Pharmacology: H1 and H2 Receptor Blockers Quiz

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Questions and Answers

What is the primary therapeutic use of H2 receptor blockers?

Increase gastric acid secretion

Inhibitors of gastric acid secretion (correct)

Enhance blood clotting

Stimulate serotonin production

From which amino acid is serotonin synthesized?

Tyrosine

Phenylalanine

L-arginine

L-tryptophan (correct)

Where is the majority of the human body's serotonin found?

Central nervous system

Gastrointestinal tract (correct)

Liver

Blood platelets

What mechanism terminates the activity of serotonin in the body?

Uptake into neurons and platelets Signup and view all the answers

Which of the following functions is NOT attributed to serotonin?

Inducing vasodilation Signup and view all the answers

What is the primary mechanism of action of H1 blockers?

They block the receptor-mediated response at the H1 receptor. Signup and view all the answers

Which of the following is NOT a characteristic of second-generation H1 antagonists?

They penetrate the blood-brain barrier. Signup and view all the answers

What is a potential adverse effect of first-generation H1 antagonists due to their ability to penetrate the CNS?

Sedation Signup and view all the answers

Which symptom is commonly associated with anaphylaxis?

Hypotension Signup and view all the answers

Why are H1 blockers considered more effective when administered before histamine release?

They block receptor-mediated responses before symptoms can develop. Signup and view all the answers

What type of patient may be more sensitive to the side effects of first-generation H1 antagonists?

Elderly patients Signup and view all the answers

What happens when large amounts of histamine are released into the systemic circulation during anaphylaxis?

It causes a rapid decrease in blood pressure. Signup and view all the answers

Which of the following describes a symptom that may progress during an anaphylactic reaction?

Angioedema Signup and view all the answers

What is the primary function of autacoids in the body?

To act as local hormones at the site of synthesis Signup and view all the answers

Which of the following substances is classified as a biogenic amine?

Histamine Signup and view all the answers

What is the primary site where histamine is stored in the body?

Mast cells and basophils Signup and view all the answers

Which statement about autacoids is true?

They can have paracrine and autocrine effects. Signup and view all the answers

Which of the following is responsible for the synthesis of histamine?

L-histidine decarboxylase Signup and view all the answers

Which autacoid plays a significant role in modulating gastric acid secretion?

Histamine Signup and view all the answers

What type of drugs can interfere with autacoids' actions?

Autacoid synthesis inhibitors and antagonists Signup and view all the answers

Which autacoid is primarily associated with modulating blood flow and inflammation?

Nitric Oxide Signup and view all the answers

What is the role of 5-HT2A receptors in the central nervous system?

They induce hallucination. Signup and view all the answers

Which drug is classified as a 5-HT1D/1B agonist and is used to treat migraine headaches?

Sumatriptan Signup and view all the answers

What effect does Lorcaserin have related to appetite?

It promotes a sense of fullness. Signup and view all the answers

What is the primary effect of the peptide Bradykinin?

Vasodilation and pain transmission Signup and view all the answers

Which condition is primarily associated with the use of the drug Ambrisentan?

Pulmonary hypertension Signup and view all the answers

What is the main function of the 5-HT4 agonists such as Tegaserod?

They regulate intestinal motility. Signup and view all the answers

Which of the following best describes the peptide Angiotensin II?

A potent vasoconstrictor formed from Angiotensin I. Signup and view all the answers

What receptor does the drug Ondansetron primarily target to manage nausea?

5-HT3 Signup and view all the answers

What is the most common adverse reaction associated with second-generation histamine H1 antagonists?

Headache Signup and view all the answers

Which of the following adverse reactions are primarily associated with first-generation histamine H1 antagonists like diphenhydramine and promethazine?

Drowsiness Signup and view all the answers

Which therapeutic use is indicated for first-generation histamine H1 antagonists?

Control of allergic inflammation Signup and view all the answers

What action do first-generation H1 antagonists have that makes them useful for motion sickness and nausea?

Blockage of central H1 and M1 receptors Signup and view all the answers

Which statement is true regarding the sedative properties of first and second-generation H1 antihistamines?

First-generation antihistamines may cause sedation Signup and view all the answers

What is a contraindication for the use of first-generation H1 antihistamines in certain jobs?

Sedation effects Signup and view all the answers

Which of the following effects is NOT typically associated with the use of first-generation histamine H1 antagonists?

Increased cognitive performance Signup and view all the answers

Which of the following is an adverse reaction linked to the use of second-generation antihistamines?

Increased appetite Signup and view all the answers

What is the primary function of angiotensin II on the AT1 receptor?

Vasoconstriction Signup and view all the answers

Which of the following is a consequence of increased aldosterone synthesis?

Increased renal sodium absorption Signup and view all the answers

What role does nitric oxide play in the vascular system?

Acts as a potent vasodilator Signup and view all the answers

What is the primary function of guanylyl cyclase in relation to nitric oxide?

To convert GTP to cGMP Signup and view all the answers

Which isozyme of nitric oxide synthase is not typically expressed under basal conditions in most cells?

Inducible NOS (iNOS) Signup and view all the answers

What molecule is involved in the dephosphorylation of myosin light chain, contributing to smooth muscle relaxation?

cGMP Signup and view all the answers

Which components are involved in the signaling pathway affected by nitric oxide?

GTP and phosphatase Signup and view all the answers

What is one effect of norepinephrine on vascular smooth muscle?

