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Biomedical subjects

G Grunberger

Publications and source records attributed to G Grunberger.

At least 55 records · Page 3Linked to original sources
PubMed1990

Repeated pregnancy without lactation: effects on maternal glycemic control, pregnancy outcome, carcass composition, and fat distribution in rats.

Repeated pregnancy without lactation in rats has been reported to produce permanently elevated carcass fat mass and hyperplasia in subcutaneous fat depot. In the present study, the pregnancy outcome, intravenous glucose tolerance ability (IVGTT), and carcass composition were further examined in Osborne-Mendel rats. Female rats were divided into pregnancy-lactation (PL), pregnancy-no lactation (PNL), and control (CON) groups. Half of the rats were killed after three pregnancy/lactation cycles, whereas the rest were given a 12-week rest period before killing. It was found that rats in PNL group had fasting hyperglycemia and insulin insensitivity during the third pregnancy (P less than or equal to .05), elevated spontaneous abortion rate (P less than or equal to .05), and elevated subcutaneous fat content (P less than or equal to .01) relative to that of PL rats or CON rats. After a 12-week rest period, a significant increase in subcutaneous fat cell number was also observed in PNL rats. PL rats, on the other hand, have significantly elevated internal/subcutaneous fat ratios (P less than or equal to .05), both immediately after weaning and after the 12-week rest period. The significance of this change is not yet known.

Adipose Tissue↗
PubMed1990

Effects of food restriction and insulin treatment on (Ca2+ + Mg2+)-ATPase response to insulin in kidney basolateral membranes of noninsulin-dependent diabetic rats.

Insulin increases (Ca2+ + Mg2+)-ATPase activity in cell membranes of normal rats but fails to do so in membranes of non-insulin-dependent diabetic (NIDD) rats. The loss of regulatory effect of the hormone on the enzyme might contribute to the insulin resistance observed in the NIDD animals. To further test this hypothesis, the effects of insulin treatment and acute food restriction on the ability of insulin to regulate the ATPase activity in kidney basolateral membranes (BLM) of NIDD rats were studied. Although insulin levels in NIDD and control rats were similar, plasma glucose was higher in the NIDD rats (18.3 +/- 1.5 v 19.3 +/- 1.7 microU/mL and 236 +/- 32 v 145 +/- 3 mg/dL, respectively). Insulin treatment (2 U/100 g), which increased plasma insulin in the NIDD rats (47.8 +/- 11.5 microU/mL; P less than .05), did not decrease their glucose (221 +/- 25 mg/dL). Higher insulin dose (4 U/100 g) decreased glucose level in the NIDD rats (73 +/- 3 mg/dL; P less than .001) but increased their plasma insulin 10-fold (202.5 +/- 52.5 microU/mL). Acute food restriction decreased glucose levels in the NIDD rats to levels seen in controls (135 +/- 3 mg/dL), while their insulin decreased by half (8.5 +/- 1.0 microU/mL; P less than .05). Basal (Ca2+ + Mg2+)-ATPase activity in BLM of all diabetic rats was higher than in controls (P less than .05). None of the treatments reversed this defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Insulin antagonistic effects of insulin receptor antibodies on plasma membrane (Ca2+ + Mg2+) ATPase activity: a possible etiology of type B insulin resistance.

The regulatory effect of insulin on plasma membrane (Ca2+ + Mg2+)ATPase activity in target tissues for insulin was proposed to be of importance in mediating the hormone's cellular action. Consequently, polyclonal insulin receptor antibodies from patients with type B insulin resistance (B7 and B10) were used as probes to further explore a possible role for this ATPase in insulin action. The antibodies B7 and B10 obtained during the active phase of the disease manifested insulinomimetic actions in rat renal cortical basolateral membranes by displacing [125I]insulin bound to the membranes and stimulating the tyrosine kinase activity of solubilized insulin receptors in a dose-dependent manner. In contrast, these antibodies had insulin antagonistic effects on the membrane (Ca2+ + Mg2+)ATPase activity. While insulin stimulated, both antibodies inhibited the ATPase basal activity in a dose-dependent manner. Furthermore, the stimulatory effect of insulin on the ATPase was completely abolished by the antibodies. Immunoglobulin fractions obtained from patient B10 in the clinically inactive phase of the disease and from pooled normal human sera did not affect basal or insulin-stimulated ATPase activity. The effects of insulin receptor antibodies on basal and insulin-stimulated (Ca2+ + Mg2+)ATPase activities were specific. The receptor antibody did not affect PTH-stimulated (Ca2+ + Mg2+) ATPase activity, nor did it affect other kidney basolateral membrane ATPase basal activities. The data reveal that insulin receptor antibodies have a direct regulatory effect on the plasma membrane (Ca2+ + Mg2+) ATPase. We suggest that the insulin antagonistic effects of the insulin receptor antibodies on the ATPase might explain in part the impaired insulin action in type B insulin resistance.

