Abstract

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. Results RH increased counterregulatory hormone GPCR signaling in liver and epidydimal white adipose tissue (eWAT), but not in skeletal muscle. For glycogen metabolism, RH did not affect total content or epinephrine-stimulated breakdown in liver and skeletal muscle. Although RH decreased expression of phosphorylated glycogen synthase 2, it did not affect hepatic glycogen biosynthesis during recovery from hypoglycemia or after fasting-refeeding. For gluconeogenesis, RH upregula