Related Experiment Video
Updated: Aug 10, 2026

Drug-induced Sensitization of Adenylyl Cyclase: Assay Streamlining and Miniaturization for Small Molecule and siRNA Screening Applications
Published on: January 27, 2014
Extraordinary potency of a novel delta opioid receptor agonist is due in part to increased efficacy
T H Kramer1, H Bartosz-Bechowski, P Davis
1Department of Anesthesia, The University of Pennsylvania School of Medicine, Philadelphia 19104-4283, USA.
Abstract:
A new cyclic opioid peptide of sequence Tyr-D-Pen-Gly-Phe-Cys-Phe (HBP2) was examined in the mouse isolated vas deferens (MVD) bioassay. Studies with receptor-selective opioid antagonists showed the peptide to be highly selective for delta opioid receptors. HBP2 and the standard delta agonist DPDPE were simultaneously compared using the technique of partial irreversible receptor blockade; data were analyzed using the operational model of pharmacologic agonism. HBP2 was approximately 160 times as potent as DPDPE; estimation of the affinity and efficacy of the two peptides revealed that the potency increase was due to a 5.3-fold increase in efficacy, as well as a 37-fold increase affinity. This contrasts with our previous findings with other cyclic enkephalin analogs, in which increased affinity was achieved without a change in apparent efficacy. Analysis of concentration-response curve shape suggested in addition the possibility of heterogeneity in transduction mechanisms for MVD delta receptors.
Related Concept Videos
Drug-Receptor Interactions
Several parameters, such as the drug's affinity for its receptor and its efficacy, which is its ability to activate the receptor, determine the drug's effect on the tissue.
Dose-Response Relationship: Potency and Efficacy
Drug-Receptor Interaction: Agonist
Agonists can bind to receptors in different ways. Some agonists bind directly to the receptor's active site, mimicking the endogenous ligand's action.
Opioid Receptors: Overview
Analgesia and Pain Management
Opioid Analgesics: Synthetic and Semisynthetic Opioids

