Non-insulin-mediated glucose uptake in several insulin-resistant states in the postabsortive period

Diabetes Mellitus of Pituitary Origin: A Case Report

We describe the case report of 36-year-old female who presented to the emergency department with diabetic ketoacidosis. On detailed clinical examination, coarse facial features in the form of large fleshy nose, thick lips, prognathism, and thickening of hands and feet were noticed, suggestive of acromegaly. Subsequently, she was diagnosed with acromegaly due to somatotropinoma. Impaired glucose tolerance and diabetes mellitus are frequently associated with acromegaly. Persistent growth hormone excess impairs insulin sensitivity, increases gluconeogenesis, reduces glucose uptake in adipose tissue and muscle, and alters pancreatic β-cell function. Rarely, diabetic ketoacidosis can be the presenting manifestation, as seen in this case.

Diabetes Mellitus of Pituitary Origin: A Case Report

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Assessment of non-insulin-mediated glucose uptake: association with body fat and glycemic status

In the fasting state, approximately 83% of glucose uptake occurs via non-insulin-mediated mechanisms. A widely accepted static rate for NIMGU is 1.62 mg kg(-1)·min(-1). To investigate the variability of NIMGU, we examined differences by glucose tolerance, sex, age, race (American Indian/African American/Caucasian), and adiposity in 616 volunteers (including individuals with normal glucose regulation [NGR] and impaired glucose regulation [IGR] and diabetes mellitus [DM]) using data from euglycemic-hyperinsulinemic clamp experiments. NIMGU was determined by plotting basal glucose output and insulin action against fasting and steady-state clamp insulin. The intercept with the y-axis after extrapolation was interpreted as NIMGU at zero insulin. Body composition was determined by dual-energy x-ray absorptiometry; and glucose regulation, by a 75-g oral glucose tolerance test. Energy expenditure was measured by indirect calorimetry in a metabolic chamber. In individuals with NGR (n = 385), NIMGU was 1.63 mg kg(estimated metabolic body size (fat free mass + 17.7 kg))(-1) min(-1) (95% confidence interval, 1.59-1.66). NIMGU increased with IGR and DM (IGR: n = 189, 1.67 [1.62-1.72]; DM: n = 42, 2.39 [2.29-2.49]; P < .0001 across groups). NIMGU did not differ by sex (P = .13), age (P = .22), or race (P = .06); however, NIMGU was associated with percentage body fat (r(2) = 0.04, P < .0001). Furthermore, NIMGU was positively associated with 24-hour and sleep energy expenditure (r(2) = 0.002, P = .03; r(2) = 0.01, P < .01). Extrapolated NIMGU in individuals with NGR is remarkably consistent with previously published data. Our results indicate that NIMGU is associated with adiposity. NIMGU increases with declining glucose tolerance perhaps to preserve glucose uptake during increased insulin resistance.

Adipose tissue from pregnant women with and without gestational diabetes mellitus: insulin-sensitive but resistant to hyperosomolarity

OBJECTIVE

We sought to determine the contribution of adipose tissue to the insulin resistance of pregnancy. We also investigated whether hyperosmolar stress (induced by sorbitol) stimulates glucose uptake in human adipose tissue and, if so, whether this effect is altered in pregnancy and gestational diabetes mellitus.

STUDY DESIGN

Subcutaneous and omental adipose tissue biopsy specimens were obtained at elective abdominal surgery or cesarean delivery from 16 normal glucose-tolerant pregnant women, 13 pregnant women with gestational diabetes mellitus, and 19 body mass index-matched nonpregnant control subjects. Basal, insulin (100 nmol/L)-, and sorbitol (250 mmol/L)-stimulated glucose uptake levels were measured.

RESULTS

Basal and insulin-stimulated glucose uptake into adipose tissue was not impaired in pregnancy or gestational diabetes mellitus compared with control subjects. Hyperosmolarity stimulated glucose uptake in human adipose tissue from the subcutaneous, but not omental depot, and not in adipose tissue from pregnant subjects.

CONCLUSION

There is no significant difference in insulin sensitivity in adipose tissue from pregnant or nonpregnant women; hyperosmolarity stimulates glucose uptake in subcutaneous adipose tissue from nonpregnant women, and adipose tissue from pregnant women is sorbitol resistant. These findings suggest the phosphotidylinositol 3-kinase-independent pathway may have pathophysiologic relevance to glucose uptake in human adipose tissue and may be impaired in pregnancy.

