People with type 1 diabetes frequently develop a blunted counterregulatory hormone response to hypoglycemia coupled with a decreased hepatic response to glucagon, and consequently, they have an increased risk of severe hypoglycemia. We have evaluated the effect of insulin lispro (Humalog) versus regular human insulin (Humulin R) on the hepatic glucose production (HGP) response to glucagon in type 1 diabetic patients on intensive insulin therapy with continuous subcutaneous insulin infusion (CSII).
Ten subjects on CSII were treated for 3 months with lispro and 3 months with regular insulin in a double-blind randomized crossover study. After 3 months of treatment with each insulin, hepatic sensitivity to glucagon was measured in each subject. The test consisted of a 4-h simultaneous infusion of somatostatin (450 μg/h) to suppress endogenous glucagon, regular insulin (0.15 mU · kg−1 · min−1), glucose at a variable rate to maintain plasma glucose near 5 mmol/l, and D-[6,6−2H2]glucose to measure HGP. During the last 2 h, glucagon was infused at 1.5 ng · kg−1 · min−1. Eight nondiabetic people served as control subjects.
During the glucagon infusion period, free plasma insulin levels in the diabetic subjects were 71.7 ± 1.6 vs. 74.8 ± 0.5 pmol/1 after lispro and regular insulin treatment, with plasma glucagon levels of 88.3 ± 1.8 and 83.7 ± 1.5 ng/1 for insulin:glucagon ratios of 2.8 and 3.0, respectively (NS). However, plasma glucose increased to 9.2 ± 1.1 mmol/l after lispro insulin compared with 7.1 ± 0.9 mmol/l after regular insulin (P < 0.01), and the rise in HGP was 5.7 ± 2.8 μmol · kg−1 · min−1 after lispro insulin versus 3.1 ± 2.9 μmol · kg−1 · min−1 after regular insulin treatment (P = 0.02). In the control subjects, HGP increased by 10.7 ± 4.2 μmol · kg−1 · min−1 under glucagon infusion.
Insulin lispro treatment by CSII was associated with a heightened response in HGP to glucagon compared with regular human insulin. This suggests that insulin lispro increases the sensitivity of the liver to glucagon and could potentially decrease the risk of severe hypoglycemia.