Dose - Response Curves Flashcards
Agonist Def
Substance that interacts with receptors. drug-receptor complex stimulates response
Endogonist Def
Naturally occurring agonists eg neurotransmitters
Exogonists Def
Synthetic agonist eg medication
Relationship between agonist conc, receptors filled and degree of response
High conc = more receptors filled = stronger response
Dose-response x and y axis
x = agonist conc and y = magnitude of response (graded curve) or %Emax (quantum)
Why are simmodial (log) graphs used
Can see point at which maximum response is reached (whether it is and which did 1st). Can see 50% Emax
Full Agonist Def
Agonist that elicits maximum response (achieve 100% Emax)
Partial Agonist Def
Agonist that doesn’t elicit maximum response (doesn’t achieve 100% Emax)
Why can partial agonists can’t elicit full response
No of receptors on tissue may be too low, receptors may have low affinity (specificity), intrinsic efficacy
EC50/ED50
Conc of drug at 50% efficacy. The lower the value = the greater the affinity receptors have for drugs = greater potency = further left on graph
Kd
Conc of drug at 50% receptors being filled
Relationship between efficacy and max response
Higher efficacy = higher response
Spare Receptor Hypothesis
Some substances reach 100 % Emax without filling all of the relevant receptors on the tissue. Any receptors left unoccupied when 100% Emax is reached are considered spare. Hormone concentration in relation to % Emax doesn’t change in response to increased binding after this point
Antagonists
Substances that reduce receptor response to another substance. Have no independent function. 2 types competitive and non-competitive
Competitive Antagonist Def
Binds to receptors binding site preventing agonist bonding. 2 Types: reversible (as agonist conc increases and antagonists dissociate inhibition stop) and irreversible (as agonist conc increases, antagonists don’t dissacociate, inhibition continues)
Reversible Competitive antagonists Mode of Action
Increase Kd= increase EC50 = lower receptor affinity for agonist (due to antagonists occupying) = graph shifting to the right. Graft shifts back and forth depending on agonist to antagonist levels
Irreversible Competitive Antagonists Mode of Action
Decrease in maximum response (further away from 100% Emax) = available receptors being permanently taken away. As more antagonist is added graph shifts down and doesn’t shift back up again (no left/right shifting)
Non- Competitive Antagonists Def
Effects agonist action by disrupting signalling chain that results from agonist binding (eg ion channels opening)
Non-Competitive Antagonists Mode of Action
Maximum response decreases as more is added. Graft shifts down
