Endothelial NOS (eNOS), also known as nitric oxide synthase 3 (NOS3) or constitutive NOS (cNOS), is an enzyme that in humans is encoded by the NOS3 gene located in the 7q35-7q36 region of chromosome 7. This enzyme is one of three isoforms that synthesize nitric oxide (NO), a small gaseous and lipophilic molecule that participates in several biological processes. The other isoforms include neuronal nitric oxide synthase (nNOS), which is constitutively expressed in specific neurons of the brain and inducible nitric oxide synthase (iNOS), whose expression is typically induced in inflammatory diseases. eNOS is primarily responsible for the generation of NO in the vascular endothelium, a monolayer of flat cells lining the interior surface of blood vessels, at the interface between circulating blood in the lumen and the remainder of the vessel wall. NO produced by eNOS in the vascular endothelium plays crucial roles in regulating vascular tone, cellular proliferation, leukocyte adhesion, and platelet aggregation. Therefore, a functional eNOS is essential for a healthy cardiovascular system. Impaired NO production is involved in the pathogenesis of several diseases such as hypertension, preeclampsia, diabetes mellitus, obesity, erectile dysfunction, and migraine.

Diabetes mellitus refers to a group of chronic diseases that affect the way the body breaks down (metabolizes) sugar or glucose (the body's primary source of energy). It results in not only defective metabolism of carbohydrates, but also proteins and fats, related to abnormal secretion and/or action or the hormone, insulin.

Diabetes is due to either the pancreas not producing enough insulin or the cells of the body not responding properly to the insulin produced. Hyperglycemia, or raised blood sugar, is a common effect of uncontrolled diabetes and over time leads to serious damage to many of the body's systems, especially the nerves and blood vessels. There are four common types of diabetes mellitus:

• Type 2 diabetes - A chronic condition that affects the way the body processes blood sugar (glucose).
• Type 1 diabetes - A chronic condition in which the pancreas produces little or no insulin.
• Prediabetes - A condition in which blood sugar is high, but not high enough to be type 2 diabetes.
• Gestational diabetes - A form of high blood sugar affecting pregnant women.

Often, there are no symptoms for diabates. When symptoms do occur, they include excessive thirst or urination, fatigue, weight loss or blurred vision. The most common types of diabetes and symptoms are:

• Type 2 diabetes - Symptoms include increased thirst, frequent urination, hunger, fatigue and blurred vision. In some cases, there may be no symptoms.
• Type 1 diabetes - Symptoms include increased thirst, frequent urination, hunger, fatigue and blurred vision.
• Prediabetes - Many people with prediabetes have no symptoms.
• Gestational diabetes - In most cases, there are no symptoms. A blood sugar test during pregnancy is used for diagnosis.

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