Autacoids and Histamine Functions

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Questions and Answers

What is the primary adverse reaction associated with first-generation H1 antihistamines?

Fatigue

Dry mouth

Sedation (correct)

Blurred vision

Which of the following is NOT a common side effect of first-generation H1 antihistamines?

Dry nasal passage

Dry skin (correct)

Incoordination

Convulsions

What potential effects should be considered when administering antihistamines to pregnant women?

Only long-acting antihistamines have teratogenic effects

Some antihistamines may have teratogenic effects in animal studies (correct)

Sedative effects are beneficial for maternal anxiety

All antihistamines are safe during pregnancy

Which statement accurately reflects the differences between first and second-generation H1 antihistamines?

Second-generation drugs have a lower incidence of sedation compared to first-generation drugs. Signup and view all the answers

What symptom indicates acute poisoning with H1 antagonists that shows similarity to atropine poisoning?

Fixed, dilated pupils Signup and view all the answers

Which of the following statements about prostaglandins is true?

They primarily act as local hormones in the tissues where they are formed. Signup and view all the answers

What is the primary reason histamine concentrations are high in certain tissues?

The presence of large numbers of mast cells. Signup and view all the answers

Which receptors does histamine primarily interact with to exert its effects?

H1, H2, H3, and H4 receptors. Signup and view all the answers

What is a common complication associated with abortion procedures using prostaglandins?

Retained tissue. Signup and view all the answers

What is the role of histamine in allergic responses?

It binds to receptors to enhance allergic symptoms. Signup and view all the answers

What is an important use of misoprostol in medical treatments?

Management of NSAID-induced peptic ulcers. Signup and view all the answers

What characterizes the formation of autacoids?

Formed by tissues on which they act. Signup and view all the answers

Which of the following is NOT a type of histamine receptor?

D4 receptor. Signup and view all the answers

What is the primary role of H1 receptors in the body?

Mediating smooth muscle contraction and increasing capillary permeability Signup and view all the answers

What mechanism does histamine use to promote vasodilation?

Stimulating cGMP production in vascular smooth muscle Signup and view all the answers

Which receptor is primarily responsible for mediating gastric acid secretion?

H2 receptor Signup and view all the answers

What is a consequence of rapidly released histamine into the bloodstream?

Full-blown anaphylactic reactions Signup and view all the answers

What immediate symptoms can occur following intravenous injection of histamine?

Burning and itching sensations Signup and view all the answers

What is the role of H2 receptors regarding cyclic adenosine monophosphate (cAMP)?

Enhancing the production of cAMP Signup and view all the answers

Which phenomenon is referred to as the triple response when histamine is injected intradermally?

Redness, swelling, and itching Signup and view all the answers

What happens to blood pressure immediately after histamine is injected?

It falls initially before recovery Signup and view all the answers

What effect do H1 antihistamines have concerning inflammation?

They down-regulate transcription factors for proinflammatory cytokines Signup and view all the answers

What can occur if the release of histamine is too slow?

Local allergic reactions due to effective inactivation Signup and view all the answers

Which statement best explains the ineffectiveness of H1-receptor blockers in treating bronchial asthma?

H1-receptor blockers exclusively block histamine, neglecting other mediators. Signup and view all the answers

What is the main reason first-generation antihistamines are used with caution as somnifacients?

They tend to have strong sedative properties. Signup and view all the answers

Which option indicates the preferred route of administration for optimizing bioavailability of antihistamines?

Oral administration for well absorption. Signup and view all the answers

Which of the following pharmacokinetic characteristics is true for H1-receptor blockers?

Onset of action generally occurs within 1 to 3 hours after ingestion. Signup and view all the answers

Which of the following is NOT a commonly used ophthalmic antihistamine?

Cetirizine Signup and view all the answers

What is a primary therapeutic use for dimenhydrinate and related H1-receptor blockers?

Prevention of motion sickness and nausea. Signup and view all the answers

Which of the following describes the metabolism of cetirizine accurately?

It is excreted largely unchanged in urine. Signup and view all the answers

Which H1-receptor blocker has been noted for having the strongest anti-cholinergic activity?

Promethazine Signup and view all the answers

Which of the following statements about tolerance to H1 antihistamines is accurate?

No tolerance to the action of H1 antihistamines has been observed. Signup and view all the answers

What is the key reason for using antihistamines prophylactically before allergen exposure?

They have a much longer action duration when taken beforehand. Signup and view all the answers

What does the 'flare' around the injection site primarily result from?

