Short-term Hyperglycemia Research Articles

No correlation between glycemic control and an increase in erythrocyte aldose reductase activity in type I and type II diabetic patients

Aldose reductase, the first enzyme of the polyol pathway, has been related to the pathogenesis of diabetic complications. The regulation of the enzyme in diabetes patients, however, has not yet been clarified. We recently reported that the activity of aldose reductase was increased in erythrocytes of insulin-dependent diabetes mellitus patients but short-term hyperglycemia did not affect the enzyme activity. It is still unclear, however, whether or not the increase in the enzyme activity is caused by long-term hyperglycemia and thus would be seen equally in both type I (insulin-dependent diabetes mellitus) and type 2 (non-insulin-dependent diabetes mellitus) individuals. To further clarify these issues we measured erythrocyte aldose reductase activity in 46 type I patients and 30 type II patients who had variable glucose control and in 16 nondiabetic subjects. We compared the enzyme activity with plasma glucose levels and hemoglobin A 1c levels. The results show that erythrocyte aldose reductase activity is increased in both type I and type II patients as compared with nondiabetic subjects (7.1 ± 0.3 U/L and 6.8 ± 0.4 U/L erythrocytes versus 5.6 ± 0.2 U/L erythrocytes, p < 0.001 and p < 0.01, respectively), but there were no significant differences between the two groups of diabetic patients. The enzyme activity varied by approximately four times among the diabetic individuals but there was no correlation between the enzyme activity and plasma glucose or hemoglobin A 1c levels. We conclude that the increased activity of erythrocyte aldose reductase seen in diabetes is not related to hyperglycemia.

Reduced ciliary neuronotrophic factor-like activity in nerves from diabetic or galactose-fed rats

This study examined the levels of ciliary neuronotrophic factor (CNTF)-like activity in the sciatic nerve of rats with short-term streptozotocin-induced diabetes or dietary supplementation with 40% galactose. CNTF-like activity, found in nerve extracts by in vitro bioassay, was reduced to 20% of control values after 1 or 2 months of galactose feeding (both P less than 0.01) and to 70% of control values after two months of streptozotocin diabetes (P less than 0.01). These data demonstrate that short-term hyperglycemia or its consequences can reduce extractable levels of Schwann cell-derived neuronotrophic factor and raise the possibility that impaired Schwann cell production of CNTF may contribute to the development of experimental diabetic neuropathy.

Effects of hyperinsulinemia and hyperglycemia on insulin receptor function and glycogen synthase activation in skeletal muscle of normal man

Insulin receptor function, glycogen synthase activity, and activation by phosphatases were studied in biopsies of human skeletal muscle under conditions of hyperglycemia and/or hyperinsulinemia for 150 minutes. Twenty-one healthy volunteers underwent either (A) a hyperinsulinemic, euglycemic clamp (serum insulin, 160.0 ± 7.7 mU/L; plasma glucose, 4.9 ± 0.1 mmol/L; n = 9), (B) a hyperglycemic clamp during normoinsulinemia (serum insulin, 18.1 ± 3.3 mU/L; plasma glucose, 12.9 ± 0.2 mmol/L; n = 6), or (C) a combined hyperinsulinemic, hyperglycemic clamp (serum insulin, 158.3 ± 15.0 mU/L; plasma glucose, 11.4 ± 0.8 mmol/L; n = 6). During all studies, the endogenous insulin secretion was inhibited with somatostatin. Insulin binding and kinase activity of insulin receptors solubilized from vastus lateralis muscle biopsies were unaffected by hyperglycemia and/or hyperinsulinemia. Hyperinsulinemia activated the muscle glycogen synthase with a decrease in the half-maximal activation constant (A 0.5) for glucose-6-phosphate (G6P) from 0.53 ± 0.04 to 0.21 ± 0.02 mmol/L (study A, P < .02) and from 0.53 ± 0.06 to 0.19 ± 0.05 mmol/L (study C, P < .03). In addition, the rate of glycogen synthase activation by phosphatases increased from 0.078 ± 0.017 to 0.134 ± 0.029 U/min/mg protein (study A, P < .03) and from 0.082 ± 0.013 to 0.145 ± 0.033 U/min/mg protein (study C, P = .05). Hyperglycemia during normoinsulinemia did not affect A 0.5 or phosphatase activity. In conclusion, (1) hyperinsulinemia for 2 1 2 hours increases glycogen synthase activity and activation by phosphatases independently on the glycemia; and (2) insulin receptor binding and basal and insulin-stimulated receptor kinase activity are not modified during short-term hyperinsulinemia and/or hyperglycemia.

