Tuesday, February 05, 2008

A Link Between Diabetes And High Blood Pressure

Almost 75% of people with diabetes have high blood pressure (greater than or equal to 130/80 mm Hg).1


We know that having consistently high blood sugars can damage arteries, predisposing them to plaque buildup and atherosclerosis. Those physical changes in the arteries can contribute to high blood pressure over time.

But a recent study in the journal Circulation Research2 shone a light on a more specific mechanism.

Researchers found that blood pressure anomalies in diabetic rats were associated with an increase in the activity of an enzyme called arginase.

Here's the process by which increased arginase activity can lead to high blood pressure:
  1. Arginase competes with another enzyme, nitric oxide synthase (NO synthase), for their common substrate - the amino acid arginine.
  2. Arginase converts arginine to ornithine and urea. This is the last step of the liver's urea cycle, a process the body uses to rid itself of harmful ammonia. (Ammonia is produced in our bodies by the breakdown of nitrogen-containing compounds such as proteins.)
  3. NO synthase converts arginine to nitric oxide (NO). NO mediates vasodilation - it lowers blood pressure.
  4. When the pool of arginase is great, it can deplete available arginine, leaving little for NO synthase to act upon ... resulting in higher blood pressure.
The researchers also found that when bovine endothelial cells (cells that line blood vessels and heart cavities) were treated with high levels of glucose, it increased their arginase activity ... and lowered NO production. Less NO = less ability for blood vessels to relax.

L-arginine is marketed as a supplement to lower blood pressure. But if people with diabetes have increased arginase activity, that arginase could deplete both endogenous (inside the body) as well as exogenous (taken as a supplement) arginine before NO synthase has a chance to act upon it. A more promising supplement, garnered from these researchers' work, may be another amino acid, L-citrulline, which was shown to blunt the effect of arginase.

Furthering our understanding of how diabetes and high blood pressure are linked can help researchers discover or develop therapies to manage hypertension. However, one drug-free, inexpensive approach that's available right now is good management of blood glucose.

1 National Diabetes Information Clearinghouse, Diabetes Dateline, New Fact Sheet On High Blood Pressure And Kidney Disease

2 Diabetes-Induced Coronary Vascular Dysfunction Involves Increased Arginase Activity

News summary (ScienceDaily):
Diabetes Makes It Hard For Blood Vessels To Relax