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

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

Binding of insulin-like growth factors (IGF-I and IGF-II) to the IGF-II/mannose 6-phosphate receptor in fetal rat myocardium

Previous studies indicate that fetal rat heart tissue contains large amounts of insulin-like growth factor (IGF)-II/mannose 6-phosphate (Man 6-P) receptor messenger RNA, with receptor messenger RNA levels falling by 20 days after birth. We examined the amount of IGF receptor protein in developing rat myocardium. To establish a model in which the role of neural, hormonal, and hemodynamic controls of IGF receptor binding could be studied, we compared binding of IGF-I and IGF-II in normally growing rat atria and ventricles with embryonic day 12 (E-12) atria and ventricles maturing in the anterior eye chamber of an adult host rat. In oculo, embryonic myocardium matures without hemodynamic load or exposure to the fetal hormonal milieu. In fetal rat hearts (E-12 to E-19), both IGF-I and IGF-II intensely bound to a protein with a molecular weight corresponding to the IGF-II/Man 6-P receptor. Receptors were identified using sodium dodecyl sulfate/polyacrylamide gel electrophoresis autoradiography and western blot analysis using Ab3637, a specific polyclonal antibody against rat IGF-II/Man 6-P receptor antigens. This antibody competed for binding of both IGF-I and IGF-II to the band with molecular radius corresponding to 260,000 (reduced). In normally growing rat atria, IGF-I binding to the IGF-II/Man 6-P receptor was similar to ventricular tissue; however, there was significantly greater binding of IGF-II than of IGF-I in both atrial and ventricular tissue. High levels of IGF-II binding to the IGF-II/Man 6-P receptor were observed in both fetal rat atrial and ventricular grafts until 6-8 weeks in oculo. As in normally growing heart tissue, there was similar IGF-I binding to the IGF-II/Man 6-P receptor in atrial grafts compared with ventricular grafts from 2-8 weeks after implantation. For the first 2 weeks after grafting, the ventricular grafts had relatively higher IGF-I binding to the IGF-II/Man 6-P receptor compared with later time points examined. The present data indicate that atrial and ventricular binding of IGFs to the IGF-II/Man 6-P receptor decreases with age, suggesting that decreased IGF binding may be independent of postnatal hemodynamic changes. The decrease is similar in in oculo embryonic rat cardiac grafts and normally growing heart tissue.(ABSTRACT TRUNCATED AT 400 WORDS)     

The effects of thyroxine on serum and tissue concentrations of insulin-like growth factors (IGF-I and -II) and IGF-binding proteins in the fetal pig

We have extensively studied the effect of hypophysectomy on the growth and development of tissues in the fetal pig. However, little is known about the effect of hypophysectomy on tissue levels of insulin-like growth factors I and II (IGF-I and -II) and how these growth factors are affected by T4 replacement. Fetal pigs were hypophysectomized (Hypox) at 70 days of gestation, and pellets containing 15 mg T4 were implanted into the lateral musculature of the hind limb at either 70 or 90 days of gestation. Fetuses were removed at either 90 or 105 days of gestation, respectively. Control (non-Hypox), Hypox, and T4 (Hypox-T4) fetal weights were similar at 90 days, but Hypox-T4 weighted less than control and Hypox fetuses at 105 days. Hypophysectomy decreased levels of serum T4, LH, cortisol, and IGF-I (105 days) when compared with controls. Heart and liver (105 days and 90 days) and fat, muscle, and kidney (90 days) IGF-I levels were lower in Hypox fetuses when compared with controls. Hypophysectomy decreased concentrations of IGF-II in only 105-day fetal kidneys. Hypophysectomy decreased serum levels of IGF binding protein 1 (IGFBP-1) (90 days) and IGFBP-2 (105 days) and increased IGFBP-4 (105 days) in comparison with control. T4 treatment of Hypox fetuses increased serum concentrations of T4 and IGF-I over Hypox levels at both 90 and 105 days gestation. Cortisol levels remained decreased in the T4-treated fetuses. Levels of IGF-I in the heart (90 and 105 days) and liver (90 days) of Hypox fetuses were increased by T4 treatment. T4 did not effect tissue IGF-II levels when compared with Hypox. T4 increased serum IGFBP-1, -2, and -4 levels over Hypox values. We suggest that T4 enhances production of IGF-I (as opposed to IGF-II), which in turn mediates some of T4's capability to enhance tissue development in the fetal pig.     