Nonenzymatic Glycosylation of Immunoglobulin G Impairs Complement Fixation

Transient hyperglycemia in patients receiving total parenteral nutrition may be associated with impaired immune function. The effects of short-term hyperglycemia on one aspect of antimicrobial immune function, ie, the ability of IgG to fix complement, were investigated. Aliquots of anti-human albumin, anti-horse ferritin, and anti-alkaline phosphatase were incubated for 0, 8, 16, 24, 48, and 96 hr with either 0 or 240 mg of glucose per deciliter of buffer. All samples were analyzed for the degree of glycation using a thiobarbituric acid assay, and for complement fixation ability using a microcomplement fixation assay. Significant increases in glycation over control samples were observed after only 16 hr (31 vs 15 mmol 5-hydroxymethylfurfural/mol IgG, p less than 0.01). Complement fixation was significantly altered after 48 hr of incubation (76 +/- 5% vs 90 +/- 8% total serum complement fixed by albumin/anti-albumin complex, p less than 0.03) when four of the 84 (4.7%) IgG lysine residues were glycated. It is demonstrated that a significant reduction in complement fixation by immunoglobulin occurs with elevated glucose concentrations and that this may play a clinically significant role in transiently hyperglycemic patients.

Short-term Hyperglycemia Depresses Immunity through Nonenzymatic Glycosylation of Circulating Immunoglobulin

Hyperglycemia accompanies a myriad of clinical conditions and causes an acceleration in the nonenzymatic glycosylation (NEG) of proteins. Since many proteins lose function when glycosylated, we assessed the effect of hyperglycemia on the function of immunoglobulin G. Twenty newborn Sprague-Dawley rats underwent splenectomy and 20, splenic mobilization alone. After 3 weeks, all animals received an intraperitoneal injection of Streptococcus pneumoniae. Twelve hours later, ten animals from each group received either control (CIG) or glycosylated (GIG) human immunoglobulin (0.3 gm/kg) intraperitoneally. Asplenic animals receiving GIG lived 28.5 hours vs. 49.6 hours for those receiving CIG (p less than 0.0001). Animals with spleens receiving GIG lived 48.2 hours vs. 51.7 hours for those receiving CIG (p = 0.03). Short-term glycosylation of immunoglobulin causes its inactivation. This may contribute to the increased risk of infection noted in hyperglycemic animals.

Effects of acute hyperglycemia on myocardial glycolytic activity in humans.

The effects of hyperglycemia on myocardial glucose metabolism were investigated in seven healthy male subjects (age 24 +/- 4 yr). [6-14C]Glucose and [U-13C]lactate were infused as tracers. Circulating glucose was elevated to two hyperglycemic levels using a clamp technique for 1 h at each level. The mean arterial glucose concentration was 4.95 +/- 0.29 (control), 8.33 +/- 0.31 and 10.84 +/- 0.60 mumols/ml, respectively. Glucose extraction increased significantly from control (0.15 +/- 0.13 mumols/ml) during each level of the glucose clamp (0.28 +/- 0.12, P less than 0.02, and 0.54 +/- 0.14 mumols/ml, P less than 0.005, respectively). Myocardial production of 14CO2 showed that during control 9 +/- 10% of exogenous glucose was oxidized immediately upon extraction. Despite a significant increase in the amount of exogenous glucose oxidized with level II hyperglycemia, it represented only 32 +/- 10% of the glucose extracted. [13C]Lactate analysis showed that the myocardium was releasing lactate; during control 40 +/- 30% of this lactate was derived from exogenous glucose and during hyperglycemia this value increased to 97 +/- 37% (P less than 0.005). Thus, these data show that during short-term hyperglycemia, myocardial glucose extraction is enhanced. However, despite increases in exogenous glucose oxidation and the contribution of exogenous glucose to lactate release, the majority of the extracted glucose (i.e., 57%) is probably stored as glycogen.

