Pioglitazone Therapy Increases Insulin-Stimulated Release of d-Chiro-Inositol-Containing Inositolphosphoglycan Mediator in Women with Polycystic Ovary Syndrome.

BACKGROUND: Insulin resistance in women with polycystic ovary syndrome (PCOS) may be mediated, in part, by a deficiency in the insulin-stimulated release of a d-chiro-inositol-inositolphosphoglycan (DCI-IPG) mediator of insulin action. Supporting this idea, several studies have reported improved insulin sensitivity in both lean and obese women with PCOS after oral administration of DCI. Pioglitazone improves insulin sensitivity in women with PCOS, but it is unknown whether this may be contributed by enhanced insulin-stimulated release of the DCI-IPG second messenger. The study aimed to determine if pioglitazone increases release of biologically active DCI-IPG per unit insulin released during an oral glucose tolerance test (OGTT). METHODS: A randomized, double-blind placebo-controlled trial was conducted in 32 women with PCOS at a tertiary referral center in Venezuela. The intervention comprised administration of pioglitazone 45 mg daily or matched placebo for 6 months. Outcome measures included area under curves (AUC) of DCI-IPG (AUCDCI-IPG), insulin (AUCinsulin), and the ratio of AUCDCI-IPG to AUCinsulin during a 2-hr OGTT. RESULTS: After treatment with pioglitazone, AUCinsulin during the OGTT decreased and whole body insulin sensitivity, as determined by the Matsuda index, increased significantly only in the pioglitazone group. The ratio of AUCDCI-IPG/AUCinsulin increased in the pioglitazone group by 1.85-fold (P < 0.0001) with no significant change in the placebo group. Change in Matsuda index correlated with change in DCI-IPG released per unit of insulin during OGTT (r = 0.47, P < 0.01). CONCLUSION: In women with PCOS, pioglitazone increased insulin-stimulated release of the DCI-IPG second messenger of insulin action, which may contribute to its insulin-sensitizing effect in these women.

Euglycemic hyperinsulinemic clamp

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Insulin is the principal hormone of glucose metabolic regulation. Reduced glucose responses to insulin constitute an underlying feature of type 2 diabetes. In addition, insulin resistance is a common condition related with the metabolic syndrome and strongly associated with an increased risk of cardiovascular disease. The importance of the insulin-resistant phenotype for the assessment of cardiovascular risk and response to intervention is increasingly being recognized. Therefore, there is a need for an accurate and reproducible method for measuring insulin resistance in vivo. The euglycemic hyperinsulinemic clamp (EHC) is currently the gold standard method available for the determination of whole glucose uptake in response to insulin, from which several derived indices of insulin sensitivity are obtained. The clamp technique is both expensive and complex to undertake and has prompted the use of surrogate methods, notably the insulin tolerance test and frequently sampled intravenous glucose tolerance test. Indices may be derived from these methods and correlate well with those derived from clamp studies. However, important limitations of these procedures are that not only does insulin sensitivity change in pathological situations, but also in normal physiology. Variations also occur in time–depending on the physiological state of the individual or following diurnal rhythms. In conclusion, the quantitative assessment of insulin sensitivity with EHC is not used for routine clinical purposes, but the emerging importance of insulin resistance has led to its wider application to research studies that have examined its pathogenesis, etiology and consequences (AU)

A new classification plot for the C-peptide suppression test.

