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Questions and Answers
What is a characteristic of autacoids?
What is a characteristic of autacoids?
Which class of autacoids includes histamine and serotonin?
Which class of autacoids includes histamine and serotonin?
What role does histamine play in the body?
What role does histamine play in the body?
Where is histamine synthesized in the body?
Where is histamine synthesized in the body?
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Which of the following is NOT a lipid-derived autacoids?
Which of the following is NOT a lipid-derived autacoids?
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Which of the following statements about serum serotonin distribution and function is correct?
Which of the following statements about serum serotonin distribution and function is correct?
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What is the primary therapeutic use of Metoclopramide?
What is the primary therapeutic use of Metoclopramide?
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Which of the following is a potential adverse effect of Cisapride?
Which of the following is a potential adverse effect of Cisapride?
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Cyproheptadine is primarily used for which of the following conditions in cats?
Cyproheptadine is primarily used for which of the following conditions in cats?
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What role does serotonin play in the gastrointestinal tract?
What role does serotonin play in the gastrointestinal tract?
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What effect does histamine have on blood pressure?
What effect does histamine have on blood pressure?
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Which type of histamine receptor is associated with increased gastric secretion?
Which type of histamine receptor is associated with increased gastric secretion?
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Which of the following statements about H1 antihistamines is correct?
Which of the following statements about H1 antihistamines is correct?
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Which mechanism results in the release of histamine from mast cells?
Which mechanism results in the release of histamine from mast cells?
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What is a primary therapeutic use of first-generation H1-antihistamines?
What is a primary therapeutic use of first-generation H1-antihistamines?
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What is a physiological effect associated with H1 receptor activation?
What is a physiological effect associated with H1 receptor activation?
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Which adverse effect is associated with first-generation H1-antihistamines?
Which adverse effect is associated with first-generation H1-antihistamines?
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Which of the following drugs is classified as a first generation H1 antihistamine?
Which of the following drugs is classified as a first generation H1 antihistamine?
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What is the mechanism of action for H2-antihistamines like cimetidine?
What is the mechanism of action for H2-antihistamines like cimetidine?
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What is the role of histamine in allergic reactions?
What is the role of histamine in allergic reactions?
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Which of the following is an adverse effect of H2-antihistamines?
Which of the following is an adverse effect of H2-antihistamines?
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What is the effect of H2 receptor activation on the body?
What is the effect of H2 receptor activation on the body?
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Which medication is effective in treating allergic conjunctivitis?
Which medication is effective in treating allergic conjunctivitis?
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What side effect might result from the antimuscarinic effects of first-generation H1-antihistamines?
What side effect might result from the antimuscarinic effects of first-generation H1-antihistamines?
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What role do sympathomimetic drugs play in relation to histamine?
What role do sympathomimetic drugs play in relation to histamine?
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Which patient condition is NOT treated with H1-antihistamines?
Which patient condition is NOT treated with H1-antihistamines?
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What is the primary role of phospholipase A2 in the synthesis of eicosanoids?
What is the primary role of phospholipase A2 in the synthesis of eicosanoids?
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Which pharmacologic effect is primarily associated with thromboxane A2 (TXA2)?
Which pharmacologic effect is primarily associated with thromboxane A2 (TXA2)?
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Which of the following is a therapeutic use of PGE and PGF2α analogs?
Which of the following is a therapeutic use of PGE and PGF2α analogs?
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Which of the following is NOT a pharmacologic effect of leukotrienes?
Which of the following is NOT a pharmacologic effect of leukotrienes?
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What is the primary function of prostacyclin (PGI2)?
What is the primary function of prostacyclin (PGI2)?
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Which compound is a leukotriene receptor antagonist used in asthma treatment?
Which compound is a leukotriene receptor antagonist used in asthma treatment?
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What is the consequence of administering PGF2α drugs?
What is the consequence of administering PGF2α drugs?
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Which of the following statements is true regarding prostaglandin E2 (PGE2)?
Which of the following statements is true regarding prostaglandin E2 (PGE2)?
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Study Notes
Autacoids
- Autacoids are biological factors that act locally near their site of synthesis and release.
- They have a brief duration of action and participate in physiological or pathophysiological processes.
- Classes of autacoids include biogenic amines, polypeptides, and lipid-derived autacoids (eicosanoids).
Classes of Autacoids
-
Biogenic amines:
- Histamine
- Serotonin (5-hydroxytryptamine, 5-HT)
-
Polypeptides:
- Angiotensin
-
Lipid-derived autacoids (eicosanoids):
- Eicosanoids
- Prostaglandins
- Leukotrienes
- Thromboxane
General Physiologic Function
- Modulate blood flow in specific tissues
- Modulate secretory processes (e.g., gastric acid secretion)
- Modulate smooth muscle function (e.g., vascular and bronchial)
- Play a key role in allergy, inflammation, pain, and certain types of drug reactions (e.g., anaphylaxis).
Histamine
- Biosynthesis: Synthesized from dietary histidine by histidine decarboxylase.