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.     

Cellular distribution and ontogeny of insulin-like growth factors (IGFs) and IGF binding protein messenger RNAs and peptides in developing rat pancreas

To determine the role of insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) in the development of the pancreas, and specifically of the islets of Langerhans, we have examined the cellular distribution and developmental changes in the expression of IGFs and IGFBPs in the pancreas of the fetal and neonatal rat between 19.5 days of gestation and postnatal day 28. This represents a period of substantial growth and restructuring of the beta cell component in islets of this species. IGF-I, IGF-II, and IGFBPs-1 to -6 mRNAs were localized by in situ hybridization, and peptides by immunohistochemistry, in histological sections. IGF-II mRNA was highly expressed in islet cells and some ductal epithelial cells in late fetal and early neonatal life, but was barely detectable by postnatal day 28. IGF-II peptide showed a similar distribution. IGF-I mRNA was barely detected in the fetus or neonate and was localized predominantly in the ductal and acinar tissues after postnatal day 7. IGF-I immunoreactivity was associated with some islet cells in the fetus and neonate, suggesting an endocrine rather than a paracrine source. We performed co-localization studies to assess whether the distribution of IGFs within the pancreas might be due to a sequestration by locally produced IGFBPs. The presence of mRNAs for both IGFBPs-1 and -2 was minimal in the pancreas prior to postnatal day 7, although subsequently IGFBP-1 mRNA was seen in islet cells, while IGFBP-2 mRNA was localized in both islets and acinar tissues. In contrast, both IGFBPs-1 and -2 immunoreactivities were identified in islets from late fetal life, suggesting a circulatory source for these IGFBPs during early pancreatic development. IGFBPs-3 to -5 mRNAs and immunoreactivities were identified within islet cells throughout fetal and neonatal life, with IGFBPs-3 and -5 being mainly associated with the alpha cell-rich islet mantle. The results show a compartmentalization of IGFs within pancreatic tissue, reflecting both paracrine and endocrine sources. The localization and action of IGFs in pancreas likely involves sequestration and distribution by endogenous as well as circulating IGFBPs.     

Analysis of insulin-like growth factors (IGF)-I, and -II, type II IGF receptor and IGF-binding protein-2 mRNA and peptide levels in normal and nephrectomized rat kidney

Immunocytochemistry, in situ hybridization, and radioimmunoassay were employed to examine the cellular distribution of mRNAs and proteins for IGF-I, II, IGF-II/M6P receptor, IGFBP2 as well as the levels of IGF-I and II in normal and unilaterally nephrectomized (Nx) adult rat kidneys. A similar distribution of immunoreactive IGF-I, and -II as well as IGF-II/M6P receptor was found in the principal cells of the cortical collecting duct and in all cells of the inner medullary collecting duct. In addition, immunostainable IGF-I and IGF-II/M6P receptor were noted in some inner medullary loops of Henle, while IGFBP2 was seen in the collecting ducts and loops of Henle of the inner medullar and the renal vasculature of all animals. By comparison, in situ hybridization revealed IGF-I mRNA only in the medullary thick ascending limbs while IGF-II mRNA was localized to the wall of the renal microvasculature in all kidneys. IGFBP2 mRNA was localized to the renal corpuscle and to inner medullary interstitial cells of all kidneys. These data suggest that renal IGF-I and IGFBP2 are synthesized at upstream sites along the nephron and then transported downstream for interaction with IGF receptors. Following nephrectomy, the renal levels of IGF-I peptide and mRNA were elevated at both 5 and 33 days post-nephrectomy, supporting a potential functional role for IGF-I in stimulating the structural and functional recovery in compensatory hypertrophy.     