Animals↗
PubMed1990

High-fat feeding induces tissue-specific alteration in proportion of activated insulin receptors in rats.

High dietary fat intake causes glucose intolerance and insulin resistance in man and in laboratory rats. We studied possible mechanisms of this insulin resistance in rat kidney, muscle and liver. In high-fat fed rats the body weight, plasma insulin concentration, plasma glucose levels, and serum triglyceride concentration were significantly higher than in the control rats. 125I-insulin binding to kidney basolateral membrane insulin receptors from high-fat fed rats was lower than in control rats. Basal as well as insulin-stimulated tyrosine kinase activity per insulin receptor was higher in the high-fat fed group, accompanied by increased autophosphorylation of the beta-subunit of the receptor and higher proportion of tyrosine-phosphorylated insulin receptors. In contrast, both in the skeletal muscle and the liver the insulin-stimulated tyrosine kinase activity per insulin receptor was significantly lower in high-fat fed animals, accompanied by diminished autophosphorylation of the beta-subunit of the receptor and lower proportion of tyrosine-phosphorylated receptors. Our results indicate tissue-specific alterations in transmembrane signaling induced by high-fat feeding in target tissues for insulin which in turn might contribute to the observed insulin resistance.

Animals↗
PubMed1990

Abnormal insulin receptor tyrosine kinase activity in kidney basolateral membranes from non-insulin-dependent diabetic rats.

Neonatal rats that receive injections of streptozotocin develop insulin resistance and non-insulin-dependent diabetes mellitus (NIDDM). Insulin resistance precedes development of overt diabetes, and some insulin bioeffects are known to be impaired at the postreceptor level in several target tissues of this rat model. We studied a possible contribution of altered insulin receptor function to the impaired insulin action in these animals. Activity of the insulin-sensitive tyrosine kinase of receptors from kidney cortical basolateral membranes (BLMs) obtained from these nonobese, normoinsulinemic, insulin-resistant rats was examined at the age of 5 weeks (before overt hyperglycemia developed) and at 10 weeks (after NIDDM was fully manifested). In experimental animals, at both 5 and 10 weeks, binding of insulin labeled with iodine 125 to crude kidney BLM was higher than in their control littermates. However, no such difference was found with insulin binding to purified insulin receptors from BLM. The insulin receptor, tyrosine kinase activity (TKA), to an exogenous substrate was higher in diabetic tissue both at basal condition and after insulin stimulation at both 5 and 10 weeks of age. Autophosphorylation of the beta-subunit of the insulin receptor and the proportion of tyrosine-phosphorylated ("active") insulin receptors from BLM was also higher in diabetic rats. There was an age-related increase in the receptor TKA between 5 and 10 weeks in both diabetic and control animals. A 24-hour fast normalized insulin binding and nearly abolished the difference in TKA of the BLM receptors from 5-week-old insulin-resistant rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Receptor-mediated endocytosis of insulin: inhibition of [125I]iodoinsulin internalization in insulin resistant diabetic states of man.

