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Biomedical subjects

H M Krans

Publications and source records attributed to H M Krans.

At least 55 records · Page 3Linked to original sources
PubMed1989

Individuals with only one allele for a functional insulin receptor have a tendency to hyperinsulinaemia but not to hyperglycaemia.

Recently, we described a leprechaun patient with a genetically transmitted severe insulin resistance due to the absence of functional insulin receptors as inferred from the loss of insulin binding to the patients' fibroblasts and the impaired autophosphorylation of the beta-chain of the receptor. This patient was homozygous for the genetic defect which was recently found to be a leucine to proline mutation at position 233 in the alpha-chain of the insulin receptor. In the present study we have examined insulin receptor functions in relatives of this patient. Some of these individuals are heterozygous for the genetic defect and have only one allele coding for a functional insulin receptor. Insulin binding to cultured fibroblasts from the heterozygous individuals is only 20-40% of control values indicating a Mendelian mode of inheritance of the binding defect. In contrast, insulin stimulated autophosphorylation of the beta-chain of the insulin receptor shows normal values, indicating compensation mechanisms operating on this process. The stimulation of the basal level of 2-deoxyglucose uptake by insulin in fibroblasts from the homozygous patient is 1.2 fold whereas the heterozygous and control individuals show stimulation values of approximately 1.65 fold. Basal levels of 2-deoxyglucose uptake are similar in these fibroblasts. Oral glucose tolerance tests on the heterozygous individuals indicate an increased requirement for insulin of the target tissues as concluded from the tendency towards hyperinsulinaemia with no observed hyperglycaemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Antilipolytic action of insulin in adipocytes from starved and diabetic rats during adenosine-controlled incubations.

Insulin action on adipocytes induces two major metabolic effects: stimulation of glucose transport and inhibition of lipolysis. Previously, we have shown that incubated isolated adipocytes from starved (S), and streptozotocin-treated diabetic (D) rats show insulin resistance on glucose transport. It is not known whether insulin resistance is also present on antilipolysis. In this study the antilipolytic action of insulin was investigated. Since basal lipolysis was low, lipolysis was first stimulated by isoproterenol (ISO). This showed that differences existed in sensitivity for ISO among control (C), S, and D adipocytes. We investigated whether changes in adenosine accumulation could attribute to the differences in ISO action and thereby influence insulin action. When endogenous accumulating adenosine was removed by adenosine deaminase and replaced by a fixed concentration (200 nM) of the nonhydrolyzable adenosine analog phenylisopropyladenosine, the differences in ISO action disappeared. This indicates that the sensitivity of C, S, and D adipocytes for ISO is strongly influenced by endogenous adenosine release. The dose-response relationship between insulin and inhibition of ISO-stimulated lipolysis showed that insulin sensitivity was increased and responsiveness unaltered in S and D compared to C adipocytes for incubations with both uncontrolled and controlled adenosine concentrations. This indicates that during S and D states, endogenous adenosine release has no major effect on insulin action. The increased sensitivity for insulin of S and D adipocytes was paralleled by an increased binding of [125I]iodoinsulin. The unaltered responsiveness for insulin indicates that there is no insulin resistance at the postbinding level for antilipolysis, i.e. intracellular processes for antilipolysis are intact. This is in contrast to glucose transport, where insulin resistance exists at the postbinding level during S and D. Thus, insulin resistance is no general phenomenon, but is confined to specific effector systems.

Adenosine↗
PubMed1989

Increased insulin action and clearance in hyperthyroid newly diagnosed IDDM patient. Restoration to normal with antithyroid treatment.

In a patient with hyperthyroidism and newly diagnosed insulin-dependent diabetes mellitus (IDDM), insulin action and clearance were studied before the initiation of antithyroid treatment and at 3-mo intervals for 1 yr thereafter. The sequential euglycemic clamp technique (5 mM) was used with insulin infusion rates of 0.5, 1.0, 2.0, and 5.0 mU.kg-1.min-1 in four steps of 2 h. The data were compared with nine control subjects and nine newly diagnosed euthyroid IDDM patients treated with insulin for 0.5 mo. Insulin sensitivity was increased in the patients (ED50 40 vs. 52 mU/L, range 43-70, in controls and 70 mU/L, range 59-120, in IDDM subjects). Insulin responsiveness was markedly elevated; the steady-state glucose infusion rate (SSGIR) of step 4 was 104 vs. 64 mumol.kg-1.min-1 (range 50-79) in controls and 61 mumol.kg-1.min-1 (range 47-69) in IDDM subjects. Insulin clearance was elevated in all steps (1-3, 20-23 vs. 9-15 ml.kg-1.min-1; 4, 18 vs. 6-12 ml.kg-1.min-1 in control and IDDM subjects). Parallel to the normalization of thyroid metabolism, insulin action (ED50 60 mU/L, SSGIR in step 4, 51 mumol.kg-1.min-1) and insulin clearance (steps 1-3, 11-14 ml.kg-1.min-1; step 4, 7 ml.kg-1.min-1) returned to the normal range in 6 mo. Both remained within the normal range until 12 mo. In the patient with newly diagnosed IDDM, the initial marked increases of insulin action and clearance were due to coexistent hyperthyroidism. With the amelioration of the hyperthyroid state, both processes became normal. The parallelism between insulin action and clearance suggests a functional relationship.

