Determination of plasma glucose during rapid glucose excursions with a subcutaneous glucose sensor

Continuous glucose monitoring has the potential to improve glucose management and reduce the risk of hypoglycemia in individuals with diabetes. Accurate sensors may also allow the development of a closed-loop insulin delivery system. The purpose of this work was to determine the delay time associated with a subcutaneous glucose sensor during rapidly changing glucose excursions. Subcutaneous glucose sensors (Medtronic MiniMed, Inc., Northridge, CA) were inserted in five healthy men. After a 2-h stabilization period, a 3-h hyperglycemic (approximately 11 mM) clamp was performed followed by a 90-min period in which plasma glucose was allowed to decline to as low as 2.8 mM. Sensors were calibrated using two points (basal and hyperglycemia), and the calibrated sensor glucose measurements were compared with those from a reference analyzer (Beckman Instruments, Fullerton, CA). Response time was estimated from a first-order kinetic model. Plasma glucose levels, determined with the subcutaneous sensor, were highly correlated with those obtained with the reference glucose analyzer (r(2) = 0.91, p < 0.001; mean absolute difference of approximately 8%). The half-time for the sensor response was estimated to be 4.0 +/- 1.0 min. The subcutaneous glucose sensor has the potential to facilitate the detection of hypoglycemia and improve overall glycemic control when used in a real-time monitor. The rapid response should be sufficient to allow a fully automated closed-loop insulin delivery system to be developed based on the subcutaneous sensing site.     

Increased glucose turnover and glucose cycling in acromegalic patients with normal glucose tolerance

Summary To characterize the diabetogenic effects of growth hormone, we simultaneously measured glucose turnover with 2-³H- and 6-³H-glucose in six acromegalic patients with normal fasting blood glucose and oral glucose tolerance tests. Eight healthy volunteers served as controls. All subjects were studied under both basal conditions and during glucose infusion (2 mg · kg^–1 · min^–1). We determined true glucose production and irreversible glucose uptake using 6-³H-glucose and glucose cycling (difference between 2-³H- and 6-³H-glucose). After an overnight fast, glucose production was higher than normal in the acromegalic patients (2.18±0.15 vs 1.85±0.03 mg · kg^–1 · min^–1,p < 0.05) despite hyperinsulinaemia. The metabolic clearance rate was normal. During the glucose infusion, glucose production was not suppressed as effectively in the acromegalic patients as in controls nor was glucose uptake augmented, while metabolic clearance rate was decreased. In acromegaly, basal glucose cycling was increased (0.44 ± 0.08 vs 0.25 ± 0.07 mg · kg^–1 · min^–1, p < 0.05). Furthermore cycling of endogenous glucose measured during glucose infusion was also augmented (0.41 ± 0.05 vs 0.24 ± 0.05 mg · kg^–1 · min^–1, p < 0.05). Hence the increase of glucose cycling (70%) was much more pronounced than that of glucose production (17%). In conclusion, small defects in glucose metabolism in acromegaly can be detected with sensitive tracer methods. These derangements are confined to the liver under fasting conditions, but are of both hepatic and extrahepatic origin during glucose loading.     

Effect of intravenous glucose on serum glucose determinations

Hyperglycemia is frequently seen in hospitalized nondiabetic patients receiving intravenous glucose solutions. As no standard method of interpreting the serum glucose value has been defined in patients receiving intravenous glucose, we have attempted to determine if any correlation can be made. It was found that with a 5% dextrose in water infusion at 100 ml/hr, the mean change in serum glucose was $\text{9}\text{mg}\text{100}\text{ml}$ above the fasting serum glucose; with a 5% dextrose in water at 200 ml/hr, the mean serum glucose rose $\text{24}\text{mg}\text{100}\text{ml}$ above the fasting serum glucose obtained in the arm opposite the intravenous infusion. It was thus determined that a serum glucose level greater than $\text{20}\text{mg}\text{100}\text{ml}$ above the fasting serum glucose level in an individual with a 5% glucose in water infusion at 100 ml/hr, or $\text{42}\text{mg}\text{100}\text{ml}$ above the fasting serum glucose in an individual with a 5% glucose in water infusion at 200 ml/hr, which are 3 SD above the mean glucose, should be early evidence for mild subclinical glucose intolerance.     

