The main factors which affect renin levels are blood pressure itself, the amount of sodium in the body and triggers from the sympathetic nervous system. There is a sensitive feedback mechanism which allows the amount of renin to go up or down according to these triggers. Renin is an enzyme which plays a major role in a complex system of hormones and enzymes in the human body called the renin-angiotensin system (RAS). It controls various functions in the body, including blood volume and blood pressure.
Produced by specific renal cells in the kidney which are activated by these triggers, renin levels are increased or decreased. When they increase, a cascade of reactions occur in the body via numerous other enzymes and hormones, ultimately causing an increase in blood pressure. This is achieved by various mechanisms including vasoconstriction of the blood vessels and increased thirst, causing increased fluid intake.
A drop in sodium levels will cause an increase in renin levels. Low sodium, or hyponatremia, may be caused by various factors including drinking too much water, age, and some medications. Conversely, high sodium levels will cause a decrease in renin levels and have the opposite action.
When the blood pressure of the body goes down, receptors which are sensitive to pressure send a message to the kidney cells to increase renin levels. This causes the whole cascade to occur and raises blood pressure again. The sympathetic nervous system of the body is, simply put, the system which controls most of the internal organs under stress situations. Triggers from this generally involuntary system can affect renin levels.
Many therapeutic drugs rely on the renin-angiotensin system for their action. A relatively new class of drugs to lower blood pressure which act directly on renin levels are renin inhibitors, like aliskiren. Blood pressure pills like lisinopril or enalapril, which are ACE-inhibitors, lower blood pressure by acting on the RAS system further down the cascade.
Renin levels may be used by doctors during diagnosis of hypertension, along with various other tests. It is a simple blood test done by the lab and will help the treating doctor to determine which antihypertensive is most suitable for a specific patient. The renin blood test is often done in combination with an aldosterone test.
Maintenance of stable renin levels in the body is essential. This allows the body to maintain a healthy blood volume and blood pressure. Regular monitoring of the blood pressure is recommended, especially in people with a family history of hypertension and those of increasing age.