Recurrent hypoglycemia increases hepatic gluconeogenesis without affecting glycogen metabolism or systemic lipolysis in rat
"Introduction: Recurrent hypoglycemia (RH) impairs secretion of counterregulatory hormones. Whether and how RH affects responses within metabolically important peripheral organs to counterregulatory hormones are poorly understood.
Objective: To study the effects of RH on metabolic pathways associated with glucose counterregulation within liver, white adipose tissue and skeletal muscle.
Methods: Using a widely adopted rodent model of 3-day recurrent hypoglycemia, we first checked expression of counterregulatory hormone G-protein coupled receptors (GPCRs), their inhibitory regulators and downstream enzymes catalyzing glycogen metabolism, gluconeogenesis and lipolysis by qPCR and western blot. Then, we examined epinephrine-induced phosphorylation of PKA substrates to validate adrenergic sensitivity in each organ. Next, we measured hepatic and skeletal glycogen content, degree of breakdown by epinephrine and abundance of phosphorylated glycogen phosphorylase under hypoglycemia and that of phosphorylated glycogen synthase during recovery to evaluate glycogen turnover. Further, we performed pyruvate and lactate tolerance tests to assess gluconeogenesis. Additionally, we measured circulating FFA and glycerol to check lipolysis. The abovementioned studies were repeated in streptozotocin-induced diabetic rat model. Finally, we conducted epinephrine tolerance test to investigate systemic glycemic excursions to counterregulatory hormones. Saline-injected rats served as controls."