Podcast
Questions and Answers
What is an advantage of second generation H1 blockers compared to first generation?
What is an advantage of second generation H1 blockers compared to first generation?
Which of the following is NOT a therapeutic use of second generation H1 blockers?
Which of the following is NOT a therapeutic use of second generation H1 blockers?
Which pharmacological effect is associated with H2 receptor antagonists?
Which pharmacological effect is associated with H2 receptor antagonists?
What side effect is often related to the use of cimetidine?
What side effect is often related to the use of cimetidine?
Signup and view all the answers
What is a common therapeutic use of H2 receptor antagonists?
What is a common therapeutic use of H2 receptor antagonists?
Signup and view all the answers
Which of the following statements about second-generation H1 blockers is true?
Which of the following statements about second-generation H1 blockers is true?
Signup and view all the answers
Which scenario would most likely require caution with first generation antihistamines?
Which scenario would most likely require caution with first generation antihistamines?
Signup and view all the answers
What are the CNS side effects associated with cimetidine?
What are the CNS side effects associated with cimetidine?
Signup and view all the answers
What is the primary action of H1 receptors in response to histamine binding?
What is the primary action of H1 receptors in response to histamine binding?
Signup and view all the answers
Which of the following best describes the physiological antagonism of histamine?
Which of the following best describes the physiological antagonism of histamine?
Signup and view all the answers
What occurs during a local histamine reaction?
What occurs during a local histamine reaction?
Signup and view all the answers
What is a disadvantage of first-generation H1 receptor antagonists?
What is a disadvantage of first-generation H1 receptor antagonists?
Signup and view all the answers
What characterizes the reaction when histamine is released too quickly?
What characterizes the reaction when histamine is released too quickly?
Signup and view all the answers
Which receptor is primarily responsible for increasing gastric acid secretion in response to histamine?
Which receptor is primarily responsible for increasing gastric acid secretion in response to histamine?
Signup and view all the answers
What effect does H3 receptor activation have?
What effect does H3 receptor activation have?
Signup and view all the answers
What is the main mechanism through which immunotherapy acts against histamine responses?
What is the main mechanism through which immunotherapy acts against histamine responses?
Signup and view all the answers
Which type of signaling involves a cell communicating with itself?
Which type of signaling involves a cell communicating with itself?
Signup and view all the answers
What is the primary function of hormones in the body?
What is the primary function of hormones in the body?
Signup and view all the answers
Where is histamine primarily stored after its synthesis?
Where is histamine primarily stored after its synthesis?
Signup and view all the answers
Which of the following is true about local hormones, or autacoids?
Which of the following is true about local hormones, or autacoids?
Signup and view all the answers
What triggers the release of histamine immunologically?
What triggers the release of histamine immunologically?
Signup and view all the answers
Which of the following best describes eicosanoids?
Which of the following best describes eicosanoids?
Signup and view all the answers
Which type of signaling is characterized by communicating with neighboring cells via small channels?
Which type of signaling is characterized by communicating with neighboring cells via small channels?
Signup and view all the answers
What effect does the enzyme amine oxidase have on histamine?
What effect does the enzyme amine oxidase have on histamine?
Signup and view all the answers
Study Notes
Autacoids (Hormones Like Substances)
- Autacoids are hormones-like substances
- They are organic regulatory substances
- Produced in one part of an organism, and transported throughout the organism (e.g. via blood/lymph)
- Stimulate specific cells/tissues and initiate actions
- Local hormones (Autocoids): Act locally at site of synthesis/release
- Paracrine
- Autocrine
Forms of Chemical Signaling
- Autocrine: A cell signals itself; a ligand binds to a receptor on its own surface
- Paracrine: Cells communicate with each other over a short distance
- Endocrine: Signals are created by specialized cells and released into the bloodstream; transported to distant target cells
- Cell-cell contact signaling: Gap junctions (animals) and plasmodesmata (plants) connect neighboring cells directly through tiny channels
Paracrine Example & Synaptic Signaling
- Paracrine Example: A cell targets a cell close by (nearby cell)
- Synaptic Signaling: A specialized form of paracrine signaling, where a neurotransmitter is released into a synapse and binds to a receptor on a receiving cell
Hormones
- Circulating Hormones: Reach the bloodstream
- Local Hormones (Autocoids): Act locally first (paracrine and autocrine)
Autacoids
- Autacoids are local hormones.
- They do not circulate throughout the body.
- They act locally at the site of synthesis and release.
- They have many diverse pharmacological and physiological activities.
- They typically have a short duration of action.
- Auto = self, acos (relief or remedy)
Classification of Autacoids
- Amine-derived: Histamine (derived from amino acid histidine), Serotonin
- Peptide-derived: Angiotensin, Bradykinin
- Lipid-derived: Eicosanoids
Histamine
- A chemical messenger that mediates wide range of cellular responses.
- Allergic and inflammatory reactions
- Gastric acid secretion
- Neurotransmission at parts of the brain
Histamine Locations
- Found in all types of tissues
- High concentrations in basophils and mast cells
- Component of venom and insect bites
- High concentrations in lungs, skin, and gastrointestinal tract (GIT)
Histamine Synthesis
- Histamine is stored in granules after synthesis.
- If not stored, it is rapidly inactivated by the enzyme amine oxidase.
