Table 2. Binding Affinity and Contractile Activity of URP and Related Analogs.
| Binding Affinity | Aortic
ring contraction |
||
|---|---|---|---|
| Peptide | pIC50 | pEC50 | Emaxa |
| URP | 8.29 ± 0.08 | 8.16 ± 0.08 | 107 ± 3 |
| [D-Phe(pI)4]URP | 8.61 ± 0.11 | 7.54 ± 0.10* | 114 ± 5 |
| [D-Bip4]URP | 8.50 ± 0.11 | 7.32 ± 0.13** | 97 ± 7 |
| [D-Pep4]URP | 7.92 ± 0.12 | 7.55 ± 0.15* | 99 ± 8** |
| [Trip4]URP | 6.87 ± 0.10*** | 8.11 ± 0.38 | 9 ± 1*** |
| [Tyr(OBn)4]URP | 8.10 ± 0.12 | <5.5 | 80%b |
| [Phe(pThio-3)4]URP | 7.44 ± 0.11*** | <5.5 | 20%b |
| [Phe(pPy-3)4]URP | 6.99 ± 0.11*** | <5.5 | 24%b |
| [Phe(pPy-4)4]URP | 6.81 ± 0.15*** | <5.5 | 5%b |
a
The maximum efficacy is defined as a percentage of the KCl-induced contraction (40 mM) divided by the hUII-induced tissue-response (10–6 M).
b
Maximum efficacy at 3 × 10–6 M. All values are expressed as mean ± SEM. Statistical analysis, using URP values as controls, were performed using unpaired Student’s t test, *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001. Experiments were conducted at least 3 times and on tissues from different animals or on different cellular passages.