Factors affecting insulin response to glucagon in man

Insulin & C-peptide levels in sulfonylurea-induced hypoglycemia: a systematic review

OBJECTIVES

We will describe insulin and C-peptide levels observed in sulfonylurea-induced hypoglycemia and determine whether these levels differed if obtained before or after hypoglycemic therapy.

METHODS

We performed a systematic review of the English literature to identify Medline articles containing "sets" (glucose <60 mg/dL with insulin and C-peptide levels). These "sets" were categorized as being obtained BEFORE, AFTER, or UNKNOWN with respect to hypoglycemic therapy.

RESULTS

22 articles, 76 patients, and 97 "sets" were included. Mean glucose (mg/dL), insulin (muIU/mL), and C-peptide (ng/mL) for all "sets' were 28.6 (+/-12.6; 26.1 to 31.2), 54.4 (+/-126.3; 28.3 to 80.5), 7.2 (+/-6.2; 5.9 to 8.5). The BEFORE measures were 24.3 (+/-7.3; 18.7 to 30.0), 36.6 (+/-26.2; 16.5 to 56.7), 5.4 (+/-4.6; 1.5 to 9.2). The AFTER measures were 33.1 (+/-9.8; 28.2 to 38.0), 126.7 (+/-278.1; 0 to 265.0), 10.3 (+/-10.5; 5.1 to 15.4). The UNKNOWN measures were 28.0 (+/-13.5; 24.7 to 31.3), 37.1 (+/-21.8; 31.7 to 42.5), 6.5 (+/-4.3; 5.4 to 7.6). Only one "set" (glucose 49 mg/dL) had insulin <3.9 muIU/mL and C-peptide <1.4 ng/mL.

CONCLUSIONS

Insulin > or =3.9 muIU/mL, C-peptide > or =1.4 ng/mL, and glucose <49 mg/dl are consistent with sulfonylurea-induced hypoglycemia. BEFORE levels were lower, but they were consistent with sulfonylurea-induced hypoglycemia.

Octreotide Therapy for Recurrent Refractory Hypoglycemia Due to Sulfonylurea In Diabetes-Related Kidney Failure

OBJECTIVE

To describe a patient with kidney insufficiency from diabetes treated with glyburide, who presented with prolonged and recurrent hypoglycemia unresponsive to large intravenous doses of glucose, which was treated successfully with intravenously administered octreotide, and to review the therapeutic options for hypoglycemia.

METHODS

We present a case report of a 66-year-old man with diabetes causing chronic kidney disease, who was treated with orally administered glyburide, 7.5 mg twice a day. He initially presented to another hospital because of hypoglycemia and was treated with intravenously administered glucose and discharged. The next day, his family brought him to our emergency department because of recurring low blood glucose levels and symptoms of sweating, fever, and nightmares. Laboratory tests revealed a blood glucose level of 33 mg/dL and a creatinine concentration of 6.2 mg/dL.

RESULTS

The patient was treated with a 5% dextrose and, subsequently, a 10% dextrose infusion without any sustained improvement. The blood glucose level remained low despite the additional administration of 3 ampules of 50% dextrose in water. The patient was given a bolus of octreotide (50 mug subcutaneously) 14 hours after his second presentation. He received another 50-mug dose of octreotide 6 hours later. After this bolus, the hypoglycemia resolved, and he no longer required intravenous administration of glucose to maintain euglycemia.

CONCLUSION

Patients with diabetes and kidney disease frequently have persistent and difficult-to-treat hypoglycemia, unresponsive to conventional therapy. Octreotide is an effective and safe treatment for patients with refractory hypoglycemia attributable to sulfonylureas.

