Final answer:
Norepinephrine (NE) is an inotropic agent that affects the tension in the heart muscles by increasing intracellular calcium levels and strengthening contractions. NE binds to beta-1 receptors and activates alpha and beta receptors to increase the force of contraction. Other hormones like thyroid hormones and glucagon also have positive inotropic effects.
Step-by-step explanation:
Inotropic agents, such as norepinephrine (NE), affect the tension in the heart muscles. NE binds to beta-1 receptors and stimulates the influx of calcium ions from the extracellular fluid, leading to an increase in intracellular calcium levels and stronger contractions. Additionally, NE activates alpha and beta receptors on the cardiac muscle cell membrane, increasing the force of contraction and metabolic rate. Other hormones like thyroid hormones and glucagon also have positive inotropic effects.