Answer: increases water permeability in certain portions of the kidney tubules.
Step-by-step explanation:
The proximal convoluted tubule is the site in nephron where selective reabsorption of water and electrolytes like sodium and potassium ions occurs. From there water and other substances are reabsorbed and reenter into the circulation. This cause an increase in blood pressure and blood volume. Only the cells of the proximal convoluted tubule are permeable for this reabsorption process and they are stimulated by a hormone named as aldosterone.