Urinary excretion of kappa light chains in patients with diabetes mellitus

The urinary excretion of kappa light chains, beta 2-microglobulin and albumin was examined in patients with newly diagnosed and long-standing insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetes mellitus, and compared to age-matched control subjects. Patients with IDDM diagnosed within two months, presented with normal albumin excretion, whereas the concentrations of beta 2-microglobulin and kappa light chain in urine were higher than in control subjects. The initiation of insulin therapy reduced, but did not completely normalize, the elevated rate of kappa light chain excretion. Patients with IDDM of long duration showed increased urine excretion of kappa light chains and albumin. In keeping with the findings in IDDM, patients with newly diagnosed NIDDM (within one year) showed increased urinary excretion of kappa light chains compared with control subjects. There was, however, no further increase in light chain excretion with longer duration of NIDDM. To study the effect of short-term hyperglycemia on urinary protein excretion, 12 normal subjects participated in a three-step hyperglycemic clamp study, during which their plasma glucose concentration was raised by +50, +125 and +300 mg/dl. The urine excretion of albumin and beta 2-microglobulin rose progressively with each hyperglycemic clamp step, whereas that of kappa light chain excretion was unaffected by hyperglycemia. We conclude that increased urinary excretion of kappa light chain is a consistent finding in all types of diabetes mellitus, and can be observed even when the albumin excretion is normal. Since the serum concentration of kappa light chain is normal in diabetes, the increased urinary excretion of kappa light chains must be of renal origin.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo insulin secretion and action in hyperglycemic rat.

This work was designed to study the effects of insulin secretion and action in vivo of moderate hyperglycemia induced by glucose infusion during 4 days in unrestrained rats. The maintenance of a glycemia around 170 mg/dl throughout the infusion time necessitated a gradual increase of glucose infusion rate from 11.5 to 19 g/day. Throughout the infusion period, plasma insulin-to-glucose ratio remained much higher in hyperglycemic rats (HG) than in controls. Glucose tolerance and insulin secretion tests were performed 2 h after the end of the infusion, when glycemia and insulinemia were back to basal values. Incremental plasma glucose values were significantly lower in HG than in control rats without significant changes in incremental plasma insulin concentrations, suggesting an increased insulin efficiency. At the same insulin level, glucose utilization was higher in HG than in control rats during euglycemic-hyperinsulinemic clamps. These data show that short-term hyperglycemia and hyperinsulinemia do not induce a defect in insulin secretion in vivo and do increase tissue sensitivity to insulin.

Compensatory growth of pancreatic beta-cells in adult rats after short-term glucose infusion.

The extent to which adult pancreatic beta-cells can respond in vivo to a sustained glucose stimulus by increasing their mass through either hyperplasia or hypertrophy has remained unanswered. Therefore, we studied the in vivo effect of short-term (96-h) hyperglycemia on the growth of beta-cells by infusing adult rats with 35 or 50% glucose or 0.45% saline. After 96 h of glucose infusion, the beta-cell mass, quantified by point-counting morphometrics of immunoperoxidase-stained paraffin sections, showed a 50% increase (9.57 +/- 0.87 mg, n = 5, 50% glucose infused; 9.50 +/- 1.23, n = 7, 35% glucose infused; 6.15 +/- 0.55, n = 6, 0.45% saline infused). This growth was selective for beta-cells; the non-beta-cell mass was unchanged. The mitotic index, measured by accumulated mitotic frequency after a 4-h colchicine treatment, increased fivefold in glucose-infused animals compared to saline-infused animals. This enhanced replication of beta-cells provides evidence for increase in cell number or hyperplasia. In addition, hypertrophy of the beta-cell was also quantified. Mean cell volume, determined from the mean cell cross-sectional area measured planimetrically from low-magnification electron micrographs, increased to 150% of control values after 96 h of 50% glucose infusion. Seven days after the 96-h infusion, in reversal experiments, the beta-cell mass had not returned to saline-infused levels. In addition, the non-beta-cell mass of glucose-infused animals had increased. The mitotic index of the beta-cell of glucose-infused rats was, however, significantly lower than that of the saline controls, but the mean cell volume of the beta-cells remained elevated.(ABSTRACT TRUNCATED AT 250 WORDS)

Peripheral nerve function during hyperglycemic clamping in healthy subjects.