Histamine-induced stimulation of axon reflexes Signup and view all the answers

Which of the following best describes the 'wheal' observed at the injection site?

A slow swelling visible after 12 minutes Signup and view all the answers

How do classic H1-receptor blockers function in relation to histamine?

They block the receptor-mediated response to histamine Signup and view all the answers

In terms of side effects, which statement about first-generation H1 antagonists is true?

They can lead to both central stimulation and depression. Signup and view all the answers

What additional effect does Cyproheptadine have aside from being an H1 antagonist?

It functions as a serotonin antagonist. Signup and view all the answers

What is the primary therapeutic use of H1-receptor blockers?

Treating allergies related to mast cell degranulation Signup and view all the answers

What characterizes the initial reaction to histamine at the injection site?

A few millimeters localized red spot Signup and view all the answers

How does central excitation typically manifest in patients overdosed on H1 antagonists?

As episodes of convulsions, especially in infants Signup and view all the answers

Which mechanism does cromolyn employ that distinguishes it from H1-receptor blockers?

It inhibits histamine release from mast cells. Signup and view all the answers

What is the main factor that causes the redness at the injection site?

Direct vasodilation mediated by histamine Signup and view all the answers

Study Notes

Autacoids

Autacoids are locally acting hormones produced by tissues, not endocrine glands
Prostaglandins are unsaturated fatty acids that act on tissues where they are synthesized
Misoprostol is a prostaglandin E1 analogue used in abortions and peptic ulcers
Histamine is a chemical messenger involved in allergic and inflammatory reactions, gastric acid secretion, and neurotransmission
High histamine concentrations are found in tissues with many mast cells, such as skin, lungs, and gut

Histamine Receptors

Histamine exerts its effects by binding to H1, H2, H3, and H4 receptors
H1 receptors mediate smooth muscle contraction, increased vascular permeability and vasodilation
H2 receptors are involved in gastric acid secretion
H3 and H4 receptors are found in a limited number of cells and their roles in drug action are not fully understood

Histamine - Actions and Reactions

Histamine release in response to various stimuli leads to a range of effects
Symptoms of histamine injection resemble those of anaphylaxis, including smooth muscle contraction, increased secretions, and vasodilation
The triple response of Lewis describes the characteristic reaction to intradermal histamine injection: reddening, flare, and wheal

H1 Receptor Antagonists

H1 receptor antagonists block the receptor-mediated response to histamine but do not affect its formation or release
First-generation H1 antagonists can cause central nervous system stimulation or depression
Some antihistamines have diverse effects, such as appetite stimulant, anti-antiemetic, and sedative properties

Antihistamine Uses

Antihistamines are effective in treating allergic rhinitis and urticaria
Antihistamines are not the primary treatment for asthma because histamine is only one of many mediators
Ophthalmic antihistamines are used for allergic conjunctivitis
Antihistamines such as diphenhydramine and dimenhydrinate are used to treat motion sickness and nausea
Some first-generation antihistamines are used for insomnia due to their sedative effects
Promethazine has local anesthetic properties

Pharmacokinetics

Antihistamines are well absorbed after oral administration with peak serum levels reached 2-3 hours after dosing
First-generation antihistamines have a high bioavailability and are distributed in all tissues, including the central nervous system
Antihistamines are metabolized by the hepatic cytochrome P450 system
The duration of action is typically 24 hours, allowing for once-daily dosing
Tolerance to antihistamines has not been observed

Adverse Effects

First-generation antihistamines lack specificity and interact with various receptors (histamine, muscarinic cholinergic, adrenergic, and serotonin)
Sedation is the most common adverse effect of first-generation antihistamines, and can be exacerbated by alcohol and other CNS depressants
Second-generation antihistamines have less sedation and central nervous system effects due to poor CNS penetration
Anticholinergic effects of antihistamines can lead to dry mouth and blurred vision
Antihistamines can cross the placenta, caution is advised during pregnancy
In acute poisoning, antihistamines can cause a syndrome resembling atropine poisoning
Second-generation antihistamines are recommended for elderly patients, especially those with cognitive impairment due to the sedative effects of first-generation drugs
First-generation antihistamines are not recommended for children due to their sedative effects

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Description

Explore the roles of autacoids, particularly histamine, and their receptors in the body. This quiz covers the actions of histamine, its implications in allergies and gastric secretion, and the functions of various histamine receptors. Test your knowledge on these locally acting hormones and their significance.