We have used electron microscopic autoradiography to quantitatively study receptor-mediated endocytosis of [125I]insulin in freshly isolated monocytes from patients with non-insulin-dependent diabetes mellitus. In obese, non-obese, and lipoatrophic patients with diabetes, internalization of [125I]insulin was impaired at 30 min of incubation at 37 degrees C. By 60 min of incubation, however, internalization was indistinguishable from that of normals. In obese non-diabetic controls, internalization at 30 min was slightly less than internalization in normals but greater than that of the diabetic group. Dieting was associated with normalization of internalization in the obese group. We conclude that the rate of [125I]insulin internalization is impaired in non-insulin-dependent diabetes and compare this to previously reported results in insulin-dependent diabetes mellitus.

Adult↗
PubMed1988

Plasma membrane phospholipid content in non-insulin-dependent streptozotocin-diabetic rats--effect of insulin.

The activity of (Ca2+ +Mg2+)-ATPase is impaired in kidney basolateral membranes from non-insulin-dependent streptozotocin-diabetic rats. To study the possible role of changes in membrane phospholipid content in the malfunction of this enzyme in kidney membranes of the diabetic animals, phospholipid (phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and sphingomyelin) content was measured in kidney and liver membranes obtained from non-insulin-dependent diabetic rats. Total phospholipid content was similar in liver and kidney membranes of diabetic and control rats (595 +/- 47 versus 624 +/- 29 in liver and 469 +/- 22 versus 458 +/- 17 nmol Pi/mg protein in kidney respectively). Phosphatidylethanolamine content in kidney and liver membranes of diabetic rats was lower than in control rats (87.7 +/- 1.8 versus 96.4 +/- 2.2 nmol Pi/mg protein, p less than 0.01 and 87.1 +/- 3.7 versus 101.8 +/- 3.5, p less than 0.02 respectively). Phosphatidylinositol content was higher in kidney (28.0 +/- 0.6 versus 23.9 +/- 2.1, p less than 0.02) but not liver membranes from diabetic rats. The in vitro direct effect of insulin on the phospholipid content in kidney membranes was also measured. Physiologic concentrations of insulin (718 pmol/l for 30 min) increased the phosphatidic acid content in membranes from control but not from diabetic rats by 34.2% (p less than 0.02). This rise was readily measurable after 3 min of exposure to insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Factitious hypoglycemia due to surreptitious administration of insulin. Diagnosis, treatment, and long-term follow-up.

Ten patients had factitious hypoglycemia due to surreptitious insulin injections diagnosed and were followed for up to 15 years (median, 5 years; range, 2 months to 15 years). When available, demonstration of anti-insulin antibodies was the most helpful diagnostic test. Decreased plasma C-peptide levels corroborated the diagnosis. Young women (nine of ten) with knowledge of the medical profession or relatives with diabetes mellitus predominated in the sample. Five of the patients had a history of insulin-requiring diabetes mellitus. Two patients eventually committed suicide despite the best efforts at therapy. Only three of ten patients made a successful transition into productive life after the diagnosis of factitious hypoglycemia was established. Factitious hypoglycemia remains a difficult diagnosis to make, and the long-term outcome after the diagnosis is established is unpredictable. All efforts have to be made to confirm the diagnosis before the patients are approached. The confrontation is to be made by an experienced team of health care professionals who have gained the patient's confidence through an understanding but firm manner. Long-term therapy must be planned and initiated before the patient's discharge.

Adult↗
PubMed1988

Insulin receptor tyrosine kinase activity is abnormal in circulating cells and cultured fibroblasts but normal in transformed lymphocytes from a type A insulin-resistant patient.

The function of the insulin receptor subunits isolated from cells of a patient with the type A syndrome of insulin resistance was examined. Iodine 125-labeled insulin binding, insulin-stimulated phosphorylation of both endogenous and exogenous substrates, and internalization of 125I-insulin were evaluated. 125I-insulin binding to intact peripheral monocytes and erythrocytes, cultured skin fibroblasts, and cultured Epstein-Barr virus-transformed lymphocytes, as well as to partially purified receptor preparations from these cells, was entirely normal. In contrast, the insulin-stimulated receptor autophosphorylation and tyrosine kinase activity of the partially purified monocyte, erythrocyte, and fibroblast receptor preparations were markedly diminished. Solubilized, lectin-purified receptors from virally transformed cultured lymphocytes, however, demonstrated normal insulin-sensitive kinase activity. The patient's peripheral monocytes did not internalize 125I-insulin at 37 degrees C, but her transformed lymphocytes internalized it normally, as assessed by electron microscopic autoradiography. Our findings suggest that the discordance between the functions of the alpha-subunits and beta-subunits of the insulin receptor from monocytes of this insulin-resistant patient (Science 1984;223:932-4) extends to other freshly isolated cell types and persists in her cultured cells. Viral transformation of her cells results directly or indirectly in normal expression of the receptor kinase activity. Whether the defective kinase activity of the insulin receptor and the impaired receptor internalization exhibited by her monocytes ultimately cause the patient's insulin resistance awaits further studies.