Is non-insulin dependent glucose uptake a therapeutic alternative? Part 1: physiology, mechanisms and role of non insulin-dependent glucose uptake in type 2 diabetes

Several decades of research for treating type 2 diabetes have yielded new drugs but the actual experience with the available oral antidiabetic compounds clearly shows that therapeutic needs are not matched. This highlights the urgent need for exploring other pathways. All cell types have the capacity to take up glucose independently of insulin, whereby basal but also hyperglycaemia-promoted glucose supply is ensured. Although poorly explored, insulin-independent glucose uptake might nevertheless represent a therapeutic target, as an alternative to the clear limits of actual drug treatments. This review not only critically examines some major pathways not requiring insulin (although they may be influenced by the hormone) but importantly, this analysis extends to the clinical applicability of these potential therapeutic principles by also considering their predictable tolerability for long-term therapy. In particular vascular safety (the ultimate problem linked with diabetes) will be envisaged because of the ubiquitous distribution of glucose transporters and some linked mechanisms. Several mechanisms can be identified which do not require insulin for their functioning. The first part of this review deals with the description, the regulation and the limits of some mechanisms representing potential pharmacological targets capable of having a highly significant impact on glucose uptake. These selected topics are: a) unmasking and/or activation of glucose transporters in cell plasma membranes, b) insulin mimetics acting at postreceptor level, c) activation of AMPK, d) increasing nitric oxide and e) increasing glucose-6P and glycogen stores.

Pharmacologic Therapies for Acromegaly

Acromegaly is associated with insulin resistance and an increased incidence of cardiovascular disease. However, it remains unclear to what extent the effects of growth hormone (GH) excess on cardiovascular morbidity and mortality are mediated through insulin resistance versus through other direct or indirect effects of GH. Adequate control of GH excess by surgery or pharmacologic interventions is associated with decreased insulin resistance, reflected in decreased plasma insulin levels and fasting glucose levels or improved glucose tolerance. Despite divergent effects of both somatostatin and somatostatin analogs on GH, insulin and glucagon secretion, and glucose absorption, treatment with the somatostatin analogs octreotide and lanreotide has only limited effects on glucose metabolism. However, glucose sensitivity has only been formally examined using a hyperinsulinemic euglycemic clamp in a minority of these studies. Treatment with the GH-receptor antagonist pegvisomant ameliorates insulin sensitivity, reflected in decreased fasting plasma insulin levels and fasting glucose levels. Nonetheless, the effect of pegvisomant on glucose sensitivity has not been formally tested by hyperinsulinemic clamp conditions. In acromegaly, preliminary observations on new octreotide analogs with greater specificity for somatostatin-receptor subtypes indicate that these compounds achieve better control of GH hypersecretion than octreotide, but may also negatively influence insulin release. Assessment of insulin secretion and glucose levels in acromegalic patients during administration of these compounds is thus mandatory.

Analysis of the relationship between body mass index, insulin resistance, and beta-cell function: a cross-sectional study using the minimal model

The objective of our research was to identify the mathematical model that would best define the relationship between obesity, insulin resistance (IR), and beta-cell function. Eighty-seven healthy subjects with a wide range of body mass index (BMI) were studied. Insulin sensitivity (IS) was calculated using Bergman's minimal model. Acute insulin response (AIRg) was calculated as the secretion of insulin during the first 10 minutes following a glucose bolus. IS x AIRg was used as an index of insulin-mediated glucose uptake (IMGU). The relationships among BMI, IS, fasting plasma insulin (FPI), and AIRg were studied in linear relationship terms and in terms of the hyperbolic function. Where the best fit was linear, the Jones and Molitoris method was used to investigate whether the 2-line fit was significantly better. The division of the population into BMI quartiles shows that from the third quartile, IS (12.4 +/- 6.0 v 11.0 +/- 6.4 v 4.8 +/- 1.8 v 3.2 +/- 2.0 E-5 min(-1)[pmol/L](-1), P < .01) diminishes. Nevertheless, a plateau was established between the last 3 quartiles for IS x AIRg. AIRg related to BMI via a breakpoint of 29.3 kg . m(-2). The best fits for both the BMI/IS and BMI/FPI relationships were hyperbolic. Our data indicate that obesity represents a continuum of IR, with severity increasing as BMI increases. Nevertheless, above a value of 29 kg . m(-2) and despite great increases in adiposity, IS tends to descend slowly. Moreover, there seems to be an IMGU threshold at a BMI value of approximately 27 kg . m(-2), above which an increase in adiposity leads to a greater fall in IS x AIRg. Furthermore, this threshold also appears to affect pancreatic response to a glucose stimulus.