Section of the vagal celiac branch in man reduces glucagon-stimulated insulin release

The purpose of this study was to determine whether section of the celiac branch of the vagus nerve in man affects the insulin response to intravenous glucagon injection. Patients who received a subtotal gastrectomy with lymph node dissection for gastric carcinoma were divided into two groups: the celiac-preserved group (n = 16) and the celiac-sectioned group (n = 13). The hepatic branches of the vagus were preserved in both groups. The glucagon test was performed twice in each patient during the operation; before and after manipulation of the celiac branch. Blood samples were collected just before and 6 min after the injection. No difference in the mean increases in blood glucose, insulin and C-peptide levels were seen between the two groups before the nerve manipulation. In the celiac-preserved group, the glucagon stimulated glucose-related C-peptide ratio (x 10(-3) was 0.5 +/- 0.7 before the nerve manipulation and 3.5 +/- 3.0 after it, a significant difference (p < 0.01). In the celiac-sectioned group, this increase was not observed, the ratio was 0.7 +/- 0.6 before the nerve manipulation and 0.8 +/- 3.4 after. These results indicate that the vagal celiac branch in man may also be involved in the control of pancreatic insulin release.

Effect of glucagon on hepatic energy charge and arterial ketone body ratio in normal rabbits

Glucagon has been regarded as a hepatotrophic factor, although it is also known to stimulate energy-consuming reactions in the liver, such as gluconeogenesis and ureogenesis. To clarify the effect of glucagon on the hepatic energy metabolism, the changes in arterial ketone body ratio, which reflects the hepatic mitochondrial redox state [( NAD+]/[NADH]), as well as those in energy charge and mitochondrial oxidative phosphorylation of the liver after IV glucagon injection were studied in normal rabbits. Arterial ketone body ratio decreased significantly from 1.04 +/- 0.08 to 0.61 +/- 0.11 (mean +/- SEM; P less than 0.01) within 30 minutes after glucagon injection. Hepatic energy charge also decreased from 0.883 +/- 0.014 to 0.789 +/- 0.014 (P less than 0.01) at 30 minutes, whereas mitochondrial phosphorylation rate inversely increased from 38.4 +/- 9.5 to 87.3 +/- 9.7 (nanomoles adenosine triphosphate per milligram mitochondrial protein per minute; P less than 0.01) at 30 minutes. Arterial ketone body ratio and energy charge were subsequently restored to the initial values at 60 minutes and 2 hours, respectively. The present study suggests that glucagon causes an increase in energy expenditure in the liver that results in a transient decrease in hepatic energy charge accompanied by a decrease in arterial ketone body ratio.

Pancreatic beta-cell secretion after oral glucose and intravenous glucagon: different responses to dietary control of plasma glucose in newly diagnosed patients with NIDDM

Pancreatic beta-cell secretion after oral glucose or intravenous glucagon stimulation was studied in newly diagnosed patients with non-insulin-dependent diabetes mellitus (NIDDM) before and after glycemic control by diet treatment alone. Insulin secretion to oral glucose showed significant improvement, while C-peptide release by glucagon showed no significant difference before and after diet treatment. The finding suggests that pancreatic beta-cell response to oral glucose varies with different metabolic states, but this is not so after glucagon stimulation in NIDDM patients.

Stimulation of insulin release and suppression of feeding by hepatic portal glucagon infusion in rats

Plasma insulin and glucose concentrations were measured in rats by remote blood sampling techniques 5 and 25 min after the start of a continuous intraportal glucagon infusion (0.33, 1.0, 3.3, 10 and 33 micrograms/kg/min). Plasma insulin levels were elevated in a dose-related fashion by glucagon, with the highest dose producing a 23-fold increase above control levels. In contrast, the glycemic effect of glucagon was not dose-related. Glucagon-induced hyperglycemia was similar for all glucagon doses, despite the fact that a glucagon dose range spanning two orders of magnitude was used. In a second experiment, plasma glucose and insulin were measured as described above at two glucagon infusion rates (1 and 10 micrograms/kg/min), but the animals were allowed to eat during the infusion. Results showed that the effects of glucagon infusions on plasma insulin and glucose were additive with the normal prandial changes in these substances. Finally, food intake was inversely related to insulin level and dissociated from the hyperglycemia during glucagon infusion. These results show that exogenous glucagon provides a potent stimulus for insulin release in the rat both in the presence and in the absence of food. Furthermore, these results in combination with other data suggest that glucagon-induced hyperinsulinemia merits further investigation as one possible determinant of glucagon satiety in the rat.

