TABLE 5.
Ki-values for inhibition of phosphodiesterase-5 (PDE5), phosphodiesterase-3 (PDE3), and inhibition of cAMP- and cGMP-efflux at temperatures ranging from 37°C to 20°C.
| Ki | PDE5-inhibition |
PDE3-inhibition |
cGMP-efflux |
cAMP-efflux |
||||
| Temperature | Sildenafil (μM) | Vardenafil (μM) | Sildenafil (μM) | Vardenafil (μM) | Sildenafil (μM) | Vardenafil (μM) | Sildenafil (μM) | Vardenafil (μM) |
| 37°C | 0.002 ± 0.000 | 0.002 ± 0.001 | 5.61 ± 0.865# | 0.757 ± 0.276# | 3.93 ± 1.46 | 2.97 ± 0.823 | 3.51 ± 1.05 | 3.55 ± 0.311 |
| 34°C | 0.004 ± 0.000 | 0.004 ± 0.001 | 4.21 ± 0.579# | 1.14 ± 0.263# | 2.08 ± 0.235# | 5.31 ± 0.431# | 3.59 ± 1.35 | 3.53 ± 0.415 |
| 32°C | 0.006 ± 0.001* | 0.004 ± 0.001 | 4.66 ± 0.647# | 1.85 ± 0.173# | 1.43 ± 0.497 | 3.67 ± 1.13 | 2.83 ± 0.828# | 7.86 ± 1.02# |
| 28°C | 0.004 ± 0.001 | 0.004 ± 0.001 | 4.38 ± 0.739# | 1.50 ± 0.505# | 1.68 ± 0.172 | 2.79 ± 0.504 | 1.66 ± 0.232 | 5.84 ± 3.51 |
| 24°C | 0.007 ± 0.001* | 0.006 ± 0.001 | 6.49 ± 2.05 | 2.54 ± 0.218 | 1.25 ± 0.245 | 2.12 ± 0.523 | − | − |
| 20°C | 0.009 ± 0.001*# | 0.006 ± 0.000# | 12.3 ± 0.675*# | 3.36 ± 1.21# | 1.56 ± 0.718 | 6.17 ± 2.71 | − | − |
Values are mean ± SEM and given in μM. *Significant difference (P-value < 0.05) when compared to normothermic control. #Significant difference (P-value < 0.05) when IC50 values of sildenafil and vardenafil are compared at same temperature. Neither of the drugs inhibited cAMP-efflux below 28°C.