Insulin action on protein metabolism in acromegalic patients

Insulin resistance in acromegaly causes glucose intolerance and diabetes, but it is unknown whether it involves protein metabolism, since both insulin and growth hormone promote protein accretion. The effects of acromegaly and of its surgical cure on the insulin sensitivity of glucose and amino acid/protein metabolism were evaluated by infusing [6,6-(2)H(2)]glucose, [1-(13)C]leucine, and [2-(15)N]glutamine during a euglycemic insulin (1 mU x kg(-1) x min(-1)) clamp in 12 acromegalic patients, six studied again 6 mo after successful adenomectomy, and eight healthy controls. Acromegalic patients, compared with postsurgical and control subjects, had higher postabsorptive glucose concentration (5.5 +/- 0.3 vs. 4.9 +/- 0.2 micromol/l, P < 0.05, and 5.1 +/- 0.1 micromol/l) and flux (2.7 +/- 0.1 vs. 2.0 +/- 0.2 micromol x kg(-1) x min(-1), P < 0.01, and 2.2 +/- 0.1 micromol x kg(-1) x min(-1), P < 0.05) and reduced insulin-stimulated glucose disposal (+15 +/- 9 vs. +151 +/- 18%, P < 0.01, and 219 +/- 58%, P < 0.001 from basal). Postabsorptive leucine metabolism was similar among groups. In acromegalic and postsurgical subjects, insulin suppressed less than in controls the endogenous leucine flux (-9 +/- 1 and -12 +/- 2 vs. -18 +/- 2%, P < 0.001 and P < 0.05), the nonoxidative leucine disposal (-4 +/- 3 and -1 +/- 3 vs. -18 +/- 2%, P < 0.01 and P < 0.05), respectively, indexes of proteolysis and protein synthesis, and leucine oxidation (-17 +/- 6% in postsurgical patients vs. -26 +/- 6% in controls, P < 0.05). Within 6 mo, surgery reverses insulin resistance for glucose but not for protein metabolism. After adenomectomy, more leucine is oxidized during hyperinsulinemia.

Growth hormone receptor antagonist improves insulin resistance in acromegaly

Growth hormone hypersecretion is a known cause of insulin resistance. This change in insulin sensitivity is believed to be mediated directly by growth hormone binding to its receptor. Five subjects ages 28-55 years who were participating in a clinical study that had been designed to assess the effects of a growth hormone receptor antagonist (Pegvisomant) on disease activity in acromegaly were evaluated to determine the role of growth hormone hypersecretion in inducing changes in insulin sensitivity. These subjects were treated with the 15-30 mg/day of Pegvisomant for periods ranging from 14 to 23 months. These doses were adequate to normalize IGF-I in four of the five subjects. The subjects were monitored to ensure that there were no significant changes in diet, exercise, or weight. Mean pretreatment IGF-I was 1104+/-277 ng/ml and decreased to a nadir of 355+/-157 ng/ml on treatment. After a 6-week withdrawal period, mean IGF-I had increased to 549+/-142 ng/ml. Fasting insulin was 35.2+/-16 uU/ml prior to treatment then decreased to a nadir of 19.9+/-14.6 uU/ml on treatment and then increased to 24.5+/-11.3 uU/ml. Fasting glucose decreased from 187+/-68 to 122+/-38 mg/dl and then increased to 159+/-41 mg/dl. Hemoglobin A(1)C decreased from 8.1+/-1.7 to 6.3+/-1.5%. Two subjects with overt type II diabetes had decreases in hemoglobin A(1)C from 8.3 to 5.9% and from 11.4 to 8.6%. These changes were associated with decreases in the amount of medication needed to control blood glucose. Weight remained stable throughout the study. The results show that the Pegvisomant is an effective agent for improving insulin resistance in subjects who have acromegaly and that this effect is independent of weight loss. The results suggest a potential role for Pevisomant in the treatment of insulin resistant states other than acromegaly.

Roles of insulin-like growth factor-I and growth hormone in mediating insulin resistance in acromegaly

Most patients with acromegaly have some degree of insulin resistance. The principal mediator of insulin resistance in acromegaly is hypersecretion of growth hormone. Growth hormone acts at several levels to block insulin actions including inhibiting phosphorylation of the insulin receptor and one of its principal signaling molecules IRS-1 in response to insulin administration. This leads to reduced sensitivity to insulin in the periphery in stimulating peripheral glucose uptake and to increased resistance to insulin's ability to suppress gluconeogenesis. Furthermore growth hormone excess leads to mobilization of free fatty acids which inhibit insulin stimulated glucose oxidation by acting as a competitive energy source thus leading to further worsening of insulin resistance. These abnormalities can be overcome by administering agents which either lower growth hormone secretion or block growth hormone action. The role of elevated IGF-I in acromegaly in mediating insulin resistance is more difficult to analyze. Indirect inferences from the data that are available suggest that IGF-I is acting to enhance insulin sensitivity and partially counteracting the insulin antagonistic effects of growth hormone. In a recent study administration of IGF-I to acromegalics was shown to improve insulin sensitivity over and above the level that could be achieved by simply blocking growth hormone action. Therefore it appears that the net effect of IGF-I is to counterbalance some of the effects of growth hormone hypersecretion on insulin resistance.