Biomedical subjects
R R Henry
Publications and source records attributed to R R Henry.
Glycogen synthase activity is reduced in cultured skeletal muscle cells of non-insulin-dependent diabetes mellitus subjects. Biochemical and molecular mechanisms.
To determine whether glycogen synthase (GS) activity remains impaired in skeletal muscle of non-insulin-dependent diabetes mellitus (NIDDM) patients or can be normalized after prolonged culture, needle biopsies of vastus lateralis were obtained from 8 healthy nondiabetic control (ND) and 11 NIDDM subjects. After 4-6 wk growth and 4 d fusion in media containing normal physiologic concentrations of insulin (22 pM) and glucose (5.5 mM), both basal (5.21 +/- 0.79 vs 9.01 +/- 1.25%, P < 0.05) and acute insulin-stimulated (9.35 +/- 1.81 vs 16.31 +/- 2.39, P < 0.05) GS fractional velocity were reduced in NIDDM compared to ND cells. Determination of GS kinetic constants from muscle cells of NIDDM revealed an increased basal and insulin-stimulated Km(0.1) for UDP-glucose, a decreased insulin-stimulated Vmax(0.1) and an increased insulin-stimulated activation constant (A(0.5)) for glucose-6-phosphate. GS protein expression, determined by Western blotting, was decreased in NIDDM compared to ND cells (1.57 +/- 0.29 vs 3.30 +/- 0.41 arbitrary U/mg protein, P < 0.05). GS mRNA abundance also tended to be lower, but not significantly so (0.168 +/- 0.017 vs 0.243 +/- 0.035 arbitrary U, P = 0.08), in myotubes of NIDDM subjects. These results indicate that skeletal muscle cells of NIDDM subjects grown and fused in normal culture conditions retain defects of basal and insulin-stimulated GS activity that involve altered kinetic behavior and possibly reduced GS protein expression. We conclude that impaired regulation of skeletal muscle GS in NIDDM patients is not completely reversible in normal culture conditions and involves mechanisms that may be genetic in origin.
Glutamine:fructose-6-phosphate amidotransferase activity in cultured human skeletal muscle cells: relationship to glucose disposal rate in control and non-insulin-dependent diabetes mellitus subjects and regulation by glucose and insulin.
We examined the activity of the rate-limiting enzyme for hexosamine biosynthesis, glutamine:fructose-6-phosphate amidotransferase (GFA) in human skeletal muscle cultures (HSMC), from 17 nondiabetic control and 13 subjects with non-insulin-dependent diabetes. GFA activity was assayed from HSMC treated with low (5 mM) or high (20 mM) glucose and low (22 pM) or high (30 microM) concentrations of insulin. In control subjects GFA activity decreased with increasing glucose disposal rate (r = -0.68, P < 0.025). In contrast, a positive correlation existed between GFA and glucose disposal in the diabetics (r = 0.86, P < 0.005). Increased GFA activity was also correlated with body mass index in controls but not diabetics. GFA activity was significantly stimulated by high glucose (22%), high insulin (43%), and their combination (61%). GFA activity and its regulation by glucose and insulin were not significantly different in diabetic HSMC. We conclude that glucose and insulin regulate GFA activity in skeletal muscle. More importantly, our results are consistent with a regulatory role for the hexosamine pathway in human glucose homeostasis. This relationship between hexosamine biosynthesis and the regulation of glucose metabolism is altered in non-insulin-dependent diabetes.
The expression of TNF alpha by human muscle. Relationship to insulin resistance.
TNFalpha is orverexpressed in the adipose tissue of obese rodents and humans, and is associated with insulin resistance. To more closely link TNF expression with whole body insulin action, we examined the expression of TNF by muscle, which is responsible for the majority of glucose uptake in vivo. Using RT-PCR, TNF was detected in human heart, in skeletal muscle from humans and rats, and in cultured human myocytes. Using competitive RT-PCR, TNF was quantitated in the muscle biopsy specimens from 15 subjects whose insulin sensitivity had been characterized using the glucose clamp. technique. TNF expression in the insulin resistant subjects and the diabetic patients was fourfold higher than in the insulin sensitive subjects, and there was a significant inverse linear relationship between maximal glucose disposal rate and muscle TNF (r = -0.60, P < 0.02). In nine subjects, muscle cells from vastus lateralis muscle biopsies were placed into tissue culture for 4 wk, and induced to differentiate into myotubes. TNF was secreted into the medium from these cells, and cells from diabetic patients expressed threefold more TNF than cells from nondiabetic subjects. Thus, TNF is expressed in human muscle, and is expressed at a higher level in the muscle tissue and in the cultured muscle cells from insulin resistant and diabetic subjects. These data suggest another mechanism by which TNF may play an important role in human insulin resistance.
