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Question 492
Endocrinology → General
Classification
Question
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A woman receiving a prolonged high-dose oxytocin infusion develops features of water intoxication. Which property of oxytocin most directly explains this complication?
Question Stem
Select the single best answer.
Options
A
It possesses approximately 0.5–1% of the antidiuretic activity of vasopressin
B
It selectively constricts the renal efferent arteriole
C
It directly increases aldosterone secretion
D
It inhibits hypothalamic synthesis of vasopressin
E
It prevents placental degradation of vasopressin
Explanation
At high doses, oxytocin has approximately 0.5–1% of the antidiuretic activity of vasopressin. Prolonged high-dose administration can therefore promote water retention and water intoxication. Oxytocin is a nonapeptide synthesized principally in the paraventricular nucleus and released from the posterior pituitary.
Option Validity
B) Selective efferent arteriolar constriction is described as an action of vasopressin, not the mechanism of oxytocin-associated water intoxication.
C) Direct stimulation of aldosterone secretion is not the mechanism described.
D) Water intoxication results from intrinsic antidiuretic activity at high oxytocin doses, not inhibition of vasopressin synthesis.
E) Placental oxytocinase inactivates oxytocin; prevention of vasopressin degradation is not the mechanism.
Further Reading
Saxena, MRCOG-1 Basic Sciences, Endocrinology: Hormones of the Posterior Pituitary - Oxytocin, pp. 306–307.