422
CASE FILES: BIOCHEMISTRY
A nsw ers
[46.1]
B. Desmopressin is a vasopressin analog. Symptoms are consistent
with DI arising from surgical trauma to the pituitary or hypothalamus
and impairment of vasopressin release. The other possibilities would
not be alleviated by desmopressin.
[46.2]
C. Vasopressin, and its analog desmopressin, acts by increasing inser-
tion of aquaporin (water channels) into the renal distal tubule mem-
brane, permitting increased resorption of water from the urinary
filtrate.
[46.3]
E. Aldosterone acts independent of vasopressin to increase water
resorption by the kidney, by stimulating the insertion of ion trans-
porters into the membrane of distal colon and kidney distal tubule.
B IO C H E M IS T R Y PE A R L S
Vasopressin (antidiuretic hormone) is a nonapeptide that controls
resorption of water by distal tubules of the kidney to regulate the
osmotic pressure of blood.
Vasopressin is synthesized in the hypothalamus and stored in the
posterior pituitary.
Vasopressin is released in response to increased extracellular osmo-
larity sensed by hypothalamic osmoreceptors, signaling by atrial
stretch receptors or after a rise in angiotensin II levels. Its secre-
tion is increased by dehydration or stress.
Vasopressin promotes increased resorption of water in the renal dis-
tal tubule by stimulating insertion of water channels or aquapor-
ins into the apical membranes of kidney tubules.
REFERENCES
Booth
RE,
Johnson
JP,
Stockand
JD.
Aldosterone.
Adv
Physiol
Educ
2002;26(1-4):8-20.
de Gasparo M, Catt KJ, Inagami T, et al. International union of pharmacology.
XXIII. The angiotensin II receptors. Pharmacol Rev 2000;52(3):415-72.
Litwack G, Schmidt TJ. Biochemistry of hormones I: polypeptide hormones. In:
Devlin TM, ed. Textbook of Biochemistry with Clinical Correlations, 5th ed.
New York: Wiley-Liss, 2002.
Pathophysiology of the endocrine system. An online textbook from Colorado State
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