Immobilized glucose oxidase in implantable glucose sensor technology

Glucose oxidase has had a central role in previous glucose sensing methods and is key to the development of certain new glucose sensors. The immobilized enzyme is specific for glucose and sufficiently long-lived for many sensor applications, but new glucose sensing applications may place increased demands on the enzyme.     

Regulation of hepatic glucose output by glucose in vivo

The effect of infusing glucose at a rate estimated to equal hepatic glucose production (2 mg/kg BW X min) was investigated in postabsorptive unrestrained miniature pigs. Glucose turnover was estimated by the use of 3-H-glucose before and during glucose infusion where the contribution of the glucose-induced hormonal changes were estimated by infusing glucose plus somatostatin with or without insulin and/or glucagon substitution. Our data give evidence for an inhibitory effect of glucose on endogenous glucose production in the postabsorptive state. This effect seems to be independent of the hormonal changes induced by glucose infusion.     

Hepatic glucose production and splanchnic glucose exchange in hyperthyroidism

Hepatic glucose production (HGP) and net splanchnic glucose balance (NSGB) were simultaneously determined in the basal state in 8 hyperthyroid patients and 10 normal subjects using iv infusion of [3H]3-glucose and the hepatic venous catheter technique. Splanchnic glucose uptake (SGU) was calculated as the difference between the HGP and NSGB. SGU was also measured by determining the splanchnic extraction ratio of [3H]3-glucose across the splanchnic bed. In 5 hyperthyroid patients and 5 normal subjects a renal vein was also catheterized in the basal state. The influence of increased endogenous insulin secretion [stimulated by a low rate iv infusion of glucose (2 mg/kg . min)] on splanchnic and hepatic glucose exchange was also examined. Basal HGP (measured with [3H]3-glucose) was increased by 20% in the hyperthyroid patients [14.2 +/- 0.6 (SEM) mumol/kg . min] as compared to normal subjects (11.9 +/- 0.6, P less than 0.02). In marked contrast, NSGB output was slightly but not significantly decreased in the hyperthyroid group. SGU in the hyperthyroid patients, as determined with both techniques, was more than 2-fold higher than in the normal group (P less than 0.02-P less than 0.005). Splanchnic uptake of gluconeogenic precursors (lactate, pyruvate, glycerol) was increased by 20-120% in the patient group. During iv infusion of glucose, plasma insulin levels increased more in the hyperthyroid group (66% vs. 37%, P less than 0.05). Nevertheless, HGP and NSGB were less markedly suppressed in the patients as compared to the normal subjects (P less than 0.01), whereas the augmented SGU in the hyperthyroid patients reverted to normal. Splanchnic uptake of gluconeogenic precursors was unchanged in both groups. No net renal glucose production could be demonstrated in either group in the basal state. We conclude that in hyperthyroidism, increased HGP occurs in the face of an unchanged or slightly reduced rate of net glucose delivery to extrasplanchnic tissue. This discrepancy can be ascribed to augmented splanchnic uptake of glucose. These findings raise the possibility of futile cycling of glucose in the liver as a mechanism of increased oxygen consumption in hyperthyroidism. The data also demonstrate a diminished inhibitory effect of endogenous insulin on splanchnic glucose production, suggesting the presence of hepatic resistance to insulin in hyperthyroidism.     

血糖和血糖波动与肝纤维化

肝纤维化(hepatic fibrosis,HF)是肝硬化的早期阶段,是各种慢性肝病的共同病理过程,并最终发展成为肝硬化.随着生活水平的提高、饮食习惯的改变,糖尿病的发病率逐年升高.目前有很多资料证实了糖尿痛与HF有关联.本文简要总结了近年来国内外学者在高血糖和波动血糖与HF关系研究中取得的共识与现状,并就其研究进展进行讨论和展望,以其加深人们对血糖和波动血糖与HF的认识并积极开展有关方面的研究.     