Forum One: Current recommendations about intensification of metabolic control in non-insulin-dependent diabetes mellitus.
PURPOSE: To review issues about intensive management of non-insulin-dependent diabetes mellitus (NIDDM) and to formulate recommendations for goals and general approaches to implementation of intensive management. METHOD: A panel of clinical scientists and practitioners specializing in diabetes initially used a formal nominal process to identify the points of agreement on major issues. These points were further refined in a general conference discussion. CONCLUSIONS: 1) On the basis of data from intervention trials in IDDM that prove that intensive glycemic control reduces microvascular and neuropathic complications, coupled with epidemiologic and basic scientific data that support the strong likelihood of a similar benefit in NIDDM, the goal of treatment in NIDDM should be near-normal glycemia (glycohemoglobin level no higher than 1.0% above the upper normal limit); 2) glycemic targets should be adjusted individually according to clinical factors such as increased risk for hypoglycemia, advanced age, or reduced life expectancy from comorbid conditions; 3) some degree of comprehensive and repetitive instruction about diet and exercise and the use of blood glucose self-monitoring for all patients is essential to achieve the chosen targets; 4) intensive management of hyperglycemia should be instituted early and should initially emphasize diet and exercise therapy; staged introduction of oral hypoglycemic agents and finally insulin regimens of increasing complexity are recommended as needed to achieve glycemic targets; 5) comprehensive care must also include aggressive attempts to reduce cardiovascular risk factors (particularly hypertension, smoking, dyslipidemia, and obesity) as well as prevention of nephropathy and neuropathy; 6) the complex interaction among treatment regimens for hyperglycemia, dyslipidemia, obesity, and hypertension ideally requires a team approach, using a physician, diabetes educator, nurse, dietitian, and other health professionals; health insurers should make these resources available to generalists who currently care for most diabetic patients.
Glucose control and insulin resistance in non-insulin-dependent diabetes mellitus.
Chronic hyperglycemia is implicated in the pathogenesis of microvascular, neurologic, and macrovascular complications of diabetes. Recent studies prove that near-normal glycemic control in insulin-dependent diabetes mellitus (IDDM) reduces the risk for the development and progression of microvascular and neurologic complications. With the expectation of comparable benefits, similar glycemic goals have been advocated for the management of non-insulin-dependent diabetes mellitus (NIDDM). However, using intensified insulin therapy to achieve near-normal glycemia in NIDDM may be problematic because of basic differences in pathophysiology of the two types of diabetes. Insulin resistance is a major contributor to the development of hyperglycemia in NIDDM and may prevent attainment of normoglycemia in most patients who are using the conventional approaches of diet, exercise, and oral hypoglycemic therapy. Near-normal glycemia in patients with NIDDM can usually be achieved with exogenous insulin but often requires large doses to overcome the insulin resistance. Intensive insulin therapy normalizes glycemia by decreasing hepatic glucose output and improving peripheral glucose uptake and may also improve insulin resistance and insulin secretion by reducing hyperglycemic glucotoxicity. However, large doses of exogenous insulin are associated with hyperinsulinemia and weight gain, but these effects may be minimized by combining insulin with other forms of therapy, for example, oral antidiabetic agents. When intensive management is instituted, the dose of exogenous insulin should be kept as low as possible. To do this, therapy for NIDDM must be part of a multifaceted approach combining insulin therapy with other effective forms of treatment such as counseling on diet and exercise therapy and the use of oral antidiabetic agents.
Mechanisms of tumor-induced hypoglycemia with intraabdominal hemangiopericytoma.