Skeletal cell stresses and bone adaptation

BACKGROUND: We have previously shown that growth hormone (GH) consistently stimulates proliferation of human osteoblasts in vitro. In rat osteoblasts, GH augments the effects of insulin-like growth factor (IGF) I on cell proliferation and differentiation. We therefore investigated the effects of IGF-I and -II alone and in combination with GH on human osteoblasts in vitro. METHODS: Human osteoblast-like cells (HOB) were established from trabecular explants (n = 18) and human marrow stromal cells (HMS) from marrow aspiration (n = 21). The cell cultures were stimulated with IGF-I or IGF-II (1, 10 or 100 ng mL-1) alone, in combination with hGH (100 ng mL-1) or after prestimulation with hGH. RESULTS: IGF-I alone, in combination with hGH and after pretreatment with hGH, increased proliferation of HOB and HMS by 49-190% (P < 0.05-0.01). IGF-II alone, in combination with hGH and after pretreatment with hGH increased proliferation of HOB by 57-158% (P < 0.01). In HMS only IGF-II in combination with hGH and after prestimulation with hGH increased proliferation. IGF-I alone and in combination with hGH decreased alkaline phosphatase (AP) in both cell types. IGF-II did not affect AP in HOB, but increased AP in HMS, this effect was abolished by hGH. In HOB, collagen production (PICP) was increased by IGF-II but unaffected by IGF-I. In HMS, PICP was decreased by IGF-I and -II but increased by hGH. Co-stimulation further increased PICP. CONCLUSION: IGF-I and -II exerted proliferative effects on both HOB and HMS. Co-stimulation with GH exhibited synergism in enhancing the proliferative response. In HMS prestimulation improved the proliferative response significantly. The effects of the IGFs on differentiation are more complex and dependent on cell maturation and of the IGF used.     

Porcine somatotropin (pST) increases IGF-I mRNA abundance in liver and subcutaneous adipose tissue but not in skeletal muscle of growing pigs

The present study was undertaken to determine the effects of exogenous porcine somatotropin (pST) on IGF-I gene expression in liver, skeletal muscle (longissimus dorsi), and s.c. adipose tissue of growing pigs. Twenty prepubertal gilts (approximately 60 kg BW) were allotted to four treatment groups (n = 5) and treated with either 0, 35, 70, or 140 micrograms/kg BW of recombinantly derived pST by daily i.m. injection for 7 d. Serum concentrations of IGF-I were determined by RIA and IGF-I mRNA levels were determined by direct counting of individual samples on slot blots. Administration of pST increased IGF-I concentration in serum. This was accompanied by significant increases (P < .05) in IGF-I mRNA abundance in liver and s.c. adipose tissue; the effects were maximal at the lowest dose of pST. Insulin-like growth factor I mRNA levels were increased 2.5- and 4.5-fold, respectively. Levels of IGF-I mRNA were very low in longissimus muscle and were unaffected by administration of pST. When expressed as picograms of mRNA/10 micrograms of total RNA, IGF-I mRNA levels were highest in s.c. adipose tissue. Levels of IGF-I mRNA were 1.9-fold higher in s.c. adipose tissue than in liver of control animals, and pST administration increased this difference to 3.2-fold. Our results suggest that 1) the effects of pST administered by daily i.m. injection on IGF-I gene expression in pigs are tissue-specific and 2) the stimulatory effects of pST administered in this manner on muscle growth in pigs are not associated with increased expression of the IGF-I gene in skeletal muscle.     

Insulin-like growth factor (IGF)-I and -II and IGFBP secretion by ovine satellite cell strains grown alone or in coculture with 3T3-L1 preadipocytes

The current study was designed to examine the effects of muscle and fat stem cell coculture on the secretion of insulinlike growth factor (IGF)-I and -II and IGF binding proteins (IGFBP) by these cells. Two sheep satellite cell strains with negligible or high potential for differentiation (10A and 0(1), respectively) were placed in coculture with 3T3-L1 preadipocytes using a filter support to separate the two cell types. Media conditioned by the cells grown alone or in coculture were analyzed for IGFs by RIA or IGFBPs by ligand blotting. The numbers of satellite cells and preadipocytes declined throughout the 5-d culture period, although coculture slowed the 3T3-L1 decline but hastened the satellite cell decline. The satellite cell strains and 3T3-L1 cells secreted small amounts of IGF-I (< or = 2 ng/ml) and IGF-II (< 10 ng/ml) over the 5-d culture period. Coculture did not increase the amount of IGF-I and -II in conditioned media. The lowly differentiating 10A cells secreted barely detectable amounts of the low molecular weight IGFBP-3 subunit (34 kDa), IGFBP-2 (28 kDa), and IGFBP-4 (18 kDa). Coculture of 10A and 3T3-L1 cells potentiated secretion of IGFBP-2 and -3. Strain 0(1), which readily differentiates, secreted high levels of both IGFBP-3 subunits (34 and 39 kDa) and IGFBP-2 (28 kDa), as well as significant amounts of the 18 kDa IGFBP-4. Coculture did not alter IGFBP secretion of 0(1) cells. This study showed that while IGF-I and -II levels in media conditioned by sheep satellite cell strains are low and relatively invariant, the intensity and complexity of IGFBP patterns increases with time in culture and with the potential for differentiation of the satellite cell strains. Coculture with preadipocytes appeared to potentiate IGFBP secretion while reducing satellite cell viability.     

