Question

A man is given a drug that inhibits the synthesis of norepinephrine. Which response would result from this treatment? (A) diarrhea (B) bronchodilation (C) renin secretion (D) decreased heart rate (E) salivation

Short answer

The treatment would result in a decreased heart rate.

Step-by-step solution

Understand the Role of Norepinephrine

Norepinephrine is a neurotransmitter involved in the fight-or-flight response and affects various organs, including increasing heart rate, dilating bronchi, and constricting blood vessels.

Analyze the Effects of Inhibiting Norepinephrine Synthesis

If the synthesis of norepinephrine is inhibited, the effects of norepinephrine will be reduced. This means decreased sympathetic responses such as lower heart rate, constriction of bronchi, and decreased blood pressure.

Evaluate Each Option for Sympathetic vs Parasympathetic Response

- (A) Diarrhea: Typically a parasympathetic response. - (B) Bronchodilation: A sympathetic response reduced by norepinephrine inhibition. - (C) Renin secretion: Partly sympathetic, potentially affected. - (D) Decreased heart rate: A result of reduced sympathetic activity. - (E) Salivation: Usually a parasympathetic response.

Identify the Correct Response

Given the inhibition of a sympathetic neurotransmitter like norepinephrine, the most likely outcome is a decrease in actions typically promoted by the sympathetic system. The correct response to the inhibition of norepinephrine synthesis is a decreased heart rate (Option D).

Key concepts

Norepinephrine

Norepinephrine is an important neurotransmitter in the human body. It plays a crucial role, particularly in the sympathetic nervous system. As a chemical messenger, it is involved in preparing the body for "fight-or-flight" situations. This reaction helps us to react swiftly to threats. When functioning normally, norepinephrine increases heart rate and blood pressure. It also dilates air passages in the lungs, making breathing easier. Additionally, this neurotransmitter assists in breaking down fat to provide more energy for the body. While norepinephrine serves these essential functions, a disruption in its synthesis can significantly affect how the body manages stress and emergency responses. When norepinephrine production is inhibited, these physiological effects are reduced. This is because the signals that norepinephrine usually sends throughout the body diminish.

Sympathetic Nervous System

The sympathetic nervous system (SNS) is part of the autonomic nervous system. It is responsible for stimulating the body's rapid involuntary response to stressful situations. Comprising a series of neurons that run throughout the spinal cord, the SNS sends signals to various parts of the body. Its primary function is to prepare the body for intense physical activity, often termed as "fight-or-flight."

When the sympathetic nervous system is activated, a variety of physiological changes occur:

• Increased heart rate to pump more blood to muscles.
• Dilation of bronchial passages to enhance airflow.
• Inhibition of digestion to focus energy on muscle exertion.
• Increased sweating to cool the body during exertion.
• Mobilization of energy stores by promoting fat breakdown.

These responses are beneficial for short-term stress but can become problematic if they occur inappropriately or excessively.

Neurotransmitter Effects

Neurotransmitters are the body's chemical messengers. These special chemicals transmit signals across synapses from one neuron to another target neuron, muscle cell, or gland cell. Each neurotransmitter binds to specific receptors, triggering a response in the receiving cell.

Norepinephrine, as a neurotransmitter, has several important effects on the body that align with the actions of the sympathetic nervous system:

• It raises heart rate and blood pressure.
• Encourages the release of glucose from energy stores.
• Boosts blood flow to skeletal muscles.
• Promotes alertness and arousal.

When the synthesis of norepinephrine is inhibited, these stimulating effects diminish. For instance, a decrease in heart rate is often observed due to reduced activation of the heart's adrenergic receptors.

Drug Mechanisms

Understanding drug mechanisms involves exploring how drugs create their effects in the body. This process includes interactions with receptors, enzymes, and ions. A drug that affects neurotransmitter synthesis can significantly impact physiological processes. For norepinephrine, inhibiting its synthesis will lead to a reduction in sympathetic nervous system activity.

When a drug inhibits norepinephrine production, it leads to:

• Decreased heart rate, as the heart's adrenergic stimulants are reduced.
• Less bronchodilation, potentially affecting inhalation.
• Reduced blood pressure due to vasodilation.
• Possible effects on energy mobilization and muscle readiness.

Such changes illustrate why understanding drug mechanisms is vital in pharmacology, enabling healthcare professionals to predict and manage potential outcomes when using specific medications.