Adult↗
PubMed1988

Improper expression of insulin receptors on fibroblasts from a leprechaun patient.

Leprechaunism is an inherited human disorder characterized by severe insulin resistance. We have examined the properties of the insulin receptor in fibroblasts from a leprechaun patient. In vitro, severe insulin resistance is reflected by a low level of insulin binding to the patients fibroblasts and impaired insulin-mediated uptake of 2-deoxyglucose. Quantification of the receptor in detergent-solubilized total glycoprotein indicates a normal receptor number, in agreement with the observed normal level of insulin receptor mRNA on northern blots. The insulin-stimulated autophosphorylation of the patient's receptor shows a normal profile. The insulin receptor is present on the plasma membrane as indicated by cell-surface iodination experiments. No abnormalities in the molecular masses of the receptor's alpha and beta chains were observed. The results indicate that an apparently normal receptor is synthesized in sufficient amounts but functional expression of the receptor on the plasma membrane is impaired.

Cell Membrane↗
PubMed1988

Fibroblasts from a leprechaun patient have defects in insulin binding and insulin receptor autophosphorylation.

Leprechaunism is an inherited human disorder associated with an extreme resistance of the target cells towards the action of insulin. We have examined the properties of the insulin receptor in fibroblasts from a leprechaun patient (Geldermalsen, the Netherlands). In vitro, severe insulin resistance is reflected by a low level of insulin stimulated uptake of 2-deoxyglucose by these fibroblasts. This defect seems to be caused by a combination of two factors: a low level of insulin binding to intact cells and a strong decrease of insulin stimulated autophosphorylation of the receptor. The stimulation of autophosphorylation by insulin was approximately six-fold in control subjects and less than two-fold in the patient. No abnormalities were observed in the total number of insulin receptors in these cells and the molecular weights of the receptor subunits. In addition, the insulin concentration required for half maximal autophosphorylation is similar for the solubilised receptor from control and patient fibroblasts.

Cells, Cultured↗
PubMed1988

Insulin action is normalized in newly diagnosed type I diabetic patients after three months of insulin treatment.

We studied insulin action at submaximal and maximal insulin levels in seven newly diagnosed type I (insulin-dependent) diabetic patients after 2 weeks (t1/2) and after 3 months (t3) of insulin treatment, and in seven control subjects. Insulin action was determined with a sequential euglycemic (5.0 mmol/L) glucose clamp technique using insulin infusion rates of 0.5, 1.0, 2.0, and 5.0 mU.kg-1.min-1 in four periods of two hours each. The final 30 minutes of each infusion period (referred to as steady-state) were taken for the assessment of insulin action. Steady-state insulin levels were similar in the diabetic patients at t1/2 and t3, and in control subjects. During the first and second infusion periods, steady-state glucose infusion rates (SSGIR) were lower at t1/2 than at t3 (12.2 +/- 1.7 v 18.8 +/- 2.4, P less than .05, and 34.3 +/- 3.8 v 47.6 +/- 2.5 mumol.kg-1.min-1, P less than .02, respectively), and were lower at t1/2 compared to controls (12.2 +/- 1.7 v 22.4 +/- 2.3, P less than .01, and 34.3 +/- 3.8 v 47.3 +/- 2.8 mumol.kg-1.min-1, P less than .02). No differences were found during the third and fourth infusion periods between t1/2 and t3, or t1/2 and controls. When these data were used to construct dose-response curves, insulin action was decreased in the diabetic patients at t1/2 at submaximal insulin levels (shift to the right), while insulin responsiveness was unchanged. This finding may be regarded as a still-present manifestation of the metabolic derangement at the onset of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

The effect of insulin, serum and dexamethasone on mRNA levels for the insulin receptor in the human lymphoblastoic cell line IM-9.

