Efficacies (Emax values) and potencies (pEC50 or pKb values) of antiparkinson agents at recombinant hα2A-, hα2B-, and hα2C-adrenoceptors
| Ligand | hα2A | hα2B | hα2C | |||
|---|---|---|---|---|---|---|
| Emax | pEC50 orpK b | Emax | pEC50orpK b | Emax | pEC50or pK b | |
| Apomorphine | 16 ± 2 | 6.92 | 0 | 6.84 | 0 | 6.55 |
| Bromocriptine | 0 | 7.42 | 0 | 6.64 | 0 | 7.38 |
| Cabergoline | 0 | 7.46 | 0 | 6.30 | 0 | 6.79 |
| Lisuride | 0 | 9.53 | 0 | 9.03 | 0 | 8.97 |
| Pergolide | 31 ± 2 | 6.50 | 70 ± 10 | 6.46 | 16 ± 5 | 6.16 |
| Piribedil2-a | 0 | 6.50 | 0 | <5 | 0 | 6.87 |
| Pramipexole | 52 ± 5 | 5.45 | IA | IA | IA | IA |
| Quinelorane | 11 ± 3 | 4.97 | IA | IA | IA | IA |
| Quinpirole | IA | IA | 27 ± 6 | 5.86 | IA | IA |
| Ropinirole | IA | IA | IA | IA | IA | IA |
| Roxindole | 0 | IA | 0 | 7.80 | 0 | 8.13 |
| Talipexole | 51 ± 5 | 6.90 | 39 ± 2 | 6.70 | 46 ± 1 | 6.64 |
| Terguride | 0 | 9.66 | 0 | 8.95 | 0 | 9.07 |
| TL 99 | 108 ± 3 | 7.19 | 79 ± 9 | 6.91 | 81 ± 9 | 7.25 |
Efficacy (Emax) and potency (pEC50 orpKb) values were determined by [35S]GTPγS binding. pEC50 values for stimulation are indicated in normal case, and pKb values for inhibition are indicated in bold. Emax values are percentages of the stimulation observed with a maximally efficacious (Emax = 100%) concentration of noradrenaline (10 μM) and are expressed as means ± S.E.M. values of at least three independent determinations performed in triplicate. pEC50 or pKb values are means of at least three independent determinations: S.E.M. values (not shown) were less than 0.2 log units. The Bmax at hα2A-, hα2B-, and hα2C-ARs was 1.8, 1.0, and 1.3 pmol/mg, respectively. Noradrenaline exhibited pEC50values of 6.45, 6.50, and 6.52 at hα2A-, hα2B-, and hα2C-ARs, respectively. Apomorphine displayed apKb of 6.58 at hα2A-ARs, and pergolide displayed a pKb of 6.96at hα2C-ARs.
IA, inactive (no agonist or antagonist effect at a concentration of 10 μM).
↵2-a Piribedil data are from Millan et al., 2001.