Studies of diabetic instability. II. Tests of insulinogenic reserve with infusions of arginine, glucagon, epinephrine, and saline

C-peptide enhances glucagon secretion in response to hyperinsulinemia under euglycemic and hypoglycemic conditions

Several studies have associated the presence of residual insulin secretion capability (also referred to as being C-peptide positive) with lower risk of insulin-induced hypoglycemia in patients with type 1 diabetes (T1D), although the reason is unclear. We tested the hypothesis that C-peptide infusion would enhance glucagon secretion in response to hyperinsulinemia during euglycemic and hypoglycemic conditions in dogs (5 male/4 female). After a 2-hour basal period, an intravenous (IV) infusion of insulin was started, and dextrose was infused to maintain euglycemia for 2 hours. At the same time, an IV infusion of either saline (SAL) or C-peptide (CPEP) was started. After this euglycemic period, the insulin and SAL/CPEP infusions were continued for another 2 hours, but the glucose was allowed to fall to approximately 50 mg/dL. In response to euglycemic-hyperinsulinemia, glucagon secretion decreased in SAL but remained unchanged from the basal period in CPEP condition. During hypoglycemia, glucagon secretion in CPEP was 2 times higher than SAL, and this increased net hepatic glucose output and reduced the amount of exogenous glucose required to maintain glycemia. These data suggest that the presence of C-peptide during IV insulin infusion can preserve glucagon secretion during euglycemia and enhance it during hypoglycemia, which could explain why T1D patients with residual insulin secretion are less susceptible to hypoglycemia.

Comparison between a flash glucose monitoring system and a portable blood glucose meter for monitoring dogs with diabetes mellitus

Background

Flash glucose monitoring system (FGMS; FreeStyle Libre) was recently validated for use in diabetic dogs (DD). It is not known if this system is clinically useful in monitoring DD.

Objective

To compare the clinical utility of FGMS against blood glucose curves (BGCs) obtained with a portable blood glucose meter (PBGM) in monitoring DD.

Animals

Twenty dogs with diabetes mellitus.

Methods

Prospective study. Dogs with diabetes mellitus on insulin treatment for at least 1 month were included. Comparisons of insulin dose recommendations based on the in‐hospital GCs acquired using FGMS and a PBGM, consecutive‐day interstitial GCs (IGCs) acquired at home using the FGMS, and consecutive‐day, home vs hospital IGCs acquired using the FGMS were made using concordance analysis.

Results

There was good concordance between insulin dose recommendations based on FGMS and PBGM generated GCs and IGCs obtained in the 2 different environments on 2 consecutive days, but almost absent concordance between IGCs obtained on 2 consecutive days at home. Glucose nadirs were detected in 34/43 (79%) of Ambulatory Glucose Profile (AGP) reports of the FGMS. In comparison, concordant glucose nadirs were identified in 14/34 (41%) BGCs using PBGM. The individual FGMS scans and PBGM identified 60% and 9% of low IG/hypoglycemic episodes, respectively.

Conclusions and Clinical Importance

Insulin dose adjustments based on BGCs can be suboptimal. The FGMS allows a more accurate identification of the glucose nadirs and hypoglycemic episodes compared to the use of a PBGM and assessment of day‐to‐day variations in glycemic control.

Glycemic variability in abdominally obese men with normal glucose tolerance as assessed by continuous glucose monitoring system

