AVP stands for arginine vasopressin, a hormone your body produces to regulate water balance, blood pressure, and several other critical functions. You may also see it called ADH (antidiuretic hormone) or simply vasopressin. It is made in the brain and released into the bloodstream, where it tells your kidneys how much water to hold onto. Normal blood levels range from 0 to 5.9 pg/mL.
Where AVP Is Made and Released
AVP is produced by specialized nerve cells in the hypothalamus, a small region at the base of the brain that acts as a control center for hormones. These neurons manufacture a precursor protein, then send it along long nerve fibers that extend down into the posterior pituitary gland. During that journey, the precursor is cut into the active AVP molecule. Once it arrives at the pituitary, AVP is stored in nerve terminals and waits for a signal to be released into the bloodstream.
What Triggers AVP Release
The most important trigger is a rise in blood concentration. Your brain contains specialized osmoreceptors that constantly monitor how concentrated your blood is. When you’re dehydrated and blood concentration climbs, these sensors fire and AVP pours into your circulation. Individual people have slightly different thresholds for when this kicks in, influenced by genetics and environment.
AVP also responds to signals that have nothing to do with hydration. Pressure sensors in the heart and major arteries detect drops in blood volume or blood pressure and trigger AVP release through nerve pathways. Pain, nausea, stress, and low oxygen levels are additional triggers. This is why you may retain extra water after surgery or during illness, even if you’re drinking normally.
How AVP Controls Water in the Kidneys
AVP’s primary job is preventing you from losing too much water through urine. It works by acting on the collecting ducts of the kidney, the final stretch of tubing that urine passes through before reaching the bladder. Without AVP, these ducts are relatively waterproof, and large volumes of dilute urine flow straight through. When AVP arrives, it binds to receptors on the duct cells and sets off a chain of events that inserts tiny water channels (called aquaporin-2) into the cell surface. Water then flows back out of the urine and into the bloodstream, producing smaller volumes of more concentrated urine.
AVP doesn’t just shuttle existing water channels to the surface. It also tells kidney cells to manufacture more of them over time. This two-pronged approach, rapid repositioning of channels plus longer-term production of new ones, lets the body fine-tune water retention on a minute-to-minute and day-to-day basis.
AVP and Blood Pressure
Beyond the kidneys, AVP acts directly on blood vessels. It binds to receptors on the smooth muscle lining arteries and veins, causing those muscles to contract and the vessels to narrow. This vasoconstriction raises blood pressure. The effect becomes especially important when blood volume drops significantly, such as during heavy bleeding or severe dehydration. In those situations, AVP works alongside its water-retaining action: holding onto fluid increases blood volume from the inside while vessel constriction maintains pressure from the outside.
The Three AVP Receptor Types
AVP produces different effects depending on which receptor it activates. The body has three main types:
- V1a receptors: Found on blood vessel walls. Responsible for vasoconstriction and blood pressure regulation.
- V1b receptors: Located in the anterior pituitary gland. These trigger the release of ACTH, a stress hormone that in turn stimulates cortisol production from the adrenal glands.
- V2 receptors: Found in the kidney collecting ducts. These drive water reabsorption by activating aquaporin-2 channels.
This receptor system explains why a single hormone can influence such different processes. The outcome depends entirely on where in the body AVP lands.
What Happens When AVP Is Too Low
When the body produces too little AVP, or none at all, a condition formerly called central diabetes insipidus develops. The newer medical term is AVP deficiency (AVP-D). Without adequate AVP signaling, the kidneys cannot concentrate urine. The result is excessive urination, sometimes many liters per day, along with intense thirst. AVP-D typically results from damage to the hypothalamus or pituitary from surgery, head trauma, tumors, or autoimmune inflammation.
A separate condition, AVP resistance (AVP-R), occurs when the kidneys themselves stop responding to normal levels of the hormone. The brain releases AVP as it should, but the kidney receptors or their signaling pathways are faulty. The symptoms look identical: large volumes of dilute urine and relentless thirst. The distinction matters because the treatments differ.
What Happens When AVP Is Too High
Excess AVP causes the body to retain too much water, diluting the sodium in your blood. This is known as the syndrome of inappropriate antidiuretic hormone secretion, or SIADH. Blood sodium drops below 135 mEq/L, which can cause headaches, confusion, nausea, and in severe cases, seizures.
Many conditions can trigger SIADH. Brain injuries, strokes, infections, and psychiatric illness can all cause the pituitary to over-release AVP. Certain lung diseases, particularly pneumonia, are common culprits. Small cell lung cancer is the tumor most frequently associated with SIADH because the cancer cells themselves can produce AVP independently. Several widely used medications also contribute, including certain anti-seizure drugs, some antidepressants (particularly SSRIs), and even the recreational drug MDMA (ecstasy), which both stimulates AVP release and increases thirst, a dangerous combination. Surgical procedures often temporarily elevate AVP as well, likely driven by pain signals.
The primary treatment for mild SIADH is simply restricting fluid intake, which allows sodium levels to normalize.
AVP in Critical Care Medicine
Synthetic vasopressin is used in hospitals as a medication, most commonly during septic shock, a life-threatening condition where blood pressure drops dangerously low due to overwhelming infection. In this setting, vasopressin is given intravenously alongside other blood-pressure-raising drugs. Its vessel-constricting effects help restore blood pressure when the body’s own supply of the hormone becomes depleted. International critical care guidelines recommend it as an add-on therapy when standard medications alone aren’t enough.
How AVP Is Measured
Measuring AVP directly in a blood sample has always been technically difficult. The molecule is tiny, breaks down within minutes in the bloodstream (its half-life is under 30 minutes), and degrades quickly even in stored blood samples. These limitations have kept direct AVP testing out of routine clinical use for decades.
Over the past ten years, doctors have largely switched to measuring copeptin instead. Copeptin is a fragment of the same precursor protein that produces AVP, and the two are released in equal amounts. The advantage is that copeptin is far more stable: it survives at room temperature for over a week and requires only a tiny blood sample. The test is faster, more reliable, and has become the preferred way to assess AVP activity in conditions like diabetes insipidus and SIADH.