Contribution of adrenergic mechanisms to glucose counterregulation in humans

Equipotency of insulin glargine 300 and 100 U/mL with intravenous dosing but differential bioavailability with subcutaneous dosing in dogs

AIMS

Insulin glargine 300 U/mL (Gla-300) contains the same units versus glargine 100 U/mL (Gla-100) in three-fold lower volume, and higher subcutaneous (SC) doses are required in people with diabetes. To investigate blood glucose (BG) lowering potency, Gla-300 and Gla-100 were compared after intravenous (IV, for 4 h) and SC (for 24 h) injection in healthy Beagle dogs.

MATERIALS AND METHODS

The dose of 0.15 U/kg Gla-300 and Gla-100 was injected IV in 12 dogs. BG, C-peptide, glucagon and the active metabolite 21A-Gly-human insulin (M1; liquid chromatography-tandem mass spectrometry method) were measured. Twelve other dogs were studied after SC injection of 0.3 U/kg Gla-300 and Gla-100.

RESULTS

After IV injection, Gla-300 and Gla-100 were equally potent [BG_AUC_{0-4 h} ratio 1.01 (95% confidence interval, 0.94; 1.09)]. After SC injection, BG decreased slower and less with Gla-300. Similar metabolism of Gla-300 and Gla-100 to M1 occurred with IV dosing [M1_AUC_{0-1 h} ratio 0.99 (95% confidence interval, 0.82; 1.22)], but with SC dosing M1_C_max and AUC_0-24h were 44% and 17% lower; mean residency time and bioavailability were 32% longer and 50% lower, with Gla-300.

CONCLUSIONS

IV Gla-300 and Gla-100 have the equivalent of BG-lowering potency and M1 metabolism. SC Gla-300 has lower M1 bioavailability with a reduced BG-lowering effect and need for greater doses versus Gla-100.

Epinephrine deficiency results in intact glucose counter-regulation, severe hepatic steatosis and possible defective autophagy in fasting mice

Epinephrine is one of the major hormones involved in glucose counter-regulation and gluconeogenesis. However, little is known about its importance in energy homeostasis during fasting. Our objective is to study the specific role of epinephrine in glucose and lipid metabolism during starvation. In our experiment, we subject regular mice and epinephrine-deficient mice to a 48-h fast then we evaluate the different metabolic responses to fasting. Our results show that epinephrine is not required for glucose counter-regulation: epinephrine-deficient mice maintain their blood glucose at normal fasting levels via glycogenolysis and gluconeogenesis, with normal fasting-induced changes in the peroxisomal activators: peroxisome proliferator activated receptor γ coactivator α (PGC-1α), fibroblast growth factor 21 (FGF-21), peroxisome proliferator activated receptor α (PPAR-α), and sterol regulatory element binding protein (SREBP-1c). However, fasted epinephrine-deficient mice develop severe ketosis and hepatic steatosis, with evidence for inhibition of hepatic autophagy, a process that normally provides essential energy via degradation of hepatic triglycerides during starvation. We conclude that, during fasting, epinephrine is not required for glucose homeostasis, lipolysis or ketogenesis. Epinephrine may have an essential role in lipid handling, possibly via an autophagy-dependent mechanism.

Hypothalamic AMP-activated protein kinase activation with AICAR amplifies counterregulatory responses to hypoglycemia in a rodent model of type 1 diabetes

