counter-regulatory hormone

A counter-regulatory hormone is any hormone that pushes blood sugar up, opposing insulin's lowering effect. They are the body's defense team against hypoglycemia: if insulin's brake threatens to push blood sugar too low, these hormones step on the accelerator. The four classic players are glucagon, epinephrine, cortisol, and growth hormone.

They act on different timescales and through different mechanisms. Glucagon and epinephrine respond within minutes, rapidly driving glycogenolysis and gluconeogenesis, while cortisol and growth hormone act over hours, promoting glucose production and reducing tissue glucose uptake. Together they create a layered, redundant safety net, with glucagon and epinephrine as the most important fast responders.

This redundancy has clinical consequences. In long-standing type 1 diabetes the glucagon response is often lost and the epinephrine response can blunt over time, leading to hypoglycemia unawareness — a dangerous state in which the usual warning surge of counter-regulatory hormones, and the symptoms it produces, fails to occur.