Contraction of vascular smooth muscle Signup and view all the answers

Study Notes

Pharmacology-I Spring 2024 (PCL332/PO315/POC316) Lecture 5: Autocoids (Part 1)

Learning Outcomes:
- Identify pharmacological actions, side effects, and drug interactions of locally acting drugs (autacoids).
- Utilize basic science data to address therapeutic issues.
- Select appropriate pharmacotherapeutic approaches based on etiology, pathophysiology, and clinical features of diseases.
- Recognize pharmacological properties of different drugs.

Autocoids:
- Histamine
- Serotonin
- Angiotensin
- Bradykinin
- Endothelin
- Nitric oxide

What are Autocoids?

Definition: naturally occurring endogenous compounds that act as local hormones, produced in numerous tissues.
They differ from circulating hormones, as they are produced by tissues at the site of synthesis and action.
Paracrine Effect: secreted by one cell and acts on adjacent cells or surrounding extracellular matrix.
Autocrine Effect: secreted by a cell and acts on the same cell.

Classification of Autocoids

Biogenic Amines (Histamine & Serotonin)
Lipid-derived (Prostaglandins & Thromboxane)
Peptides (Angiotensin, Bradykinin, Endothelin)
Gases (Nitric Oxide)

Function of Autocoids

Modulate blood flow: Prostaglandins maintain renal blood flow
Modulate secretory processes: Histamine affects gastric acid secretion.
Key role in: allergy, inflammation, pain, and certain drug reactions.

1- Histamine

Synthesis: L-histidine amino acid is decarboxylated to histamine.
Location: Stored in mast cells and basophils (mostly in skin, respiratory tract, and blood vessels), and enterochromaffin-like (ECL) cells in the gastrointestinal tract.
Stimulation: Stimulates acid secretion in the stomach, and acts as a neurotransmitter in the brain.

Release of Histamine

Triggered by membrane-bound immunoglobulin E (IgE) interacting with an antigen, causing mast cell degranulation.

Histamine Release Triggers

Allergies
Toxins from organisms
Venoms (insects and spiders)
Trauma

Histamine Receptors and Effects

Histamine exerts its effect by binding to various histamine receptors (H1, H2, H3)
H1 receptors: activation of these receptors affect vascular smooth muscle, bronchial smooth muscle, intestinal smooth muscle, and mucocutaneous nerve endings. This causes effects from local constrictions to increases in blood vessel permeability, contributing to allergic response.
H2 receptors: activation primarily in the stomach, impacting gastric acid secretion
Interactions with different receptors influence conditions from respiratory issues to hypotension.

Role in allergy and anaphylaxis

Allergic inflammation: localized reaction impacting tissues involved in the response
Anaphylaxis: life-threatening, systemic hypersensitivity reaction often progressing to respiratory collapse.
Typical symptoms are related to histamine release and engagement of H1 receptors.

H1 Receptor Blockers

First Generation: examples are chlorpheniramine, diphenhydramine, etc. More lipid soluble; penetrate blood-brain-barrier; sedating; and short duration.
Second Generation: examples are cetirizine, fexofenadine, etc. Less lipid soluble; do not penetrate blood-brain-barrier; less sedating; and longer duration.

H1 Receptor Antagonists -- Adverse Reactions

First Generation: Possible CNS side effects such as sedation. Autonomic receptor-blocking effects (blurred vision, dry mouth, constipation, and urinary retention). Older adults are particularly sensitive to these side effects.
Second Generation: Most common adverse reaction is headache. Possible other side effects including drowsiness, dry mouth, and hypotension.

H2 Receptor Blockers

Examples include cimetidine, ranitidine, famotidine, and nizatidine.
Mechanism of Action: Block histamine (H2) receptors in parietal cells, suppressing gastric acid secretion.
Therapeutic Uses: Used in treating ulcers and heartburn.

2- Serotonin

Synthesis: Derives from L-tryptophan.
Location: Found predominantly within the gastrointestinal tract (enterochromaffin cells); plays a role in regulating intestinal motility and secretion and it is found in blood platelets.
Function: Affects mood, appetite, body temperature, sleep, and is involved in blood clotting following an injury.

2- Serotonin Receptors and Actions

The actions of serotonin (5-HT) are complex, influencing various bodily functions, such as mood, appetite, and body temperature.
Several distinct families of serotonin receptors are implicated in a wide spectrum of physiological functions.

3- Bradykinin

Origin: Derived from kininogen via enzymes like kallikreins.
Actions: Primarily involved in inflammation, edema, and pain transmission; bronchoconstriction, plays role in hereditary angioedema (HAE).
Receptor Roles: Acts through two types of receptors, (B1 and B2), affecting various biological functions.

4- Endothelin

Origin: Produced by endothelial cells within blood vessels.
Forms: Three distinct forms (ET-1, ET-2, and ET-3) present with subtle variations in their amino acid sequences.
Action: A major function is vasoconstriction, largely mediated by ETA receptors.

5- Nitric Oxide

Nature: gaseous signaling molecule acting by diffusing across cell membranes.
Role: Plays vital roles in physiological functions including cardiovascular, inflammatory, and neuronal processes.
Synthesis: Generated from L-arginine through the agency of nitric oxide synthase (NOS).

Differences in the Action of First and Second Generation H1 Blockers

First Generation:
- More lipid-soluble
- More likely to cross the blood-brain barrier
- Often more sedating
- Shorter duration of action
Second Generation:
- Less lipid-soluble
- Less likely to cross the blood-brain barrier
- Less sedating
- Longer duration of action

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Description

Test your knowledge on the pharmacological aspects of H1 and H2 receptor blockers. This quiz covers their mechanisms of action, therapeutic uses, and potential adverse effects, along with related concepts like anaphylaxis. Prepare to assess your understanding of serotonin and histamine in the body.