The association of hypoglycemia with nonislet cell tumors is well recognized and in nearly all instances has been related to the production of hormones with insulin-like activity. To determine the mechanism of such tumor-induced hypoglycemia and the response to pharmacological intervention, we studied a 54-yr-old man with refractory hypoglycemia and a large intraabdominal hemangiopericytoma. During a supervised fast, plasma glucose decreased to 2.2 mmol/L. Circulating insulin (< 7 pmol/L), C peptide (< 0.04 nmol/L), and GH levels (< 0.6 microgram/L) were all undetectable, insulin-like growth factor I (IGF-I; 5 nmol/L) was low, IGF-II was in the normal range (87 nmol/L), and free IGF-II and big IGF-II (E1-21 fragment) were elevated at 18 and 142 nmol/L, respectively. On another day, after maintaining euglycemia overnight with a 20% dextrose infusion, a euglycemic (5.0-5.5 mmol/L) glucose clamp study using [3-3H]glucose tracer infusion combined with arteriovenous leg catheterization was performed in the postabsorptive basal state and during 3 h of crystalline somatostatin infusion (0.08-0.24 pmol/kg min). In the postabsorptive state at euglycemia, free IGF-II and big IGF-II remained elevated at 16 and 162 nmol/L, respectively. Whole body glucose disposal was elevated at 21.1 mumol/kg.min, whereas the rate of glucose infusion was 12.1 mumol/kg.min, and depatic glucose output was 7.8 mumol/kg.min. The leg arterio-venous plasma glucose difference was increased at 0.6 mmol/L, as was leg glucose uptake at 203.9 mumol/min. After 3 h of somatostatin infusion, both free and big IGF-II decreased by 35-40% to 10 and 102 nmol/L, respectively. Whole body glucose disposal also decreased to near normal (12.8 mumol/kg.min), whereas leg arterio-venous plasma glucose difference and leg glucose uptake became negligible. The plasma glucose level remained at 5.0-5.5 mmol/L despite a marked fall in hepatic glucose output to 2.9 mumol/kg.min and a decrease in glucose infusion rate to 8.7 mumol/kg.min. During somatostatin treatment, GH remained suppressed at less than 0.6 microgram/L, and glucagon decreased from 99 to 78 ng/L. In this patient with a hemangiopericytoma, hypoglycemia was associated with increased circulating insulin-like activity from elevated free and big IGF-II, which stimulated glucose uptake primarily into muscle tissue. A continuous infusion of crystalline somatostatin effectively reduced the elevated levels of IGF-II and glucose uptake, but was unable to adequately control hypoglycemia without the simultaneous infusion of exogenous glucose or glucagon.
Abnormalities of insulin pulsatility and glucose oscillations during meals in obese noninsulin-dependent diabetic patients: effects of weight reduction.
Twenty-seven obese patients, including 8 with normal glucose tolerance, 10 with subclinical NIDDM, and 9 with overt noninsulin-dependent diabetes mellitus (NIDDM), were studied before and after prolonged weight loss to assess the effects of the underlying defects of diabetes per se from those of obesity and chronic hyperglycemia on the regulation of pulsatile insulin secretion. Serial measurements of insulin secretion and plasma glucose were obtained during 3 standardized mixed meals consumed over 12 h. Insulin secretion rates were calculated by deconvoluting plasma C peptide levels using a mathematical model for C peptide clearance and kinetic parameters derived individually in each subject. Absolute (nadir to peak) and relative (fold increase above nadir) amplitudes of each insulin secretory pulse and glucose oscillation were calculated. Compared to the obese controls, the subclinical and overt NIDDM patients manifested the following abnormal responses: 1) decreased relative amplitudes of insulin pulses, 2) reduced frequency of glucose oscillations, 3) increased absolute amplitudes of glucose oscillations, 4) decreased temporal concomitance between peaks of insulin pulses and glucose oscillations, 5) reduced correlation between the relative amplitudes of glucose oscillations concomitant with insulin pulses, and 6) temporal disorganization of the insulin pulse profiles. These defects were more severe in the overt NIDDM patients, and weight loss only partially reversed these abnormalities in both NIDDM groups. These findings indicate that beta-cell responsiveness is reduced, and the regulation of insulin secretion is abnormal under physiological conditions in all patients with NIDDM, including those without clinical manifestations of the disease. These abnormalities are not completely normalized with weight loss, even in patients who achieve metabolic control comparable to that in obese controls. The results are consistent with the presence of an inherent beta-cell defect that contributes to secretory derangements in subclinical NIDDM patients. This abnormality precedes frank hyperglycemia and may ultimately contribute to the development of overt NIDDM.
