The hormone responsible for the actions of the sympathetic nervous system is:

The hormone that plays a key role in the actions of the sympathetic nervous system is epinephrine. This hormone, also known as adrenaline, is released by the adrenal glands during a stress response, commonly referred to as the "fight or flight" response. When epinephrine is released into the bloodstream, it leads to several physiological changes that prepare the body to react to stressful situations. These changes include increased heart rate, dilation of airways, improved blood flow to muscles, and enhanced availability of energy, all of which are crucial for responding quickly to perceived threats.

Epinephrine acts as a signaling molecule that amplifies the sympathetic nervous system's effects, ensuring that the body is prepared to take immediate action. Its functions are vital in managing acute stress and play a significant role in survival. In contrast, hormones like insulin, thyroxine, and aldosterone do not primarily govern the sympathetic response; instead, they regulate other aspects of metabolism and bodily functions.