Effects on the Kidney
The single most important effect of antidiuretic hormone is to conserve body water by reducing the loss of water in urine. A diuretic is an agent that increases the rate of urine formation. Injection of small amounts of antidiuretic hormone into a person or animal results in antidiuresis or decreased formation of urine, and the hormone was named for this effect.
The most important variable regulating antidiuretic hormone secretion is plasma osmolarity, the concentration of solutes in blood. Osmolarity is sensed in the hypothalamus by neurons known as an osmoreceptors, and those neurons, in turn, simulate secretion from the neurons that produce antidiuretic hormone.
The most common disease related to antidiuretic hormone is diabetes insipidus. This condition can arise from either of two situations:
Hypothalamic ("central") diabetes insipidus results from a deficiency in secretion of antidiuretic hormone from the posterior pituitary. Causes of this disease include head trauma, and infections or tumors involving the hypothalamus.
Nephrogenic diabetes insipidus occurs when the kidney is unable to respond to antidiuretic hormone. Most commonly, this results from some type of renal disease, but mutations in the ADH receptor gene or in the gene encoding aquaporin-2 have also been demonstrated in affected humans.
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