Acquired defects of glycogen synthase activity in cultured human skeletal muscle cells: influence of high glucose and insulin levels.
To determine whether defects of muscle glycogen synthase (GS) activity can be acquired by exposure to elevated glucose or insulin levels, human skeletal muscle cells obtained by needle biopsy from normal control subjects were grown in culture for 4-6 weeks followed by 4 days of fusion and differentiation in media containing either normal (5.5 mmol/l glucose and 22 pmol/l insulin) or increased concentrations of glucose (20 mmol/l), insulin (30 micromol/l), or both. After fusion in normal media, acute stimulation by 33 nmol/l insulin for 1 h increased GS fractional velocity (FV) approximately twofold (from 9.01 +/- 1.26 to 16.31 +/- 2.40, P < 0.05). Increasing the media glucose concentration alone to 20 mmol/l during fusion had no effect on basal FV but caused a marginal impairment of the insulin-stimulated GS response (from 8.51 +/- 1.33 to 12.99 +/- 1.90, P = 0.08). Increasing the media insulin concentration to 30 micromol/l during fusion at 5.5 mmol/l glucose also did not alter basal GS FV (10.61 +/- 1.69%) but completely abolished the normal insulin-stimulated increase in GS activity (to 11.63 +/- 1.55%, NS). The combination of high insulin (30 micromol/l) and high glucose (20 mmol/l) during fusion had no greater effect on the FV of either basal (11.66 +/- 2.16%, NS) or insulin-stimulated (9.20 +/- 1.80%, NS) GS activity than high insulin alone. Fusion in hyperinsulinemic media altered the kinetic parameters of GS with a near doubling of the basal Km0.1 and Vmax0.1 for uridinediphospho-glucose. Hyperinsulinemia also totally prevented the normal insulin-stimulated threefold increase in the Vmax0.1 and the 65% decrease in the A0.5 for glucose-6-phosphate. GS mRNA and protein expression, determined by RNase protection assay and immunoblotting, respectively, were unaffected by changes in media conditions. We conclude that exposure of human skeletal muscle cells primarily to high insulin induces severe insulin resistance through multiple acquired posttranslational defects, which affect both the kinetic characteristics and absolute activity of the GS enzyme.
Acute effects of intraperitoneal versus subcutaneous insulin delivery on glucose homeostasis in patients with NIDDM. Veterans Affairs Implantable Insulin Pump Study Group.
OBJECTIVE: The objective of this study is to compare the effect of intraperitoneal versus subcutaneous insulin injection on hepatic glucose production (HGP) and systemic glucose utilization (Rd) in patients with NIDDM. RESEARCH DESIGN AND METHODS: Eight male volunteers with NIDDM, each of whom had a programmable-rate, implantable insulin pump, were given an injection of insulin (0.15 units/kg body wt) by intraperitoneal or subcutaneous injection on separate days in randomized order. Plasma glucose was kept constant for 5 h using the glucose clamp technique, and HGP and Rd were measured using isotope dilution. RESULTS: Intraperitoneal insulin injection resulted in higher and earlier peak systemic insulin concentrations (1,469 +/- 245 vs. 454 +/- 48 pmol/l, P < 0.01). Glucose Rd doubled within 1 h after intraperitoneal injection and was greater than that attained with subcutaneous injection (3.91 +/- 0.27 vs. 2.60 +/- 0.19 mg.kg-1.min-1, P < 0.01). Intraperitoneal and subcutaneous injections suppressed HGP and plasma free fatty acid to a similar extent during the first 3 h, effects tht persisted through 5 h after subcutaneous insulin injection but waned 3-4 h after intraperitoneal injection. CONCLUSIONS: In patients with NIDDM, intraperitoneal insulin injection achieves more rapid and greater peak values for stimulation of glucose Rd than subcutaneous insulin injection. With regard to HGP and lipolysis, intraperitoneal and subcutaneous injections achieve similar initial suppression but this is maintained for a more limited duration with intraperitoneal as compared with subcutaneous injection. These differences in insulin action seem directly related to the rapidity of insulin absorption with intraperitoneal injection.