In nondiabetic rodents, AMP-activated protein kinase (AMPK) plays a role in the glucose-sensing mechanism used by the ventromedial hypothalamus (VMH), a key brain region involved in the detection of hypoglycemia. However, AMPK is regulated by both hyper- and hypoglycemia, so whether AMPK plays a similar role in type 1 diabetes (T1DM) is unknown. To address this issue, we used four groups of chronically catheterized male diabetic BB rats, a rodent model of autoimmune T1DM with established insulin-requiring diabetes (40 +/- 4 pmol/l basal c-peptide). Two groups were subjected to 3 days of recurrent hypoglycemia (RH), while the other two groups were kept hyperglycemic [chronic hyperglycemia (CH)]. All groups subsequently underwent hyperinsulinemic hypoglycemic clamp studies on day 4 in conjunction with VMH microinjection with either saline (control) or AICAR (5-aminoimidazole-4-carboxamide) to activate AMPK. Compared with controls, local VMH application of AICAR during hypoglycemia amplified both glucagon [means +/- SE, area under the curve over time (AUC/t) 144 +/- 43 vs. 50 +/- 11 ng.l(-1).min(-1); P < 0.05] and epinephrine [4.27 +/- 0.96 vs. 1.06 +/- 0.26 nmol.l(-1).min(-1); P < 0.05] responses in RH-BB rats, and amplified the glucagon [151 +/- 22 vs. 85 +/- 22 ng.l(-1).min(-1); P < 0.05] response in CH-BB rats. We conclude that VMH AMPK also plays a role in glucose-sensing during hypoglycemia in a rodent model of T1DM. Moreover, our data suggest that it may be possible to partially restore the hypoglycemia-specific glucagon secretory defect characteristic of T1DM through manipulation of VMH AMPK.

Counterregulatory hormone and symptom responses to insulin-induced hypoglycemia in the postprandial state in humans

Plasma counterregulatory hormones and symptoms were measured during hypoglycemia in the postprandial and in the fasting state in humans to establish differences in physiological responses. We studied 8 nondiabetic subjects and 10 subjects with type 1 diabetes on two different occasions during clamped insulin-induced hypoglycemia (2.4 mmol/l) in the sitting position. On one occasion, subjects ate a standard mixed meal, and on the other they remained fasting. In response to postprandial as compared with fasting hypoglycemia, nondiabetic subjects exhibited lower total symptom scores (6.6 +/- 0.4 vs. 11.5 +/- 0.8, P = 0.001), which was due to less hunger (1.1 +/- 0.1 vs. 4.2 +/- 0.2), lower suppression of plasma C-peptide (0.23 +/- 0.1 vs. 0.08 +/- 0.07 nmol/l, P = 0.032), and greater responses of plasma glucagon (248 +/- 29 vs. 163 +/- 25 ng x l(-1) x min(-1), P = 0.018), plasma adrenaline (4.5 +/- 0.6 vs. 3.1 +/- 0.4 nmol x l(-1) x min(-1), P = 0.037), norepinephrine (3.8 +/- 0.3 vs. 3.2 +/- 0.2 nmol x l(-1) x min(-1), P = 0.037), and pancreatic polypeptide (217 +/- 12 vs. 159 +/- 22 pmol x l(-1) x min(-1), P = 0.08). Except for plasma C-peptide, responses in diabetic subjects were similarly affected. Notably, in diabetic subjects responses of glucagon, which were absent in the fasting state, nearly normalized after a meal. In conclusion, in the postprandial compared with the fasting hypoglycemic state, total symptoms are less, but counterregulatory hormones are greater and responses of glucagon nearly normalize in type 1 diabetic subjects.

Prior exercise and the response to insulin-induced hypoglycemia in the dog

To test whether hepatic insulin action and the response to an insulin-induced decrement in blood glucose are enhanced in the immediate postexercise state as they are during exercise, dogs had sampling (artery, portal vein, and hepatic vein) catheters and flow probes (portal vein and hepatic artery) implanted 16 days before a study. After 150 min of moderate treadmill exercise or rest, dogs were studied during a 150-min hyperinsulinemic (1 mU.kg(-1).min(-1)) euglycemic (n = 5 exercised and n = 9 sedentary) or hypoglycemic (65 mg/dl; n = 8 exercised and n = 9 sedentary) clamp. Net hepatic glucose output (NHGO) and endogenous glucose appearance (R(a)) and utilization (R(d)) were assessed with arteriovenous and isotopic ([3-(3)H]glucose) methods. Results show that, immediately after prolonged, moderate exercise, in relation to sedentary controls: 1) the glucose infusion rate required to maintain euglycemia, but not hypoglycemia, was higher; 2) R(d) was greater under euglycemic, but not hypoglycemic conditions; 3) NHGO, but not R(a), was suppressed more by a hyperinsulinemic euglycemic clamp, suggesting that hepatic glucose uptake was increased; 4) a decrement in glucose completely reversed the enhanced suppression of NHGO by insulin that followed exercise; and 5) arterial glucagon and cortisol were transiently higher in the presence of a decrement in glucose. In summary, an increase in insulin action that was readily evident under euglycemic conditions after exercise was abolished by moderate hypoglycemia. The means by which the glucoregulatory system is able to overcome the increase in insulin action during moderate hypoglycemia is related not to an increase in R(a) but to a reduction in insulin-stimulated R(d). The primary site of this reduction is the liver.

