Is the ADA/EASD algorithm for the management of type 2 diabetes (January 2009) based on evidence or opinion? A critical analysis

The ADA and the EASD recently published a consensus statement for the medical management of hyperglycaemia in patients with type 2 diabetes. The authors advocate initial treatment with metformin monotherapy and lifestyle modification, followed by addition of basal insulin or a sulfonylurea if glycaemic goals are not met (tier 1 recommendations). All other glucose-lowering therapies are relegated to a secondary (tier 2) status and only recommended for selected clinical settings. In our view, this algorithm does not offer physicians and patients the appropriate selection of options to individualise and optimise care with a view to sustained control of blood glucose and reduction both of diabetes complications and cardiovascular risk. This paper critically assesses the basis of the ADA/EASD algorithm and the resulting tiers of treatment options.

Irbesartan has no short-term effect on insulin resistance in hypertensive patients with additional cardiometabolic risk factors (i-RESPOND)

AIMS

Intervention studies have shown that angiotensin receptor blockers (ARB) may reduce the incidence of type 2 diabetes mellitus. It is currently unclear whether short-term therapy with ARBs affects metabolic parameters.

METHODS

i-RESPOND, a randomised, controlled, multicentre, double-blind study evaluated the effect of 16 weeks of irbesartan vs. hydrochlorothiazide (HCTZ) on insulin resistance as well as on lipid and inflammatory parameters in hypertensive subjects with metabolic syndrome. Patients received irbesartan (150 mg/d; n = 211) or HCTZ (12.5 mg/d; n = 215), titrated to 300 mg/day and 25 mg/day respectively. In a second part of the study (weeks 16-28), patients initially randomised to irbesartan received additional HCTZ and vice versa.

RESULTS

At week 16 both irbesartan and HCTZ had no effect on insulin resistance measured by the Matzuda index and beta-cell function. Similarly, in the second part of the study (week 16-28) no differences between irbesartan and HCTZ with respect to glucose metabolism were observed. However, irbesartan induced beneficial changes in high-sensitivity-C-reactive protein (hs-CRP) (irbesartan: -5.5 +/- 5.2%; HCTZ + 19.9 +/- 6.5%, p = 0.0024) and in urinary albumin/creatinine ratio (ACR) (irbesartan: -13%; HCTZ + 9%; p = 0.0041) compared with HCTZ despite a similar decrease in blood pressure in both treatment groups. Irbesartan and HCTZ were well tolerated and adverse events were comparable.

CONCLUSION

Irbesartan did not show significant favourable effects on insulin resistance compared with HCTZ in this study; however, may have beneficial effects on inflammation and microalbuminuria in hypertensive patients with metabolic syndrome.

Recombinant human insulin-like growth factor I treatment for 1 week improves metabolic control in type 2 diabetes by ameliorating hepatic and muscle insulin resistance

The administration of recombinant human insulin-like growth factor I (rhIGF-I) reduces hyperglycemia and insulin requirements in subjects with severe insulin resistance syndromes and in patients with type 2 diabetes mellitus (T2DM). However, the mechanisms responsible for the improved metabolic control are incompletely understood. One proposed mechanism is that rhIGF-I therapy in T2DM may bypass early defects in insulin action (i.e. signal transduction), leading to improved hepatic and/or peripheral insulin sensitivity. To test this hypothesis, we used the euglycemic insulin clamp to measure the response to 7 days of rhIGF-I therapy (80 microg/kg, sc, twice daily) in eight poorly controlled T2DM subjects. rhIGF-I significantly improved fasting (203 +/- 12 vs. 134 +/- 14 mg/dL; P < 0.01) and day-long (0800-1700 h; 234 +/- 11 vs. 153 +/- 10 mg/dL; P < 0.01) plasma glucose levels. Basal endogenous glucose production decreased from 3.2 +/- 0.2 to 2.7 +/- 0.2 mg/kg lean body mass x min (P < 0.03) despite a concomitant decline in the fasting plasma insulin concentration from 13 +/- 5 to 5 +/- 1 microU/mL (P < 0.01). The decrement in basal endogenous glucose production was closely correlated with the decrement in fasting plasma glucose concentration (r = 0.78; P < 0.01). Whole body insulin-stimulated glucose disposal increased by 27% (from 5.6 +/- 0.8 to 7.1 +/- 0.8 mg/kg lean body mass x min; P < 0.01), but remained well below that observed in age- and weight-matched healthy subjects. The effects of rhIGF-I on endogenous glucose production and peripheral insulin sensitivity resemble those observed with intensified insulin regimens in T2DM. We conclude that 7 days of sc rhIGF-I improves glucose control by improving hepatic and muscle insulin sensitivity, but it remains markedly abnormal. This indicates that an intrinsic defect(s) responsible for insulin resistance in T2DM cannot be overcome by rhIGF-I treatment.

