Podcasts about igf ii

In this episode of the Epigenetics Podcast, we caught up with Dr. Wolf Reik, Director at the Babraham Institute in Cambridge, UK, to talk about his work on the role of epigenetic factors in cellular reprogramming. In the beginning of his research career, Dr. Wolf Reik worked on cellular reprogramming during embryogenesis. Epigenetic marks like DNA methylation or post-translational modifications of histone tails are removed and reprogrammed during embryogenesis, which can limit the amount of epigenetic information that can be passed on to future generations. However, this process is sometimes defective, which can lead to transgenerational epigenetic inheritance. More recently, the laboratory of Dr. Wolf Reik has done pioneering work in the emerging field of single-cell experimental methods. The Reik lab developed a single-cell reduced representation bisulfite sequencing (scRRBS) approach to investigate DNA methylation at single-cell resolution. They also developed an integrated multi-omics approach called single-cell nucleosome, methylation, and transcription sequencing (scNMT-Seq) to map chromatin accessibility, DNA methylation, and RNA expression at the same time during the onset of gastrulation in mouse embryos. In this interview, we discuss the story behind how Dr. Wolf Reik almost discovered 5-hmC and how he later moved into developing single-cell methods like scRRBS and single-cell multi-omics approaches.   References W. Reik, A. Collick, … M. A. Surani (1987) Genomic imprinting determines methylation of parental alleles in transgenic mice (Nature) DOI: 10.1038/328248a0 W. Dean, F. Santos, … W. Reik (2001) Conservation of methylation reprogramming in mammalian development: aberrant reprogramming in cloned embryos (Proceedings of the National Academy of Sciences of the United States of America) DOI: 10.1073/pnas.241522698 Miguel Constância, Myriam Hemberger, … Wolf Reik (2002) Placental-specific IGF-II is a major modulator of placental and fetal growth (Nature) DOI: 10.1038/nature00819 Adele Murrell, Sarah Heeson, Wolf Reik (2004) Interaction between differentially methylated regions partitions the imprinted genes Igf2 and H19 into parent-specific chromatin loops (Nature Genetics) DOI: 10.1038/ng1402 Irene Hernando-Herraez, Brendan Evano, … Wolf Reik (2019) Ageing affects DNA methylation drift and transcriptional cell-to-cell variability in mouse muscle stem cells (Nature Communications) DOI: 10.1038/s41467-019-12293-4 Tobias Messmer, Ferdinand von Meyenn, … Wolf Reik (2019) Transcriptional Heterogeneity in Naive and Primed Human Pluripotent Stem Cells at Single-Cell Resolution (Cell Reports) DOI: 10.1016/j.celrep.2018.12.099 Contact Active Motif on Twitter Epigenetics Podcast on Twitter Active Motif on LinkedIn Active Motif on Facebook Email: podcast@activemotif.com

Episode 347 is an updated guide to somatropic hormone and GOD did I go crazy on this one! I honestly want to know more about growth hormone than anyone alive and thus, begins this string of GH based guides! I DID finally discuss the MoA for how GH causes localized fat loss which really had me excited since no one in our industry has EVER talked about this so that definitely was an interesting avenue to go down! Below I am going to reference a lot of the literature for this hormone that I was read through over the past few years on this topic so please DO NOT TAKE MY WORD FOR THIS - READ THESE YOURSELF! Keep in mind this is a brief snippet of every bit of literature on the topic however. REFERENCES   Daughaday WH, Rotwein P. Insulin-like growth factors I and II. Peptide, messenger ribonucleic acid and gene structures, serum, and tissue concentrations. Endocr Rev. 1989;10:68–91. [PubMed] [Google Scholar] Jones JI, Clemmons DR. 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Die biochemische Analyse von Hormonen wird durch drei Variablen beeinflusst – die präanalytischen, analytischen und postanalytischen Variabilität. Bezüglich der analytischen und biologischen Variabilität wurden für Nager schon zahlreiche Arbeiten veröffentlicht, jedoch ist die Präanalytik in der Untersuchung von Blutproben von Ratten, in Bezug auf die Hormonanalytik, bislang kaum beachtet worden. Deswegen wurden in dieser Arbeit einige Aspekte der Präanalytik bei der Hormonmessung in Ratten genauer untersucht; auch um Anhaltspunkte zu geben, in wie weit vorbehandelte Blutproben von Ratten zur Messung unterschiedlicher Hormone genutzt werden können und wie sich die Verwendung unterschiedlicher Probenmaterialien, als auch Einfrier-Auftau-Zyklen, auf die Messergebnisse verschiedener Stoffwechselhormone auswirken können. In Bezug auf die biologische Variabilität wurde der Einfluss von Alter und Fasten auf ausgewählte Stoffwechselhormone bei der Ratte genauer untersucht. Ziel dieser Arbeit war es, in Analyseprozessen insbesondere auf den Faktor „Präanalytik“ einzugehen und aufzuzeigen, in welchem Ausmaß Ergebnisse in der Messung von Hormonen mittels Immunassays beeinflusst werden können. Im Vergleich zu reinem Serum waren die gemessenen Konzentrationen von IGF-I (+9,2%, p