Systemic and local adrenergic regulation of muscle glucose utilization during hypoglycemia in healthy subjects

Adrenergic responses are crucial for hypoglycemic recovery. Epinephrine increases glucose production, lipolysis, and peripheral insulin resistance as well as blood flow and glucose delivery. Sympathetic activation causes vasoconstriction and reduces glucose delivery. To determine the effects of alpha- and beta-adrenergic activity on muscle glucose uptake during hypoglycemia, we studied forearm blood flow (FBF) (plethysmography), arteriovenous glucose difference (AV-diff), and forearm glucose uptake (FGU) during insulin infusion with 60 min of euglycemia followed by 60 min of hypoglycemia. Twelve healthy subjects (27 plus minus 5 years of age) were randomized to intravenous propranolol (IV PROP, 80 microg/min), intravenous phentolamine (IV PHEN, 500 microg/min), intra-arterial propranolol (IA PROP, 25 microg/min), intra-arterial phentolamine (IA PHEN, 12 microg/min per 100 ml forearm tissue), and saline (SAL). FBF increased during hypoglycemia with SAL (P < 0.001) but not with IA or IV PROP. FGU (P = 0.015) and AV-diff (P = 0.099) fell during hypoglycemia with IA PROP but not with IV PROP. FBF increased during hypoglycemia with IA and IV PHEN (P < 0.005). AV-diff fell during hypoglycemia with IA and IV PHEN (P < 0.01), but FGU was unchanged. Blood pressure fell (P < 0.001), and adrenergic and neuroglycopenic symptoms increased with IV PHEN (P < 0.01). Thus, systemic but not local propranolol prevents a decrease in forearm glucose extraction during hypoglycemia, suggesting that epinephrine increases peripheral muscular insulin resistance through systemic effects. alpha-Adrenergic activation inhibits vasodilation and helps maintain brain glucose delivery.

Epipen as an alternative to glucagon in the treatment of hypoglycemia in children with diabetes

OBJECTIVE

Fear of a severe hypoglycemic reaction is a major obstacle to achieving near-normal plasma glucose levels. Although parenteral glucagon is effective in treating these reactions, it is cumbersome to use, causes severe nausea, and is impractical in the school setting. Epinephrine is available as a premixed injection (Epipen) that may be used by all care providers. Using Epipen to treat hypoglycemia may be an effective, safe, and easy-to-use alternative to glucagon.

RESEARCH DESIGN AND METHODS

Ten children (age 11.7 +/- 2.4 years) with type 1 diabetes were studied on two occasions. After an overnight equilibration period, hypoglycemia was induced via an insulin pump (1 mU x kg(-1) x min(-1)). At a blood glucose level of 2.8 mmol/l, either glucagon (1 mg) or epinephrine (0.3 mg), in random order, was administered intramuscularly and responses were monitored.

RESULTS

Plasma free insulin concentrations were similar in both studies. Plasma glucose levels increased by 1.7 +/- 0.2 mmol/l (mean +/- SEM) in 10 min and by 2.6 +/- 0.2 mmol/l in 15 min with administration of glucagon and were not consistently increased with administration of epinephrine (P < 0.01). Peak glucagon concentrations after administration of glucagon were >60-fold higher than basal concentrations. After administration of epinephrine, peak epinephrine levels were 20-fold higher than basal concentrations.

