MCQ 16

The posterior pituitary secretes arginine vasopressin (antidiuretic hormone) under which of the following stressors?

a. Hyperosmolarity
b. Hypernatremia
c. Volume depletion
d. A and B
e. A and C

Answer and explanation

The answer is 'd'

Arginine vasopressin is a neurohormone released from the post pituitary gland to help maintain water balance in the body. Also known as antidiuretic hormone, vasopressin is primarily released under conditions of hyperosmolarity and volume depletion. Although sodium is the main determinant of hyperosmolarity, sodium is not the only stimulus that affects the secretion of vasopressin. Other, less potent stimuli of vasopressin release include pregnancy, nausea, pain stress and hypoglycemia . In addition, many drugs can cause stimulation of the in appropriate secretion of vasopressin. This hormone acts on the principal cell in the distal convoluted tubule of the  kidney to cause resorption of water. This occurs through nuclear mechanisms encoded by the aquaporin-2 gene that cause water channels to be inserted into the luminal membrane. The net effect is to cause the passive resorption of water along the osmotic gradient in the distal convoluted tubule