- Produced from the amino acid histidine
Foods That Contain Histamine
- Displayed as images (no text)
Histamine Release
- Immunologically: Released from cells in response to an antibody called immunoglobulin E (IgE); secreted in response to invaders (virus, bacteria) or allergens (e.g. pollen)
- Chemically: Like morphine
- Destruction of cells: Result of cold, toxins, venom, or trauma
Histamine Mechanism of Action
- Released in response to stimuli
- Binds to various histamine receptors (H1, H2, H3, H4)
- H1 and H2 are targets for clinically useful drugs
Mechanism of Action of Histamine
- Details on effects related to H1, H2, H3, and H4 receptors (e.g., smooth muscle contraction, increased gastric acid secretion, decreased histamine release, immunomodulator, etc.)
Histamine Mechanism (additional details)
- In the stomach, converts histidine to Histamine, which stimulates the production of HCl acid
- In the brain, acts as a neurotransmitter, regulating sleep, hormonal secretion, memory formation, and brain arousal
- In the immune system, acts as a vasodilator in response to allergies/immune system responses
Actions mediated by H1 and H2 receptors
- H1 receptors: Effects on exocrine excretion, bronchial smooth muscle, intestinal smooth muscle, sensory nerve endings, skin.
- H2 receptors: Effects on stomach (stimulation of gastric acid secretion), skin, cardiovascular system
Histamine Reactions
- Local Reaction:
- Histamine release is slow enough for it to be inactivated before it enters bloodstream
- Causes dilation and increased permeability of capillaries, leading to protein and fluid leakage in the skin
- Results in Lewis' Triple Response (red spot/line, redness around the line, wheal formation/edema)
- Anaphylactic Shock:
- Rapid histamine release cannot be inactivated
- Complete anaphylactic reaction occurs
Antihistamine
- Shown diagrammatically; antihistamine binds to receptors, inhibiting histamine effects
Histamine Antagonists
-
Physiological antagonism:
- Adrenaline
-
Pharmacological antagonism:
- H1 and H2 receptor antagonists (e.g. Nedocromil, Cromolyn, Sodium and Ketotifen)
- Immunotherapy: Inhibits antibody/antigen reaction
Histamine Receptor Blocking Agents
- First-Generation: Brompheniramine, Chlorpheniramine, Cyclizine, etc. Potential for sedation
- Second-generation: Cetirizine, Desloratadine, Fexofenadine, etc. Less sedating
- Diagram and tables provided, showing relative drowsiness potential of different drugs
- Claritine provided as example
H1 Receptor Antagonists
-
First generation:
- Effective and inexpensive
- Disadvantages: Crosses blood-brain barrier, causes sedation, interactions with other receptors (serotonin) contributing to side effects
- Short duration of action
-
Second generation:
- Specific H1 blockers, less sedation
- Longer duration of action, making daily dosing easier
- Efficacy is maximized if taken before exposure to allergen
Therapeutic Uses of Histamine Antagonists
- Allergies and inflammation: Treats symptoms like pink eye, urticaria, allergic rhinitis.
- Motion sickness and morning sickness: Effective for nausea associated with motion sickness and pregnancy.
- Sleep induction: First generation less effective because of sedation
Side Effects of Histamine Antagonists
- Sedation: Reduced with 2nd generation drugs
- Atropine-like effects: Reduced with 2nd generation drugs (e.g., dry mouth, urinary retention, blurred vision, tachycardia)
H2 Receptor Antagonists
- Competitive antagonists of histamine; fully reversible
- No effect on H1 receptors
- Mechanism: block histamine binding to H2 receptors, reduces intracellular cAMP concentrations, decreases gastric acid secretion
Mechanism of Gastric Acid Secretion
- Illustrative diagram of the steps involved, focusing on the roles of acetylcholine, histamine, prostaglandin E₂, G proteins, and protein kinase
H2 Receptor Antagonists (Therapeutic Uses)
- Used in the treatment of peptic ulcer
- Specific drugs for this use are Cimetidine, Ranitidine, Famotidine, and Nizatidine
H2 Receptor Antagonist (Therapeutic Uses) expanded
- Gastric and duodenal ulcers
- Gastroesophageal reflux disease (GERD)
- Prevent the occurrence of stress ulcers
- Prevent peptic ulcer recurrence
- Reduce acidic gastric contents aspiration during anesthesia
Side Effects related to Cimetidine
-
Antiandrogenic effects: Prolonged use at high doses can decrease androgen binding to receptors, inhibit estradiol hydroxylation, and affect estrogen metabolism
- Possible side effects for men and women
- CNS adverse effects: Dizziness, headaches, and confusion
- Drug interactions: Due to enzyme-inhibiting activity
- Hepatitis and elevated serum creatinine
Case Study
- A healthy 45-year-old physician experiences dizziness, skin redness, tachycardia, and orthostatic hypotension after eating a meal.
- Another physician at the table experiences similar symptoms.
- The menu included green salad, sautéed fish, rice, and apple pie.
- Probable diagnosis: scombroid poisoning (due to a fish containing high histamine levels after being improperly preserved). Treatment involves using histamine blockers
Answer (to the Case Study questions)
- Typical symptoms caused by histamine from improperly preserved fish.
- Maximum doses of histamine blockers (especially H1 blockers) are sufficient to control the symptoms.
- Epinephrine is unnecessary unless severe cases of hypotension or airway obstruction are apparent
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