Role for membrane and secreted insulin-like growth factor-binding protein-2 in the regulation of insulin-like growth factor action in lung tumors

The insulin-like growth factors (IGFs) have been implicated in the autocrine and/or paracrine growth of a number of tumor types, including lung tumors. Importantly, insulin-like growth factor-binding proteins (IGFBPs), which both enhance and inhibit the physiological and biological actions of the IGFs, have been shown to be secreted in vitro by a wide range of tumors. In particular, IGFBP-2 is frequently produced by human tumor cells, suggesting that this protein may be an important determinant of IGF action in tumors. In the present study, we investigated IGFBP-2 effects in lung tumor cells by examining the influence of IGFBP-2 on IGF-receptor interaction and the biological actions of IGF-I and IGF-II. Affinity cross-linking studies demonstrated expression of type-I and type-II IGF receptors on small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) cells and the presence of abundant membrane-associated IGFBP in SCLC cells but not in NSCLC cells. An antiserum specific for IGFBP-2 was used in immunoprecipitation and immunoblotting studies which demonstrated that the membrane-associated IGFBP identified by affinity cross-linking in SCLC cells is IGFBP-2. In NSCLC cells, both IGF-I and IGF-II bound predominantly to IGF-I receptors, whereas in SCLC cells binding was principally to surface-associated IGFBP-2. SCLC cells failed to respond to IGF-I and -II stimulation in a DNA synthesis assay. For NSCLC cells, IGF-II was a more potent stimulator of DNA synthesis than IGF-I. Soluble IGFBP-2 inhibited the binding of radiolabeled IGF-I and -II to both SCLC and NSCLC cells in a concentration-dependent manner and inhibited IGF-stimulated DNA synthesis in NSCLC cells. These observations indicate that both soluble and membrane-associated IGFBP-2 compete with IGF receptors for ligand binding and, thus, are likely to be important determinants of IGF responsiveness. The findings of the present study also indicate that the type-I receptor on NSCLC cells contains a high-affinity binding site for IGF-II which presumably mediates the biological effects of IGF-II in these cells, thereby implicating IGF-II in the autocrine/paracrine growth of NSCLC.     

Insulin-like growth factor binding proteins-2 and -3 stimulate growth hormone receptor binding and mitogenesis in rat osteosarcoma cells

GH exerts its biological actions on osteoblasts through a specific high affinity receptor expressed on these cells. GH receptor binding is positively modulated by a number of factors, including retinoic acid and dexamethasone, whereas fetal calf serum strongly decreases the binding. To identify responsible factors in serum, components of serum, the insulin-like growth factors (IGFs)-I and -II, and IGF binding proteins (IGFBPs)-2 and -3 were tested for a possible negative modulatory role. IGF-I and -II decreased [125I]hGH binding at an optimal concentration of 30 ng/ml for IGF-I and 100 ng/ml IGF-II, reducing the binding to 51% and 55%, respectively, of control values. A stimulation of [125I]hGH binding was observed with IGFBP-2 as well as IGFBP-3, inducing an increase to 148% and 151% of control binding at an optimal concentration of 3000 ng/ml for both peptides. The effects of all peptides were dependent on the incubation time, being significantly increased after 8 h of incubation and reaching the full effect thereafter. The effects were declined at 24 h compared with 16 h for IGFBP-2 and -3 but not for IGF-I and -II. Coincubation of the cells with IGF-I and -II and IGFBP-2 and -3 neutralized the effects of the factors alone. In conclusion, these results show that IGF-I and -II on the one hand and IGFBP-2 and -3 on the other hand exert opposite actions on [125I]hGH binding, IGFBP-2 and -3 exerting probably an IGF-independent effect. Further, IGF-I and -II decreased GH receptor messenger RNA (mRNA) levels, as quantified by a solution hybridization ribonuclease protection assay, from 8.65 +/- 1.78 attomoles (amol)/microgram DNA (control) to 2.4 +/- 0.68 and 2.16 +/- 0.92 amol/microgram DNA, respectively. IGFBP-2 increased GH receptor mRNA levels from 5.26 +/- 1.17 (control) to 13.19 +/- 3.48. Incubation with IGFBP-3 did not result in stimulation of GH receptor mRNA levels (8.59 +/- 2.91 amol/microgram DNA). This shows that the mechanism of regulation of the GH receptor is, except for IGFBP-3, at least in part on the mRNA level. Lastly, IGFBP-2 and IGFBP-3 are mitogenic for UMR-106.01 rat osteosarcoma cells, inducing an increase in cell number to 125% and 142% of control cell counts after 48 h of incubation with 1000 ng/ml IGFBP-2 and -3, whereas IGF-I, IGF-II and Long R3 IGF-I did not stimulate proliferation. IGFBP-2 and -3 potentiate hGH induced mitogenesis at low hGH concentrations of both factors, whereas at higher concentrations no such effect is observed.(ABSTRACT TRUNCATED AT 400 WORDS)     