CONTEXT AND OBJECTIVE: To evaluate the C-peptide suppression test as a screening test in patients with symptoms of hypoglycemia as compared to the standard fasting test. DESIGN: Retrospective discriminant analysis of data from C-peptide suppression tests. SETTING: Clinical study. PATIENTS: Patients with insulinomas and patients without insulinomas but having symptoms compatible with hypoglycemia. INTERVENTIONS: The results from C-peptide suppression tests of 26 patients with insulinomas and 100 patients without insulinomas were compared. MAIN OUTCOME MEASURES: A classification plot which introduces two discriminant parameters for the C-peptide suppression test: the ratio of [blood glucose]/[C-peptide] at the lowest C-peptide concentration and mean glycemia during insulin infusion. RESULTS: In patients with insulinomas, minimal serum C-peptide levels were higher (1.81+/- 0.87 ng/mL; median 1.83 ng/mL; maximal suppression 37 +/- 24% of basal C-peptide levels) as compared to patients without insulinoma (0.40 +/- 0.15 ng/mL; median 0.30 ng/mL; maximal suppression of 75 +/- 9%; P<0.001). Mean glycemia during the test was lower in patients with insulinomas (30.8 +/- 3.3 vs. 47.5 +/- 8.3 mg/dL; P<0.001) as was the [blood glucose]/[C-peptide] ratio (21.9 +/- 14.6 vs. 139.2 +/- 43.8; P<0.001). Discriminant analysis revealed a specificity of 96% to rule out the diagnosis of 'insulinoma' at a 1% probability threshold with a sensitivity of 100%. CONCLUSIONS: We developed a new classification plot for the C-peptide suppression test in order to accurately identify those patients whose symptoms of hypoglycemia are not due to endogenous hyperinsulinemia/insulinomas. Thus, the need for fasting tests and hospitalization costs can be reduced.

Endothelin-1 infusion inhibits plasma insulin responsiveness in normal men.

OBJECTIVES: Elevated plasma endothelin (ET)-1 levels have been described in insulin-resistant states such as syndrome X, obesity, non-insulin-dependent diabetes mellitus, and in some studies in essential hypertension. To investigate whether increases in circulating ET-1 to levels observed in insulin-resistant states can modulate insulin levels and/or insulin sensitivity in humans, we assessed these variables during low, non-pressor-dose ET-1 compared with placebo infusion. DESIGN: In a randomized, single blind, crossover design, 10 lean normotensive male subjects received either an intravenous infusion of subpressor doses of ET-1 dissolved in polygeline or a control infusion of polygeline only (placebo). Using dynamic assessment by the minimal model approach with the modified frequent sampling intravenous glucose tolerance test (FSIGT) the following and other parameters were measured: insulin sensitivity; acute insulin response to glucose (AIR(G)) calculated as the average of the three peak values between 2 and 5 min after injection of glucose from which the basal insulin levels were subtracted; the initial area under the curve (AUC(1-19)) from insulin values between time 0 and 19 min and the first-phase insulin secretion (phi1) from insulin kinetics parameters. RESULTS: ET-1 infusion reduced AIR(G) (to 34.85 +/- 4.27 compared with 49.3 +/- 6.9 microU/ml during placebo, P=0.017) and the acute C-peptide response to glucose (to 2.33 +/- 0.41 compared with 3.1 +/- 0.44 ng/ml, P=0.018), decreased plasma insulin levels during the FSIGT compared with placebo (analysis of variance P<0.0001) and decreased the AUC(1-19) (to 2.1 +/- 0.2 compared with 2.9 +/- 0.3 U/l per 20 min, P<0.01) while phi1 tended to be lower. S1 measured during ET-1 infusion was unaltered (11.11 +/- 1.91 x 10(-4) versus 10.88 +/- 2.11 10(-4)/min per mU per l, NS). CONCLUSIONS: These findings demonstrate that an increase in circulating ET-1 to levels observed in insulin-resistant states acutely diminishes the insulin secretory response but does not significantly modify insulin sensitivity.

Insulin antagonism: a novel role for human serum transferrin.