Recombinant human insulin-like growth factor I treatment for 1 week improves metabolic control in type 2 diabetes by ameliorating hepatic and muscle insulin resistance

The administration of recombinant human insulin-like growth factor I (rhIGF-I) reduces hyperglycemia and insulin requirements in subjects with severe insulin resistance syndromes and in patients with type 2 diabetes mellitus (T2DM). However, the mechanisms responsible for the improved metabolic control are incompletely understood. One proposed mechanism is that rhIGF-I therapy in T2DM may bypass early defects in insulin action (i.e. signal transduction), leading to improved hepatic and/or peripheral insulin sensitivity. To test this hypothesis, we used the euglycemic insulin clamp to measure the response to 7 days of rhIGF-I therapy (80 microg/kg, sc, twice daily) in eight poorly controlled T2DM subjects. rhIGF-I significantly improved fasting (203 +/- 12 vs. 134 +/- 14 mg/dL; P < 0.01) and day-long (0800-1700 h; 234 +/- 11 vs. 153 +/- 10 mg/dL; P < 0.01) plasma glucose levels. Basal endogenous glucose production decreased from 3.2 +/- 0.2 to 2.7 +/- 0.2 mg/kg lean body mass x min (P < 0.03) despite a concomitant decline in the fasting plasma insulin concentration from 13 +/- 5 to 5 +/- 1 microU/mL (P < 0.01). The decrement in basal endogenous glucose production was closely correlated with the decrement in fasting plasma glucose concentration (r = 0.78; P < 0.01). Whole body insulin-stimulated glucose disposal increased by 27% (from 5.6 +/- 0.8 to 7.1 +/- 0.8 mg/kg lean body mass x min; P < 0.01), but remained well below that observed in age- and weight-matched healthy subjects. The effects of rhIGF-I on endogenous glucose production and peripheral insulin sensitivity resemble those observed with intensified insulin regimens in T2DM. We conclude that 7 days of sc rhIGF-I improves glucose control by improving hepatic and muscle insulin sensitivity, but it remains markedly abnormal. This indicates that an intrinsic defect(s) responsible for insulin resistance in T2DM cannot be overcome by rhIGF-I treatment.

Direct measurement of the lumped constant for 2-deoxy-[1-(14)C]glucose in vivo in human skeletal muscle

The lumped constant (LC) is used to convert the clearance rate of 2-deoxy-D-glucose (2-DG(CR)) to that of glucose (Glc(CR)). There are currently no data to validate the widely used assumption of an LC of 1.0 for human skeletal muscle. We determined the LC for 2-deoxy-[1-(14)C]glucose (2-DG) in 18 normal male subjects (age, 29+/- 2 yr; body mass index, 24.8+/-0.8 kg/m(2)) after an overnight fast and during physiological (1 mU x kg(-1) x min(-1) insulin infusion for 180 min) and supraphysiological (5 mU x kg(-1) x min(-1) insulin infusion for 180 min) hyperinsulinemic conditions. Normoglycemia was maintained with the euglycemic clamp technique. The LC was measured directly with the use of a novel triple tracer-based method. [3-(3)H]glucose, 2-[1-(14)C]DG, and [(12)C]mannitol (Man) were injected as a bolus into the brachial artery. The concentrations of [3-(3)H]glucose and 2-[1-(14)C]DG (dpm/ml plasma) and of Man (micromol/l) were determined in 50 blood samples withdrawn from the ipsilateral deep forearm vein over 15 min after the bolus injection. The LC was calculated by a formula involving blood flow calculated from Man and the Glc(CR) and 2-DG(CR). The LC averaged 1.26+/-0.08 (range 1.06-1.43), 1.15+/-0.05 (0.99-1.39), and 1.18+/-0.05 (0.97-1.37) under fasting conditions and during the 1 and 5 mU x kg(-1). min(-1) insulin infusions (not significant between the different insulin concentrations, mean LC = 1.2, P<0.01 vs. 1.0). We conclude that, in normal subjects, the LC for 2-DG in human skeletal muscle is constant over a wide range of insulin concentrations and averages 1. 2.

