**Question:** Nitroglycerin caused all except which of the following effects?

**Core Concept:** Nitroglycerin is a potent vasodilator drug used to relieve chest pain (angina pectoris) and to lower blood pressure. It works by activating soluble guanylate cyclase in smooth muscle cells, leading to increased production of cyclic guanosine monophosphate (cGMP) and relaxation of blood vessels.

**Why the Correct Answer is Right:** Nitroglycerin has numerous effects due to its vasodilatory action, but the question asks for the effects it does not have. Some of its key effects include:

1. **Increased cardiac output:** Nitroglycerin dilates blood vessels, particularly systemic and coronary arteries, which increases blood flow to the heart and lowers preload and afterload. This leads to increased cardiac output.

2. **Lowering blood pressure:** Nitroglycerin acts on the smooth muscle cells of the arterial walls, causing vasodilation and reducing systemic vascular resistance. This results in a decrease in blood pressure.

3. **Relaxation of smooth muscle:** Nitroglycerin causes relaxation of smooth muscles in various organs, including the gastrointestinal tract, bladder, and uterus. This explains its use in overactive bladder symptoms and menopausal symptoms.

4. **Increased heart rate:** Although nitroglycerin increases cardiac output, it does not directly affect heart rate. Therefore, it is not mentioned in the question's correct answer.

5. **Cardiac contractility:** Nitroglycerin does not directly affect cardiac contractility. It increases cardiac output by increasing heart rate, but not by directly stimulating the heart muscle.

**Why Each Wrong Option is Incorrect:** Let's discuss the incorrect options:

1. **Increased heart rate:** As mentioned earlier, nitroglycerin primarily increases cardiac output by vasodilation and lowering blood pressure. It does not directly stimulate the heart muscle, so this is incorrect.

2. **Cardiac contractility:** Similar to option 1, nitroglycerin does not directly affect cardiac contractility. Its primary mechanism is vasodilation and blood pressure reduction, leading to increased cardiac output.

3. **Cardiac output:** Although nitroglycerin improves cardiac output, it does not directly affect cardiac output itself. It increases cardiac output by dilating blood vessels and lowering blood pressure.

4. **Vasoconstriction:** Nitroglycerin is a vasodilator, not a vasoconstrictor. It dilates blood vessels, resulting in vasodilation.

5. **Increased cardiac contractility:** As mentioned before, nitroglycerin does not directly affect cardiac contractility. Its primary mechanism is vasodilation, leading to increased cardiac output.

6. **Increased heart rate and cardiac contractility:** Nitroglycerin primarily improves cardiac output by dilating blood vessels and lowering blood pressure. It does not directly stimulate the heart muscle or increase heart rate or contractility.

7. **Vasoconstriction:** As mentioned earlier, nitroglycerin works as a vasodil