We have purified alpha2-glycoprotein (alpha2-GP), an insulin antagonist from human plasma which is induced by growth hormone (GH), and shown that pure alpha2-GP is a potent antagonist of severe insulin-induced hypoglycemia, producing acute hyperglycemia in intact rats and ketonuria in diabetic rats. The N-terminal amino acid sequence of alpha2-GP and the reactivity of alpha2-GP with an antitransferrin monoclonal antibody show that alpha2-GP is identical to human serum transferrin. Furthermore, pure human serum transferrin and non-glycosylated recombinant human transferrin reproduce the insulin antagonist effects of alpha2-GP in rats, whereas ovotransferrin shows no such effect. The neutralization of the insulin antagonism of human serum transferrin by an anti-transferrin monoclonal antibody shows that transferrin has a new function as a potent insulin antagonist. This novel role for human serum transferrin in the regulation of glucose metabolism provides a reasonable mechanism for the diabetogenic effect of GH, and has important implications for the etiology and progression of diabetes.

Insulin mediators in man: effects of glucose ingestion and insulin resistance.

Insulin mediators (inositol phosphoglycans) have been shown to mimic insulin action in vitro and in intact mammals, but it is not known which mediator is involved in insulin action under physiological conditions, nor is it known whether insulin resistance alters the mediator profile under such conditions. We therefore investigated the effects of glucose ingestion on changes in the bioactivity of serum inositol phosphoglycan-like substances (IPG) in healthy men and insulin resistant (obese, non-insulin-dependent diabetic) men. Two classes of mediators were partially purified from serum before and after glucose ingestion. The first was eluted from an anion exchange resin with HCl pH 2.0, and bioactivity was determined by activation of pyruvate dehydrogenase in vitro. The second was eluted with HCl pH 1.3, and bioactivity was determined by inhibition of cyclic AMP-dependent protein kinase. In healthy men, the bioactivity of the pH 1.3 IPG was not altered by glucose ingestion, whereas bioactivity of the pH 2.0 IPG increased to approximately 120% of the pre-glucose ingestion value at 60-240 min post-glucose ingestion (p < 0.05 vs pre-glucose). There was no change in either IPG after glucose ingestion in the insulin-resistant group. These data suggest that the pH 2.0 IPG plays an important role in mediating insulin's effect on peripheral glucose utilization in man under physiological conditions. The data further show, for the first time, a defective change in the bioactivity of an insulin mediator isolated from insulin-resistant humans after hyperinsulinaemia, suggesting that inadequate generation/release of IPGs is associated with insulin resistance.

[The mechanism of anti-insulin effect of apoprotein B]. / K mekhanizmu kontrinsuliarnogo éffekta apoproteina B.

The existence of common epitope in insulin molecule and apolipoprotein B one was shown by means of enzyme immunoassay. Similar epitopes were revealed in apoB-containing lipoproteins (VLDL and LDL) by dot-immunobinding and immunoelectroblotting. Epitopes locate on the surface of lipoproteins and are not screened by lipids. The existence of common epitopes is the reason of competition between insulin and LDL. The experiments with isolated perfused rat hindquarter demonstrate that insulin increased the glucose uptake by muscle and LDL decreased it. Simultaneous perfusion with LDL and insulin leads to reduced insulin action due to completion for insulin receptors. After the recovery of S-S bounds apoB forms some proteins, containing common epitopes with insulin. The presence of such proteins was shown in lipoprotein-free serum. Apoprotein B and its derivates seem to be insulin antagonists with marked antiinsulin action.

Circulating factors and insulin resistance. I. A novel myoinositol 1,2-cyclic phosphate phosphoglycan insulin antagonist from human plasma is elevated in noninsulin-dependent diabetes mellitus.

A novel low mol wt inositol phosphoglycan inhibitor (M tau 1200-1500) of insulin action in rat adipocytes has been partially purified from normal human plasma. This inhibitor, termed fraction V after the first purification step and fraction V3 after the second, is different from other reported serum insulin antagonists. It contains myoinositol, galactosamine, and mannose in approximate molar ratios of 1:1:3.3. The myoinositol has a 1,2-cyclic phosphate substituent, which is essential for the inhibitory activity. Its inhibitory activity is significantly elevated (161%, P < 0.05 for fraction V; 278%, P < 0.05 for fraction V3) in plasma of humans with noninsulin-dependent diabetes mellitus as compared with plasma of nondiabetic controls. These findings represent the first report of a naturally occurring mammalian inositol 1,2-cyclic phosphate containing phosphoglycan related to insulin action.