Regulation of hexokinase II expression in human skeletal muscle in vivo

The phosphorylation of glucose to glucose-6-phosphate (G-6-P) is the first committed step in glucose uptake in skeletal muscle. This reaction is catalyzed by hexokinase (HK). Two HK isoforms, HKI and HKII, are expressed in human skeletal muscle, but only HKII is regulated by insulin. The present study was undertaken to determine the time course for the regulation of HK activity and expression by physiological plasma insulin concentrations in human skeletal muscle in vivo. A hyperinsulinemic-euglycemic glucose clamp and percutaneous muscle biopsy were performed in separate groups of healthy subjects after 60, 120, 180, and 360 minutes of euglycemic hyperinsulinemia. Muscle biopsies were subfractionated into soluble and particulate fractions to determine HKI and HKII activities. RNA was extracted from a separate portion of the muscle biopsy, and HKI and HKII mRNA content was determined using an RNase protection assay. Glycogen synthase (GS) activity and fractional velocity were also determined. HKII mRNA was increased 2-fold by 120 minutes and remained high versus the basal value for up to 360 minutes. HKI mRNA was unchanged throughout the study. HKII activity increased after 360 minutes of insulin infusion, and this increase was limited to the soluble fraction. In contrast, insulin induced a 1.5- to 2-fold increase in GS fractional velocity that was sustained for 360 minutes. The time course of the ability of hyperinsulinemia to increase HKII mRNA indicates that insulin is likely a physiological regulator of HKII expression in human skeletal muscle in vivo.

Diabetic nephropathy: pathogenetic basis for treatment

For maximal effectiveness, interventions to prevent diabetic nephropathy are initiated prior to clinically detectable proteinuria--during the microalbuminuria stage. Effects of therapy in relation to pathologic processes are described.

Influence of basal androgen levels in euandrogenic women on glucose homeostasis

OBJECTIVE

To evaluate possible relationships between insulin action and the normal variations of serum androgens in euandrogenic women.

DESIGN

Prospective evaluation of insulin action in normal nonobese women using hyperglycemic and euglycemic hyperinsulinemic clamp techniques, correlating insulin action to serum testosterone (T), free T, androstenedione (A), and dehydroepiandrosterone sulfate (DHEAS). Statistical analysis used Spearman's rank correlation.

SETTING

Yale University Clinical Research Center.

PARTICIPANTS

Nonobese females with normal oral glucose tolerance tests, on no medications known to affect glucose metabolism, having the following range of serum androgen levels: T, 0.69 to 3.12 nmol/L; free T, 0.17 to 1.25 nmol/L; A, 2.48 to 11.31 nmol/L; DHEAS, 0.68 to 10.61 mumol/L. Total number of patients studied: hyperglycemic clamps, n = 58; euglycemic hyperinsulinemic clamps, n = 43.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Pancreatic insulin secretion in response to hyperglycemia and insulin action as assessed by insulin-mediated glucose utilization using the euglycemic, hyperinsulinemic clamp technique.

RESULTS

We identified no significant correlation between serum androgens and either glucose uptake or insulin-mediated glucose utilization. Glucose-stimulated insulin release was negatively correlated with serum T and free T throughout the normal range of these hormones.

CONCLUSION

We conclude that, within the normal range, variations of serum androgens are not correlated with changes in the response to insulin. It seems unlikely, therefore, that modest increases of serum androgens within the normal range are responsible for inducing insulin resistance.

A patient with hyperkalemia and metabolic acidosis

Uptake of potassium by extrarenal tissues, primarily muscle and liver, represents a major defense mechanism in the maintenance of normokalemia following an acute elevation in the serum potassium concentration. Insulin, epinephrine, and aldosterone all play major roles in maintaining the normal distribution of potassium between the intracellular and extracellular environment. In addition to hormonal regulation, changes in blood pH and tonicity also exert a strong influence on extrarenal potassium metabolism. Last, the serum potassium concentration per se directly influences its own cellular uptake and this transport mechanism appears to be inhibited by uremia.