We have investigated molecular mechanisms for muscle mass accretion in a non-inbred mouse model (DU6P mice) characterized by extreme muscle mass. This extreme muscle mass was developed during 138 generations of phenotype selection for high protein content. Due to the repeated trait selection a complex setting of different mechanisms was expected to be enriched during the selection experiment. In muscle from 29-week female DU6P mice we have identified robust increases of protein kinase B activation (AKT, Ser-473, up to 2-fold) if compared to 11- and 54-week DU6P mice or controls. While a number of accepted effectors of AKT activation, including IGF-I, IGF-II, insulin/IGF-receptor, myostatin or integrin-linked kinase (ILK), were not correlated with this increase, phosphatase and tensin homologue deleted on chromosome 10 (PTEN) was down-regulated in 29-week female DU6P mice. In addition, higher levels of PTEN phosphorylation were found identifying a second mechanism of PTEN inhibition. Inhibition of PTEN and activation of AKT correlated with specific activation of p70S6 kinase and ribosomal protein S6, reduced phosphorylation of eukaryotic initiation factor 2α (eIF2α) and higher rates of protein synthesis in 29-week female DU6P mice. On the other hand, AKT activation also translated into specific inactivation of glycogen synthase kinase 3ß (GSK3ß) and an increase of muscular glycogen. In muscles from 29-week female DU6P mice a significant increase of protein/DNA was identified, which was not due to a reduction of protein breakdown or to specific increases of translation initiation. Instead our data support the conclusion that a higher rate of protein translation is contributing to the higher muscle mass in mid-aged female DU6P mice. Our results further reveal coevolution of high protein and high glycogen content during the selection experiment and identify PTEN as gate keeper for muscle mass in mid-aged female DU6P mice.

Insulin-like growth factors (IGF) are not only mediators of metabolic actions, but also regulate cell growth, differentiation and apoptosis. IGF-II is of particular interest because of its mitogenic effects. It is known that endothelial progenitor cells (EPC) improve myocardial function after acute myocardial infarction. The aim of this study was to investigate whether overexpression of IGF-II in EPC further contributes to improvement in left ventricular function after myocardial infarction. Human CD34+ cells from cord blood were isolated and cultured in adequate cell medium. Early passage EPC were transduced ex vivo by a retroviral vector expression of IGF-II (EPC-IGF-II) or empty vector (EPC-pLXSN) and expanded up to 46 population doublings. Expression levels were confirmed by RT-PCR. Athymic, nude rats were thoracotomized and ligation of the LAD (left anterior descending artery) was performed for 30 minutes before reperfusion was initiated. Vector only transduced EPC or EPC-IGF-II cells were injected immediately after reperfusion in the border of the infarct zone. Serial echocardiographic measurements were performed to analyze left ventricular ejection fraction (EF) up to 2 weeks after myocardial infarction when animals were mercy killed. Transplantation of EPC-derived cells improved left ventricular function after experimental myocardial infarction from 47,3 ± 1,8 % (EF of the control group, n = 11) to 51,4 ± 0,7 % EF 2 weeks after infarction (p < 0,05, n = 9). Overexpression of IGF-II further improved left ventricular ejection fraction to 53,6 ± 0,5 % EF at 2 weeks as compared to empty vector transduced cells (p < 0,05, n = 10). In vitro experiments revealed that IGF-II dose-dependently enhanced the proliferation capacity of H9C2 rat cardiomyoblasts measured by a BrdU incorporation assay. Immunhistological analysis of proliferating cells in the myocardium showed an increased number of Ki67+ cells within the infarct zone 7 days after transplantation of IGF-II overexpressing cells as compared to empty vector transduced cells. It was shown that transplantation of IGF-II overexpressing EPC impaired the infarction size by nearly 20 % in comparison to EPC-pLXSN (p < 0,05). Thus, transplantation of IGF-II overexpressing EPC in acute myocardial infarction may improve myocardial function by enhancing the proliferation capacity of resident cardiomyocyteprogenitors.

