like growth factor (IGF) system. Pituitary weights of male and female L mice were significantly smaller than those of C and H mice. Relative to body weight, pituitary weights of male mice from the three lines did not differ, however pituitary weight-to-body weight-ratios of female L mice were significantly greater than those of H females. Mean volume densities of somatotropic cells were significantly smaller in L mice than in C and H mice. Serum IGF-I concentrations were significantly lower in the L line than in the C and H lines. H mice displayed significantly increased serum insulin levels both after ad libitum feeding and after a 14 hour fasting period. Ligand blot analysis of serum IGF-binding proteins (IGFBPs) revealed a significant reduction of circulating IGFBP-3 in L mice as compared to C and H mice. In contrast, serum IGFBP-2 mRNA levels were significantly increased in male L mice and showed non significant increases in female L mice. Hepatic IGFBP-2 mRNA levels were significantly increased in L mice and decreased in H mice as compared to C mice. Expression of IGFBP-4 mRNA in the liver was significantly decreased in both selection lines (L, H) as compared to the random-bred controls. Our findings demonstrate that altered growth of mice resulting from selection for body weight is associated with complex changes in the endocrine network of the GH/IGF system.     

Preeclampsia is associated with low circulating levels of insulin-like growth factor I and 1,25-dihydroxyvitamin D in maternal and umbilical cord compartments

Insulin-like growth factor I (IGF-I) stimulates renal and placental 1,25-dihydroxyvitamin D [1,25-(OH)2D] and is considered an important regulator of fetal growth. As 1,25-(OH)2D and birth weight are low in preeclampsia, this study was undertaken to determine whether circulating levels of IGF-I were associated with serum 1,25-(OH)2D concentrations in preeclamptic (PE group) and normotensive (NT group) pregnancies. Maternal and umbilical cord serum levels of IGF-I and 1,25-(OH)2D were significantly (P < 0.01) lower in the PE group than in the NT group. The concentrations of these two hormones correlated significantly in the umbilical cord (P < 0.05) and in the maternal (P < 0.001) compartments of the PE and NT groups, respectively. The amount of IGFBP-3 was 64% lower whereas that of IGFBP-1 was 2.9-fold higher in umbilical cord serum of the PE group compared with the NT group. In addition, maternal and umbilical cord serum IGF-I correlated significantly (P < 0.05) with weight and length at birth only in the PE group. In conclusion, the results of this study indicate that circulating IGF-I and 1,25-(OH)2D levels in both maternal and umbilical cord compartments are low in preeclampsia. Furthermore, this study suggests a differential regulatory effect of IGF-I on 1,25-(OH)2D synthesis and fetal growth depending on the presence or absence of preeclampsia.     

Abnormalities of renal function in essential hypertension with increased circulating levels of insulin-like growth factor I.

An increase in glomerular filtration rate and in tubular Na+ reabsorption from the parenteral administration of insulin-like growth factor I (IGF-I) have been reported in human subjects. To evaluate whether glomerular hyperfiltration and Na+ hyper-reabsorption present in some essential hypertensives are associated to an excess of IGF-I, the plasma levels of this factor and several parameters of renal function were studied in 30 non-treated essential hypertensives and in 30 normotensive controls. IGF-I levels were higher in hypertensive as compared to controls. With the 95% (upper) limit of the normotensive population as a cut-off point, a subgroup of six hypertensives had an abnormally high IGF-I level. Mean blood pressure was slightly lower in these six patients (112 +/- 7 mmHg) than in the remaining patients (120 +/- 2 mmHg). As compared to normotensives and hypertensives with normal IGF-I levels, patients with increased IGF-I levels were characterized by lower (P < 0.01) fractional Na+ excretion and higher (P < 0.05) creatinine clearance. The analysis of the relation of plasma renin activity and the concurrent daily rate of Na+ excretion showed that patients with increased IGF-I were low-renin hypertensives and patients with normal IGF-I were normal-renin hypertensives. These results indicate that an association exists between exaggerated circulating levels of IGF-I and abnormalities of renal function present in some patients with essential hypertension. It is suggested that IGF-I can play a role in low-renin essential hypertension.     

Normal growth and development in the absence of hepatic insulin-like growth factor I

The somatomedin hypothesis proposed that insulin-like growth factor I (IGF-I) was a hepatically derived circulating mediator of growth hormone and is a crucial factor for postnatal growth and development. To reassess this hypothesis, we have used the Cre/loxP recombination system to delete the igf1 gene exclusively in the liver. igf1 gene deletion in the liver abrogated expression of igf1 mRNA and caused a dramatic reduction in circulating IGF-I levels. However, growth as determined by body weight, body length, and femoral length did not differ from wild-type littermates. Although our model proves that hepatic IGF-I is indeed the major contributor to circulating IGF-I levels in mice it challenges the concept that circulating IGF-I is crucial for normal postnatal growth. Rather, our model provides direct evidence for the importance of the autocrine/paracrine role of IGF-I.     