The effect of insulin, serum and dexamethasone on mRNA levels in the insulin receptor in the human lymphoblastoic cell line IM-9 was examined. To this end, mRNA levels were quantitated by Northern blot analysis using a labeled cDNA probe for the insulin receptor. The presence of 0.1 microM dexamethasone in the medium had a strong stimulatory effect on mRNA levels in insulin receptor, suggesting the presence of a glucocorticoid inducible enhancer element near the insulin receptor gene. Also, the nature of the serum had an effect on insulin receptor mRNA levels, as cells maintained in 10% fetal calf serum had insulin receptor mRNA levels that were 40-50% of those found in IM-9 cells maintained in 1% newborn serum. Variations in insulin receptor mRNA levels led in each situation to concordant variations in insulin binding. Insulin levels of up to 1 microM had no effect on hybridizable insulin receptor mRNA levels making an insulin-induced feed-back mechanism on gene expression or mRNA stability unlikely.

Blood↗
PubMed1986

Characterization of the sulfonylurea-induced potentiation of the insulin response in cultured 3T3 adipocytes.

Studies were carried out to determine the role of sulfonylureas in the regulation of insulin-sensitive hexose uptake in cultured 3T3 adipocytes. Exposure (0-72 hr) of cells to the sulfonylurea-derivative tolbutamide (0.05-0.3 mg/ml) induced a time- and concentration-dependent potentiation of the stimulatory effect of insulin on hexose uptake (500 vs 340%). The effect was maximal within 24 hr and completely reversible. It was strictly limited to the presence of insulin. Basal hexose uptake and insulin binding were not affected by the drug. High concentrations of the agent (greater than 0.3 mg/ml) induced a decrease in insulin response, suggesting a concentration optimum. Lineweaver-Burk analysis of uptake data revealed that the potentiating effect of tolbutamide was due to enhancement of the insulin-induced increase in apparent Vmax, i.e. in the number or activity of hexose transporters. This enhancement was inhibited by cycloheximide (1 microgram/ml), indicating involvement of protein synthesis in the induction of the effect. It is concluded that sulfonylureas act by influencing synthesis of protein(s) which potentiate the effect of insulin on hexose uptake.

Adipose Tissue↗
PubMed1985

Transport-associated phosphorylation of 2-deoxyglucose in rat adipocytes.

The relationship between ATP levels and 2-deoxyglucose uptake was investigated. When the concentration in the medium lies between 1 and 10 mM 2-deoxyglucose uptake causes a marked decrease in ATP level. This could partly be explained by an inhibiting effect of 2-deoxyglucose and 2-deoxyglucose 6-phosphate on ATP synthesis in the mitochondria. A good correlation between the various ATP levels induced by 2,4-dinitrophenol and the rate of uptake of 5 microM and 0.5 mM (but not 5 mM) 2-deoxyglucose was observed. The addition of glucose and 2-deoxyglucose to cells incubated in the presence of trace amounts of 2-deoxy-[1-14C]glucose induced marked changes in the uptake of the tracer that were associated with a rapid decline in ATP level. It appeared that the phosphorylation of 2-deoxyglucose is an important step in the uptake of the sugar. It is hypothesized that the processes of transport and phosphorylation of 2-deoxyglucose are coupled in rat adipocytes.

2,4-Dinitrophenol↗
PubMed1985

Glucose as a regulator of insulin-sensitive hexose uptake in 3T3 adipocytes.

In the present study we examined the role of glucose in the regulation of its own transport activity in the cultured 3T3 fat cell. A regulatory control of glucose became apparent after these cells were cultured in the absence of glucose. Glucose deprivation of the cells was accompanied by a specific time and protein synthesis-dependent increase in dGlc (2-deoxyglucose) uptake (up to 5-fold), which was due to an increase in the apparent Vmax of the transport system. Concomitantly, the stimulatory effect of insulin on hexose uptake almost completely disappeared. Addition of glucose to the glucose-deprived cells rapidly reversed the deprivation effects. Cycloheximide experiments revealed that the glucose deprivation-induced increase in hexose uptake required protein synthesis as well as a protein synthesis-independent response to glucose deprivation that retarded the turnover of hexose transport activity. Taken together, these data indicate that glucose deprivation is accompanied by retardation of the rate of degradation, internalization, or inactivation of hexose transporters while the increase in dGlc uptake requires at least the continuation of protein synthesis-dependent de novo synthesis, insertion, or activation of hexose transporters. Hexose competitively taken up with dGlc, including the nonmetabolizable glucose analogue 3-O-methylglucose, could replace glucose in the process of prevention and reversal of the deprivation effects, indicating that competitive transport but not the metabolism of hexose is a prerequisite for the regulatory effect of glucose on the activity of its own transport system. In conclusion, our results indicate that in cultured 3T3 fat cells glucose itself is involved in the regulation of the activity of its own transport system by influencing the rate of degradation, internalization, or inactivation of hexose transporters by a protein synthesis-independent mechanism.

