Activation of the Sympathetic Nervous System. The sympathetic nervous system consists of the nerve cells that automatically govern and regulate the beating heart.
- This nervous system responds to the failing heart pump by signaling the release of stress hormones, in particular a powerful one called norepinephrine.
- These hormones flood the heart, causing it to beat even faster.
- These rapid heart beats, although intended to accommodate the weakened pumping actions, only accelerate the damage.
The Renin-Angiotensin-Aldosterone System (RAAS). The renin-angiotensin-aldosterone system (RAAS) is a group of hormones that are responsible for the opening and narrowing of blood vessels and retention of fluids. They also affect cell development in the heart.
- The RAAS hormones are called into action by the failing heart.
- They respond to the lower blood volume of the weakened heart by constricting the blood vessels and retaining fluids and sodium.
- The heart then works harder to pump blood through these narrowed vessels. Blood pressure, then, is forced to increase, which creates a vicious cycle.
Immune System Response. The immune system may also compound the damage. In response to injury in the heart muscle cells or in other parts of the body that occurs as the heart fails, the immune system releases factors intended to protect these areas.
In excess, however, they can cause inflammation and damage.
- The most important of these factors are called cytokines. Active cytokines include tumor necrosis factor (TNF) and possibly interleukins 1 and 6.
- High levels of these cytokines have been observed in patients with the most severe classes of heart failure.
- They may play an important role in the process leading to remodeling. High levels of these cytokines may actually trigger muscle cell growth and enlargement of the heart.
Other Players. Other molecules or compounds have been identified that might play a positive or negative role in the process of the failing heart.
- Natriuretic peptides are a family of compounds released to counterbalance the effects of RAAS. Atrial natriuretic peptide (ANP) is a specific member of this family that opens blood vessels and counteracts the sodium-retaining properties of aldosterone (one of the RAAS hormones). It is of particular interest to researchers looking for new treatments.
- Endothelin is a powerful protein involved in blood vessel constriction, cell proliferation and build-up, and other negative effects on the heart.
- Nitric oxide is important for blood vessel dilation and elasticity.
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