Adult↗
PubMed1987

Posterior vitreous fluorophotometry in diabetic patients with minimal or no retinopathy.

Vitreous fluorophotometry (VFP) using the Fluorotron Master was performed in 25 insulin-dependent diabetic patients with either minimal or no retinopathy and 22 controls. At 30 minutes, baseline corrected vitreous fluorescence values 3 mm from the retina were significantly greater in diabetic patients with minimal retinopathy than in either controls or patients with no retinopathy but were similar in patients with no retinopathy and controls. At 1 hour, vitreous fluorescence values and fluorescein permeability indexes were similar in all three groups. The absence of increased posterior vitreous fluorescein leakage in the diabetic patients with no retinopathy suggests that the alteration in permeability of the blood retinal barrier, as assessed by current VFP measures, does not precede the development of clinical diabetic retinopathy. However, the significantly increased 30-minute 3-mm fluorescence values suggest that posterior fluorescein leakage is increased in minimal background diabetic retinopathy.

Adult↗
PubMed1987

Relationship of insulin binding and insulin-stimulated tyrosine kinase activity is altered in type II diabetes.

The insulin receptor contains an alpha subunit with insulin binding properties and a beta subunit with insulin-stimulated tyrosine kinase function. Preparations containing insulin and insulinlike growth factor I (IGF-I) receptors were obtained from solubilized human red cell membranes by affinity chromatography. After separate assays for insulin binding and insulin-stimulated tyrosine kinase activities, a high degree of correlation was found between these activities in preparations from normals and diabetics. Identical studies using IGF-I as the ligand showed a lesser degree of correlation. We compared 24 normal subjects and 14 untreated type II diabetics and found significant diminution in the slope of the line coupling insulin binding and insulin-stimulated kinase activities in the diabetics. This difference was not observed in a similar study of IGF-I-related activities. Compared to normal controls, untreated type II diabetics have reduced tyrosine kinase activity stimulated per unit insulin binding.

Adult↗
PubMed1986

Glycosylation defects alter insulin but not insulin-like growth factor I binding to Chinese hamster ovary cells.

Insulin binding to two Chinese hamster ovary cell lines with well-defined defects in their glycosylation pathway has been characterized and compared to insulin-like growth factor I (IGF-I) binding in the same cell lines. Insulin competition curves indicate that B4-2-1 cells, which transfer co-translationally to proteins an endoglycosidase H insensitive, truncated lipid-linked oligosaccharide, bind insulin with higher than normal affinity. Lec 1 cells, which fail to process oligosaccharide side chains to complex types, bind with a reduced affinity. The potencies of chicken and guinea pig insulins are appropriate for an insulin receptor in the control (WTB) and both mutant cell lines, whereas rat IGF-II is 3 times more potent than expected in the Lec 1 cells and human IGF-I is less potent than anticipated. Insulin bound to Lec 1 cells dissociates more quickly upon dilution than does insulin bound to either WTB or B4-2-1 cells. The Lec 1 insulin receptor is insensitive to pH change, whereas the other lines show the usual optimum of 8. 125I-IGF-I binds well to all three cell lines and is equally pH-sensitive in all three. Serum from a patient with circulating autoantibodies to the insulin receptor competes for insulin but not IGF-I binding, whereas alpha IR3, a monoclonal antibody directed toward the human IGF-I receptor inhibits IGF-I but not insulin binding. Cross-linking of either 125I-insulin or 125I-IGF-I reveals a typical alpha-subunit in the WTB and B4-2-1 cells but a band with faster mobility in the Lec 1 cells. Insulin (10(-8) M) stimulates autophosphorylation of a beta-subunit in all three lines, but again the Lec 1 subunit demonstrates an anomalous mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These data demonstrate the differential effect of glycosylation on two closely related receptor molecules.

