Glucose counterregulatory responses to hypoglycemia

Abstract

The brain relies almost exclusively on glucose for fuel. Therefore, adequate uptake of glucose from the plasma is key for normal brain function and survival. Despite wide variations in glucose flux (i.e., fed state, fasting state, etc), blood glucose is maintained in a very narrow range. This is accomplished by a series of hormonal and physiologic responses. As a result, hypoglycemia is a rare occurrence in normal individuals. However, glucose counterregulatory responses are altered in patients with diabetes treated with insulin especially after repeated hypoglycemia or antecedent exercise.

Figure 1

Glycemic thresholds for physiological responses to hypoglycemia. Adapted from Cryer PE. Hypoglycemia. Pathophysiology, Diagnosis and Treatment. New York: Oxford University Press, 1997, pp. 184, with permission from the author and publisher.

Figure 2

Schematic representation of glucose metabolism. 1: Hexokinase/glucokinase, 2: Glycogen synthase, 3: Phosphorylase, 4: Phosphofructokinase, 5: Pyruvate kinase, 6: Pyruvate carboxylase, 7: Phosphoenolpyruvate carboxykinase, 8: Fructose-1,6-biphosphatase, 9: Glucose-6-phosphatase.

Figure 3

Diagnostic approach to hypoglycemia in infants and children. Adapted from Shepherd SP, Kalla A, Arbelaez AM. Endocrine Diseases, Chapter 14. In: Dusenbery SM, White A, eds. The Washington Manual of Pediatrics. Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins, 2009;198–222. Adapted from the original with permission from the publisher.