A Kidney Problem Causing High Blood Pressure
Author: Michael Webb

Interestingly, certain cases of high blood pressure are caused by a kidney problem. The kidneys play a large role in determining what our blood pressure is. The kidneys have a complex system of hormones that affect blood pressure under certain circumstances.

The primary kidney problem that leads to high blood pressure is that of a blockage of blood flow to one or more kidneys as well as kidney diseases. In response to a lack of adequate blood flow, the kidneys release angiotensin into the blood that causes constriction of the blood vessels and an increased blood pressure. The adrenal cortex also releases aldosterone when angiotensin is released.

To understand the kidney problem more easily, you need to understand how angiotensin is made. It is made by a precursor molecule called angiotensinogen. This is an alpha-2-globulin that is released by the liver. It is a protein made from 453 amino acids. The molecule, angiotensin I, is made by the action of renin (made by the kidneys when blood pressure is perceived to be low) on the protein angiotensinogen. Angiotensin I is simply a precursor to angiotensin II.

The kidney problem in high blood pressure gets worse when an enzyme called ACE (angiotensin converting enzyme) transforms angiotensin I to angiotensin II. The angiotensin II is what causes the blood pressure to rise. The molecule does degrade into angiotensin III and angiotensin IV that have lesser activity on blood pressure.

The primary kidney problem impacting high blood pressure is the constriction of the arteries and veins by angiotensin II. It also causes adhesion and the aggregation of platelets, promoting blood clots. In addition, it is possibly playing a role in the thickening and enlargement of the heart. Angiotensin II also increases the resorption of sodium by the kidneys, which also worsens the blood pressure. In an attempt to fix the low blood flow to the kidneys, the molecule also increases the rate at which blood flows through the kidneys.

In order to fix the kidney problem causing high blood pressure, there are medications now that help block the affects of the molecules involved. The most commonly used medication is called an ACE inhibitor and includes medications like Vasotec, Univasc, Prinivil and Zestril. They block the conversion of angiotensin I to angiotensin II. Newer medications block the receptor site for angiotensin II.

There is a relatively uncommon type of kidney problem causing high blood pressure. That condition is called renovascular hypertension. It is a condition to be examined for in cases of high blood pressure in teens and other young people. It occurs when there is a natural narrowing of one of the renal arteries leading to the kidneys. This causes an increase in the release of renin from the kidney and the cascade toward having high levels of angiotensin II is begun. The only good way to evaluate for this disease is to do an X-Ray dye study particularly one using a catheter into the renal arteries to check for narrowing.

 

¶ 2:56 PM