3-O-Methylglucose↗
PubMed1985

Long-term regulation of hexose transport by insulin in cultured mouse (3T3) adipocytes.

Observations in vivo suggest that insulin acts as a long-term regulator of hexose uptake in fat cells. In the present study, we examined the long-term effect of insulin on hexose uptake in vitro. Exposure of fully differentiated mouse 3T3-L1 adipocytes to insulin induced a time-, concentration-, and protein synthesis-dependent increase in basal 2-deoxyglucose uptake (up to 40%) and a decrease in the 'acute' insulin response. The decrease in insulin effect was due to post-receptor alterations, since insulin binding was not substantially altered. The increase in basal 2-deoxyglucose uptake was due to an increase in the apparent Vmax of the transport system rather than to the observed increase (30%) in hexokinase activity, since the concentration of non-phosphorylated 2-deoxyglucose inside the cell was far below the extracellular concentration. The increase in apparent Vmax was most likely due to a protein synthesis-dependent increase in de novo synthesis of hexose transporters. Glucose was not essential for the effect. The mechanism responsible for the loss in insulin response remains to be solved. It can be concluded that insulin has the ability to act as a long-term regulator of hexose uptake in fat cells in vitro.

Adipose Tissue↗
PubMed1985

Corticosteroids as long-term regulators of the insulin effectiveness in mouse 3T3 adipocytes.

Since corticosteroid treatment is often accompanied by insulin resistance, we explored the role of corticosteroids in the regulation of the insulin effectiveness in cultured 3T3 (mouse) adipocytes. Exposure of the fat cells to dexamethasone or corticosterone (0-5 days) induced a time-, concentration-, and protein synthesis-dependent and reversible decrease in insulin binding and in basal and insulin-stimulated 2-deoxyglucose uptake. The decrease in binding (50%) was primarily due to a decrease in receptor affinity i.e. to an increase in the rate of dissociation of insulin from its receptors, and was independent from the effects of pH and temperature on the affinity. The reduction in the 2-deoxyglucose uptake (30-50%) was due to a decrease in the hexose transport capacity rather than to a decrease in the phosphorylation component of the 2-deoxyglucose uptake process. Lineweaver-Burk analysis revealed the dexamethasone induced a decrease in the apparent Vmax of the transport system i.e. in the number or activity of the hexose transporters. The effect of dexamethasone seemed to be superimposed on that of long-term insulin treatment, suggesting a different mechanism. It is concluded that corticosteroids act as long-term regulators of the insulin effectiveness by influencing the rate at which insulin dissociates from its receptors and by altering the number or activity of the hexose transporters by a common mechanism, which differs from that of the long-term regulatory effect of insulin.

Adenosine Triphosphate↗
PubMed1985

Long-term regulation of hexose uptake by isoproterenol in cultured 3T3 adipocytes.

Catecholamines are known to have short-term regulatory effects on fat cell hexose uptake. We examined the long-term effects of catecholamines on the insulin-sensitive 2-deoxyglucose (dGlc) uptake in cultured 3T3-L1 adipocytes. Prolonged exposure (48 h) to isoproterenol (beta-adrenergic agonist) stimulated the basal dGlc uptake up to 90%. The effect was specific, time, concentration, and protein synthesis dependent and reversible. The effect of insulin was unaltered and superimposed on the increase in basal dGlc uptake. The long-term effect of isoproterenol was mimicked by epinephrine, dibutyryl cAMP (DBcAMP), and 1-methyl-3-isobutylxanthine (IBMX). By contrast, short-term exposure to isoproterenol (and epinephrine) induced a protein synthesis-independent increase in basal dGlc uptake (30%) not accompanied by an increase in insulin responsiveness. Moreover, on short-term basis, DBcAMP and IBMX suppressed both the basal and insulin-stimulated uptake up to 50%. Determination of the intracellular nonphosphorylated dGlc during the uptake and of the hexokinase activity revealed that the long-term effect of isoproterenol was most likely due to alterations low in dGlc transport. In conclusion, long-term regulators of hexose uptake are in cultured 3T3-L1 adipocytes, isoproterenol, and other cAMP stimulators. The long-term effect is independent from the short-term regulatory effect of the agents and from the effect of insulin.

