Which of the following is considered an antagonistic hormone to insulin?

Glucagon is recognized as an antagonistic hormone to insulin because it has effects that directly counteract the actions of insulin in the body. Insulin lowers blood glucose levels by facilitating the uptake of glucose into cells and promoting the storage of glucose as glycogen in the liver. In contrast, glucagon is secreted by the pancreas when blood glucose levels are low. Its primary function is to raise blood glucose levels by stimulating the liver to convert stored glycogen back into glucose and release it into the bloodstream. This regulatory mechanism ensures that the body maintains an appropriate level of glucose in the blood, especially between meals or during periods of fasting.

Cortisol, adrenaline (epinephrine), and thyroxine do have roles in glucose metabolism and can influence insulin action, but their primary functions relate more to stress response, metabolic regulation, and growth respectively, rather than serving as direct antagonists to insulin like glucagon does.