The purpose of this study was to observe both the glycemic variability in abdominally obese men with normal glucose tolerance (NGT) and the relationship between glycemic variability and early atherosclerosis. This case-control study included 23 abdominally obese men (waist circumference (WC) ≥90 cm) and 23 nonabdominally obese men (WC <90 cm) with NGT who were between 20 and 50 years of age. All subjects were of the Han ethnicity. The cases and controls were age-matched. A continuous glucose monitoring system (CGMS) was used in this study. With the CGMS, the standard deviation of blood glucose (SDBG) and the mean amplitude of glucose excursion (MAGE) were calculated to estimate glycemic variability. The carotid intima-media thickness (CIMT) was used as a surrogate marker of early atherosclerosis. Mean blood glucose (MBG) (6.13 ± 0.94 vs. 5.55 ± 0.87 mmol/l), SDBG (0.89 ± 0.34 vs. 0.64 ± 0.24 mmol/l), MAGE (2.05 ± 0.83 vs. 1.57 ± 0.52 mmol/l), and CIMT (0.73 ± 0.12 vs. 0.67 ± 0.05 mm) were significantly higher in the abdominally obese men than in the nonabdominally obese men (P < 0.05). WC positively correlated with MBG (r = 0.302, P = 0.041), SDBG (r = 0.362, P = 0.013), MAGE (r = 0.302, P = 0.041), and CIMT (r = 0.487, P = 0.001). CIMT did not correlate with MBG (r = 0.206, P = 0.169), SDBG (r = 0.114, P = 0.450), and MAGE (r = 0.085, P = 0.574). After multivariate analysis, WC was still significantly associated with MBG (β = 0.025, P = 0.041), SDBG (β = 0.010, P = 0.013), MAGE (β = 0.019, P = 0.042), and CIMT (β = 0.008, P = 0.022). This study demonstrates that glycemic variability is increased in abdominally obese men with NGT. A relationship between glycemic variability and atherosclerosis was not observed in this study and requires further investigation.

Glycemic variability correlates strongly with postprandial beta-cell dysfunction in a segment of type 2 diabetic patients using oral hypoglycemic agents

OBJECTIVE

Glucose fluctuations trigger activation of oxidative stress, a main mechanism leading to secondary diabetes complications. We evaluated the relationship between glycemic variability and beta-cell dysfunction.

RESEARCH DESIGN AND METHODS

We conducted a cross-sectional study in 59 patients with type 2 diabetes (aged 64.2 +/- 8.6 years, A1C 6.5 +/- 1.0%, and BMI 29.8 +/- 3.8 kg/m(2)[mean +/- SD]) using either oral hypoglycemic agents (OHAs) (n = 34) or diet alone (nonusers). As a measure of glycemic variability, the mean amplitude of glycemic excursions (MAGE) was computed from continuous glucose monitoring data recorded over 3 consecutive days. The relationships between MAGE, beta-cell function, and clinical parameters were assessed by including postprandial beta-cell function (PBCF) and basal beta-cell function (BBCF) obtained by a model-based method from plasma C-peptide and plasma glucose during a mixed-meal test as well as homeostasis model assessment of insulin sensitivity, clinical factors, carbohydrate intake, and type of OHA.

RESULTS

MAGE was nonlinearly correlated with PBCF (r = 0.54, P < 0.001) and with BBCF (r = 0.31, P = 0.025) in OHA users but failed to correlate with these parameters in nonusers (PBCF P = 0.21 and BBCF P = 0.07). The stepwise multiple regression analysis demonstrated that PBCF and OHA combination treatment were independent contributors to MAGE (R(2) = 0.50, P < 0.010), whereas insulin sensitivity, carbohydrate intake, and nonglycemic parameters failed to contribute.

CONCLUSIONS

PBCF appears to be an important target to reduce glucose fluctuations in OHA-treated type 2 diabetes.

Evaluation of day-to-day variability of serial blood glucose concentration curves in diabetic dogs

OBJECTIVE

To evaluate day-to-day variability of serial blood glucose concentration curves in dogs with diabetes mellitus.

DESIGN

Prospective clinical study.

ANIMALS

10 dogs with diabetes mellitus.

PROCEDURE

Paired 12-hour serial blood glucose concentration curves performed during 2 consecutive days were obtained on 3 occasions from each dog. Dogs received the same dose of insulin and meal every 12 hours on both days. For each pair of curves, comparison was made between the results of days 1 and 2.