No evidence for isotope discrimination of tritiated glucose tracers in measurements of glucose turnover rates in man

Under non-steady-state conditions, glucose turnover rates determined with tritiated glucose tracers are often underestimated. To examine whether isotope discrimination or a tracer contaminant can contribute to this, we compared the turnover rates of unlabelled and tritiated glucose under isotopic steady-state conditions. The turnover rates were measured in 20 healthy subjects at two insulin concentrations (79 +/- 3 mU.l-1 and 704 +/- 62 mU.l-1). Euglycaemia was maintained by infusing unlabelled glucose mixed with (3(3)H)- or (6(3)H)-glucose. In both studies, the isotopically determined glucose disposal rate was virtually identical to the exogenous glucose infusion rate (low insulin 7.66 +/- 0.48 vs 7.58 +/- 0.44 mg.kg-1.min-1, high insulin 13.36 +/- 0.74 vs 13.55 +/- 0.98 mg.kg-1.min-1). The individual values were correlated in both the low (r = 0.85, p less than 0.001) and high dose insulin (r = 0.81, p less than 0.001) studies. Tritiated glucose specific activities were also compared in arterialized and deep venous blood across forearm tissues during the high-dose insulin infusion. Glucose specific activities were similar in arterialized and deep venous blood when analysed with HPLC and conventional methods. In summary: (1) Under isotopic steady-state conditions the turnover rates of unlabelled and labelled glucoses are similar. (2) Unlabelled and labelled glucose are handled identically across forearm tissues. (3) We found no tracer impurity in our tritiated glucose preparations. We conclude that (3(3)H)- and (6(3)H)-glucose tracers can be used to reliably measure glucose turnover rates in man.

Effect of insulin on renal potassium metabolism

The effect of insulin on renal potassium excretion was examined by employing the euglycemic insulin clamp technique in combination with renal clearance measurements. While euglycemia was maintained, insulin was infused at rates of 4.8 (n = 7) and 12 (n = 5) mU X kg-1 X min-1. Steady-state plasma insulin levels of 164 +/- 8 and 370 +/- 15 microU/ml were achieved in the low- and high-dose studies, respectively. Base-line plasma potassium concentration declined progressively by a mean of 0.14 +/- 0.09 (P less than 0.05) and 0.40 +/- 0.05 meq/liter (P less than 0.01) during the low- and high-dose insulin infusion protocols. Urinary potassium excretion did not change significantly from base line with either insulin dose. Because the decline in plasma potassium concentration could have masked a stimulatory effect of insulin on UKV, six rats received a 12-mU X kg-1 X min-1 euglycemic insulin clamp in combination with an exogenous potassium infusion to maintain the plasma potassium concentration constant at the basal level (4.03 +/- 0.03 vs. 4.05 +/- 0.05 meq/l). Under these conditions of normokalemia, insulin augmented UKV 2.4-fold, from 0.20 +/- 0.05 to 0.48 +/- 0.04 meq/l (P less than 0.001).

Ultrastructure of rat initial collecting tubule. Effect of adrenal corticosteroid treatment

This study examines the effects of adrenalectomy and physiological replacement of mineralocorticoids and glucocorticoids on the cellular ultrastructure of the rat initial collecting tubule (late distal tubule). Animals were adrenalectomized (ADX) and for 10 d received by osmotic minipump either: vehicle, aldosterone (0.5 micrograms X 100 g-1 X d-1), aldosterone (2.0 micrograms X 100 g-1 X d-1), dexamethasone (1.2 micrograms X 100 g-1 X d-1), or aldosterone (0.5 micrograms X 100 g-1 X d-1) with dexamethasone (1.2 micrograms X 100 g-1 X d-1). Radioimmunoassay revealed that the low dose of aldosterone restored plasma aldosterone to control levels. The higher dose of aldosterone increased plasma levels by threefold. Morphometric techniques were used to measure membrane length of individual principal and intercalated cells in each condition. The basolateral membrane length of principal cells decreased by 35% in ADX animals. Low dose aldosterone replacement (0.5 micrograms X 100 g-1 X d-1) in ADX animals maintained membrane length at control values; at a higher level of aldosterone (2.0 micrograms X 100 g-1 X d-1) membrane length increased by 111% compared with control. Dexamethasone treatment, at a level that restored glomerular filtration rate to normal, had no effect on cellular ultrastructure. Combined aldosterone and dexamethasone replacement had no greater effect on basolateral membrane length than aldosterone alone. The length of the luminal membrane of the principal cell type was not affected by ADX or hormone treatment. Intercalated cell membrane length was not affected by ADX or hormone replacement. Thus, chronic aldosterone levels have an important, selective effect on the basolateral membrane of the principal cell. The correlation between these morphological results and the steroid hormone effects on renal electrolyte excretion, reported in the companion paper (15), suggests that basolateral membrane length is an important factor controlling the rate of sodium and potassium transport by the initial collecting tubule.

