Antidiuretic hormone (ADH):

A. Is related to oxytocin, and both are released from the posterior pituitary in conjunction with neurophysins.

B. Is released into the circulation by the posterior pituitary in response to a rise in plasma osmolality above 285 mOsm. or a decrease in circulating blood volume.

C. May be stimulated by catecholamines and inhibited by phenytoin, alcohol, and lithium.

D. In excess, may produce a syndrome of euvolemic hyponatremia with inappropriately concentrated urine that is responsive

E. Deficiency causes prolonged polyuria and polydipsia and may be diagnosed by a combination of high plasma osmolality and low urine osmolality following water deprivation.

 DISCUSSION: ADH and oxytocin are nine–amino acid peptides derived from a common ancestral peptide, vasotocin. ADH is released from the posterior pituitary with neurophysin II in response to a rise in plasma osmolality greater than 285 mOsm/kg. H 2O. by a 5% or greater decrease in blood volume, and by catecholamines. The syndrome of inappropriate ADH release (SIADH) produces euvolemic hyponatremia and is responsive to free water restriction. Diabetes insipidus (DI) reflects a deficiency of ADH and causes prolonged polyuria and polydipsia. Diabetes insipidus is diagnosed by a combination of high plasma osmolality and low urine osmolality following water deprivation. Exogenously administered ADH differentiates central (ADH-responsive) DI from nephrogenic (ADH-unresponsive) DI.