Proglumide antagonizes cholecystokinin effects on plasma glucose and insulin in rats in vivo.

Proglumide was shown to possess a low affinity for cholecystokinin (CCK) receptors and to inhibit the synergistic action of CCK8 on glucose-mediated insulin release in vitro. Proglumide (400 mg/kg i.p., given 15 min before an i.v. combination of CCK8 and glucose) reversed the CCK8 (0.5 nmol/kg)-induced increase of plasma insulin levels and decrease of glucose levels. It had no effect on plasma insulin and glucose levels when the glucose bolus was administered alone. Camostate (400 mg/kg p.o.; Foy-305; a trypsin inhibitor acting via endogenously released CCK) increased plasma insulin levels by 10 microU/ml during an oral glucose (500 mg/kg) tolerance test. Pretreatment with proglumide (400 mg/kg i.p.) antagonized this effect. The data indicate that proglumide has an antagonistic effect on either exogenously added or endogenously released CCK with respect to plasma insulin and glucose levels and that it has no effect on plasma insulin and glucose levels when glucose is given alone. Therefore, proglumide and the newly developed, more potent CCK receptor antagonists are able to disturb insulin and glucose homoeostasis.

[Hepatic and peripheral insulin resistance as a cause of hyperglycemia in non-insulin-dependent (type 2) diabetes mellitus: a review]. / Hepatische und periphere Insulinresistenz als Urasche der Hyperglykämie bei nicht-insulinabhängigem (Typ-2-)Diabetes mellitus: Eine Ubersicht.

In diabetic patients, fasting hyperglycaemia is attributed to both, reduced clearance by peripheral tissues and augmented endogenous glucose release. In normal-weight, non-insulin-dependent diabetic patients, basal hepatic glucose production (HGP) was determined by means of tracer kinetic analysis. HGP was enhanced to 3.00 +/- 0.20 mg/kg X min as compared to 1.90 +/- 0.05 in healthy, non-diabetic subjects, even though hyperglycaemia and fasting hyperinsulinaemia prevailed. HGP correlated positively with fasting blood glucose (r = 0.577; P less than 0.01). Glucose clearance rate was reduced by 20%. Marked hyperinsulinaemia during an isoglycaemic (0.75 mU/kg X min) insulin clamp study suppressed HGP by only 82% as compared to greater than 95% in healthy subjects. Furthermore, significant residual HGP was also observed when hyperglycaemia was augmented by exogenous glucose administration. Thus, in the fasting state, HGP is increased and directly correlated with severity of hyperglycaemia. Due to a reduction in glucose clearance, blood glucose concentration rises until glucose utilization rate equals HGP. Under conditions of hyperinsulinaemia and hyperglycaemia, suppressibility of HGP is diminished. Thereby, HGP and diminished glucose clearance by peripheral tissues contribute to basal as well as postprandial hyperglycaemia in type 2 diabetic patients.

[Comparative research on the basal blood level of contrainsular hormones in diabetics with compensated and subcompensated nephropathy]. / Sravnitelni prouchvaniia vurkhu bazalnoto kruvno nivo na kontrainsularnite khormoni pri diabetitsi s kompensirana i subkompensirana nefropattia.

The blood levels of II contrainsular hormones were studied in patients with diabetes mellitus, with compensated and subcompensated nephropathy. No significant difference in both subgroups was established in any of the hormones. Those data suggest that the changes, established by us, in the blood levels of the hormones studied resulted from the changes in their secretion, and not from the changes in their renal elimination due to the existing light renal insufficiency in some of them. On the other hand, the existing light renal insufficiency in the diabetics should not be the reason for avoiding examinations and reserve to the results obtained from the hormonal dosage, when it is necessary.

Treatment of autonomic neuropathy with a somatostatin analogue SMS-201-995.