Insulin-like growth factor I (IGF-I) and -II (IGF-II) are single chain peptides produced by many tissues, functioning in an endocrine, autocrine or paracrine fashion to regulate cellular proliferation, survival and differentiation. IGF actions are initiated upon binding to the insulin-like growth factor I receptor (IGF-IR) and are modulated through interactions with a family of six secreted IGF-binding proteins (IGFBP-1 to -6). IGF-I is necessary for normal growth and differentiation during both, embryonic and postnatal development. IGF-II is a stimulator of fetal growth but its functions in the postnatal period are still unclear. Notably, expression of IGF-II is shut down shortly after birth in rodents (but not in humans). Previous studies in phosphoenolpyruvate-carboxykinase (PEPCK)-IGF-II transgenic mice demonstrated that overexpression of IGF-II resulted in disproportionate growth of specific organs but a significant increase in body size was not observed. Homozygous IGF-I deficient mice were shown to be severely retarded in growth. The aim of this study was to test whether elevated levels of circulating IGF-II can rescue the dwarfism in IGF-I deficient mice and thereby function as a stimulator of postnatal growth in the absence of IGF-I. For this purpose, we crossed heterozygous IGF-I deficient mice [I+/- IIwt] with heterozygous IGF-I deficient mice carrying PEPCK-IGF-II transgenes [I+/- IItg]. The resulting offspring comprised six different groups: homozygous IGF-I knockout and PEPCK-IGF-II wildtype mice [I-/- IIwt], homozygous IGF-I knockout and PEPCK-IGF-II transgenic mice [I-/- IItg], animals lacking one IGF-I allele and wildtype for the PEPCK-IGF-II transgene [I+/- IIwt], lacking one IGF-I allele and harbouring the PEPCK-IGF-II transgene [I+/- IItg], wildtype for the IGF-I mutation and carrying the PEPCK-IGF-II transgene [I+/+ IItg], and completely wildtype [I+/+ IIwt]. The genotype of all mice was determined by PCR. Body weight of mice was recorded daily until the age of 8 weeks. The nose-rump length (NRL) and the weights of individual organs and of the carcass were recorded and the femurs and lumbar vertebras prepared for further investigations. At an age of 8 weeks, mean serum concentrations of IGF-I were beyond detection level in [I-/- IIwt] and [I-/- IItg] mice, intermediate in [I+/- IIwt] and [I+/- IItg] animals and highest in [I+/+ IIwt] and [I+/+ IItg] mice. IGF-II levels were significantly increased in animals harbouring the PEPCK-IGF-II transgene ([I-/- IItg], [I+/- IItg], and [I+/+ IItg]) when compared to their wildtype counterparts ([I-/- IIwt], [I+/- IIwt], and [I+/+ IIwt]). This reflected the genotype, demonstrating the appropriateness of our experimental model. Analysis of body weight data from day 3-4 after birth until day 60 revealed that in the absence of IGF-I, elevated levels of IGF-II have no effect on body weight gain. The same was found for the nose-rump length and the carcass. The weight of specific organs, however, was altered. Compared to the wildtype counterparts ([I-/- IIwt]), the relative kidney weight in [I-/- IItg] mice was significantly increased. IGF-I is known to play an important role in bone growth and in cancellous bone homeostasis. Investigations of geometric and structural bone parameters showed that in the presence or absence of IGF-I, an increase in the circulating levels of IGF-II was without effect on the skeleton and could not substitute for the skeletal functions of IGF-I in IGF-I-ablated mice. Homozygous IGF-I deficient mice are known to have elevated levels of growth hormone (GH). To demonstrate that the lack of effect on growth in our [I-/- IItg] animals was not due to a loss of these elevated GH-levels, a GH-Western immunoblot was performed, revealing that, despite elevated levels of IGF-II, increased levels of GH were still present in [I-/- IItg] animals. Evaluation of the serum levels of IGFBPs by Western ligand blot analysis demonstrated that IGFBP-1 and IGFBP-4 levels were similar in all groups, whereas the levels of IGFBP-2 and IGFBP-3 were strongly reduced in [I-/- IIwt] animals. In the presence of IGF-II ([I-/- IItg]), they were partially restored but the amounts were still smaller than in the IGF-I wildtype animals ([I+/+ IIwt] and [I+/+ IItg]). In summary, these results show that under our experimental conditions, IGF-II is not able to rescue the postnatal growth deficit of IGF-I knockout mice and apparently does not exert a negative feedback on the secretion of growth hormone. However, it could be demonstrated, that the IGFs have differentiated effects on the regulation of the expression/stability of individual IGFBPs.