RESULTS

Mean absolute difference (without regard to sign) between days 1 and 2 for each parameter was significantly > 0, disproving the hypothesis that there is minimal day-to-day variability of serial blood glucose concentration curves when insulin dose and meals are kept constant. Coefficient of variation of the absolute difference between days 1 and 2 for each parameter ranged from 68 to 103%. Evaluation of the paired curves led to an opposite recommendation for adjustment of the insulin dose on day 2, compared with day 1, on 27% of occasions. Disparity between dosage recommendations was more pronounced when glucose concentration nadir was < 180 mg/dL (10 mmol/L) on 1 or both days. In this subset of 20 paired curves, an opposite recommendation for dosage adjustment was made on 40% of occasions.

CONCLUSIONS AND CLINICAL RELEVANCE

There is large day-to-day variation in parameters of serial blood glucose concentration curves in diabetic dogs. Day-to-day variability of serial blood glucose concentration curves has important clinical implications, particularly in dogs with good glycemic control.

Hypoglycemia induced by excessive rebound secretion of insulin after removal of pheochromocytoma

During an 8-year-period from 1981, a total of 6 of 45 patients with pheochromocytoma developed severe hypoglycemia (plasma glucose, 12-50 mg/dl) 2-4 1/2 hours after removal of the tumor. In order to elucidate the pathogenesis of the hypoglycemic attack, the levels of plasma immunoreactive insulin (IRI) and glucose were sequentially measured at surgery in 10 patients with pheochromocytoma, from the beginning of the operation until usually 5 hours after tumor resection. The same examinations were carried out in 4 patients with primary aldosteronism and 1 patient with Cushing's syndrome as controls. The highest plasma IRI levels observed in the 2 patients with postexcisional hypoglycemia were 174 and 2,081 microU/ml and those in the 8 patients without hypoglycemia were 13-222 microU/ml (mean, 77), but they were only 14-33 microU/ml (mean, 22) in the 5 control patients. The mean of the highest plasma IRI/glucose ratios in the immediate postoperative phase was 1.37 +/- 0.87 in the 10 patients with pheochromocytoma but only 0.16 +/- 0.04 in the 5 control patients (p less than 0.01). Review of the clinical data in our series disclosed that patients with higher levels of preoperative urinary epinephrine excretion and those with either diabetes mellitus or impaired glucose tolerance tended to develop postoperative hypoglycemia. These observations suggest that endogenous insulin secretion is suppressed by increase plasma catecholamines, and that excessive rebound secretion of insulin after removal of a pheochromocytoma is a rather common phenomenon. Intravenous infusion of glucose is necessary and plasma glucose levels should be monitored after resection of a pheochromocytoma.

Effect of meal components on peripheral and portal plasma glutamate levels in young pigs administered large doses of monosodium-L-glutamate

Mean peak plasma glutamate concentrations and area under the plasma glutamate concentration-time curve are much lower in adult humans ingesting monosodium L-glutamate (MSG) in formula than in water. The present study investigated the effects of individual meal components on portal and vena caval plasma glutamate concentration in young pigs administered MSG. Portal vein catheters and gastrojejunal tubes were placed in four young male pigs, and the animals were allowed to recover. Each animal was then administered four water solutions providing 500 mg/kg body weight MSG in a Latin square design. One solution provided only MSG; the second provided MSG and 1 g/kg body weight metabolizable carbohydrate (partially hydrolyzed corn starch); the third provided MSG and 1 g/kg body weight nonmetabolizable carbohydrate (beta-cellobiose); and the fourth provided MSG and 0.4 g/kg body weight of an amino acid mixture (Aminosyn, Abbott Laboratories, North Chicago, Ill). Mean peak plasma glutamate concentration and area under the plasma glutamate concentration-time curve were significantly lower (P less than 0.05) in both portal and vena caval blood when MSG was administered with metabolizable carbohydrate than when administered in water. Simultaneous ingestion of MSG with nonmetabolizable carbohydrate (beta-cellobiose) or amino acids had no significant effect on either mean peak portal or vena caval plasma glutamate concentration or area under the plasma glutamate concentration-time curves when compared to values observed when MSG was administered alone. The data suggest that metabolizable carbohydrate is the meal component affecting plasma glutamate concentration.

