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Module 8 Notes.docx

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Pharmacology 2060A/B
Angela Nissen

Module 8 - two receptor theories to describe receptor interactions - SIMPLE OCCUPANCY THEORY o Intensity of response = number of receptors drug occupies o Max response = when all receptors are occupied o All full = saturated (response plateaued) o Two drugs at same receptor same effect NOT TRUE  Different efficacys! - MODIFIED OCCUPANY THEORY o Intensity of response = number of receptors drug occupies o Two drugs occupying same receptor can have different binding strengths (affinity) o Two drugs occupying same receptor can have different abilities to activate receptor (intrinsic activity) o Number plus affinity and ability! o AFFINITY  Attraction drug has for receptor  High affinity = highly attractive, likes to bind, bind even in low conc  Low affinity = weakly attractive, high conc drug tends not to bind well  Primary determinant of POTENCY!! High affinity = high potency and vice versa o INTRINSIC ACTIVITY  Ability of drug to activate receptor  High = intense receptor activation  Reflected in EFFICACY high activity = high max efficacy - After drug binds it can either activate receptor or block other ligands from binding - AGONIST: bind and activate, mimic action of endogenous ligands greater intrinsic activity (ability) ...increases activity o Endogenous also considered agonist o Have affinity and ability...bind and activate o Do not always increase physiological response...may decrease o Some agonists can bind to different receptors cause different effects  Ex. Dopamine  Low dose: dopamine receptor: renal artery vasodilation  Moderate: b1 adrenergic receptor: increase cardiac  High: a1 adrenergic receptor: renal artery vasoconstriction - ANTAGONIST: bind to not activate o HAVE AFFINITY but no intrinsic activity o Can have pharmacological effects o Generate effect by blocking other endogenous or agonist drugs  Effect dependent on presence of something that activates receptor o TREAT Over dose! o Antagonist can kick out agonist o Examples of Antagonists  Beta1 Blocker...block ephinephrine ...slow down heart Antihistamine: block binding of histamine to receptor symptom of allergies  Gastric acid reducers: block histamine 2 in gut..decrease acid secretion into stomach  Opioid receptors ...treat overdose! Block binding of opiates (morphine or heroin) o Types of Antagonists  Competitive : binding occurs at same site as agonist ...REVERSIBLE  Compete for binding, antagonist can be outcompeted if agonist is increased  Both given: HIGHEST AFFINITY = binding site...increasing conc
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