Insulin-like growth factors (IGF-I and IGF-II) are expressed in many cell types and tissues and act in endocrine, autocrine or paracrine manner to regulate cellular proliferation, survival and differentiation. IGF actions are initiated upon binding to the type I IGF receptor (IGF-IR) and are modulated through interactions with a family of six secreted IGF-binding proteins (IGFBP-1 to -6). Although the six conserved IGFBPs are structurally related, each of them has specific characteristics and may have specific functions. Most knowledge about the IGFBPs has been gained from the numerous in vitro studies, their specific roles in vivo are largely unknown. Transgenic mice overexpressing a particular IGFBP allow us to investigate the specific functions of the corresponding IGFBP in vivo. To this end, IGFBP-4- and IGFBP-6-overexpressing models were established and analyzed in the present study. First, an expression vector containing the murine H-2Kb promoter and a human beta-globin splicing cassette was used to construct the transgenes, to obtain ubiquitous expression of the mouse Igfbp4 and Igfbp6 cDNA. Two lines of H-2Kb-mcIGFBP-4 and ten lines of H-2Kb-mcIGFBP-6 transgenic mice were generated. The transgene was ubiquitously expressed at RNA level in both transgenic models, however, at protein level, transgene expression was only detected in the spleen, thymus, lung and kidney of both H-2Kb-mcIGFBP-4 transgenic lines, but in no organ of H-2Kb-mcIGFBP-6 transgenic mice. Phenotypic analyses of the H-2Kb-mcIGFBP-4 transgenic model revealed that overexpression of IGFBP-4 had no significant effect on the postnatal body and organ growth, except that the weight and volume of thymus in 8- and 12-week-old transgenic mice were significantly reduced (p < 0.05) compared to the controls. Histomorphometric analysis demonstrated that the volume of the thymic cortex was significantly decreased in transgenic mice (p < 0.05), whereas that of the thymic medulla was not changed. The fractions of various cell types in the bone marrow, thymus, spleen, lymph node and peripheral blood were determined by flow cytometry. No significant difference was found between transgenic and control groups, suggesting that IGFBP-4 excess in the lymphoid organs did not affect the development of the lymphatic cells. The proliferative capacity of the splenocytes of transgenic animals was significantly reduced after Con A and LPS stimulation (p < 0.05), but not altered after the stimulation by anti-CD3 and anti-IgM/IL2. This is probably due to transgenic IGFBP-4 expression restricted in the non-lymphatic cells. However, detailed expression of the transgene warrants further investigation. In order to realize IGFBP-6-overexpressing mice, a second construct was designed, namely CMV-mgIGFBP-6, in which the mouse Igfbp6 genomic sequence was cloned under the control of the cytomegalovirus (CMV) promoter. Four independent lines of transgenic mice were generated. Transgene expression was high in the exocrine pancreas and relatively low in the lung and liver. The activities of serum IGFBPs were not different between transgenic mice and controls. In transgenic mice, high levels of active IGFBP-6 were detected in the luminal content of the duodenum, but neither in the luminal contents of other segments of the gastrointestinal tract (GIT), nor in tissue extracts of all GIT segments. Glucose homeostasis was not altered by IGFBP-6 expression. Postnatal body and organ growth was not affected in transgenic mice, except for the absolute and relative weight and length of duodenum which were significantly reduced in 4-month-old transgenic mice as compared to controls (p < 0.05). This reduction was mainly due to a significantly smaller volume and surface area of the tunica mucosa as determined by histomorphometric analsis. Our analysis of the first IGFBP-6 transgenic mouse model provides direct evidence for inhibition of intestinal growth by luminal IGFBP-6 excess. This finding is important in the context of neonatal intestinal growth of mammals, considering the fact that milk contains large amount of IGFBPs which may at least in part arrive intact in the intestine.