CONCLUSIONS

Epinephrine does not seem to be an adequate substitute for glucagon in the treatment of severe hypoglycemia. The effectiveness of glucagon in reversing hypoglycemia and its side effects of nausea and vomiting are likely related to the markedly supraphysiologic plasma levels achieved with the standard intramuscular dose.

Reference intervals for glucose, beta-cell polypeptides, and counterregulatory factors during prolonged fasting

To establish reference intervals for the pancreatic beta-cell response and the counterregulatory hormone response to prolonged fasting, we studied 33 healthy subjects (16 males, 17 females) during a 72-h fast. Glucose, insulin, C-peptide, and proinsulin levels decreased (P < 0.001), and the levels of counterregulatory factors increased during the fast [P < 0.05; glucagon and free fatty acids (FFA) with a linear increase and epinephrine, norepinephrine, and cortisol with a clear underlying circadian rhythm]. Growth hormone secretion increased from the first to third day of fasting (P < 0.05) but actually decreased from the second to third day of fasting (P = 0.03). Males had higher glucose and glucagon levels and lower FFA levels during the fast (P < 0.05), whereas no effect of gender on beta-cell polypeptides was observed. A high body mass index resulted in higher insulin and C-peptide levels during the fast (P < 0.05). In conclusion, we have provided reference intervals for glucoregulatory factors during a 72-h fast. We observed a diminished beta-cell response concomitant with an increased secretion of counterregulatory hormones. These results should be of clinical and scientific value in the investigation of hypoglycemic disorders.

Adrenergic mechanisms contribute to the late phase of hypoglycemic glucose counterregulation in humans by stimulating lipolysis

Three studies were performed on nine normal volunteers to assess whether catecholamine-mediated lipolysis contributes to counterregulation to hypoglycemia. In these three studies, insulin was intravenously infused for 8 h (0.30 mU.kg-1.min-1 from 0 to 180 min, and 0.40 mU.kg-1.min-1 until 480 min). In study I (control study), only insulin was infused; in study II (direct + indirect effects of catecholamines), propranolol and phentolamine were superimposed to insulin and exogenous glucose was infused to reproduce the same plasma glucose (PG) concentration of study I. Study III (indirect effect of catecholamines) was the same as study II, except heparin (0.2 U.kg-1.min-1 after 80 min), 10% Intralipid (1 ml.min-1 after 160 min) and variable glucose to match PG of study II, were also infused. Glucose production (HGO), glucose utilization (Rd) [3-3H]glucose, and glucose oxidation and lipid oxidation (LO) (indirect calorimetry) were determined. In all three studies, PG decreased from approximately 4.8 to approximately 2.9 mmol/liter (P = NS between studies), and plasma glycerol and FFA decreased to a nadir at 120 min. Afterwards, in study I plasma glycerol and FFA increased by approximately 75% at 480 min, but in study II they remained approximately 40% lower than in study I, whereas in study III they rebounded as in study I (P = NS). In study II, LO was lower than in study I (1.69 +/- 0.13 vs. 3.53 +/- 0.19 mumol.kg-1.min-1, P less than 0.05); HGO was also lower between 60 and 480 min (7.48 +/- 0.57 vs. 11.6 +/- 0.35 mumol.kg-1.min-1, P less than 0.05), whereas Rd was greater between 210 and 480 min (19 +/- 0.38 vs. 11.4 +/- 0.34 mumol.kg-1.min-1, respectively, P less than 0.05). In study III, LO increased to the values of study I; between 4 and 8 h, HGO increased by approximately 2.5 mumol.kg-1.min-1, and Rd decreased by approximately 7 mumol.kg-1.min-1 vs. study II. We conclude that, in a late phase of hypoglycemia, the indirect effects of catecholamines (lipolysis mediated) account for at least approximately 50% of the adrenergic contribution to increased HGO, and approximately 85% of suppressed Rd.