Animals↗
PubMed1986

Impaired 6-phosphofructokinase activity in mononuclear leukocytes from patients with type II diabetes mellitus.

Seven cytoplasmic enzyme activities were measured in extracts of mononuclear leukocytes (lymphocytes plus monocytes) obtained from 19 type II diabetic humans and 10 healthy control subjects. 6-Phosphofructokinase activity was significantly decreased in cell extracts from diabetics, while other enzyme activities were similar in diabetics and controls. Since the effects of starvation on enzyme activities are sometimes similar to the effects of diabetes, the studies were repeated in 5 control subjects after a 2-day fast. This short period of starvation did not mimic the effect of diabetes on 6-phosphofructokinase activity. The decreased enzyme activity was not correlated with percent specific insulin binding to monocytes in the same cell preparations nor to clinical variables such as obesity or the broad range of fasting plasma glucose values encountered among the diabetics. We conclude that 6-phosphofructokinase activity in mononuclear leukocytes, as in other tissues, may be a marker for a postreceptor lesion associated with the insulin resistance found in type II diabetes mellitus.

Adult↗
PubMed1986

Insulin receptor of human cerebral gliomas. Structure and function.

The insulin receptor from human brain tumors of glial origin was examined for the first time using intact cells (from an established cultured human glioblastoma cell line) and partially purified solubilized membranes (from cultured cells and freshly isolated human brain tumors). The structure of the glial insulin receptor subunits was assessed by affinity cross-linking of 125I-insulin with the alpha-subunit of the receptor, neuraminidase treatment of the cross-linked receptor, behavior of the receptor on lectin columns, and electrophoretic mobility of the phosphorylated beta-subunit. The functions of the insulin receptor were examined by measuring specific 125I-insulin binding (receptor concentration, affinity, specificity, pH-, time-, and temperature dependence), insulin-induced down-regulation of the receptor, insulin-stimulated autophosphorylation of the beta-subunit, and phosphorylation of exogenous substrates as well as insulin-stimulated glucose uptake in glioblastoma cells. All of these properties were typical for the insulin receptor from target tissues for insulin action. The insulin receptor of the normal human brain showed the altered electrophoretic mobility and lack of neuraminidase sensitivity of its alpha-subunit previously reported for the rat brain receptor. There was no difference, however, in the functions of the receptor subunits (binding, phosphorylation) from the normal brain tissue and the eight human gliomal tumors. Since the glial elements compose a majority of the brain cells, the "normal" structure and function of their insulin receptor might provide a key to understanding the role of insulin in the carbohydrate metabolism of the human central nervous system.

Biological Transport↗
PubMed1986

Immunological similarity between the insulin receptor and the protein encoded by the src oncogene.

Insulin receptors resemble receptors for certain growth factors (epidermal growth factor, platelet-derived growth factor, and insulin-like growth factor I) in that all possess tyrosine-specific protein kinase activity. These cell surface receptors resemble protein kinases encoded by viral oncogenes in that both groups of enzymes phosphorylate proteins on tyrosine. Recently, we reported that there is immunological similarity between the insulin receptor and pp60src [the protein encoded by the src oncogene of Rous sarcoma virus (RSV)]. This is supported by the observation that anti-pp60src antiserum (TBR serum) immunoprecipitated radiolabeled insulin receptors derived from cultured human cells (IM-9 lymphoblasts and U-937 monocytes) and rabbit liver. Moreover, highly purified preparations of src protein inhibit the immunoprecipitation of insulin receptors by TBR serum, and the inhibition is correlated with the src kinase activity present in the preparation used. However, two observations suggested that there were immunological differences between pp60src and mammalian insulin receptors. 1) Even at a relatively high concentration (dilution, 1:10), TBR serum immunoprecipitated a relatively small percentage (approximately 20%) of the labeled insulin receptors. 2) Some lots of TBR serum with a high titer against pp60src failed to immunoprecipitate the insulin receptor. Viral oncogenes are thought to have been derived from proto-oncogenes in the host cell. Therefore, because the chicken is the natural host for RSV, we inquired whether there might be closer homology between pp60src and avian insulin receptors. Surprisingly, under conditions where TBR serum immunoprecipitates human insulin receptors, we could not detect immunoprecipitation of avian insulin receptors from chicken liver, chicken embryo fibroblasts, or turkey erythrocytes. The immunoprecipitation of human insulin receptor is not dependent on the method used for labeling the cells ([125I]insulin cross-linking), inasmuch as the receptor labeled by autophosphorylation with [gamma-32P]ATP could also be immunoprecipitated by TBR serum. These observations suggest that there is structural homology between pp60src and the insulin receptor (most likely the beta-subunit). Nevertheless, it seems unlikely that the insulin receptor gene is the proto-oncogene for the src gene of RSV.

