**Question:** All of the following are effects of thiopental, except:

A. Reduction in heart rate
B. Increase in blood pressure
C. Depressed breathing
D. Altered mental status

**Core Concept:** Thiopental is a barbiturate drug used as an anesthetic agent. It exerts its effects primarily through the inhibition of the central nervous system and the modulation of neurotransmitters, particularly gamma-aminobutyric acid (GABA) and glutamate. This leads to sedation, analgesia, and amnesia, while also affecting cardiovascular and respiratory functions.

**Why the Correct Answer is Right:**

Option A, "Reduction in heart rate", is incorrect because thiopental primarily inhibits the GABAergic system in the central nervous system. This inhibition does not directly impact the autonomic nervous system, which controls heart rate. As a result, heart rate might not be significantly affected.

Option B, "Increase in blood pressure": Similar to heart rate, thiopental does not primarily affect the cardiovascular system. While it can cause a transient decrease in blood pressure in some cases, it is not a consistent or notable effect compared to its other actions.

Option C, "Depressed breathing": Thiopental can cause respiratory depression, especially when administered in high doses or in combination with other anesthetics. This effect is related to its interaction with the GABAergic system, which plays a role in respiratory control.

Option D, "Altered mental status": Thiopental is known to cause sedation and anterograde amnesia, both of which are consistent with its effects on the GABAergic system.

**Why Each Wrong Option is Incorrect:**

A. Reduction in heart rate: As explained above, thiopental primarily affects the CNS, not the autonomic nervous system responsible for heart rate regulation.
B. Increase in blood pressure: Similar to heart rate, thiopental's impact on blood pressure is not consistent or significant compared to its other actions.
C. Depressed breathing: Thiopental's respiratory depression is related to its effects on the GABAergic system and its contribution to respiratory control.
D. Altered mental status: Thiopental's sedation and anterograde amnesia are consistent with its effects on the GABAergic system.

**Clinical Pearl:**

Thiopental's primary mode of action is through its interaction with the gamma-aminobutyric acid (GABA) receptor. This receptor is crucial for modulating the CNS and is involved in processes like sedation, anterograde amnesia, respiratory depression, and cardiovascular effects. While thiopental can cause respiratory depression and anterograde amnesia, its effects on heart rate and blood pressure are not significant compared to these actions.