Question

3) You are trying to characterize a receptor which you think is present in both the muscle and the liver.

a) Which type of dose-response curve would be better to use: agonist or antagonist with a constant concentration of agonist?

b) Why?

Answer 1

a->the dose response curve of antagonist with a constant concentration of agonist would be better to use.

b->

Example-->>Insulin receptors (comprising 2 α and 2 β subunits) are present on the surface of target cells such as liver,
muscle and fat. Insulin binding results in tyrosine autophosphorylation of the β subunit. This then phosphorylates
other substrates so that a signalling cascade is initiated and biological responses ensue. Downstream effects of
stimulation of the insulin receptor include both immediate/short-term actions (for example translocation of the
glucose transporter GLUT4 to the surface of target cell) and longer-term actions (for example increased expression
of glucokinase and reduced expression of gluconeogenic and ketogenic enzymes in the liver).

By definition, antagonists display no efficacy to activate the receptors they bind. Antagonists do not maintain
the ability to activate a receptor. Once bound, however, antagonists inhibit the function of agonists, inverse agonists,
and partial agonists. In functional antagonist assays, a dose-response curve measures the effect of the ability of a range
of concentrations of antagonists to reverse the activity of an agonist. The potency of an antagonist is usually defined by
its half maximal inhibitory concentration (i.e., IC50 value). This can be calculated for a given antagonist by determining
the concentration of antagonist needed to elicit half inhibition of the maximum biological response of an agonist.
Elucidating an IC50 value is useful for comparing the potency of drugs with similar efficacies, however the dose-response curves
produced by both drug antagonists must be similar. The lower the IC50 the greater the potency of the antagonist, and the lower the
concentration of drug that is required to inhibit the maximum biological response. Lower concentrations of drugs may be associated
with fewer side-effects.