Practical aspects in performing the glucagon test in the measurement of C-peptide secretion in diabetic patients

The secretion of plasma C-peptide after intravenous glucagon stimulation was studied in 15 insulin-treated diabetic patients with onset of diabetes after the age of 30. The mean stimulation of C-peptide secretion caused by glucagon given in the fasting state and by a standardized breakfast were similar. Low blood glucose values (less than 3.5 mmol/l) were found to suppress the stimulating action of glucagon on the pancreas almost completely. When the glucagon test was performed 1.5 hours after a standardized breakfast, the mean concentration of plasma C-peptide was 62% higher than in the test in the fasting state, showing that the stimulating actions of glucagon and breakfast on the secretion of insulin are additive. The results indicate that when determining the level of plasma C-peptide after stimulation with glucagon, in order to distinguish between insulin-dependent and non-insulin-dependent diabetic patients, it is critical to take into account the consequence of low blood glucose values and to standardize the test conditions in regard to pre-test meals.

Glucagon-stimulated plasma C-peptide and insulin levels in active and non-active acromegalics

The glucagon-stimulated insulin and C-peptide release in patients with active acromegaly, cured acromegalic patients and healthy controls were studied. There was an elevation of the fasting insulin levels in active acromegalics and the fasting C-peptide levels in both patient groups. After i.v. injection of glucagon the insulin and C-peptide levels increased. The highest levels were recorded in active acromegalics, but cured patients also had higher levels than the control group. The insulin/C-peptide ratio was increased in active acromegalics in comparison with that found for inactive acromegalics and normal controls. In addition, the plasma half-lives (T1/2) of endogenous insulin and C-peptide were measured. It was found that the T1/2 for insulin was increased in active acromegalics only. From this study we conclude that even when the treatment of acromegaly is effective insulin and C-peptide secretion do not normalize due, probably, to increased synthesis and release upon stimulation of the pancreatic beta-cells. In active acromegaly the removal of insulin is probably also reduced.

Pancreatic beta-cell function in cirrhotic patients with and without overt diabetes. C-peptide response to glucagon and to meal

To study the role of pancreatic beta-cell function in glucose intolerance and frank diabetes that sometimes develops in cirrhosis, the C-peptide response to a bolus IV injection of 1 mg of glucagon was measured in nine controls and in two groups of patients with cirrhosis. The first group comprised nine subjects with normal or high-normal fasting plasma glucose and no glycosuria; five of them had impaired glucose tolerance. The second group consisted of eight cirrhotics in whom frank diabetes had developed six to 48 months after the diagnosis of cirrhosis. They were characterized by fasting plasma glucose greater than 140 mg/dL and permanent glycosuria. No differences in the degree of liver impairment or portal-systemic shunting were observed between the two groups. Plasma glucose response to glucagon was similarly reduced in cirrhotic subjects. Basal C-peptide was high normal in patients with cirrhosis, and significantly increased in nondiabetic subjects. By contrast peak C-peptide levels and total C-peptide responses to glucagon were low normal in cirrhotics and significantly reduced in patients with cirrhosis and diabetes. In 14 patients the C-peptide response to a standard meal was also measured. It was significantly reduced in patients with cirrhosis and diabetes (six cases), as compared to cirrhotic subjects without diabetes. Peak C-peptide after IV glucagon significantly correlated with peak C-peptide after the meal (r = .927), or total C-peptide response to meal (r = .871). Impaired insulin secretion may add to insulin resistance in patients with liver cirrhosis, leading to the development of frank diabetes, characterized by fasting hyperglycemia and glycosuria.