The effect of dexamethasone on renal potassium excretion and acute potassium tolerance

In order to further characterize the kaliuretic action of dexamethasone, the effect of the hormone on renal electrolyte excretion and potassium tolerance was evaluated. In the first set of experiments, dexamethasone was administered acutely to unreplaced adrenalectomized rats, to adrenalectomized rats replaced with a single daily injection of dexamethasone (10 micrograms/100 g X day), and to intact control rats. After dexamethasone injection (10 micrograms/100 g), urinary potassium excretion increased by 105% in unreplaced adrenalectomized rats (0.99 +/- 0.13 to 2.02 +/- 0.26 mueq/min, P less than 0.005) and by 59% in rats maintained on glucocorticoid (0.87 +/- 0.10 to 1.38 +/- 0.18 mueq/min, P less than 0.05). The kaliuresis in adrenalectomized rats was associated with a significant increase in phosphate excretion and by a tendency for urinary chloride excretion to rise. In contrast, potassium excretion was unchanged by dexamethasone in control rats. These results indicate that the kaliuretic effect of dexamethasone is influenced by the degree of glucocorticoid deficiency before hormone administration. An additional study with K loading was performed in these same three groups of rats to evaluate the effect of dexamethasone replacement on potassium tolerance. Adrenalectomized rats maintained in daily dexamethasone replacement received an additional dose of hormone (50 micrograms/100 g) before study. After KCl, plasma potassium concentration rose significantly higher in unreplaced adrenalectomized rats vs. control (2.2 +/- 0.2 vs. 1.3 +/- 0.4 meq/liter, P less than 0.05) and peak renal potassium clearance was significantly blunted (577 +/- 90 vs. 1104 +/- 120 microliter/min. P less than 0.001). This impairment in potassium tolerance could not be attributed to hypotension, acidemia, diminished urinary flow, or sodium delivery in the distal nephron in unreplaced adrenalectomized rats but may be explained by decreased renal perfusion since glomerular filtration rate at the end of study was lower than in controls. Dexamethasone replacement improved potassium tolerance (peak delta Pk = 1.7 +/- 0.1 meq/liter) and renal potassium clearance (942 +/- 60 microliter/min). These data demonstrate that dexamethasone, at the high dose employed during KCl loading, improves renal potassium tolerance by enhancing renal K clearance in adrenalectomized rats. These results explain our previous report of near normal potassium excretion in glucocorticoid replaced adrenalectomized rats.

Increased peripheral insulin sensitivity and muscle mitochondrial enzymes but unchanged blood glucose control in type I diabetics after physical training

Nine male, insulin-dependent diabetic patients participated in a 16-wk training program consisting of 1 h of jogging, running, ball games, and gymnastics, performed 2-3 times/wk. The training resulted in an 8% increase of maximal oxygen uptake (P less than 0.01). Insulin sensitivity as determined by the insulin clamp technique increased 20% (P less than 0.05). Glycosylated hemoglobin showed no change (10.4 +/- 0.7% versus 11.3 +/- 0.5%), 24-h urinary glucose excretion was not reduced, and home-monitored urine tests were unchanged. The frequency of hypoglycemic attacks did not change during the training period and body weight remained constant. There was a 14% fall in plasma cholesterol (P less than 0.01) and a rise in the proportion of HDL-cholesterol from 24 +/- 2% to 30 +/- 3% (P less than 0.01). Thigh muscle oxidative capacity increased, as indicated by a 24% increase in succinate dehydrogenase activity (P less than 0.05). The number of capillaries/muscle fiber increased 15% (P less than 0.01). However, as the mean muscle fiber cross-sectional area increased to a similar extent (11%, P less than 0.05), capillary density (cap x mm-2) was unchanged. In conclusion, this study demonstrates that physical training in insulin-dependent diabetics results in increased peripheral insulin sensitivity, a rise in muscle mitochondrial enzyme activities, decreased total plasma cholesterol levels, and unchanged blood glucose control. The findings suggest that in the absence of efforts to alter dietary regulation and insulin administration, physical training consisting of 2-3 weekly bouts of moderate exercise may not of itself improve blood glucose control in type I diabetes.