Relationship between glucose oxidation and glucose tolerance in man

The study was performed to determine the influence of peripheral glucose utilization on glucose tolerance. Glucose oxidation was measured in a group of 6 normal subjects by means of continuous indirect calorimetry during a 100 g oral glucose tolerance test for 3 hr, comparing the control state with experimental inhibition or stimulation of glucose oxidation. Suprabasal oxidation, corresponding to oxidation in response to the load, mainly by insulin-dependent tissue, was obtained by subtracting basal oxidation (essentially by non-insulin dependent tissues) from total oxidation. Suprabasal oxidation of glucose was inhibited by a neutral fat infusion, and stimulated by means of dichloracetate. In the control test, from the 100 g glucose administered, 18 g participated to suprabasal oxidation during the 3 hr of the test. A neutral fat infusion, started 2 hr before the glucose load and lasting throughout the test, decreased suprabasal oxidation to 7.5 g, i.e. to 42% of the control value. With the fat infusion, a larger fraction of the energy consumption was shown to originate from lipid oxidation (37% versus 25% in controls, p < 0.05) at the expense of carbohydrate (CHO) oxidation (44% versus 60% in controls, p < 0.05). However, these major changes in peripheral glucose oxidation were accompanied by only a moderate decrease in glucose tolerance. Dichloracetate administered prior to the test increased suprabasal oxidation to 25 g glucose oxidized in the 3 hours following the glucose load, i.e. an increment of 39% above the control value. A larger fraction of energy consumption was derived from carbohydrates (77% versus 60% in controls, p < 0.05). However, no significant change was observed in glucose tolerance. These results indicate that marked changes of peripheral glucose oxidation have little influence on glucose tolerance and suggest that another mechanism, i.e. glucose storage, plays a larger role in regulating plasma glucose levels during oral glucose tolerance tests.     

Transport of glucose polymer-derived glucose by rabbit jejunum.

Mechanisms for the assimilation of glucose polymers have been inferred from perfusion studies. To further define these mechanisms, the results of measurements of unidirectional glucose fluxes across short-circuited rabbit jejunal segments in vitro are reported. Glucose polymer-stimulated short-circuit current was similar to that of glucose [19 +/- 6.0 microA/cm2 (n = 7) and 26 +/- 5.7 microA/cm2 (n = 13), respectively] and was inhibited by both acarbose and phlorizin. Acarbose, an alpha-glucosidase inhibitor with no effects of glucose transport, was used to uncouple digestion from absorption. Mucosal-to-serosal flux of glucose polymer-derived glucose was lower than that of an equal weight/volume of glucose [124 +/- 62 nmol.h-1.cm-2 (n = 4) vs. 452 +/- 121 nmol.h-1.cm-2 (n = 6); P less than 0.05] and was inhibited by both phlorizin and acarbose. No glucose polymers were detected in the serosal bath solutions by thin-layer chromatography. It is concluded that glucose polymer-derived glucose is transported by a phlorizin-inhibitable process at a rate slower than that of free glucose, a finding that suggests that hydrolysis limits glucose polymer assimilation.     

Nocturnal decrease in glucose tolerance during constant glucose infusion

Studies comparing glucose tolerance in the morning vs. that in the evening have suggested that time of day may influence glucose regulation. To examine the variation in glucose tolerance throughout the 24-h span, normal subjects were given an iv glucose infusion at a constant rate of either 5 or 8 g/kg.24 h during 30 h, and plasma levels of insulin and glucose were measured at 15-min intervals for the last 24 h of the infusion. The timing of initiation of the infusion was varied to differentiate effects of time of day from effects of duration of the infusion. A nocturnal elevation of glucose levels, culminating around midsleep and corresponding to an increase of about 15% above daytime levels, was observed in all subjects. The timing of this nocturnal maximum was not dependent on the rate of the infusion or on the time elapsed since the beginning of the infusion. Insulin levels did not show a consistent diurnal pattern. Both insulin and glucose exhibited large ultradian oscillations recurring at 100- to 150-min intervals. The amplitude of these oscillations increased with the rate of glucose infusion. These ultradian oscillations of glucose and insulin levels were temporally correlated, with a tendency for glucose pulses to lead insulin pulses by 15-30 min. These results demonstrate in normal subjects the existence of a diurnal variation in glucose tolerance distinct from the dawn phenomenon observed in diabetic subjects and indicate that spontaneous 100- to 150-min oscillations in peripheral glucose and insulin levels characterize stimulated pancreatic function, with the amplitude of the oscillations being dependent on the size of the stimulus.     