-
Distribution and storage sites:
- Mast cells and basophils: stored in vesicles
- Stomach mucosa: causes gastric acid secretion
- Lungs and skin: release causes allergic responses
- CNS: acts as a neurotransmitter
- Many venoms and insect stings contain histamine
Physiologic and Pathologic Roles of Histamine
- Stimulates gastric acid secretion
- Involved in allergic reactions and anaphylactic shock
- Increases capillary permeability associated with inflammation
- Decreases blood pressure because it relaxes arterioles
- Causes bronchial occlusion and increased mucus secretion associated with asthma
- Causes pain and itching by activating sensory nerves
Histamine Release
- Immune (allergy): binding of antigenic substances to IgE on mast cells or basophils causes degranulation and release of histamine associated with hypersensitivity reactions
- Drugs and chemicals: morphine, tubocurarine, codeine, penicillin
- Physical injury: heat, cold, trauma
- Plant and animal stings
Histamine Receptors
-
H1 Receptor:
- Signal: Gq protein, phospholipase C
- Response: contraction of GI muscle, bronchoconstriction, dilation of arterioles and capillaries, increased heart rate, increased vascular permeability
-
H2 Receptor:
- Signal: Gs protein, adenyl cyclase
- Response: gastric secretions, salivary secretion, lacrimation
Histamine Antagonists
- Receptor antagonist
- Release inhibitors
- Physiologic antagonists
H1 Antihistamines
-
First Generation: Diphenhydramine, Dimenhydrinate, Hydroxyzine, Meclizine, Promethazine, Cyproheptadine.
- Unionized at physiological pH, easily cross the blood-brain barrier (BBB), therefore produce CNS side effects (sedation)
-
Second Generation: Loratadine, Cetirizine, Fexofenadine.
- Ionized at physiological pH, difficult to cross BBB, therefore less CNS side effects.
Pharmacologic effects of H1-antihistamines
- Relaxation of contracted bronchiolar smooth muscle
- Relaxation of contracted intestinal smooth muscle
- Inhibition of histamine-induced vasodilation and capillary permeability
- Inhibition of itch sensation
- Sedation (first-generation H1-antihistamines)
- Antimuscarinic effects
- Anti motion sickness (antiemetic) effects
Therapeutic uses of H1-antihistamines
- Treatment of allergic conditions (urticaria, pruritus, allergic reactions, anaphylaxis)
- Prevention of motion sickness
- Sedation induction
Adverse effects of H1-antihistamines
- CNS depression (lethargy, somnolence, ataxia)
- Antimuscarinic effects (dry mouth, urinary retention, intestinal atony)
H2-antihistamines (Cimetidine and Ranitidine)
- Pharmacologic effects: competitively inhibits histamine (H2-receptors) in parietal cells, decreasing gastric acid production
-
Therapeutic uses:
- Ulcer treatment
- Erosive gastritis
- Gastroesophageal reflux
- Adverse effects: uncommon when used as recommended
- Drug interactions: inhibits hepatic cytochrome P450 enzymes, prolonging the concentration of drugs metabolized by the liver.
Inhibitors of histamine release
- Cromolyn sodium: inhibits histamine release from mast cells
- Therapeutic uses:
- Recurrent airway obstruction and heaves in horses
- Control allergic conjunctivitis (eye drop)
- Physiologic antagonists to histamine:
- Sympathomimetic drugs (Epinephrine, Phenylephrine, Ephedrine)
Serotonin (5-hydroxytryptamine, 5-HT)
- Biosynthesis: From tryptophan via tryptophan hydroxylase and L-aromatic acid decarboxylase.
-
Distribution and function:
- GI tract (enterochromaffin cells): regulates motility
- Platelets: stores 5-HT and upon activation causes vasoconstriction and platelet aggregation.
- CNS: acts as a neurotransmitter
Serotonin-receptor modifying drugs
- GI prokinetic agents: increase GI motility by increasing Ach release.
-
Cisapride: agonist of 5-HT4 receptor which increases Ach release.
- Therapeutic uses: gastric/intestinal stasis, reflex esophagitis, constipation
- Adverse effects: diarrhea, abdominal pain
-
Metoclopramide: D2-receptor antagonist and 5-HT3 agonist.
- Therapeutic uses: vomiting disorders (antiemetic), reflux esophagitis, gastric stasis or hypomotility
- Adverse effects: restlessness, drowsiness, depression
Cyproheptadine
- 5-HT2 antagonist and H1-antihistamine
- Therapeutic uses: appetite stimulant in cats, treatment of feline asthma and pruritus in cats, managing hives in horses
- Adverse effects: sedation, anticholinergic activity, lethargy.
Eicosanoids
- Derived from membrane phospholipids via phospholipase A2 and arachidonic acid.
- Pathways include cyclooxygenase (prostaglandins, thromboxanes) and lipoxygenase (leukotrienes).
Leukotrienes (LTs)
- Synthesized by lipoxygenase in various cells.
- Pharmacologic effects: potent vasoconstrictors, potent bronchoconstrictors, increase capillary permeability, increased mucous secretion.
- LT antagonists (Montelukast) : used in asthma treatment.
Polypeptides (Angiotensin)
- Mechanism: A series of reactions starting from renin converting angiotensinogen to angiotensin I, then to angiotensin II in the lungs, which causes the body to retain water and salt, leading to vasoconstriction, increasing blood pressure.
-
Antagonists of the renin-angiotensin system: ACE inhibitors, Beta1-adrenergic antagonists, Angiotensin I (AT1) receptor antagonists, Renin receptor inhibitors.
- These drugs counteract the effect of the system, reducing blood pressure or blocking sodium absorption.
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Description
Explore the fascinating world of autacoids, which are local biological factors pivotal in various physiological processes. This quiz covers their classes, including biogenic amines, polypeptides, and lipid-derived autacoids, along with their general functions like modulating blood flow and secretory processes.
