What is hypertension?

Hypertension, often referred to as high blood pressure, is a medical condition characterized by elevated pressure exerted by the blood against the walls of the arteries. Blood pressure is typically measured in millimeters of mercury (mm Hg) and is recorded as two numbers: systolic pressure (the top number) and diastolic pressure (the bottom number).


  • Systolic pressure represents the force exerted by the blood against the artery walls when the heart beats or contracts to pump blood out (systole).
  • Diastolic pressure represents the force exerted by the blood against the artery walls when the heart relaxes between beats (diastole).


Normal blood pressure is generally considered to be around 120/80 mm Hg. Hypertension is diagnosed when blood pressure consistently exceeds 130/80 mm Hg over time.


Hypertension can be classified into two main types:


  • Primary (essential) hypertension: This type of hypertension develops gradually over time and has no identifiable cause. It is the most common type of hypertension and is often related to a combination of genetic factors, lifestyle factors (such as diet, physical inactivity, and obesity), and environmental influences (such as stress).


  • Secondary hypertension: This type of hypertension is caused by an underlying medical condition or medication. Conditions that can lead to secondary hypertension include kidney disease, adrenal gland disorders, thyroid disorders, sleep apnea, certain medications (such as nonsteroidal anti-inflammatory drugs, oral contraceptives, and decongestants), and illicit drug use (such as cocaine or amphetamines).


What is the relationship between hypertension and oxidative stress?

The relationship between hypertension and oxidative stress involves complex interplay between various physiological and molecular mechanisms. Here’s how hypertension may be related to oxidative stress:


  • Endothelial Dysfunction: Hypertension is associated with dysfunction of the endothelium, the inner lining of blood vessels. Endothelial dysfunction impairs the ability of blood vessels to dilate properly and regulate blood flow. Increased blood pressure and altered blood flow patterns in hypertensive conditions can lead to oxidative stress in the endothelial cells. Reactive oxygen species (ROS) are produced within the endothelium, contributing to oxidative damage to blood vessel walls and promoting inflammation and vascular dysfunction.


  • Activation of the Renin-Angiotensin-Aldosterone System (RAAS): In hypertensive conditions, the renin-angiotensin-aldosterone system (RAAS) is often activated, leading to increased production of angiotensin II, a potent vasoconstrictor. Angiotensin II stimulates the production of ROS within blood vessels, promoting oxidative stress and endothelial dysfunction. Additionally, angiotensin II can directly induce oxidative stress in the kidney, heart, and blood vessels, contributing to organ damage and dysfunction in hypertension.


  • Inflammation and Immune Activation: Chronic inflammation is a hallmark of hypertension and is associated with increased oxidative stress. Immune cells, such as macrophages and T cells, are recruited to inflamed blood vessels and release inflammatory cytokines and ROS. Oxidative stress contributes to the activation of inflammatory pathways and further amplifies the inflammatory response in hypertensive tissues. This chronic low-grade inflammation and oxidative stress contribute to the progression of hypertension and its complications, such as atherosclerosis and organ damage.


  • Vascular Remodeling and Fibrosis: Hypertension leads to structural changes in blood vessels, including vascular remodeling and fibrosis. Oxidative stress plays a key role in mediating these processes by promoting the proliferation of vascular smooth muscle cells, deposition of extracellular matrix proteins (such as collagen), and stiffening of blood vessel walls. These structural changes further impair vascular function and contribute to the development of hypertension-related complications, such as heart failure, stroke, and kidney disease.


  • Antioxidant Defense Mechanisms: The body has natural antioxidant defense mechanisms to counteract oxidative stress and maintain redox balance. However, in hypertensive conditions, the production of ROS overwhelms the antioxidant defense systems, leading to oxidative damage and cellular dysfunction. Antioxidant enzymes, such as superoxide dismutase (SOD), catalase, and glutathione peroxidase, may become depleted or less effective in neutralizing ROS, further exacerbating oxidative stress in hypertension.


Overall, oxidative stress is intimately involved in the pathogenesis of hypertension and contributes to endothelial dysfunction, inflammation, vascular remodeling, and organ damage associated with this condition.