Animals↗
PubMed1986

Receptor-mediated endocytosis of polypeptide hormones is a regulated process: inhibition of [125I]iodoinsulin internalization in hypoinsulinemic diabetes of rat and man.

Much data suggest that receptor-mediated endocytosis is regulated in states of hormone excess. Thus, in hyperinsulinemic states there is an accelerated loss of cell surface insulin receptors. In the present experiments we addressed this question in hypoinsulinemic states, in which insulin binding to cell surface receptors is generally increased. In hepatocytes obtained from hypoinsulinemic streptozotocin-induced diabetic rats, [125I]iodoglucagon internalization was increased, while at the same time [125I]iodoinsulin internalization was decreased. The defect in [125I]iodoinsulin internalization was corrected by insulin treatment of the animal. In peripheral blood monocytes from patients with type I insulinopenic diabetes, internalization of [125I]iodoinsulin was impaired; this defect was not present in insulin-treated patients. These data in the hypoinsulinemic rat and human diabetes suggest that receptor-mediated endocytosis is regulated in states of insulin deficiency as well as insulin excess. Delayed or reduced internalization of the insulin-receptor complex could amplify the muted signal caused by deficient hormone secretion.

Adolescent↗
PubMed1986

Diacylglycerol modulation of insulin receptor from cultured human mononuclear cells. Effects on binding and internalization.

Tumor-promoting phorbol esters alter binding of growth factors and hormones to their specific receptors. Action of diacylglycerols, endogenous phorbol ester analogues, on 125I-labeled insulin binding to its receptor from human cells was therefore investigated. A variety of 1,2-diacylglycerols and 1,3-diacylglycerols inhibited 125I-insulin binding to intact human monocyte-like (U-937) and lymphoblastoid (IM-9) cells in a dose-, time-, and temperature-dependent manner within 30 sec at 37 degrees C in a fashion analogous to that of the tumor-promoting phorbol diester 12-O-tetradecanoylphorbol-13-acetate (TPA). Inhibition of insulin binding by diacylglycerols, analyzed by Scatchard plot, seems to be due to altered binding affinity of the insulin receptor. Diacylglycerol effects were reversible, were seen regardless of the order of addition of 125I-insulin and diacylglycerols, and were demonstrated only with occupied insulin receptors. Corresponding fatty acids or phospholipids did not affect specific insulin binding to the intact U-937 cells. Diacylglycerols also inhibited binding of 125I-insulin-like growth factor (IGF) I but not that of 125I-human growth hormone (HGH) to the human cells. The non-tumor-promoting phorbols (phorbol, 4-alpha-phorbol, phorbol-12,13-distearate) did not affect insulin binding to intact cells. Both diacylglycerols and TPA stimulated internalization of 125I-insulin by U-937 and IM-9 cells. The ability of diacylglycerol to mimic the effects of TPA on the insulin receptor supports the concept of diacylglycerols as endogenous phorbol diester analogues even though the sole role of protein kinase C in our system is doubtful.(ABSTRACT TRUNCATED AT 250 WORDS)

Cells, Cultured↗