A healthy 22-year-old female medical student with normal kidneys decreases her sodium intake by 50% for a period of 2 months. Which of the following parameters is expected to increase in response to the reduction in sodium intake?

A reduction in sodium intake leads to a decrease in extracellular fluid volume and therefore a decrease in aerial pressure. The decrease in aerial pressure stimulates renin release, which in turn leads to an increase in the formation of angiotensin II. The angiotensin II increases the renal retention of salt and water (ie, decreases sodium excretion, which returns the extracellular fluid volume nearly back to normal. Atrial natriuretic peptide is released from the two atria of the hea as a result of an increase in the extracellular fluid volume. Therefore, a decrease in sodium intake would tend to decrease the release of atrial natriuretic peptide.