Which molecules are known to influence the force of contraction in the heart?

Catecholamines, such as epinephrine and norepinephrine, are hormones that significantly influence the contractile force of the heart's muscle fibers. They achieve this by binding to beta-adrenergic receptors on cardiac myocytes, leading to an increase in intracellular calcium levels, which in turn enhances the force of contraction. This process is part of the body’s fight-or-flight response, wherein catecholamines increase heart rate and myocardial contractility to improve cardiac output during stressful situations.

In contrast, while glucose is an essential source of energy for cardiac tissues, it does not directly influence the contractility of the heart muscle. Nitrites have a primary role in vasodilation and can affect blood flow rather than directly changing the contraction force of the myocardium. Carbon dioxide, on the other hand, plays a role in respiratory drive and acid-base balance but does not directly modulate the force of contraction in cardiac muscle. Thus, catecholamines are the key molecules involved in regulating cardiac contractility.