Insulin-like growth factor system abnormalities in hepatitis C-associated osteosclerosis. Potential insights into increasing bone mass in adults

Hepatitis C-associated osteosclerosis (HCAO) is a rare disorder characterized by a marked increase in bone mass during adult life. Despite the rarity of HCAO, understanding the mediator(s) of the skeletal disease is of great interest. The IGFs-I and -II have potent anabolic effects on bone, and alterations in the IGFs and/or IGF-binding proteins (IGFBPs) could be responsible for the increase in bone formation in this disorder. Thus, we assayed sera from seven cases of HCAO for IGF-I, IGF-II, IGF-IIE (an IGF-II precursor), and IGFBPs. The distribution of the serum IGFs and IGFBPs between their ternary ( approximately 150 kD) and binary (approximately 50 kD) complexes was also determined to assess IGF bioavailability. HCAO patients had normal serum levels of IGF-I and -II, but had markedly elevated levels of IGF-IIE. Of the IGFBPs, an increase in IGFBP-2 was unique to these patients and was not found in control hepatitis C or hepatitis B patients. IGF-I and -II in sera from patients with HCAO were carried, as in the case of sera from control subjects, bound to IGFBP-3 in the approximately 150-kD complex, which is retained in the circulation. However, IGF-IIE was predominantly in the approximately 50-kD complex in association with IGFBP-2; this complex can cross the capillary barrier and access target tissues. In vitro, we found that IGF-II enhanced by over threefold IGFBP-2 binding to extracellular matrix produced by human osteoblasts and that in an extracellular matrix-rich environment, the IGF-II/IGFBP-2 complex was as effective as IGF-II alone in stimulating human osteoblast proliferation. Thus, IGFBP-2 may facilitate the targeting of IGFs, and in particular IGF-IIE, to skeletal tissue in HCAO patients, with a subsequent stimulation by IGFs of osteoblast function. Our findings in HCAO suggest a possible means to increase bone mass in patients with osteoporosis.     

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

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

Insulin-like growth factors-I and -II differentially regulate endogenous acetylcholine release from the rat hippocampal formation

Insulin-like growth factors-I and -II (IGF-I and -II) are structurally related mitogenic polypeptides with potent growth promoting effects. These peptides and their corresponding IGF-I and -II receptors are selectively localized in the brain. To date, most of the effects of IGFs are believed to be mediated by IGF-I receptors whereas the significance of IGF-II receptor in mediating biological responses remains unclear. In the present study, we characterized the distribution of IGF-I and IGF-II receptor sites and investigated the effects of both factors on endogenous acetylcholine (ACh) release in adult rat hippocampus. [125I]IGF-I receptor binding sites are recognized by IGF-I> IGF-II> insulin, whereas [125I]IGF-II binding was competed potently by IGF-II> IGF-I but not by insulin. At the cellular level, IGF-I receptor sites were primarily noted in the molecular layer of the dentate gyrus and the CA2-CA3 subfields of the Ammon's horn whereas IGF-II sites were localized predominantly in the pyramidal cell layer of the CA1-CA3 subfields and in the granular cell layer of the dentate gyrus. IGF-I (10(-14)-10(-8) M) and des(1-3) IGF-I (10(-10)-10(-8) M) were found to inhibit whereas IGF-II (10(-14)-10(-8) M) potentiated K+-evoked ACh release from hippocampal slices. Tetrodotoxin altered the effects of IGF-I but not those of IGF-II suggesting that IGF-I acts indirectly via the release of other modulators whereas IGF-II acts directly on or in close proximity to the cholinergic terminals. The inhibitory effects of IGF-I were also observed in the frontal cortex but not in the striatum. In contrast, the stimulatory effects of IGF-II were evident both in the frontal cortex and striatum. Taken together, these results reveal the differential localization of IGF-I and IGF-II receptor sites in the hippocampal formation and the opposite role for these growth factors in the acute regulation of ACh release likely via two distinct mechanisms. Additionally, these data provide the first evidence for a direct role for IGF-II and its receptors in the regulation of transmitter release in the central nervous system.     

