Final answer:
High levels of ANP and BNP in the blood work usually lead to an increase in the excretion of sodium and water, reducing blood volume and pressure by counteracting the renin-angiotensin-aldosterone system.
Step-by-step explanation:
Increased levels of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in Ms. Mattson's blood work suggest that her body is responding to an increased blood volume. These peptides, which are produced by the heart, have important physiological roles in maintaining fluid balance and blood pressure. ANP and BNP lead to the excretion of Na+ and water, acting as potent diuretics. Consequently, they help in counteracting the effects of the renin-angiotensin-aldosterone system by inhibiting aldosterone and renin release, as well as diminishing the reabsorption of sodium in the kidneys.
This response results in decreased blood volume and pressure, which would be the opposite effect of water retention and increased tubular sodium reabsorption. Furthermore, these peptides do not stimulate the sympathetic nervous system; instead, they contribute to the downregulation of the system's effect on blood pressure and volume. Therefore, the most likely effect of high levels of ANP and BNP in this patient is the reduction of fluid volume through increased diuresis and natriuresis.