Review of glucose oxidases and glucose dehydrogenases: a bird's eye view of glucose sensing enzymes

The evolution from first-generation through third-generation glucose sensors has witnessed the appearance of a number of very diverse oxidoreductases, which vary tremendously in terms of origin, structure, substrate specificity, cofactor used as primary electron acceptor, and acceptable final electron acceptor. This article summarizes our present knowledge of redox enzymes currently utilized in commercially available glucose monitoring systems to promote a fuller appreciation of enzymatic properties and principles employed in blood glucose monitoring to help avoid potential errors.     

游离脂肪酸增高对肝糖产生、葡萄糖循环和总葡萄糖输出率的影响

目的 探讨FFA增加肝脏葡萄糖生成和肝脏胰岛素抵抗(IR)的作用位点. 方法分别给清醒大鼠输注24h脂肪乳+肝素和盐水,在输注的最后2h行高胰岛素正葡萄糖钳夹试验,测定肝脏葡萄糖生成率(HGP)、总葡萄糖输出率(TGO)和葡萄糖循环(GC). 结果 脂肪乳使血浆FFA升高3倍.在基础状态,脂肪乳使HGP和TGO增高(P<0.01).在钳夹状态,脂肪乳降低了胰岛素(Ins)增加GC的作用(P<0.01),并使Ins抑制HGP和TGO的作用下降(P<0.01). 结论 FFA能使Ins增加GC和抑制HGP与TGO的作用下降,说明FFA在不同位点诱导了肝脏IR.     

Assessing 1-h plasma glucose and shape of the glucose curve during oral glucose tolerance test

OBJECTIVE: To assess the cutoff values at different time points for impaired glucose regulation (IGR) and diabetes, the glucose curve and isolated 1-h hyperglycemia were monitored during an oral glucose tolerance test (OGTT). METHODS: Two thousand eight hundred and eighty-six subjects (1300 men and 1586 women) were recruited to have an OGTT. Plasma was collected at 0, 30, 60, 120, and 180 min to analyze glucose and insulin. The diagnosis of impaired fasting glucose, impaired glucose tolerance, and diabetes was based on World Health Organization and American Diabetes Association's criteria. Those with fasting plasma glucose (FPG) < 5.6 and 2-h plasma glucose (PG) < 7.8, but 1-h PG > or = 7.8 and < 11.1 mmol/l were defined as 1h-High7.8, and those with FPG < 7.0 and 2-h PG < 11.1, but 1-h PG > or =11.1 mmol/l as 1h-High11.1. The cutoff values were calculated by receiver operating characteristic (ROC) curve. The correlation between beta-cell function and the area under the curve of glucose (AUCg) and the shape index was analyzed with linear regression. RESULTS: The cutoff values for IGR were 5.6, 9.7, 10.1, 7.8 and 6.1 mmol/l for blood glucose at 0, 30, 60, 120 and 180 min, 24 for AUCg and 1.3 mmol/l for the shape index. The cutoff values for diabetes were 6.8, 11.2, 13, 11.1 and 7 mmol/l for 0, 30, 60, 120 and 180 min, 30.9 for AUCg and 2 mmol/l for the shape index. Both AUCg and the shape index were inversely related to beta-cell function. The profiles of glucose and insulin in the subgroup with isolated 1-h hyperglycemia were very different from those seen in subjects with normal glucose tolerance or IGR. CONCLUSIONS: The present study provides new information on measures other than the fasting and 2-h PG to evaluate glucose metabolism in vivo and stimulates further research aimed at assessing the value of the OGTT 1-h PG concentration prospectively.