1-Methyl-3-isobutylxanthine↗
PubMed1985

Low pH and ketoacids induce insulin receptor binding and postbinding alterations in cultured 3T3 adipocytes.

The etiology of insulin resistance during diabetic ketoacidosis is still poorly understood. Changes in insulin receptor binding and the existence of postreceptor alterations have been proposed. In an attempt to clarify the role of low pH and ketone bodies in the insulin resistance, we examined the effectiveness of insulin during and after 48 h of exposure of cultured 3T3-L1 adipocytes to low pH and ketoacids. In the "acute" stage, lowering of physiologic pH (pH 7.4) to pH 6.9 induced a decrease in insulin binding (50%), which was due to a decrease in the rate of association. Concomitantly, the insulin sensitivity was decreased (ninefold). The basal hexose uptake and insulin responsiveness were only slightly decreased at low pH. Beta-hydroxybutyrate partially counteracted the effect of low pH on insulin binding and sensitivity in a dose-dependent fashion (ED50: 10 mM). The binding-enhancing effect of ketoacids was more pronounced at low pH than at physiologic pH and absent at optimum pH (pH 8.0). After 48 h of exposure of the cells to pH 6.9, insulin binding and insulin sensitivity (measured at physiologic pH) were similar as in cells cultured at pH 7.4. The insulin response, however, was substantially impaired (40%), due to an increase in basal hexose uptake as well as a decrease in maximal insulin-stimulated uptake. These postbinding alterations induced by low pH could be reversed by culturing the cells at physiologic pH for another 48 h. Prolonged exposure to ketoacids did not affect the insulin effectiveness.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1984

The effects of 1-methyl-3-isobutylxanthine on insulin-sensitive 2-deoxyglucose transport.

The effect of 1-methyl-3-isobutylxanthine on insulin-sensitive 2-deoxyglucose uptake in rat adipocytes was studied. 1-Methyl-3-isobutylxanthine inhibited 2-deoxyglucose uptake rate substantially in both the absence and presence of insulin. The lag-time for the effect of insulin on 2-deoxyglucose uptake was prolonged. At the same time 1-methyl-3-isobutylxanthine caused a decrease in ATP levels. From experiments with isolated rat liver mitochondria it appeared that 1-methyl-3-isobutylxanthine inhibits glutamate plus malate oxidation in State 3.

1-Methyl-3-isobutylxanthine↗
PubMed1984

Stimulatory and inhibitory effects of adrenaline and 8-bromo-cAMP on insulin-sensitive 2-deoxyglucose transport in rat adipocytes.

The effects of adrenaline and 8-bromo-cAMP on 2-deoxyglucose uptake in isolated rat adipocytes were investigated under conditions of unidirectional flux, in which the transport process is rate limiting. Adrenaline showed a dualistic effect in the absence of insulin. At concentrations below 1 microM adrenaline stimulated 2-deoxyglucose uptake; at higher concentrations adrenaline inhibited the uptake. In the presence of insulin at the maximum effective concentration, addition of adrenaline further increased the 2-deoxyglucose uptake by about 50%. In the presence of insulin 8-bromo-cAMP had the same effect as adrenaline. In the absence of insulin, 8-bromo-cAMP only inhibited 2-deoxyglucose uptake.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1983

Phloretin - an uncoupler and an inhibitor of mitochondrial oxidative phosphorylation.

The effect of phloretin on respiration by isolated mitochondria and submitochondrial particles was studied. In submitochondrial particles, both NADH- and succinate-dependent respiration was inhibited by phloretin. 50% maximum inhibition was reached at phloretin concentrations of 0.1 mM (NADH oxidation) and 0.7 mM (succinate oxidation). In isolated mitochondria, phloretin inhibited glutamate oxidation in both State 3 and State 4; 50% maximum inhibition occurred at about 30 microM. Succinate oxidation is inhibited in State 3 by phloretin, inhibition being half its maximum value at 0.5 mM, but in State 4 it is stimulated about 2-fold by phloretin at a concentration of 0.6 mM. Ascorbate oxidation is stimulated in both State 3 and State 4, maximum stimulation being equal to that obtained with an uncoupler of oxidative phosphorylation. Under all circumstances, phloretin lowered the transmembrane electrical potential difference in isolated mitochondria. These results are discussed in terms of mosaic non-equilibrium thermodynamics. We conclude that phloretin is both an uncoupler and an inhibitor of oxidative phosphorylation.

Animals↗