Final answer:
A protagonist drug of SPAK/OSR1 would cause increased sodium reabsorption.
Step-by-step explanation:
A protagonist drug of SPAK/OSR1 would cause increased sodium reabsorption. Aldosterone, the hormone released in response to increased blood levels of potassium or decreased blood levels of sodium or blood pressure, promotes sodium reabsorption in the kidneys, leading to increased water retention and ultimately, increased sodium levels in the body. This helps to conserve and increase water levels in the plasma.