Anemia in children with cartilage-hair hypoplasia is related to body growth and to the insulin-like growth factor system

Cartilage-hair hypoplasia (CHH) is a metaphyseal chondrodysplasia characterized by severe short-limbed short stature, hypoplastic hair, and defective immunity. The patients also have anemia. As GH may regulate both body growth and erythropoiesis, we used CHH as a clinical model to study their interrelationships. Retrospective analysis of hematological data of 114 patients showed that the severity of the anemia and macrocytosis in CHH varies with age. The anemia was most severe in early childhood. A prospective study of 21 patients with CHH showed that height correlates with hemoglobin (P = 0.006) and mean corpuscular volume of red blood cells (P < 0.0001). The individual hemoglobin levels correlated with the GH parameters [P = 0.035 for insulin-like growth factor I (IGF-I) and P = 0.002 for IGF-binding protein-3], and the mean corpuscular volume of red blood cell values correlated with fetal hemoglobin. Bone marrow cultures obtained from six patients with CHH showed reduced or totally absent erythroid colony formation, which was not influenced by GH or IGF-I in vitro or by GH treatment in vivo. In patients with CHH, we observed an association between erythropoiesis and growth. We conclude that body growth and erythropoiesis share common regulators. One of these is the GH-IGF-I axis; other factors, as not yet identified, may also be important.     

Combination of renin-angiotensin system polymorphisms is associated with altered renal sodium handling and hypertension

Genes of the renin-angiotensin-aldosterone system (RAAS) are natural candidates for sodium homeostasis and blood pressure regulation. To investigate the effect of a combination of polymorphisms of RAAS genes on renal sodium handling and blood pressure, 918 participants to the Olivetti Heart Study were genotyped for the following polymorphisms: I/D of angiotensin converting enzyme (ACE), M235T of angiotensinogen (AGT), A1166C of angiotensin II type-1 receptor (AT1R), and C-344T of aldosterone synthase (CYP11B2). The segmental renal sodium handling was evaluated by the fractional excretions of exogenous lithium (FE-Li), uric acid (FE-UA), and sodium (FE-Na). Twenty-eight carriers of triple homozygosity for M (AGT), A (AT1R), and C (CYP11B2) in the presence of the D allele of ACE (DD/ID) showed lower FE-Li (20.0%+/-5.9% versus 25.0%+/-7.5%; P=0.004; mean+/-sD), FE-UA (6.3%+/-2.0% versus 8.2%+/-2.7%; P=0.001), and FE-Na (0.96%+/-0.41% versus 1.22%+/-0.61%; P=0.004) as compared with all other allelic combinations (n=890), independently from age and body mass, suggesting an enhanced rate of proximal tubular sodium reabsorption. The carriers of the MM, AA, CC, DD/ID combination showed a substantially higher probability of being hypertensive (OR: 3.4 [(99% CI: 1.1 to 10.1]), independently of age and body mass. This relatively rare combination of allelic variants of candidate genes of the RAAS is associated with a significant alteration in proximal renal sodium handling and with higher risk of hypertension, suggesting that a combination of polymorphic variants at different candidate loci may affect phenotypic expression even in the absence of detectable effects of each variant at any single locus.     

Integrity of the growth hormone/insulin-like growth factor system is maintained in patients with chronic fatigue syndrome

GH deficiency states and chronic fatigue syndrome (CFS) share several characteristics, and preliminary studies have revealed aspects of GH dysfunction in CFS. This study assessed indexes of GH function in 37 medication-free CFS patients without comorbid psychiatric illness and 37 matched healthy controls. We also assessed GH function before and after treatment with low dose hydrocortisone, which has been shown recently to reduce fatigue in CFS. We measured basal levels of serum insulin-like growth factor I (IGF-I), IGF-II, IGF-binding protein-1 (IGFBP-1), IGFBP-2 and IGFBP-3 together with 24-h urinary GH excretion. We also performed 2 dynamic tests of GH function: a 100-microg GHRH test and an insulin stress test using 0.15 U/kg BW insulin. There were no differences between patients and controls in basal levels of IGF/IGFBP or in urinary GH excretion. GH responses to both the GHRH test and the insulin stress test were no different in patients and controls. CFS patients did have a marginally reduced suppression of IGFBP-1 during the insulin stress test. Hydrocortisone treatment had no significant effect on any of these parameters. There is no evidence of GH deficiency in CFS. At the doses used, hydrocortisone treatment appears to have little impact on GH function.