Receptor Agonists and Selectivity
An agonist activates a receptor-linked response in an experimental system. Selectivity is a comparison. To interpret “selective agonist”, find out which ligand was tested, which alternative targets or responses were examined, and under what conditions. [1]
Four terms answer different questions
| Term | Question |
|---|---|
| Affinity | How does the ligand bind in the measured system? |
| Efficacy | What response can it produce in that system? |
| Potency | What concentration produces the specified response? |
| Selectivity | How does the result compare across the stated targets or responses? |
Affinity describes binding. Efficacy concerns the capacity to produce a response, while potency concerns the amount or concentration needed for a defined response. An EC50 is the concentration giving half the agonist’s maximum response in that assay. Results from two assays can differ because the cells or readouts differ. See the IUPHAR pharmacology glossary for the quantitative terminology. [1]
Read “selective” with its comparison attached
Raun and colleagues examined ipamorelin in rat pituitary cells and in animal experiments. In swine they compared growth hormone release with other hormone measurements. Under the tested conditions, ACTH and cortisol after ipamorelin did not differ significantly from the GHRH comparator. Two other secretagogues increased those hormones in the study. [2]
The comparison supports a statement about those measured hormone responses in swine. It leaves other targets, other species, effects in humans and the properties of a co-formulated vial open. Those questions need their own evidence.
Extract the minimum study context
For each result, record the exact ligand, receptor or biomarker, species, cell or tissue system, readout and comparator. Keep the maximum response beside a potency estimate when it is available. Two concentration values alone can hide different maximal effects.
Suppose a fictional experiment measures a response at receptor A but never tests receptor B. Its result establishes activity at A under that protocol. A claim of selectivity over B needs an appropriate measurement at B under comparable conditions.
Keep identity and function connected
Use the compound index to resolve molecular names and the research catalogue for the actual presentations. The CJC-1295 and Ipamorelin blend contains two named components. ARA-290 10 mg and KPV 10 mg are separate records. Choose evidence for the exact construct or terminal form named in the experiment.
The melanocortin receptor family gives a subtype example. The CJC-1295 and ipamorelin comparison and compound identifier guide address the identity questions that come before applying a functional result to a listing.
Explore the related evidence
| Resource | Why open it |
|---|---|
| Receptor-Targeted Research Peptides | Browse receptor-related materials with variant limits visible. |
| ARA-290 (Cibinetide) | Reconcile the ARA-290/cibinetide construct and aliases. |
| Half-Life Modification: DAC, Acylation and Conjugation | Distinguish molecular modification from a storage-life claim. |
| Guides & Resources | Choose another scientific, analytical or procurement guide. |
Sources and scope
- IUPHAR Pharmacology Education Project: Receptors IUPHAR teaching resource on agonists, antagonists, partial agonists and the relationship between occupancy and response.
- Raun et al. (1998). Ipamorelin selectivity experiments. European Journal of Endocrinology. The ipamorelin study used pituitary and animal experiments. The ACTH and cortisol comparison comes from the swine portion.