Synthesis and Metabolism of Histamine

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Questions and Answers

What effect does histamine have on nerve endings related to the flare component of the triple response?

It enhances the action of histamine on nerve endings.

It increases the sensitivity of nerve endings.

It has no effect on the nerve endings.

It suppresses the action of histamine on nerve endings. (correct)

Which of the following functions does neuronal histamine NOT perform in the CNS?

Stimulate wakefulness

Promote cognition

Regulate blood pressure (correct)

Suppress appetite

What is a notable inhibitory effect of neuronal histamine in the central nervous system?

Enhances nociception

Promotes locomotion

Increases energy metabolism

Suppresses convulsions (correct)

Which receptors are primarily responsible for gastric acid secretion?

H2 receptors Signup and view all the answers

What is the effect of antimuscarinic properties of H1 antagonists?

They contribute to lessened secretion in certain glands. Signup and view all the answers

What is the main reaction that leads to the formation of histamine?

Decarboxylation of L-Histidine Signup and view all the answers

Which enzyme is responsible for catalyzing the formation of histamine?

L-Histidine decarboxylase Signup and view all the answers

What happens to histamine after its formation, in terms of metabolic processes?

It is stored or rapidly inactivated Signup and view all the answers

What are some of the components released during the exocytosis triggered by histamine?

Serotonin, enzymes, and cytokines among others Signup and view all the answers

Which physiological effect is caused by the granulation of mast cells due to histamine release?

Inflammatory response Signup and view all the answers

Which drug is preferred for motion sickness?

Piperidine Signup and view all the answers

What is a notable side effect of Diphenhydramine?

Weight gain Signup and view all the answers

Which of the following drugs has both antihistamine and anti-serotonin activity?

Cyproheptadine Signup and view all the answers

What class of drugs does Cyproheptadine belong to?

Antihistamines Signup and view all the answers

Which statement about Diphenhydramine is incorrect?

It is primarily used as an appetite suppressant. Signup and view all the answers

What role do H3 auto-receptors play in histamine regulation?

They inhibit histamine release. Signup and view all the answers

Which receptor type is responsible for modulating the release of other neurotransmitters?

H3 heteroreceptors Signup and view all the answers

What effect does histamine have on systemic blood pressure?

It lowers systemic blood pressure. Signup and view all the answers

What is a potential application of H4 receptor antagonists?

To alleviate allergic reactions. Signup and view all the answers

What is observed at the injection site within 1-2 minutes after histamine administration?

Swelling or edema. Signup and view all the answers

Which characteristic does NOT describe H4 receptors?

Inhibition of other receptor types. Signup and view all the answers

What is a consequence of histamine's effect on blood vessels?

Vasodilation leading to decreased vascular resistance. Signup and view all the answers

Which statement about histamine is FALSE?

It has no direct effect on neurotransmitter release. Signup and view all the answers

What is one purpose of corticosteroids in asthma therapy?

Suppress inflammatory chain production Signup and view all the answers

How are corticosteroids primarily absorbed when delivered via inhalation?

From airway and alveolar surfaces Signup and view all the answers

What happens to a portion of an inhaled corticosteroid dose?

It reaches the systemic circulation Signup and view all the answers

What role do corticosteroids have at the cellular level in asthma?

They affect both inflammatory and structural cells Signup and view all the answers

What is a consequence of the resolution of respiratory edema in asthma related to corticosteroid use?

Decreased inflammation in the airways Signup and view all the answers

What occurs when a fraction of an inhaled steroid is deposited in the oropharynx?

It leads to decreased systemic effects Signup and view all the answers

What type of action do corticosteroids have in asthma treatment?

Anti-inflammatory action Signup and view all the answers

What is a potential effect of corticosteroid absorption in the systemic circulation?

Widespread immune suppression Signup and view all the answers

Study Notes

Synthesis of Histamine

Histamine is synthesized via the decarboxylation of L-Histidine, catalyzed by the enzyme L-Histidine decarboxylase in mammalian tissues.
Post-formation, histamine can be stored or rapidly metabolized, with minimal excretion in unchanged form.

Function and Mechanism of Action

Histamine plays a pivotal role in acid secretion by gastric parietal cells.
H3 receptors act as auto-receptors on histaminergic neurons, inhibiting histamine release, while hetero-receptors on non-histaminergic neurons modulate neurotransmitter release.
H4 receptors have unique localization and their antagonists are potential candidates for therapeutic applications.

Pharmacological Effects

Histamine causes systemic blood pressure (SBP) depression, contributing to decreased contractility and altered cardiac electrical events.
Histamine-induced reactions include capillary permeability increase leading to edema formation, observable as swelling at injection sites shortly after administration.

Anti-Allergy Medications

1st generation H1 receptor antagonists, such as Diphenhydramine and Cyproheptadine, suppress histamine effects, including the itch response and flare component in allergic reactions.
Antimuscarinic properties of some H1 antagonists may help reduce gastric acid secretion, though they do not directly impact it.
Cyproheptadine is noted for appetite stimulation and has both antihistaminic and anti-serotonin activity, with weight gain as a notable side effect.

CNS Involvement

Neuronal histamine has both stimulatory and inhibitory roles: promoting wakefulness, cognition, and locomotion while suppressing appetite and convulsions.
Mast cell stabilizers exhibit anti-inflammatory effects, contributing to overall respiratory health.

Corticosteroids in Asthma

Corticosteroids exhibit anti-inflammatory action at the cellular level, targeting both inflammatory and structural cells in bronchial airways.
For inhalational corticosteroids, absorption occurs through airway and alveolar surfaces, with a portion reaching systemic circulation.
Inhaled corticosteroids deposited in the oropharynx may undergo gut absorption when swallowed.

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Description

This quiz focuses on the synthesis, storage, and metabolism of histamine, a crucial biogenic amine in the body. Questions will cover the formation processes, including decarboxylation of L-Histidine, as well as the exocytosis of secretory granules. Assess your understanding of histamine's biochemical roles and functions.