Relationships of serum insulin-like growth factor II concentrations to growth, compositional, and reproductive traits of swine

Insulin-like growth factors I and II (IGF-I and -II) are peptide hormones involved in metabolic regulation of growth. The objective of this study was to determine whether IGF-II concentration was predictive of growth, compositional, and reproductive traits of pigs. Forty male and sixty female pigs, divided equally between two locations, were weighed at 3-wk intervals from birth to 21 wk and bled at 9 and 21 wk of age. At each sampling, two blood samples were collected via jugular venipuncture at an interval of at least 1 h. Serum was separated and IGF-I, IGF-II, and growth hormone (GH) concentrations were determined via RIA. Traits measured included age at puberty and first parity litter size for gilts and backfat and longissimus muscle area. Blood was collected from a random sample of 52 progeny from 13 litters at 9 wk of age and serum was assayed for IGF-II concentrations. Effects of age, sex, location, and pig within sex x location on square-root transformed IGF-II concentrations were determined by analyzing data as a splitplot. Performance traits were fitted to a model including the effects of IGF-II concentration and combinations with IGF-I concentration, sex, location, and interactions. Concentrations of IGF-II were greater at 9 than at 21 wk of age (226.7 vs 159.3 ng/mL, respectively; P < .001) but did not differ between sexes. The correlation between serum IGF-II concentrations assayed from samples collected at 9 and 21 wk was .08. The partial correlations between IGF-I and IGF-II concentrations were .33 and .14 at 9 and 21 wk, respectively. The heritability of IGF-II concentration estimated from offspring-midparent regression was .08 +/- .20. Nine-week IGF-II concentration was positively associated with increased weight from weaning to 12 wk (P < .001). However, the sum of 9-wk IGF-I and IGF-II concentrations had a greater relationship to weight and gain in the growing phase than the concentration of either hormone alone. Concentration of IGF-II at 9 or 21 wk alone did not affect backfat thickness, longissimus muscle area, percentage lean, days to 100 kg, weight at 21 wk, age at puberty, or litter size. The sum of IGF-I and IGF-II concentrations was, however, associated with increased backfat and decreased days to 100 kg.     

Expression of insulin-like growth factors (IGFs), their receptors and IGF binding protein-3 in normal, benign and malignant smooth muscle tissues

To assess the role of insulin-like growth factors (IGFs) in growth and transformation of normal (myometrium) and tumorous smooth muscle cell (SMC) tissues, in situ hybridization (ISH) analysis for insulin-like growth factor I and II (IGF-I and IGF-II) mRNAs was combined with detection of IGF peptides, their receptors and IGF binding protein-3 (IGFBP-3). mRNAs for both IGFs were detected in smooth muscle cells in normal, benign and malignant SMC tissues, together with the IGF peptides, both IGF receptors and IGFBP-3. This suggests an autocrine role for both IGFs. Leiomyomas had higher IGF-I peptide levels and higher levels of type I IGF receptors than myometrium, supporting the idea that IGFs play a role in the growth and transformation of these tumours. Low-grade leiomyosarcomas contained more IGF-II mRNAs than myometrium and leiomyoma, fewer type II IGF/mannose 6-phosphate receptors and less IGFBP-3 than myometrium and, in addition, fewer IGF-I mRNAs and type I IGF receptors than leiomyoma. Intermediate- and high-grade leiomyosarcomas had intermediate levels of IGF-II mRNAs and peptide, ranging between those in myometrium and low-grade leiomyosarcomas. Thus, growth and transformation of leiomyosarcomas may be regulated by IGF-II, although more markedly in low-grade than in high-grade leiomyosarcomas. In conclusion, the various categories of SMC tissues are associated with a distinct expression pattern of the IGF system. This suggests that each category of SMC tumours arises as a distinct entity and that there is no progression of transformation in these tissues.