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Neurohypophyseal Hormones

For medical students2 min readUpdated 2026-10-10

The posterior pituitary (neurohypophyssis) does not synthesize its own hormones. Instead, it serves as an important reservoir for vasopressin and oxytocin, which are synthesized higher up in hypothalamic structures and transported downward along nerve fibers.

Site of synthesisMagnocellular nuclei of the anterior hypothalamus

ADH targetRenal collecting ducts (V2 receptors)

TransportAxonal transport to the posterior pituitary

Extrabrain synthesisAdrenal medulla and gonads

Synthesis and Transport Pathways

Physiologically, oxytocin and antidiuretic hormone (ADH, also known as vasopressin) are classified as effector hormones. The process of their formation and secretion is strictly segregated anatomically.

The primary site of production of these biologically active substances is the anterior hypothalamus. Specific magnocellular nuclei—the supraoptic and paraventricular nuclei—are responsible for their synthesis. Interestingly, synthesis is not exclusively restricted to the central nervous system: small amounts of these hormones can be produced peripherally, specifically in the gonadal tissue and the adrenal medulla.

To reach the systemic circulation, the hormones must travel a complex pathway from their site of origin:

Main pathway: Molecules travel directly down the axons of hypothalamic neurons into the neurohypophyseal tissue. Final secretion into the general bloodstream occurs from here.
Accessory pathway: A portion of nerve terminals does not reach the posterior pituitary, terminating instead in the median eminence. Here, small amounts of vasopressin can be released directly into the hypophyseal portal system, influencing neighboring structures.

Anatomical Organization of Regulatory Pathways

The connection between the hypothalamus and the pituitary gland is organized into two key pathways, which operate depending on the body's current metabolic demands.

Pathway to the posterior pituitary (neurohypophysis): Originates in the supraoptic and paraventricular nuclei. It mediates direct axonal transport of ready-made effector hormones (oxytocin and vasopressin).
Pathway to the anterior pituitary (adenohypophysis): Originates from another group of nuclei—the infundibular (arcuate), ventromedial, and dorsomedial nuclei. These produce releasing and inhibiting hormones (various statins and liberins), which are released into the hypophyseal portal circulation. Their role is the local regulation of trophic cell activity in the anterior lobe.

Vasopressin (ADH): Receptors and Effects

Vasopressin exerts a wide range of actions mediated by binding to various receptor types in target organs. Its physiological effects can be divided into four main categories:

Renal effects: By acting on V2 receptors located in the renal collecting ducts, the hormone critically increases water reabsorption, thereby decreasing urine output.
Vascular effects: Binding to V1 receptors in blood vessel walls leads to a pronounced vasoconstrictor response (narrowing of the lumen).
Endocrine effects: The fraction of the hormone secreted into the portal system via the accessory pathway reaches the adenohypophysis and stimulates the production of adrenocorticotropic hormone (ACTH).
Central effects: Within the central nervous system, vasopressin acts as a neuromodulator and classical neurotransmitter. It plays an active role in generating thirst and drinking behavior, and is involved in complex memory mechanisms.

Physiological Role of Oxytocin

Oxytocin is often associated exclusively with the female reproductive system; however, it performs important functions in both sexes, ensuring the contractility of smooth muscle in specific ducts and organs.

In females, the hormone's effects are most prominent in two states:

During labor: The hormone powerfully stimulates and enhances the contractility of the myometrium (the muscular layer of the uterus), facilitating fetal expulsion.
During lactation: Acting in close synergy with prolactin, oxytocin ensures the active milk ejection reflex from the mammary glands.

In males, the physiological role of oxytocin involves facilitating normal ejaculation by inducing rhythmic contractions of the vas deferens walls.

Mnemonic

To remember vasopressin receptors: V1 = Vasoconstriction (vessel narrowing), V2 = Water (water retention in the kidneys).

Frequently asked questions

What is the intracellular mechanism of action of vasopressin on V2 receptors?

The intracellular mechanism of vasopressin action on V2 receptors is mediated by adenylate cyclase activation.

Receptor binding — ADH binds to V2 vasopressin receptors in the renal tubules.
Second messenger generation — The enzyme adenylate cyclase is activated, converting ATP into cyclic adenosine monophosphate (cAMP).
Kinase activation — cAMP activates protein kinase.
Phosphorylation and synthesis — Phosphorylation of the aquaporin-2 gene occurs, followed by mRNA synthesis and aquaporin-2 protein production.
Insertion — Aquaporin-2 is inserted into the nephron tubular membrane, forming water channels that facilitate water reabsorption into the blood.

What stimuli trigger antidiuretic hormone secretion?

The triggering stimuli for antidiuretic hormone (ADH) secretion are increased osmotic pressure/osmolality and hypohydration combined with decreased blood volume.

Hyperosmolality — Water deficit in the blood or high salt intake increases plasma osmotic pressure/osmolality, which stimulates osmoreceptors in the anterior hypothalamic nuclei.
Hypohydration — Tissue water depletion, colloid dehydration, and decreased blood volume trigger signals from baroreceptors, volume receptors, and osmoreceptors.

These signals activate the supraoptic and paraventricular hypothalamic nuclei, increasing vasopressin (ADH) secretion.

How is the reflex arc of oxytocin secretion mediated during breastfeeding?

Reflex regulation of oxytocin secretion during breastfeeding begins with the stimulation of nipple receptors during suckling. This stimulus triggers the release of oxytocin by the hypothalamo-neurohypophyseal system. Oxytocin acts on myoepithelial cells surrounding the alveoli and ducts of the mammary glands, causing them to contract. As a result, milk is ejected from the alveoli into the lactiferous sinuses and ducts.

Does the neurohypophysis synthesize hormones independently?

No, the posterior pituitary tissue is incapable of synthesis. It merely stores oxytocin and vasopressin, which are transported down axons from the magnocellular nuclei of the hypothalamus.

Does vasopressin affect the function of other endocrine glands?

Yes, a small amount of the hormone is released into the hypophyseal portal system and stimulates ACTH secretion, which in turn regulates the adrenal cortex.

Is oxytocin produced in the male body?

Yes, this hormone is also present in men. Its primary function is to stimulate contractions of the reproductive ducts during ejaculation.

Go deeper

Mechanisms of axonal transport from the hypothalamus to the neurohypophysis
Secretion of ADH into the portal vein via the median eminence
Involvement of vasopressin in memory mechanisms
Synergistic action of oxytocin and prolactin during lactation
Extrahypothalamic synthesis of hormones in the adrenals and gonads