The influence of hyperglycemia with physiological hyperinsulinemia on peripheral nerve function was studied in 10 non-diabetic subjects. Blood glucose concentration was raised from 3.8 +/- 0.2 mmol/l (mean +/- SEM) to 17.1 +/- 1.4 mmol/l (mean +/- SEM) within 15 min and kept at this level for 120 min by intravenous glucose infusion. Sensory and motor nerve conduction velocity, and distal motor latency in the ulnar nerve were determined before, immediately after induction of hyperglycemia, and again after 120 min of hyperglycemia. Mean sensory nerve conduction velocity increased from 57.7 m/s to 59.5 m/s (P less than 0.005) immediately after induction of hyperglycemia, and after 120 min of hyperglycemia mean sensory nerve conduction velocity was 59.6 m/s (P less than 0.05). An insignificant increase was seen in motor nerve conduction velocity during hyperglycemia. Mean distal motor latency decreased from 3.1 ms to 3.0 ms (P less than 0.025) immediately after induction of hyperglycemia, and after 120 min of hyperglycemia distal motor latency was 2.9 ms (P less than 0.05). We conclude that short term hyperglycemia with physiological hyperinsulinemia seems to increase sensory nerve conduction velocity and decrease motor latency.

Influence of hyperglycemia on Ca2+-Mg2+ -ATPase of red blood cells from diabetic patients.

The influence of hyperglycemia on calmodulin-stimulated Ca2+-Mg2+-ATPase activity was studied in 20 diabetic subjects. A clear inverse relationship between short-term hyperglycemia as well as chronic hyperglycemia and calmodulin-stimulated Ca2+-Mg2+-ATPase activity could be demonstrated. Such a relationship could not be shown for basal enzyme activity.

Hyperglycemia decreases glucose uptake in type I diabetes.

It has recently been postulated that hyperglycemia per se may contribute to insulin resistance in diabetes. To examine this possibility directly, we measured glucose uptake after 24 h of hyperglycemia (281 +/- 16 mg/dl) and normoglycemia (99 +/- 6 mg/dl) in 10 type I (insulin-dependent) diabetic patients (age 33 +/- 3 yr, relative body wt 102 +/- 3%) treated with continuous subcutaneous insulin infusion. Hyperglycemia was induced by an intravenous glucose infusion, whereas saline was administered during the control day. During both studies the patient received a similar diet and insulin dose. After hyper- and normoglycemia, a primed continuous infusion of insulin (40 mU X m-2 X min-1) was started, and plasma glucose was adjusted to and maintained at 142 +/- 2 and 140 +/- 2 mg/dl, respectively, during 60-160 min of insulin infusion. The rate of glucose uptake after hyperglycemia averaged 8.3 +/- 1.1 mg X kg-1 X min-1, which was lower than the rate after the normoglycemic period (10.1 +/- 1.2 mg X kg-1 X min-1, P less than .001). In conclusion, short-term hyperglycemia reduces glucose uptake in type I diabetic patients. Thus, part of the glucose or insulin resistance in these patients may be caused by hyperglycemia per se.

SERUM GLYCOSYLATED PROTEINS (GP): PREDICTORS OF MATERNAL-FETAL HYPERGLYCEMIA AND FETAL B.WT.?