Eight patients with postprandial hypotension and orthostatic hypotension were treated with the somatostatin analogue SMS-201-995. Low doses of this drug (0.2-0.4 microgram/kg) raised the blood pressure after breakfast in all six patients with postprandial hypotension. 60 min after breakfast the mean sitting blood pressure was 35 +/- 10 (SEM) mm Hg higher after administration of SMS-201-995 0.4 microgram/kg than after placebo (p less than 0.001). Larger doses (up to 1.6 micrograms/kg) raised upright blood pressure during the postprandial period in five of seven patients. Before therapy three patients were unable to stand after eating; after an injection of SMS-201-995 0.8 microgram/kg at the beginning of breakfast they were able to walk for 35-100 min. The duration of therapeutic effect of each injection was 3-6 h. Treatment was followed by abdominal cramps and nausea in two patients with gastroparesis diabeticorum. SMS-201-995 holds promise as a treatment for postprandial hypotension and orthostatic hypotension.

Human plasma fractions inhibit the action of insulin on adipocytes and somatomedin on cartilage.

Since human immunoglobulins exert an insulin-like stimulatory effect on adipocyte lipogenesis at concentrations markedly lower than those found in vivo, and since human serum or plasma are only midly stimulatory, we predicted that human serum probably contains an inhibitor of adipocyte lipogenesis. Supernatant preparations, obtained from the precipitation of immunoglobulins from plasma in 2.5 mol/l ammonium sulphate, were extensively dialysed and tested for their activity on bioassay systems commonly used for measuring insulin. The supernatants produced a marked inhibition of basal and insulin- or IgG-stimulated lipogenesis and glucose oxidation by adipocytes at protein concentrations of 10 mg/l. The supernatants were further purified through ultrafiltration to demonstrate two main inhibitory fractions, 10 to 30 K and 30 to 50 K, which again produced marked inhibition of basal and insulin- or IgG-stimulated adipocyte lipogenesis and glucose oxidation. These fractions were then tested for basal and serum somatomedin-stimulated 35S sulphate uptake by porcine cartilage: both basal and serum somatomedin-stimulated 35S uptake were significantly inhibited (p less than 0.01). Therefore, normal human serum contains at least two peptides which are markedly inhibitory to glucose metabolism and insulin action on adipocytes and 35S transport and somatomedin action on cartilage.

Insulin resistance, acanthosis nigricans, and polycystic ovaries associated with a circulating inhibitor of postbinding insulin action.

A 21-yr-old moderately obese woman with hirsutism, acanthosis nigricans, and oligomenorrhoea was diagnosed as having polycystic ovary syndrome. Despite hyperinsulinemia, binding of insulin to her red cells was within the range for normal, young adult subjects. Her serum did not bind or degrade [125I]insulin or alter its binding to fat cells, and was negative for insulin receptor antibodies. However, her serum caused a dose-dependent inhibition of insulin-stimulated lipogenesis (conversion of [3-3H]glucose to [3H]lipid) in rat fat cells significantly greater than that produced with control serum (relative potency, 3.5:1) and (at a 1:20 dilution) markedly impaired the response of both lipogenesis and 2-deoxy-D-glucose uptake to maximum concentrations of insulin. After the patient was treated with clomiphene for 4 months, her menses resumed, hair growth slowed, fasting blood glucose and plasma insulin concentrations decreased, and serum inhibitory activity decreased to the control range. Serum inhibitory activity was stable to freezing and thawing and to heating at 56 C for 30 min, and could be extracted into acid-ethanol. By dialysis, its mol wt was below 1000, whereas by ultracentrifugation, it was above 3500; both high and low mol wt forms were detected after Sephadex G-50 gel chromatography of serum, suggesting that the inhibitor was of low mol wt but loosely bound to a higher mol wt component in serum. These findings indicate that insulin resistance in this patient with acanthosis nigricans and polycystic ovaries could be attributed to a circulating low mol wt inhibitor of postbinding insulin action.

