Final answer:
Option 2, 'Causes the renal excretion of sodium, potassium, and water,' is not a true characteristic of ADH secreted by the posterior pituitary gland. ADH primarily regulates water retention in the kidneys.
Step-by-step explanation:
The answer to the question 'Which of the following is not true of ADH secreted by the posterior pituitary gland?' is option 2) Causes the renal excretion of sodium, potassium, and water. Antidiuretic hormone (ADH), also known as vasopressin, is secreted by the hypothalamus and released from the posterior pituitary gland. Its main function is to regulate the excretion of water by the kidneys, not the excretion of electrolytes such as sodium and potassium.
ADH is indeed secreted in response to low blood volume and concentrated plasma (as in dehydration), and its deficiency causes diabetes insipidus, where not enough water is reabsorbed by the kidneys, leading to chronic dehydration and possible electrolyte imbalances.