Antidiuretic hormone . See

Alcohol inhibits the release of vasopressin (antidiuretic hormone see Chapter 29) from the posterior pituitary gland, resulting in enhanced diuresis. The volume loading that accompanies imbibing complements the diuresis that occurs as a result of reduced vasopressin secretion. Alcoholics have less urine output than do control subjects in response to a challenge dose with ethanol, suggesting that tolerance develops to the diuretic effects of ethanol. Alcoholics withdrawing from alcohol exhibit increased vasopressin release and a consequent retention of water, as well as dilutional hyponatremia. 

The collecting duct system (connecting tubule, initial collecting tubule, cortical collecting duct, and outer and inner medullary collecting ducts) is an area of fine control of ultrafiltrate composition and volume and is where final adjustments in electrolyte composition are ttuide. In addition, vasopressin (also called antidiuretic hormone see Chapter 29) modulates water permeability of this part of the nephron. 

The principal hormones of the human posterior pituitary include the two nonapeptides, oxytocin [50-56-6] and arginine vasopressin [11000-17-2] (antidiuretic hormone, ADH). Many other hormones, including opioid peptides (see Opioids, endogenous), cholecystokinin [9011-97-6] (CCK) (see Hormones, BRAIN oligopeptides), and gastrointestinal peptides, also have been located in mammalian neurohypophysis (6), but are usually found in much lower concentrations (7). Studies have demonstrated that oxytocin and vasopressin are synthesized in other human organs, both centrally and peripherally, and there is considerable evidence for their role as neurotransmitters (see Neuroregulators) (8). 

There may be a decreased resistance and inability to The posterior pituitary gland produces two hormones localize infection. The nurse observes the skin daily for vasopressin (antidiuretic hormone) and oxytocin (see localized signs of infection, especially at injection sites Chap. 53). Posterior pituitary hormones are summarized or IV access sites. Visitors are monitored to protect the in the Summary Drag Table Anterior and Posterior patient against those witii infectious illness. Pituitary Hormones. 

Aquaporins help water to pass through biological membranes. They form hydrophilic pores that allow H2O molecules, but not hydrated ions or larger molecules, to pass through. Aquaporins are particularly important in the kidney, where they promote the reuptake of water (see p. 328). Aquaporin-2 in the renal collecting ducts is regulated by antidiuretic hormone (ADH, vasopressin), which via cAMP leads to shifting of the channels from the ER into the plasma membrane. 

Water. Water resorption in the proximal tubule is a passive process in which water follows the osmotically active particles, particularly the Na" ions. Fine regulation of water excretion (diuresis) takes place in the collecting ducts, where the peptide hormone vasopressin (antidiuretic hormone, ADH) operates. This promotes recovery of water by stimulating the transfer of aquaporins (see p. 220) into the plasma membrane of the tubule cells via V2 receptors. A lack of ADH leads to the disease picture of diabetes insipidus, in which up to 30 L of final urine is produced per day. 

Historically vasopressin and oxytocin, two nonapep-tides, were the first peptide neurohormones to be considered they are stored in the neurohypophysis and released into the bloodstream upon an appropriate stimulus. In the periphery, oxytocin stimulates the contraction of epididymal and uterine smooth muscle (see Chapter 62) and vasopressin (antidiuretic hormone) facilitates the reabsorption of water from the kidney tubules. In addition to these well-accepted roles as neurohormones, there is convincing evidence that these compounds function as neurotransmitters they both possess potent inhibitory actions on neurohypophyseal neurons. The significance of their neurotransmitter function is not yet clear. 

Minocycline, 200 mg orally daily for 5 days, can eradicate the meningococcal carrier state, but because of side effects and resistance of many meningococcal strains, rifampin is preferred. Demeclocycline inhibits the action of antidiuretic hormone in the renal tubule and has been used in the treatment of inappropriate secretion of antidiuretic hormone or similar peptides by certain tumors (see Chapter 15). 

Antidiuretic hormone is a posterior pituitary peptide hormone that binds to vasoconstrictive Via receptors (via Gaq to activate PLC and thence increase cytsosolic Ca2+), to V2 receptors (causing kidney water reabsorption via Gas and increased cAMP) and to corticotropin secretion-regulating Vlb (V3) receptors (mediated by Gaq to activate PLC and thence increase cytosolic Ca2+). For bioactive-G protein interactions see Table 5.9. 

The syndrome of inappropriate secretion of antidiuretic hormone secretion (SIADH) maybe treated with frusemide if there is a dangerous degree of volume overload, (see also p. 713). 

Desmopressin replacement therapy is the first choice. Thiazide diuretics (and chlortalidone) also have paradoxical antidiuretic effect in diabetes insipidus. That this is not due to sodium depletion is suggested by the fact that the nondiuretic thiazide, diazoxide (see Index), also has this effect. It is probable that changes in the proximal renal tubule result in increased reabsorption and in delivery of less sodium and water to the distal tubule, but the mechanism remains incompletely elucidated. Some cases of the nephrogenic form, which is not helped by antidiuretic hormone, may be benefited by a thiazide. 

Determination of plasma and urine osmolality can be useful in the assessment of electrolyte and acid-base disorders. Comparison of plasma and urine osmolalities can determine the appropriateness and status of water regulation by the kidneys in settings of severe electrolyte disturbances, as might occur in diabetes insipidus or the syndrome of inappropriate antidiuretic hormone (SIADH) (see Chapters 45 and 50). The major osmotic substances in normal plasma are Ha, Cr, glucose, and urea thus expected plasma osmolality can be calculated from the following empirical equation ... 

---