The usefulness of serum GP in detection of subtle hyperglycemia was studied in 3 groups of mother/infant pairs: 20 normal/20 AGA(GrI): 20 normal/20 MACRO, > 4.0kg (GrIII) and 9 diabetic mothers/10 neonates (GrIII). Two diabetics were class A, 4 class B and 3 class C. Maternal serum HbA1c and GP and cord GP were measured at delivery. Maternal age, gravidity, parity and gest. age were similar. GrII mothers gained more wt(p<0.01) than GrI(mean±SD, 41±13 vs 28±7 lbs resp.) but not sig. diff. than GrIII mothers (33±12 Ibs). B.Wt. and B.Wt.ratios were greater (p<0.01) in GrII (4.4±.3kg; 1.39±.1 resp.) than in GrI (2.9±.3kg; 0.9±.08) or GrIII(3.3±.9kg; 1.08±.25) neonates. HbA1c and GP were: GP values were above the 95th %ile in 44% of moms and 80% of newborns in GrIII as compared to 5% in GrII or GrI patients (p<0.01). Maternal GP correlated sig. (p<0.001) with cord GP in GrI (r=.87) and GrII (r=.77) but not in GrIII pairs. B.Wt., B.Wt.ratio and plasma glucose at 1hr correlated poorly with HbA1c and maternal or cord GP; however, B.Wt. and B.Wt.ratio correlated sig. (p<0.01) with maternal wt. gain. In summary, 1) GP are more useful than HbA1c in detecting short term hyperglycemia in diabetic mothers and infants at delivery; 2) glucose intolerance in macrosomic newborns and their mothers may be too subtle for detection by serum GP; 3) B.Wt. can be sig. correlated with maternal wt. gain but not with serum GP. ** p < 0.001

The influence of optic nerve section on blood metabolite levels in Carcinus maenas (Crustacea: Brachyura)

1. 1. Blood metabolite levels were assayed in Carcinus maenas as an indicator of the functioning of the hyperglycemic hormone, HGH, secreted by the crab's eyestalk neuroendocrine tissue. 2. 2. Bilateral eyestalk ablation eventually resulted in a hypoglycemic response after 2–3 days. 3. 3. Bilateral optic nerve section produced a significant, long-term hypoglycemic response suggesting that release of HGH from the eyestalk sinus gland is controlled, via a promotive neural pathway, by the CNS and probably by the cerebral ganglia. 4. 4. Injection of eyestalk extract into operated crabs consistently produced significant, short-term hyperglycemia.

Effects of short-term hyperglycemia on insulin secretion in normal humans.

Stepwise glucose clamps were used to study beta-cell insulin response to glucose in normal and noninsulin-dependent diabetic subjects and to study changes in response after hyperglycemia. In normal subjects, insulin increment, delta I, correlated with glucose increment above basal, delta G, during the first 6 min of hyperglycemia, r = 0.748, P less than 0.0001. After 1 h of hyperglycemia, mean delta I/ delta G was reduced from 50 to 23 (mean difference 23 +/- 5) pmol/mmol, P = 0.0002; but delta I/% change in glucose (delta G') was unaltered (2.3 vs. 1.7, mean difference 0.4 +/- 0.3 pmol/%). Second-phase response correlated with mean glucose elevation (r = 0.835, P less than 0.0001), and no plateau was reached after 3 h at 3 mmol/l above basal glucose (rate of change of insulin concentration = 0.5; range, 0.3-0.8 pmol . l-1 . min-1). In diabetic subjects, delta I/ delta G was 20% of normal, while delta I/ delta G' was 63% of normal and second-phase response 30% of normal. We conclude that hyperglycemia per se reduces delta I/ delta G and must be considered when assessing insulin responses. Noninsulin-dependent diabetic subjects have defective first- and second-phase responses.

Sorbitol content of plasma and erythrocytes during induced short-term hyperglycemia

Plasma glucose concentration was increased from a mean basal value of 3.3 +/- 0.1 to 13.3 +/- 1.5 mmol/L by the intravenous administration of glucose for 60 minutes to four healthy volunteers. The sorbitol content of erythrocytes was increased during the period of hyperglycemia from a mean basal value of 65 +/- 9 to 106 -/+ 6 mumol/L. The plasma sorbitol concentration remained constant at 12 +/- 1 mumol/L. This dissociated response indicates that the plasma concentration of sorbitol is not significantly affected by a short-term hyperglycemia sufficient to cause intracellular sorbitol accumulation.