C-peptide secretion and insulin antibodies as determinants of stability in diabetes mellitus

The relative significance of residual beta-cell secretory activity and human insulin antibodies in determining diabetic stability has been examined in 35 diabetic subjects. The response of plasma C-peptide immunoreactivity following 50 g oral glucose has been used as an index of beta-cell function. Glucose-stimulated C-peptide secretion was observed in 58% of stable diabetics, but in no labile diabetics. When present, C-peptide secretion following a glucose load in diabetics was of smaller amplitude and slower in onset, but more prolonged than in normal subjects. In secretors, stability of diabetes was significantly correlated with the magnitude of the C-peptide response. As a group, labile diabetics had lower insulin antibody levels than stable patients, but stability and antibody levels were not correlated in individual patients. In non-secretors there was no difference in antibody levels between the stable and labile groups. Neither the equilibrium binding affinities nor the dissociation rate constants differed significantly for antibodies from stable and labile diabetics. Thus stability of diabetes depends upon residual beta-cell secretory activity, but not on the concentration or binding characteristics of insulin antibodies.

C-peptide in juvenile diabetes

C-peptide can be used as a measure of endogenous insulin secretion in insulin treated diabetics with insulin antibodies. At the onset of juvenile diabetes insulin production is thought to be absent or minimal, but we have found rather high levels of C-peptide, even in ketoacidotic patients. The ketoacidosis does not mean an irreversible beta cell failure. In the postinitial remission period with stable metabolism many patients have normal or almost normal C-peptide levels and their beta cells have the capacity to respond to natural stimulation with an increased insulin secretion. For some unknown reason the metabolism becomes more labile coinciding with decreasing C-peptide values. However, even several years beyond the postinitial remission period many juvenile diabetics have some persistent beta cell function, and it has been shown that even trace remnants of beta cell function are of importance for stabilization of the metabolism. There is no reason to believe that the beta cell failure should be predetermined e.g. by genetic factors. However, little is known how to influence the progression and stop the increasing beta cell failure. Some of our results suggest that an early detection and an intensive treatment of diabetes before severe metabolic disturbances and pronounced insulin deficiency have appeared, may increase the possibility of preserving some beta cell function.

Hormonal and metabolic responses to glucagon in diabetes mellitus

The metabolic and hormonal responses to glucagon (1 mg, subcutaneous) were studied in twelve diabetic and twelve non-diabetic subjects. Diabetics showed a GH response, which although commencing slightly earlier, did not otherwise differ from that of the controls. There was the expected diminished insulin response to glucagon among the patients on oral agents. The GH response to glucagon in the diabetics began before there was any significant fall in blood glucose (BG). The hyperglycaemic response in the diabetics peaked later, was greater in amplitude and was more prolonged. In this group both pyruvate and lactate changes were delayed and diminished in amplitude. The diabetics showed a biphasic response of both acetoacetate and 3-hydroxybutyrate to glucagon; a small transient significant rise in the first 2 h followed by a second rise after 3h. In contrast the controls showed a significant fall in these metabolites during the initial 2 h, before a rise after 3 h. The significance of these hormonal and metabolic responses is discussed.

Amino acid modulation of glucose-induced insulin and glucagon release in diabetic patients

In order to determine whether amino acids have a beneficial effect on glucose tolerance in diabetes, the effect of intravenous infusion of mixed amino acids on plasma insulin, glucagon, and blood glucose responses to oral glucose loading was studied in patients with mild to moderate diabetes. Intravenous infusion of mixed amino acids over a period of 30 min which was started 30 min or immediately before oral glucose loading significantly augmented the insulin response but did not improve the blood glucose curve, probably due to excessive glucagon response. However, amino acid infusion over a period of 60 min started immediately before oral glucose loading evoked a sustained rise of plasma insulin associated with a lesser degree of glucagon secretion, thus causing significant improvement of the blood glucose curve.