Influence of fibre ingestion on carbohydrate utilization and absorption

To evaluate the mechanism whereby the addition of fibre to the diet lowers postprandial plasma glucose levels, the effects of ingestion of 10 g guar gum, a non-absorbable storage polysaccharide, on carbohydrate utilization and absorption were examined in healthy subjects. Total glucose utilization independent of gastrointestinal absorption of glucose was determined by the hyperglycaemic clamp technique in which constant hyperglycaemia is maintained with a variable intravenous infusion of glucose. Net splanchnic glucose uptake was also measured. As compare to a control study without guar, ingestion of guar failed to increase total glucose utilization or the uptake of glucose by splanchnic tissues. In contrast, when guar was ingested together with 25 g D-xylose, a non-metabolizable pentose, blood xylose levels were 25-40% lower than when xylose was ingested alone (P less than 0.01). We conclude that the plasma-glucose-lowering effects of high-fibre diets are a consequence of decreased carbohydrate absorption rather than increased total glucose utilization or augmented uptake of glucose by the liver.

1,25(OH)2D3 is not the only D metabolite involved in the pathogenesis of osteomalacia

Three patients are described in whom there was no simple correlation between plasma 1,25(OH)2D3 concentration and the occurrence of osteomalacia. One patient had severe osteomalacia with high plasma 1,25(OH)2D3 and normal mineral ion product; the second had a normal mineral ion product and no evidence of osteomalacia even though plasma 1,25(OH)2D3 was undetectable; and the third had osteomalacia, low plasma 1,25(OH)2D3 and a reduced mineral ion product. In considering these data in the light of presently available information, it is concluded that osteomalacia can occur as a consequence of a lack of a vitamin D metabolite other than 1,25(OH)2D3, or a consequence of a reduced mineral ion product, but not as a consequence of 1,25(OH)2D3 lack if the mineral ion product is normally maintained and other D metabolites are present. However, a deficiency of 1,25(OH)2D3 normally leads to a reduction in the mineral ion product hence 1,25(OH)2D3 deficiency may play a role in the development of certain forms of osteomalacia.

Insulin sensitivity and insulin binding to monocytes in maturity-onset diabetes

Tissue sensitive to insulin and insulin binding to monocytes were evaluated in 15 nonobese maturity-onset diabetics and in 16 healthy controls. Insulin sensitivity was determined by the insulin clamp technique in which the plasma insulin is acutely raised and maintained 100 muU/ml above the fasting level and plasma glucose is held constant at fasting levels by a variable glucose infusion. The amount of glucose infused is a measure of overall tissue sensitivity to insulin. In the diabetic group, the fasting plasma glucose concentration (168+/-4 mg/dl) was 85% greater than controls (P < 0.01) whereas the plasma insulin level (15+/-1 muU/ml) was similar to controls. During the insulin clamp study, comparable plasma insulin levels were achieved in the diabetics (118+/-5) and the controls (114+/-5 muU/ml). However, the glucose infusion rate in the diabetics (4.7+/-0.4 mg/kg.min) was 30% below controls (P < 0.01). Among the diabetics, the glucose infusion rate correlated directly with the fasting plasma glucose level (r = 0.57, P < 0.05). In five diabetic subjects, glucose metabolism was similar to controls, and these diabetics had the highest fasting glucose levels. When they were restudied after prior normalization (with insulin) of the fasting plasma glucose (100+/-1 mg/dl), the glucose infusion rate during the insulin clamp was 30% lower than observed in association with hyperglycemia (P < 0.01). Studies that employed tritiated glucose to measure endogenous glucose production indicated comparable 90-95% inhibition of hepatic glucose production during hyperinsulinemia in the diabetic and control subjects.(125)I-insulin binding to monocytes in the diabetics (5.5+/-0.6%) was 30% below that in controls (P < 0.01). Insulin binding to monocytes and insulin action as determined with the insulin clamp were highly correlated in both control (r = 0.67, P < 0.01), and diabetic subjects (r = 0.88, P < 0.001). We conclude that (a) tissue sensitivity to physiologic hyperinsulinemia is reduced in most maturity-onset diabetics; (b) this decrease in sensitivity is located, at least in part, in extrahepatic tissues; (c) the resistance to insulin may be mediated by a reduction in insulin binding; and (d) in maturity-onset diabetics with normal tissue sensitivity to insulin, hyperglycemia may be a contributing factor to the normal rates of insulin-mediated glucose uptake.

