Final answer:
An agonist drug of the atrial natriuretic peptide receptor would be expected to lower blood pressure by acting as a vasodilator, increasing sodium and water excretion, and inhibiting systems that raise blood pressure like the renin-angiotensin-aldosterone system.
Step-by-step explanation:
An agonist drug of the atrial natriuretic peptide receptor (D) would be expected to lower blood pressure. The atrial natriuretic peptide (ANP) has several actions that contribute to the lowering of blood pressure. It acts as a vasodilator, which widens the blood vessels, thus reducing the resistance that the heart has to overcome to pump blood through the body. In addition, ANP enhances the excretion of sodium and water (diuretic effect) by the kidneys, which decreases the overall blood volume and thereby lowers blood pressure. ANP also inhibits the effects of other systems that tend to raise blood pressure, such as the renin-angiotensin-aldosterone system (RAAS), and the release of aldosterone and antidiuretic hormone (ADH).
The renin-angiotensin system has a significant role in the regulation of blood pressure and volume. Renin, secreted by the juxtaglomerular complex of the kidney, converts angiotensinogen to angiotensin I, which is then converted to the potent vasoconstrictor angiotensin II by the angiotensin-converting enzyme (ACE). Angiotensin II, in turn, stimulates the release of aldosterone from the adrenal cortex and ADH, leading to increased sodium reabsorption, water retention, and vasoconstriction - all of which raise blood pressure. Thus, agents that increase renin, angiotensin II, or aldosterone activity would generally be expected to raise blood pressure, not lower it.