Which hormone has functions opposite to those of Angiotensin II?

Atrial Natriuretic Peptide (ANP) functions in opposition to Angiotensin II by promoting natriuresis, which is the excretion of sodium in the urine. Angiotensin II plays a critical role in fluid retention by stimulating aldosterone secretion, increasing sodium reabsorption in the kidneys, and promoting thirst to enhance blood volume and pressure. In contrast, ANP is released by the atria of the heart in response to increased blood volume and pressure. It serves to decrease blood pressure and volume by promoting vasodilation and increasing the excretion of sodium and water through the urine. This counter-regulatory mechanism is essential in the regulation of blood pressure and overall fluid balance in the body.

The other hormones listed do not have the same opposing actions to Angiotensin II. Aldosterone works to retain sodium and water, contributing to increased blood volume. Antidiuretic Hormone (ADH) increases water reabsorption in the kidneys, also supporting higher blood volume. Cortisol, a glucocorticoid, affects metabolism and can have some fluid-retaining properties. Thus, ANP is specifically designed to counteract the effects of Angiotensin II, making it the correct answer.