Insulin binding and insulin sensitivity in isolated growth hormone deficiency

125I-insulin binding to monocytes was examined in five children and one adult with isolated growth hormone deficiency before and after three to 12 weeks of growth hormone treatment, and in eight controls. Before treatment, mean plasma glucose was 15 mg per deciliter below controls, and plasma insulin was reduced by 40 per cent. Insulin binding to monocytes was 70 per cent greater than controls (P less than 0.005). Insulin-mediated glucose uptake (determined in the adult patient) was 25 per cent greater than mean control levels. After treatment, plasma glucose rose to control levels, plasma insulin increased to 75 per cent above controls (P less than 0.01), and insulin binding fell to 50 per cent below controls (P less than 0.01). Insulin-mediated glucose uptake fell to 30 per cent below the mean control rate. Insulin binding increases in growth hormone deficiency and falls after treatment. These changes may contribute to alterations in insulin sensitivity accompanying altered growth hormone availability.

Glucose homeostasis during prolonged suppression of glucagon and insulin secretion by somatostatin

Somatostatin was infused for 5-8 hr into five normal men and eleven normal, conscious dogs. This infusion resulted in a persistent decline in plasma glucagon (40-60%) and insulin (30-45%). Plasma gluccose fell 15-25% during the initial 1-2 hr, but subsequently rose to hyperglycemic levels (130-155 mg/100ml) by 3-6 hr, despite persistent hypoglucagonemia. Glucose production initially declined by 40-50%, but later rose to levels 15-20% above basal rates while peripheral glucose utilization fell to levels 20-30% below basal, thereby accounting for hyperglycemia. Infusion of exogenous insulin so as to restore plasma insulin to preinfusion values or cessation of the somatostatin infusion with restoration of endogenous insulin secretion resulted in a prompt reduction of plasma glucose to baseline values. Prevention of the initial somatostatin-induced hypoglycemic response by intravenous infusion of glucose failed to prevent the delayed hyperglycemia. We conclude that somatostatin caused only transient hypoglycemia in normal subjects and that hyperglycemia eventually developes as a consequence of insulin deficiency. These data indicate that basal glucagon secretion is not essential for the development of fasting hyperglycemia and support the conclusion that insulin deficiency rather than glucagon excess is the primary factor responsible for abnormal glucose homeostasis in the diabetic.

Effectiveness of bumetanide in nephrotic syndrome: a double-blind crossover study with furosemide

A double-blind crossover study was undertaken to delineate the renal tubular sites of action of bumetanide and to compare its effects upon electrolyte excretion to that of furosemide in six nephrotic patients with various degrees of renal insufficiency. Bumetanide was found to be a potent oral natriuretic agent without producing changes in either GFR or effective renal plasma flow. The natriuresis was associated with inhibition of proximal tubular transport as evidenced by an increased distal delivery (CH2O+CNA+K) and inhibition of sodium transport in the loop of Henle as shown by a fall in CH2O/CH2O+CC1 during sustained water diuresis and an unchanged TCH2O with continued hydropenia. The increases in free-water clearance induced by furosemide and bumetanide were equivalent, but bumetanide produced significantly higher flow rate, greater solute delivery from the proximal tubule, and a greater natriuresis. The data indicate that at the dosages used, bumetanide has a proportionately greater inhibitory effect than furosemide in both the proximal tubule and the ascending limb of the loop of Henle.