What could cause hypotension after the administration of nitroglycerin?

The administration of nitroglycerin leads to hypotension primarily due to its vasodilatory effects. Nitroglycerin is a nitrate that relaxes vascular smooth muscle, resulting in the dilation of both veins and arteries. This vasodilation decreases the systemic vascular resistance and allows for improved blood flow, but it also reduces the preload and afterload on the heart. As a consequence, when blood vessels dilate, there is a lower resistance against which the heart must pump, which can result in a significant drop in blood pressure.

While factors like heart rate or fluid status can also impact blood pressure, they do not directly relate to the mechanism of action of nitroglycerin. Increased heart rate may sometimes occur in response to blood pressure changes, and fluid overload or decreased blood volume affects blood pressure but are not specific responses to nitroglycerin. Hence, it is the direct vasodilatory action of nitroglycerin that primarily leads to hypotension following its administration.