PharmacodynamicsStudy of the biochemical andphysiological effects of drugs on theBodyMicroorganismsParasites within or on the body andMechanisms of drug action and therelationship between drugconcentration and effect
Continued… “Action of Drugs on the Body” Abbreviated as PDEffects on the Body (when drugs acts on body)??? Stimulating action Depressing action Blocking action Exchanging action Direct beneficial chemical reaction Direct harmful chemical reaction
Continued…Desired Effect Cellular membrane disruption Chemical reaction with downstream effects Interaction with enzyme proteins Interaction with structural proteins Interaction with carrier proteins Interaction with ion channels Ligand binding to receptors
Continued…Undesirable effects Increased probability of cell mutation(carcinogenic activity) Interaction (additive, multiplicative, ormetabolic) Induced physiological damage, or abnormalchronic conditions
Receptor Receptor is a molecule found on the surface of acell, which receives specific chemical signals fromneighbouring cells or the wider environmentwithin an organism.
Ligands Is a substance that forms a complex with abiomolecule to serve a biological purpose. “Signaltriggering molecules”
Major Receptor Families Ligand-gated ion channels G protein- coupled receptors Enzyme-linked receptors Intracellular receptors Spare receptors Desensitization of receptors
Ligand-gated ion channels(LGICs)Are one type of ionotropic receptor or channel-linkedreceptor. They are a group of transmembrane ionchannels that are opened or closed in response tothe binding of a chemical messenger (i.e., aligand),such as a neurotransmitter.An ionotropic receptor, when activated, directlyaffects the activity of a cell by directly opening ionchannels.
Continued…Metabotropic receptor influences theactivity of a cell indirectly by firstinitiating a metabolic change in the cell.This metabolic change may ultimatelyaffect the opening or closing of an ionchannel or may alter some other activityof the cell such as protein transcription.
G protein-coupled ReceptorsG protein-coupled receptors (GPCRs),also known as : seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors (GPLR)
Continued… Comprise a large protein family oftransmembrane receptors that sense moleculesoutside the cell and activate inside signaltransduction pathways and, ultimately, cellularresponses
Classes of GPCRs Class A (or 1) (Rhodopsin-like) Class B (or 2) (Secretin receptor family) Class C (or 3) (Metabotropic glutamate/pheromone) Class D (or 4) (Fungal mating pheromone receptors) Class E (or 5) (Cyclic AMP receptors) Class F (or 6) (Frizzled/Smoothened)
Second Messengers Second messengers are molecules that relaysignals from receptors on the cell surface totarget molecules inside the cell, in the cytoplasmor nucleus. They relay the signals of hormones likeepinephrine (adrenalin), growth factors, andothers, and cause some kind of change in theactivity of the cell.
Types of Second MessengerHydrophobic molecules: water-insolublemolecules, like: diacylglycerol,andphosphatidylinositols,are membrane-associated anddiffuse from the plasma membrane intothe intermembrane space where theycan reach and regulate membrane-associated effector proteins
Continued…Gases:nitric oxide (NO)carbon monoxide (CO) andhydrogen sulphide (H2S) (whichcan diffuse both through cytosoland across cellular membranes.)
Properties of SecondMessengers They can be synthesized/released and brokendown again in specific reactions by enzymes orion channels. Some (like Ca2+) can be stored in specialorganelles and quickly released when needed. Their production/release and destruction can belocalized, enabling the cell to limit space and timeof signal activity.
Enzyme-linked Receptors An enzyme-linked receptor is a transmembranereceptor, where the binding of an extracellularligand causes enzymatic activity on theintracellular side. They have two important domains: Extra-cellular ligand binding domain Intracellular domainThe signaling molecule binds to the receptoroutside of the cell and causes aconformational change on the Catalyticfunction located on the receptor inside of thecell
Examples of Enzymatic Action Receptor tyrosine kinase, as in fibroblastgrowth factor receptor. Most enzyme-linkedreceptors are of this type Serine/threonine-specific protein kinase, as inbone morphogenetic protein Guanylate cyclase, as in atrial natriureticfactor receptor
Intracellular Receptors Intracellular receptors are receptors locatedinside the cell rather than on its cell membrane. Examples are the class of nuclear receptorslocated in the cell nucleus and the IP3 receptorlocated on the endoplasmic reticulum. The ligands that bind to them are usuallyintracellular second messengers like (IP3) andextracellular lipophilic hormones like steroidhormones.
Intracellular Receptors : TypesSteroid hormone receptor:Sex hormone receptors (sexhormones) Estrogen receptor (α and β) Androgen receptor (one type)Vitamin D receptor (vitamin D, onetype)Glucocorticoid receptor(glucocorticoids, one type)Mineralocorticoid receptor(mineralocorticoids, one type)
Continued… Thyroid hormone receptor (α and β) Retinoic acid receptor (vitamin A and relatedcompounds); Peroxisome proliferator-activated receptors(PPARs, α, γ and δ) Retinoid X receptor Farnesoid X receptor Liver X receptor Constitutive androstane receptor
Spare Receptors Term used to describe the situation in whichmaximum tissue response occurs when not all thereceptors of the tissue are occupied by the drug
Desensitization of Receptors The rapid signal attenuation in response tothe stimulation of cell by agonists or anantagonists. Or, decrease in response due to overadministration of durgs Adptation Refractoriness Down regulationIt is of 2 types….