Ghrelin Protects Against Insulin-Induced Hypoglycemia in a Mouse Model of Type 1 Diabetes Mellitus

Abstract

Insulin-induced hypoglycemia is a major limiting factor in maintaining optimal blood glucose in patients with type 1 diabetes and advanced type 2 diabetes. Luckily, a counterregulatory response (1) system exists to help minimize and reverse hypoglycemia, although more studies are needed to better characterize its components. Recently, we showed that the hormone ghrelin is permissive for the normal CRR to insulin-induced hypoglycemia when assessed in mice without diabetes. Here, we tested the hypothesis that ghrelin also is protective against insulin-induced hypoglycemia in the streptozotocin (2) mouse model of type 1 diabetes. STZ-treated ghrelin-knockout (KO) (3) mice as well as STZ-treated wild-type (WT) littermates were subjected to a low-dose hyperinsulinemic-hypoglycemic clamp procedure. The STZ-treated ghrelin-KO mice required a much higher glucose infusion rate than the STZ-treated WT mice. Also, the STZ-treated ghrelin-KO mice exhibited attenuated plasma epinephrine and norepinephrine responses to the insulin-induced hypoglycemia. Taken together, our data suggest that without ghrelin, STZ-treated mice modeling type 1 diabetes are unable to mount the usual CRR to insulin-induced hypoglycemia.

Keywords: ghrelin; glucose clamp; glucose counterregulation; hypoglycemia; type 1 diabetes.

Figure 1

Effects of STZ on islets, plasma insulin, and blood glucose in WT and ghrelin-KO mice. (A) A representative islet co-labeled for insulin-immunoreactivity (red) and glucagon-immunoreactivity (green) from a vehicle-treated WT mouse (1st row), a vehicle-treated ghrelin-KO mouse (2nd row), an STZ-treated WT mouse (3rd row), and an STZ-treated ghrelin-KO mouse (4th row). Scale bar = 100 μm. (B) Ad lib-fed plasma insulin levels and (C) corresponding blood glucose levels in vehicle- and STZ-treated mice. Data are presented as mean ± SEM. n = 5–7. ^****P < 0.0001, ^#P = 0.09, NS, no significant difference.

Figure 2

Low-dose hyperinsulinemic–hypoglycemic clamps in STZ-treated mice. (A) Ad lib-fed blood glucose levels before and 3 d after STZ administration. (B) Blood glucose levels during the clamps. (C) Glucose infusion rate (GIR) to achieve the target blood glucose (35–45 mg/dL) by the steady-state period (100–120 min) in mice receiving Humulin-R insulin (4 mU/kg/min) from 0 to 120 min. (D) Plasma ghrelin levels at the start (“Basal”; t = −5 min) and end (“Clamp”; t = 120 min) of the clamps. (E) Plasma insulin levels at the end (“Clamp”; t = 120 min) of the clamps. n = 10–11. Data are presented as mean ± SEM. ^***P < 0.001, ^****P < 0.0001, NS, no significant difference.

Figure 3

Effects of ghrelin deletion on plasma CRR hormone levels obtained at the end of the hyperinsulinemic-hypoglycemic clamps. Plasma levels of (A) epinephrine, (B) norepinephrine, (C) glucagon, (D) corticosterone, and (E) GH at the end of the clamps (t = 120 min). n = 10–11. Data are presented as mean ± SEM. ^*P < 0.05, ^****P < 0.0001, NS, no significant difference.