A 45-year-old man with type 2 diabetes mellitus is brought to the emergency department in a hypoglycaemic coma (blood glucose 32 mg/dL). His wife reports he took his usual insulin dose but skipped dinner. IV access is difficult to establish due to severe dehydration. The hormone marked **B** in the diagram is administered as 1 mg intramuscularly. Which of the following best explains why this intervention is effective in this acute setting but would likely FAIL in a chronic alcoholic with similar hypoglycaemia?