Although the stimulating effect of insulin-like growth factor I (IGF-I) on adrenal steroidogenesis has been well established, the role of IGF-II in the adult adrenal gland remains unknown. We, therefore, investigated the effect of recombinant human IGF-II on cortisol and cAMP synthesis from adult bovine adrenocortical cells. IGF-II, time and dose dependently, stimulated basal cortisol secretion maximally 3-fold. In combination with ACTH, IGF-II (13 nM) synergistically increased cortisol secretion from 1-fold (10(-8) M ACTH) to 28-fold of untreated control levels. In contrast, IGF-I at equimolar concentrations did not show an effect on basal cortisol secretion, and in combination with ACTH elicited a significant weaker stimulatory effect than IGF-II (22-fold increase). The synergistic effect of IGF-II on ACTH-promoted cortisol secretion was paralleled by accumulation of cAMP in the culture medium. Although both IGF receptors are present in adult bovine adrenocortical cells, the effect of IGF-II seems to be mediated through interaction with the IGF-I receptor, as [Arg54,55]IGF-II, which only binds to the IGF-I receptor, was equipotent to native IGF-II, whereas [Leu27]IGF-II, which preferentially binds to the type II IGF receptor, did not show any effect. By Western ligand blotting, four different molecular forms of IGF-binding proteins (IGFBPs) were identified in conditioned medium of bovine adrenocortical cells with apparent molecular masses of 39-44, 34, 29, and 24 kilodaltons. ACTH treatment increased the abundance of all binding proteins, on the average, 2.3-fold, except for the 29-kDa band, which was predominantly induced 6.8-fold. Additionally, [des1-3]IGF-I, a truncated IGF variant that exhibits only minimal binding to IGFBPs, was significant more potent than IGF-I and elicited the same maximum stimulatory effect on cortisol secretion as IGF-II and [des1-6]IGF-II. In conclusion, these results demonstrate that 1) IGF-II stimulates basal as well as ACTH-induced cortisol secretion from bovine adrenocortical cells more potently than IGF-I; 2) this effect is mediated through interaction of IGF-II with the IGF-I receptor; 3) bovine adrenocortical cells synthesize various IGFBPs that are induced differentially by ACTH; and 4) IGFBPs apparently play a modulatory role in IGF-induced stimulation of adrenal steroidogenesis. Therefore, bovine adult adrenocortical cells provide a useful tissue culture model in which the interactions among locally produced IGFs, IGFBPs, and the IGF-I receptor can be evaluated.

The putative effects of diabetes and metabolic control on circulating levels of insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) remain controversial. In the present study, serum levels of IGF-I and IGF-II and IGFBP-1, -2, and -3 were measured in 58 patients (age, 0.8-17 yr) with treated (51 subjects) or untreated (7 subjects) insulin-dependent diabetes mellitus (IDDM) and were compared with the levels in normal subjects. In the untreated patients IGF-I and IGF-II were decreased as compared with the healthy controls. In the treated diabetics IGF-I and IGF-II were reduced; IGFBP-2 (only in prepubertal subjects) and IGFBP-3 were increased. Furthermore, age-adjusted values of IGF-I, IGF-II, and IGFBP-3 were lower in prepubertal than in pubertal patients. Regression analysis revealed a negative correlation between hemoglobin (Hb)A1c and standard deviation scores (SDS) of IGF-I and a positive association between HbA1c and IGFBP-1 SDS or IGFBP-2 SDS. In the treated patients HbA1c was positively related to IGFBP-1 SDS and IGFBP-2 SDS when applying simple regression analysis and to IGFBP-2 SDS when using a multiple regression model. Strong correlations were observed between height SDS and IGF-I SDS, IGF-II SDS, and IGFBP-3 SDS in prepubertal subjects who had had IDDM for at least 2 yr, but not in adolescents. Such correlations have also been found in healthy children and adolescents. In conclusion; 1) IDDM is associated with alterations of the IGF-IGFBP system, which are partially accounted for by differences in metabolic control and pubertal status; 2) the lower plasma concentrations of serum IGF-I may play a role in the pathogenesis of growth impairment of poorly controlled prepubertal, but not pubertal, children and adolescents with IDDM; and 3) in addition, a potential role of the altered IGF-IGFBP system for the development of diabetic late complications is hypothesized.

