Effects of differing antecedent increases of plasma cortisol on counterregulatory responses during subsequent exercise in type 1 diabetes

The endocrine pancreas during exercise in people with and without type 1 diabetes: Beyond the beta-cell

Although important for digestion and metabolism in repose, the healthy endocrine pancreas also plays a key role in facilitating energy transduction around physical exercise. During exercise, decrements in pancreatic β-cell mediated insulin release opposed by increments in α-cell glucagon secretion stand chief among the hierarchy of glucose-counterregulatory responses to decreasing plasma glucose levels. As a control hub for several major glucose regulatory hormones, the endogenous pancreas is therefore essential in ensuring glucose homeostasis. Type 1 diabetes (T1D) is pathophysiological condition characterised by a destruction of pancreatic β-cells resulting in pronounced aberrations in glucose control. Yet beyond the beta-cell perhaps less considered is the impact of T1D on all other pancreatic endocrine cell responses during exercise and whether they differ to those observed in healthy man. For physicians, understanding how the endocrine pancreas responds to exercise in people with and without T1D may serve as a useful model from which to identify whether there are clinically relevant adaptations that need consideration for glycaemic management. From a physiological perspective, delineating differences or indeed similarities in such responses may help inform appropriate exercise test interpretation and subsequent program prescription. With more complex advances in automated insulin delivery (AID) systems and emerging data on exercise algorithms, a timely update is warranted in our understanding of the endogenous endocrine pancreatic responses to physical exercise in people with and without T1D. By placing our focus here, we may be able to offer a nexus of better understanding between the clinical and engineering importance of AIDs requirements during physical exercise.

Plasma Epinephrine Contributes to the Development of Experimental Hypoglycemia-Associated Autonomic Failure

BACKGROUND

Recurrent hypoglycemia blunts counter-regulatory responses to subsequent hypoglycemic episodes, a syndrome known as hypoglycemia-associated autonomic failure (HAAF). Since adrenergic receptor blockade has been reported to prevent HAAF, we investigated whether the hypoglycemia-associated rise in plasma epinephrine contributes to pathophysiology and reported interindividual differences in susceptibility to HAAF.

METHODS

To assess the role of hypoglycemia-associated epinephrine responses in the susceptibility to HAAF, 24 adult nondiabetic subjects underwent two 2-hour hyperinsulinemic hypoglycemic clamp studies (nadir 54 mg/dL; 0-2 hours and 4-6 hours) on Day 1, followed by a third identical clamp on Day 2. We challenged an additional 7 subjects with two 2-hour infusions of epinephrine (0.03 μg/kg/min; 0-2 hours and 4-6 hours) vs saline on Day 1 followed by a 200-minute stepped hypoglycemic clamp (90, 80, 70, and 60 mg/dL) on Day 2.

RESULTS

Thirteen out of 24 subjects developed HAAF, defined by ≥20% reduction in average epinephrine levels during the final 30 minutes of the third compared with the first hypoglycemic episode (P < 0.001). Average epinephrine levels during the final 30 minutes of the first hypoglycemic episode were 2.3 times higher in subjects who developed HAAF compared with those who did not (P = 0.006).Compared to saline, epinephrine infusion on Day 1 reduced the epinephrine responses by 27% at the 70 and 60 mg/dL glucose steps combined (P = 0.04), with a parallel reduction in hypoglycemic symptoms (P = 0.03) on Day 2.

CONCLUSIONS

Increases in plasma epinephrine reproduce key features of HAAF in nondiabetic subjects. Marked interindividual variability in epinephrine responses to hypoglycemia may explain an individual's susceptibility to developing HAAF.

Effects of γ-Aminobutyric Acid A Receptor Activation on Counterregulatory Responses to Subsequent Exercise in Individuals With Type 1 Diabetes

The effects of γ-aminobutyric acid (GABA) A receptor activation on physiologic responses during next-day exercise in type 1 diabetes are unknown. To test the hypothesis that GABA A activation with the benzodiazepine alprazolam would blunt counterregulatory responses during subsequent exercise, 29 (15 male, 14 female) individuals with type 1 diabetes (HbA1c 7.8 ± 1%) were studied during separate 2-day protocols. Day 1 consisted of morning and afternoon 2-h euglycemic or 2.9 mmol/L hypoglycemic clamps with or without 1 mg alprazolam given 30 min before each clamp. Day 2 consisted of a 90-min euglycemic cycling exercise at 50% VO2max Tritiated glucose was used to measure glucose kinetics. Despite equivalent day 2 insulin (93 ± 6 pmol/L) and glucose levels (5.3 ± 0.1 mmol/L), plasma epinephrine, norepinephrine, glucagon, cortisol, and growth hormone responses were similarly reduced after alprazolam or day 1 hypoglycemia compared with euglycemic control. Endogenous glucose production, lipolysis (glycerol, nonesterified fatty acid), and glycogenolysis (lactate) were also reduced during day 2 exercise after day 1 GABA A activation. We conclude that activation of GABA A receptors with alprazolam can result in widespread neuroendocrine, autonomic nervous system, and metabolic counterregulatory failure during subsequent submaximal exercise and may increase the risk of exercise-associated hypoglycemia in individuals with type 1 diabetes.

