Question

The effect of amphetamine on blood pressure will be blunted if an animal has first been treated with a. reserpine b. terbutaline c. trimethaphan d. physostigmine e. botulinum toxin

Short answer

Answer: a. Reserpine

Step-by-step solution

Understand each substance's mechanism of action

Before answering the question, let's briefly explain the mechanism of action of each substance: a. Reserpine: It is an antihypertensive drug that depletes the levels of norepinephrine (and other monoamines) in the nerve terminals. b. Terbutaline: A Beta-2 adrenergic agonist primarily used for bronchodilation in asthma, it has minimal effects on alpha-adrenergic receptors and therefore limited effects on blood pressure. c. Trimethaphan: A ganglionic blocker that inhibits the transmission between sympathetic and parasympathetic nervous system to decrease blood pressure. d. Physostigmine: A cholinesterase inhibitor that increases acetylcholine levels at synaptic clefts with potential bradycardic effects. e. Botulinum toxin: A potent neurotoxin that blocks acetylcholine release, causing muscle paralysis and is not related to blood pressure regulation.

Understand the effect of amphetamine on blood pressure

Amphetamines increase blood pressure by inducing the release of norepinephrine in the nerve endings and promoting alpha-adrenergic receptor stimulation, resulting in vasoconstriction and an increase in blood pressure.

Identify the substance that blunts the effect of amphetamine on blood pressure

Considering the mechanism of action of each substance, we can identify that reserpine (option a) is the most likely substance to blunt the effect of amphetamine on blood pressure. This is because reserpine depletes the levels of norepinephrine in the nerve terminals, which is essential for increased blood pressure induced by amphetamines. With low levels of norepinephrine, the amphetamine will not be able to exert its effect on blood pressure significantly. So, the correct answer is: a. Reserpine

Key concepts

Amphetamine effects

Amphetamines are a class of stimulant drugs. They work by increasing the concentration of certain chemicals in the brain, primarily norepinephrine and dopamine. This heightened activity can lead to an increased sense of energy, alertness, and focus. However, it also results in raised blood pressure and heart rate.

• Amphetamines promote the release of stored neurotransmitters, amplifying their effects.
• They stimulate adrenergic receptors, particularly alpha-adrenergic receptors, causing vasoconstriction.
• This vasoconstriction contributes to the increase in blood pressure.

The effect of amphetamines, especially on the cardiovascular system, can be intense and may lead to adverse effects if not carefully managed. However, understanding these mechanisms allows for more informed decisions when using amphetamines therapeutically.

Blood pressure regulation

Blood pressure is a vital sign that reflects the force exerted by circulating blood upon the walls of blood vessels. It is regulated by various physiological mechanisms in the body to maintain steady levels despite differing demands or conditions.

• The autonomic nervous system plays a crucial role, influencing heart rate and vascular tone.
• Neurotransmitters like norepinephrine modulate the constriction and dilation of blood vessels.
• Hormonal systems, including the renin-angiotensin-aldosterone system, also contribute to long-term regulation.

Factors such as stress, activity level, and pharmaceuticals can induce shifts in blood pressure. For instance, amphetamines raise blood pressure by enhancing norepinephrine release, thus requiring adjustments with medications like reserpine to counterbalance this effect.

Neurotransmitter depletion

Neurotransmitter depletion occurs when the availability of neurotransmitters in the brain and nervous system diminishes. This can happen naturally or as a result of medical treatments.

• Reserpine is known to deplete neurotransmitters, notably norepinephrine, by inhibiting their storage in nerve terminals.
• This results in decreased availability for release, thereby reducing their physiological effects.
• The depletion of norepinephrine, for instance, can blunt the stimulant effects of drugs like amphetamines.

This mechanism is beneficial in conditions such as hypertension, where limiting norepinephrine can help control elevated blood pressure. However, it also necessitates caution, as severe depletion could lead to depression or other side effects.