Effects of troglitazone on insulin sensitivity.
Studies to date confirm that troglitazone has therapeutic benefits to NIDDM and can normalize IGT in those individuals at increased risk of developing NIDDM. Hyperinsulinaemia is reduced by such treatment in association with reduced insulin resistance and there are favourable effects on blood pressure with troglitazone therapy as well. Since insulin resistance and hyperinsulinaemia are usually present in obesity and impaired glucose tolerance (IGT), troglitazone may be useful in preventing the development of NIDDM in these susceptible populations.
Role of basal insulin in maintenance of intracellular glucose metabolic pathways in non-insulin-dependent diabetes mellitus.
Impairments of both basal and insulin-stimulated oxidative (Gox) and nonoxidative (Nox) glucose metabolism are documented to exist in non-insulin-dependent diabetes mellitus (NIDDM). Although these defects have been well characterized during insulin stimulation, little is known about the effects of basal insulin or its deficiency on intracellular glucose metabolism in NIDDM. To determine the physiological significance of basal insulin in the maintenance of glucose metabolism in NIDDM, we studied nine subjects with NIDDM in the basal and insulin-deficient state produced by 3 hours of somatostatin (SRIF) infusion (0.08 pmol/kg/min). Glucose turnover rates were quantified by [3-3H]glucose turnover, and substrate oxidation was assessed by a combination of indirect calorimetry and urinary nitrogen measurements. Skeletal muscle glycogen synthase (GS) and pyruvate dehydrogenase (PDH) activities were also measured in the basal state and during SRIF infusion. Basal glucose levels were maintained during SRIF infusion by exogenous glucose infusion (12.5 +/- 0.9 mmol/L in the basal state v 12.8 +/- 0.8 during SRIF infusion, P = NS). During the last hour of SRIF infusion, plasma C-peptide levels declined by 88% from 0.73 +/- 0.11 to 0.09 +/- 0.02 nmol/L (P < .001), and serum insulin concentrations were undetectable (< 14 pmol/L). During insulinopenic conditions, rates of glucose uptake (GU) were decreased by 12% from basal level of 2.26 +/- 0.13 to 1.99 +/- 0.12 mg/kg/min (P < .05), and were entirely accounted for by reduced rates of Gox (1.01 +/- 0.10 to 0.65 +/- 0.14 mg/kg/min, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)
Impaired muscle fat metabolism: a cause or effect of visceral obesity?
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Glucose transport in cultured human skeletal muscle cells. Regulation by insulin and glucose in nondiabetic and non-insulin-dependent diabetes mellitus subjects.
A primary human skeletal muscle culture (HSMC) system, which retains cellular integrity and insulin responsiveness for glucose transport was employed to evaluate glucose transport regulation. As previously reported, cells cultured from non-insulin-dependent diabetic (NIDDM) subjects displayed significant reductions in both basal and acute insulin-stimulated transport compared to nondiabetic controls (NC). Fusion/differentiation of NC and NIDDM HSMC in elevated media insulin (from 22 pM to 30 microM) resulted in increased basal transport activities but reduced insulin-stimulated transport, so that cells were no longer insulin responsive. After fusion under hyperinsulinemic conditions, GLUT1 protein expression was elevated in both groups while GLUT4 protein level was unaltered. Fusion of HSMC under hyperglycemic conditions (10 and 20 mM) decreased glucose transport in NC cells only when combined with hyperinsulinemia. Hyperglycemia alone down-regulated transport in HSMC of NIDDM, while the combination of hyperglycemia and hyperinsulinemia had greater effects. In summary: (a) insulin resistance of glucose transport can be induced in HSMC of both NC and NIDDM by hyperinsulinemia and is accompanied by unaltered GLUT4 but increased GLUT1 levels; and (b) HSMC from NIDDM subjects demonstrate an increased sensitivity to impairment of glucose transport by hyperglycemia. These results indicate that insulin resistance in skeletal muscle can be acquired in NC and NIDDM from hyperinsulinemia alone but that NIDDM is uniquely sensitive to the additional influence of hyperglycemia.
Insulin action and glucose metabolism in nondiabetic control and NIDDM subjects. Comparison using human skeletal muscle cell cultures.