A postbinding inhibitor of insulin action. Increased concentrations in the plasma of non-insulin-dependent diabetic subjects.

"Postreceptor" insulin resistance in persons with non-insulin-dependent diabetes (NIDDM) could be due to an intrinsic defect in insulin-sensitive pathways or to the action of a circulating inhibitor. Since evidence for the former is lacking, we have addressed the question of a circulating inhibitor by examining the effect of plasma and plasma extracts from NIDDM subjects on the lipogenic response of rat adipocytes to insulin. A majority (77%) of plasma samples (1:20 dilution) from unselected, treated NIDDM subjects (N = 69) inhibited insulin-stimulated conversion of 3-3H-glucose to 3H-lipid in rat adipocytes to a greater extent than did control samples (N = 24). The mean +/- SD inhibition by NIDDM plasma (81 +/- 21%) was significantly greater (P less than 0.01) than by control plasma (50 +/- 14%). Diabetic and, to a lesser degree, control plasma both caused a significant decrease in the maximal response of lipogenesis to insulin. Inhibitory activity was extracted into acid/ethanol, present in the flow of a Sep-pak C18 column, heat-stable (56 degrees C for 30 min [plasma], 80 degrees C for 30 min [acid/ethanol]), resistant to proteases, and dialyzable through 1000-dalton-mol wt exclusion dialysis tubing. The inhibition by NIDDM plasma or partially purified inhibitor could not be explained by the presence of insulin antibodies, insulin receptor antibodies, other inhibitors of insulin binding, or the concentrations of known counterregulatory factors. There was no correlation between inhibitory activity and plasma glucose (r = 0.26), insulin (r = 0.33), C-peptide (r = 0.26), or HbA1c (r = 0.26).(ABSTRACT TRUNCATED AT 250 WORDS)

Counterregulatory hormones during moderate, insulin-induced, blood glucose decrements in man.

To verify whether a significant increase in levels of counterregulatory hormones occurs in the course of mild blood glucose decrements, we infused regular insulin iv over 65 min in two groups of healthy volunteers (group A, n= 7; group B, n = 6) at a constant rate (group A, 0.05 U/kg; group B, 0.025 U/kg). All subjects were connected to an artificial endocrine pancreas (Biostator) for continuous blood glucose (BG) monitoring. Plasma insulin, glucagon, and GH were determined by specific RIAs. Plasma norepinephrine, epinephrine, and cortisol were measured by sensitive fluorimetric methods. A moderate fall in BG occurred from 91 +/- 1.5 mg/dl (mean +/- SEM) to a nadir of 56 +/- 4.5 mg/ml at 45 min in group A and from 81 +/- 2.5 to a nadir of 64 +/- 4.9 mg/dl at 45 min in group B. In both groups A and B, the increases in plasma glucagon and catecholamine levels, which remained strictly in the physiological range, appeared concomitant and were significant at 45 min (P less than or equal to 0.05 vs. basal), while the increases in plasma cortisol and GH concentrations were clearly delayed. The increments for all counterregulatory hormones (expressed as the area to minutes ratio) except GH, were significantly greater in group A than in group B ( P less than or equal to 0.01). There was a significant correlation between these increases, including that of GH and the BG decrease, calculated in all subjects investigated. These results suggest that the mechanisms involved for the release of counterregulatory hormones such as glucagon, catecholamines, cortisol, and GH are very sensitive to a moderate decrease in BG concentration and that there is a close relationship between this hormonal response and the degree of the BG decrements obtained.

Insulin degradation in serum of a patient with apparent insulin resistance.

A case is presented of a thin diabetic male who was resistant to large doses of sc and im insulin but responded to small dose of insulin given iv. His serum contained an enzyme that degraded [125I]insulin in vitro. We postulate that his apparent insulin resistance was due to inactivation of insulin at the injection site. We propose that the sera of patients with insulin resistance be tested for [125I]insulin-degrading activity as a possible means of identifying patients with this syndrome.