Carvedilol prevents impairment of the counterregulatory response in recurrently hypoglycaemic diabetic rats

Abstract

Aim: It has been suggested that repeated activation of the adrenergic system during antecedent episodes of hypoglycaemia contributes to the development of counterregulatory failure. We previously reported that treatment with carvedilol, a non-specific β-blocker, prevented the development of counterregulatory failure and improved hypoglycaemia awareness in recurrently hypoglycaemic non-diabetic rats. The current study investigated whether carvedilol has similar benefits in diabetic rats.

Methods: Recurrently hypoglycaemic streptozotocin-diabetic rats (STZ+RH) were treated with carvedilol for one week prior to undergoing a hypoglycaemic clamp. Hypoglycaemia awareness was evaluated in streptozotocin-diabetic rats made hypoglycaemia unaware using repeated injections of 2-deoxyglucose.

Results: Compared to hypoglycaemia-naïve STZ-diabetic controls, exogenous glucose requirements were more than doubled in the STZ+RH animals and this was associated with a 49% reduction in the epinephrine response to hypoglycaemia. Treating STZ+RH animals with carvedilol improved the epinephrine response to hypoglycaemia. Of note, neither recurrent hypoglycaemia nor carvedilol treatment affected the glucagon response in diabetic animals. Additionally, carvedilol treatment improved the feeding response to insulin-induced hypoglycaemia in diabetic animals made 'hypoglycaemia unaware' using repeated injections of 2-deoxyglucose, suggesting the treatment improved awareness of hypoglycaemia as well.

Conclusion: Our data suggest that carvedilol may be useful in preventing impairments of the sympathoadrenal response and the development of hypoglycaemia unawareness during recurring episodes of hypoglycaemia in diabetic animals.

Keywords: adrenergic sensitivity; beta‐blocker; carvedilol; diabetes; hypoglycaemia; hypoglycaemia awareness; streptozotocin.

FIGURE 1

A, Hypoglycaemic Clamp Study Design. Schematic outlining the treatment time course. Diabetes was induced on day 0. Surgery for the implantation of catheters and microdialysis guide cannulas was performed one week later. Saline or carvedilol treatments were administered daily starting on day 7 and continued until day 13. Recurrent saline or insulin treatments was conducted from day 11–13. The hypoglycaemic clamp was conducted on Day 14. B, Plasma glucose concentrations throughout the clamp procedure. STZ Controls are represented as circles. STZ +recurrently hypoglycaemic diabetic (RH) animals are shown as squares, the RH diabetic rats treated with 4.5 mg/kg carvedilol (STZ+RH+4.5 Carvedilol) are shown as solid triangles. The hypoglycaemic phase of the study was from 0’ to 90’

FIGURE 2

Isoproterenol Test. Schematic outlining the treatment time course. Diabetes was induced on day 0. Saline or 4.5 mg/kg carvedilol treatment was initiated on day 7 and continued until day 13. Recurrent saline or insulin treatments were given from days 11–13. The isoproterenol test was conducted on day 14 in lightly anesthetized rats

FIGURE 3

Evaluating Hypoglycaemia Awareness. Schematic outlining the treatment time course. Diabetes was induced on day 0. All rats had catheters implanted three days after induction of diabetes. Saline or carvedilol (4.5 or 6 mg/kg) treatments were initiated on day 3 and continued until day 9. Recurrent saline or 2‐deoxyglucose treatments were given once daily from days 7–9. On day 10, the animals were given either subcutaneous injections of saline or insulin, and food intake was assessed to evaluate hypoglycaemia awareness

FIGURE 4

A, Total glucose infused over the final 30 min of the hypoglycaemic clamp procedure. B, Peak plasma glucagon and C, peak epinephrine responses during the hypoglycaemic phase of the clamp; and D, baseline extracellular lactate concentrations in the ventromedial hypothalamus of diabetic (STZ), recurrently hypoglycaemic diabetic (STZ+RH) and recurrently hypoglycaemic diabetic animals treated with 4.5 mg/kg carvedilol (STZ+RH+4.5 carvedilol). Data presented as mean ± SEM. *p < 0.05; ***p < 0.001

FIGURE 5

Isoproterenol test. This figure shows percentage change in heart rate from baseline levels in diabetic (STZ), recurrently hypoglycaemic diabetic (STZ+RH) and recurrently hypoglycaemic diabetic rats treated with 4.5 mg/kg carvedilol (STZ+RH+4.5 carvedilol) following intravenous administration of isoproterenol. There was no significant difference between the three treatment groups. Data presented as mean ±SEM.

FIGURE 6

Evaluation of hypoglycaemia awareness. A, Blood glucose levels during the induction of hypoglycaemia. B, Diabetic rats made hypoglycaemic (STZ+Insulin) consumed significantly (***p < 0.001) more food than hypoglycaemia‐naïve rats given a saline injection (STZ+Saline). Diabetic rats treated with 2‐deoxyglucose (STZ+2DG) consumed significantly less food when hypoglycaemic compared to the STZ+Insulin group (***p < 0.001, 2DG+Insulin vs Saline+Insulin). Although treatment with 4.5 mg/kg carvedilol increased food consumption in STZ+2DG diabetic animals, the increase did not reach statistical significance. In contrast, when the STZ+2DG animals were treated with 6 mg/kg carvedilol, the animals consumed more food than the STZ+2DG group (*p < 0.05). Data presented as mean ± SEM