Myoblasts from human skeletal muscle were isolated from needle biopsy samples of vastus lateralis and fused to differentiated multinucleated myotubes. Specific high-affinity insulin and insulin-like growth factor I (IGF-I) binding, glucose transporter proteins GLUT1 and GLUT4, glycogen synthase and pyruvate dehydrogenase proteins, and their specific mRNAs were identified in fused myotubes. Insulin and IGF-I stimulated 2-deoxyglucose uptake twofold with half-maximal stimulation by insulin at 0.98 +/- 0.12 nmol/l and maximal stimulation at 17.5 nmol/l. Acute insulin treatment (33 nmol/l) doubled glycogen synthase activity and glucose incorporation into glycogen while increasing pyruvate dehydrogenase approximately 30%. In cells cultured from NIDDM subjects, both basal (6.9 +/- 1.0 vs. 13.0 +/- 1.7 pmol.mg protein-1.min-1) and acute insulin-stimulated transport (13.5 +/- 2.0 vs. 22.4 +/- 1.3 pmol.mg protein-1.min-1) were significantly reduced compared with nondiabetic control subjects (both P < or = 0.005). GLUT1 protein content of total membranes from NIDDM subjects was decreased compared with control subjects, while GLUT4 levels were similar between groups. A significant correlation (r = 0.65, P < or = 0.05) was present when maximal rates of insulin-stimulated glucose transport in cell culture from subjects were compared with their corresponding in vivo glucose disposal determined by hyperinsulinemic glucose clamp. In summary, differentiated human skeletal muscle cultures exhibit biochemical and molecular features of insulin-stimulated glucose transport and intracellular enzyme activity comparable with the in vivo situation. Defective insulin-stimulated glucose transport persists in muscle cultures from NIDDM subjects and resembles the reduced insulin-mediated glucose uptake present in vivo. We conclude that this technique provides a relevant cellular model to study insulin action and glucose metabolism in normal subjects and determine the mechanisms of insulin resistance in NIDDM.
Contribution of obesity to defects of intracellular glucose metabolism in NIDDM.
OBJECTIVE: To examine the contribution of obesity to insulin resistance and abnormalities of intracellular glucose and fat metabolism in NIDDM. RESEARCH DESIGN AND METHODS: Glucose turnover measurements and indirect calorimetry were performed in 10 obese non-insulin-dependent diabetes mellitus (NIDDM) and 10 lean NIDDM subjects (body mass index 35.3 +/- 1.0 vs. 24.1 +/- 0.5 kg/m2, P < or = 0.001) in the basal state and during hyperinsulinemic (720 pmol.m-2.min-1) euglycemic (5.0-5.5 mmol/l) clamps. RESULTS: Obese and lean NIDDM subjects demonstrated similar basal rates of glucose uptake (GU) (1.15 +/- 0.08 vs. 1.26 +/- 0.08 mmol/min, NS) as well as oxidative (0.49 +/- 0.07 vs. 0.53 +/- 0.05 mmol/min, NS) and nonoxidative (0.67 +/- 0.10 vs. 0.73 +/- 0.12 mmol/min, NS) glucose metabolism. During hyperinsulinemic glucose clamp studies, rates of GU were lower in obese NIDDM subjects (34.1 +/- 2.3 vs. 55.2 +/- 3.8 mumol.kg fat-free mass [FFM]-1.min-1, P < or = 0.001) as were rates of oxidative (14.1 +/- 1.3 vs. 22.1 +/- 2.1 mumol.kg FFM-1.min-1, P < or = 0.005) and nonoxidative (20.0 +/- 2.3 vs. 33.1 +/- 3.6 mumol.kg FFM-1. min-1, P < or = 0.01) glucose metabolism. Although absolute rates of insulin-stimulated GU were decreased in the obese group, the relative distribution into glucose oxidation (GOX) and nonoxidative glucose metabolism (NOX) was comparable in both groups (GOX 42% in obese and 41% in lean subjects; NOX 58% in obese and 59% in lean subjects). The NIDDM groups had similar basal free fatty acid levels that were suppressed equally during hyperinsulinemic clamps. However, basal fat oxidation (Fox) was greater in the obese NIDDM group (103 +/- 11 vs. 73 +/- 8 mumol/min, P < or = 0.05) and was less suppressed to insulin (74 +/- 13 vs. 16 +/- 3 mumol/min, P < or = 0.001). CONCLUSIONS: These results indicate that when obesity is present in NIDDM subjects with this degree of hyperglycemia, insulin-stimulated GU is lower by 35-40%. Reduced GU in obese NIDDM subjects leads to decreased intracellular substrate availability and lower rates of oxidative and nonoxidative glucose metabolism. Insulin suppression of Fox is also impaired when obesity is present and may contribute to decreased insulin-mediated GU in NIDDM. We conclude that obesity increases insulin resistance in NIDDM primarily by effects on GU rather than the intracellular pathways of glucose metabolism.