Insulin-like growth factor-II (IGF-II) is an important regulator of embryonic growth and differentiation, but its function in postnatal life is unclear. To address this point, we generated transgenic mice harboring fusion genes in which a human IGF-II complementary DNA is placed under the transcriptional control of the rat phosphoenolpyruvate carboxykinase promoter. Transgene-specific messenger RNA was detected in liver, kidney, and several parts of the gut. Serum IGF-II levels in transgenic mice were 2-3 times higher than those in controls and increased after starvation. Circulating IGF-I correlated negatively and IGF-binding protein-2 (IGFBP-2) positively with IGF-II levels, suggesting that IGF-I is displaced from IGFBPs by IGF-II and that IGFII is a major regulator of IGFBP-2. Serum levels of IGFBP-3 and IGFBP-4 tended to be higher in phosphoenolpyruvate carboxykinase- IGF-II transgenic mice than in controls, as evaluated by ligand blot analysis. Starvation reduced serum IGF-I, but increased IGFBP-2 in transgenic mice more markedly than in controls. Fasting insulin levels were significantly reduced in transgenic mice, whereas glucose levels were not influenced by elevated IGF-II. The body growth of 4- and 12- week-old mice was not significantly influenced by elevated IGF-II, but transgenic mice displayed increased kidney and testis weight at the age of 4 weeks, and increased adrenal weight at the age of 12 weeks. Our results demonstrate that elevated IGF-II in postnatal life has multiple endocrine consequences and subtle time-specific effects on organ growth.

Cultured cardiac myocytes from adult Sprague-Dawley rats express both insulin-like growth factor-I (IGF-I) receptors and insulin-like growth factor-II/mannose 6-phosphate (IGF-II/Man6P) receptors and respond to IGF-I with a dose-dependent accumulation of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and inositol 1,4-bisphosphate [Ins(1,4)P2]. Specific binding of [125I]IGF-I to isolated membranes from cultured cardiac myocytes amounted to 1-1.2%. Binding of [125I]IGF-I was inhibited by unlabeled IGF-I at nanomolar concentrations and insulin at much higher concentrations. These data suggest that IGF-I binds to its own receptor on rat cardiac myocytes. Competitive binding studies using isolated membranes from cardiac myocytes and [125I]IGF-II showed 2-4% specific binding. Binding of [125I]IGF-II was inhibited by IGF-II and much less potently by IGF-I and insulin. Immunoglobulin G (IgG) 3637 (an IgG directed against the IGF-II/Man6P receptor) partially inhibited binding of [125I]IGF-II whereas nonimmune IgG did not. Affinity cross-linking studies with [125I]IGF-II and cardiac myocyte membranes and subsequent analysis of the ligand-receptor complex using SDS-PAGE and autoradiography showed a radiolabeled band of approximately 250 kilodalton (kDa). The formation of the [125I]IGF-II-receptor complex was inhibited by incubation with IGF-II and IgG 3637 but not by insulin or nonimmune IgG. Western blotting of protein extracts from cultured cardiac myocytes was performed using IgG 3637 and an immunoperoxidase technique for the visualization of the IGF-II/Man6P receptor protein. A specific band at 220 kDa under nonreducing conditions was detected on the blots, providing further evidence for the expression of the IGF-II/Man6P receptor by cardiac myocytes. The effect of IGFs on the accumulation of inositol phosphates was measured by HPLC analysis of perchloric acid extracts from myo-[3H]inositol-labeled cultured cardiac myocytes. IGF-I (50 ng/ml) stimulated the accumulation both of Ins(1,4,5)P3 and Ins(1,4)P2 after 30 sec by 43% and 63%. IGF-II (up to 500 ng/ml) had no significant effect on inositol phosphate accumulation under the same conditions. However, in the presence of millimolar concentrations of Man6P, IGF-II (500 ng/ml) also increased Ins(1,4,5)P3 accumulation by 59%. We conclude that cardiac myocytes from adult rats express IGF receptors and respond to IGFs with the accumulation of Ins(1,4,5)P3 and Ins(1,4)P2. This effect seems to be mediated by an IGF-I receptor-specific pathway.