Philip E. Cryer, MD: Seminal Contributions to the Understanding of Hypoglycemia and Glucose Counterregulation and the Discovery of HAAF (Cryer Syndrome)

Optimized glycemic control prevents and slows the progression of long-term complications in patients with type 1 and type 2 diabetes. In healthy individuals, a decrease in plasma glucose below the physiological range triggers defensive counterregulatory responses that restore euglycemia. Many individuals with diabetes harbor defects in their defenses against hypoglycemia, making iatrogenic hypoglycemia the Achilles heel of glycemic control. This Profile in Progress focuses on the seminal contributions of Philip E. Cryer, MD, to our understanding of hypoglycemia and glucose counterregulation, particularly his discovery of the syndrome of hypoglycemia-associated autonomic failure (HAAF).

Physical activity and type 1 diabetes: time for a rewire?

While being physically active bestows many health benefits on individuals with type 1 diabetes, their overall blood glucose control is not enhanced without an effective balance of insulin dosing and food intake to maintain euglycemia before, during, and after exercise of all types. At present, a number of technological advances are already available to insulin users who desire to be physically active with optimal blood glucose control, although a number of limitations to those devices remain. In addition to continued improvements to existing technologies and introduction of new ones, finding ways to integrate all of the available data to optimize blood glucose control and performance during and following exercise will likely involve development of "smart" calculators, enhanced closed-loop systems that are able to use additional inputs and learn, and social aspects that allow devices to meet the needs of the users.

Relationship of hypoglycemia and glucose variability with autonomic dysfunction in children and adolescents with type 1 diabetes

Aim. Glucose variability (GV) and hypoglycaemia frequency and duration, depending on cardiovascular autonomic dysfunction, in children and adolescents with type 1 diabetes mellitus (T1DM) were evaluated. Materials and methods. One hundred and thirty T1DM patients, aged 6?18 years, were included in this study. The study included 3 tests:. continuous glucose monitoring (CGM) with GV evaluation, frequency and duration of hypoglycaemia;24-h ECG monitoring with automatic calculation of QTc interval and heart rate variability (HRV) parameters;cardiovascular autonomic tests.Results. The estimated prevalence of cardiovascular autonomic neuropathy (CAN) was 19.2%. CAN positive (CAN+) patients had lower values from cardiovascular autonomic tests and HRV and longer QTc intervals compared with CAN negative (CAN-) patients (p 

Exercise-related hypoglycemia in diabetes mellitus

Current recommendations are that people with Type 1 and Type 2 diabetes mellitus exercise regularly. However, in cases in which insulin or insulin secretagogues are used to manage diabetes, patients have an increased risk of developing hypoglycemia, which is amplified during and after exercise. Repeated episodes of hypoglycemia blunt autonomic nervous system, neuroendocrine and metabolic defenses (counter-regulatory responses) against subsequent episodes of falling blood glucose levels during exercise. Likewise, antecedent exercise blunts counter-regulatory responses to subsequent hypoglycemia. This can lead to a vicious cycle, by which each episode of either exercise or hypoglycemia further blunts counter-regulatory responses. Although contemporary insulin therapies cannot fully mimic physiologic changes in insulin secretion, people with diabetes have several management options to avoid hypoglycemia during and after exercise, including regularly monitoring blood glucose, reducing basal and/or bolus insulin, and consuming supplemental carbohydrates.

Adrenomedullary function in patients with nonclassic congenital adrenal hyperplasia

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is classified into three types based on disease severity: classic salt-wasting, classic simple virilizing, and nonclassic. Adrenomedullary dysplasia and epinephrine deficiency have been described in classic CAH, resulting in glucose dysregulation. Our objective was to investigate adrenomedullary function in nonclassic CAH and to evaluate adrenomedullary function according to disease severity. Adrenomedullary function was evaluated in response to a standardized cycle ergonometer test in 23 CAH patients (14 females, age 9-38 years; 6 salt-wasting, 7 simple virilizing, 5 nonclassic receiving glucocorticoid treatment, 5 nonclassic not receiving glucocorticoid), and 14 controls (7 females, age 12-38 years). Epinephrine, glucose, and cortisol were measured at baseline and peak exercise. CAH patients and controls were similar in age and anthropometric measures. Patients with nonclassic CAH who were not receiving glucocorticoid and controls experienced the expected stress-induced rise in epinephrine, glucose, and cortisol. Compared to controls, patients with all types of CAH receiving glucocorticoid had impaired exercise-induced changes in epinephrine (salt-wasting: p=0.01;simple virilizing: p=0.01; nonclassic: p=0.03), and cortisol (salt-wasting: p=0.004; simple virilizing: p=0.006; nonclassic: p=0.03). Salt-wasting patients displayed the most significant impairment, including impairment in glucose response relative to controls (p=0.03). Hydrocortisone dose was negatively correlated with epinephrine response (r=-0.58; p=0.007) and glucose response (r=-0.60; p=0.002). The present study demonstrates that untreated patients with nonclassic CAH have normal adrenomedullary function. The degree of epinephrine deficiency in patients with CAH is associated with the severity of adrenocortical dysfunction, as well as glucocorticoid therapy.