Effects of varying carbohydrate content of diet in patients with non-insulin-dependent diabetes mellitus.
OBJECTIVE: To study effects of variation in carbohydrate content of diet on glycemia and plasma lipoproteins in patients with non-insulin-dependent diabetes mellitus (NIDDM). DESIGN: A four-center randomized crossover trial. SETTING: Outpatient and inpatient evaluation in metabolic units. PATIENTS: Forty-two NIDDM patients receiving glipizide therapy. INTERVENTIONS: A high-carbohydrate diet containing 55% of the total energy as carbohydrates and 30% as fats was compared with a high-monounsaturated-fat diet containing 40% carbohydrates and 45% fats. The amounts of saturated fats, polyunsaturated fats, cholesterol, sucrose, and protein were similar. The study diets, prepared in metabolic kitchens, were provided as the sole nutrients to subjects for 6 weeks each. To assess longer-term effects, a subgroup of 21 patients continued the diet they received second for an additional 8 weeks. MAIN OUTCOME MEASURES: Fasting plasma glucose, insulin, lipoproteins, and glycosylated hemoglobin concentrations. Twenty-four-hour profiles of glucose, insulin, and triglyceride levels. RESULTS: The site of study as well as the diet order did not affect the results. Compared with the high-monounsaturated-fat diet, the high-carbohydrate diet increased fasting plasma triglyceride levels and very low-density lipoprotein cholesterol levels by 24% (P < .0001) and 23% (P = .0001), respectively, and increased daylong plasma triglyceride, glucose, and insulin values by 10% (P = .03), 12% (P < .0001), and 9% (P = .02), respectively. Plasma total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol levels remained unchanged. The effects of both diets on plasma glucose, insulin, and triglyceride levels persisted for 14 weeks. CONCLUSIONS: In NIDDM patients, high-carbohydrate diets compared with high-monounsaturated-fat diets caused persistent deterioration of glycemic control and accentuation of hyperinsulinemia, as well as increased plasma triglyceride and very-low-density lipoprotein cholesterol levels, which may not be desirable.
Skeletal muscle protein tyrosine phosphatase activity and tyrosine phosphatase 1B protein content are associated with insulin action and resistance.
Particulate and cytosolic protein tyrosine phosphatase (PTPase) activity was measured in skeletal muscle from 15 insulin-sensitive subjects and 5 insulin-resistant nondiabetic subjects, as well as 18 subjects with non-insulin-dependent diabetes mellitus (NIDDM). Approximately 90% of total PTPase activity resided in the particulate fraction. In comparison with lean nondiabetic subjects, particulate PTPase activity was reduced 21% (P < 0.05) and 22% (P < 0.005) in obese nondiabetic and NIDDM subjects, respectively. PTPase1B protein levels were likewise decreased by 38% in NIDDM subjects (P < 0.05). During hyperinsulinemic glucose clamps, glucose disposal rates (GDR) increased approximately sixfold in lean control and twofold in NIDDM subjects, while particulate PTPase activity did not change. However, a strong positive correlation (r = 0.64, P < 0.001) existed between particulate PTPase activity and insulin-stimulated GDR. In five obese NIDDM subjects, weight loss of approximately 10% body wt resulted in a significant and corresponding increase in both particulate PTPase activity and insulin-stimulated GDR. These findings indicate that skeletal muscle particulate PTPase activity and PTPase1B protein content reflect in vivo insulin sensitivity and are reduced in insulin resistant states. We conclude that skeletal muscle PTPase activity is involved in the chronic, but not acute regulation of insulin action, and that the decreased enzyme activity may have a role in the insulin resistance of obesity and NIDDM.