Figure 1.
A: The combination of ephedrine (20 mg/kg) and ambrisentan (0.1 mg/kg), but not the single compounds, significantly increase the time run to fatigue of rats under simulated high altitude (Log rank test p = 0.0024 after correction for multiple comparison). Lower concentrations of ephedrine (2 mg/kg) were not ergogenic, neither alone nor if combined with ambrisentan (not shown). N = 28–31 per treatment group. B: Methylphenidate (10 mg/kg) combined with ambrisentan, but not the single compounds, enhanced time run to fatigue under simulated high altitude (Log Rank test p = 0.044 after correction for multiple comparison). Lower dose methylphenidate (4 mg/kg) did not have ergogenic effects, alone or in combination with ambrisentan (not shown). N = 14–15 per treatment group. N = 10–11 per treatment group. All drugs were injected IP.
Figure 2.
Hemodynamic effects of high-dose ephedrine in anesthetized rats.
“Pre-injection” were averaged data −5 to 0 minutes pre injection, “post injection” was averaged −5 to 0 minutes before onset of hypoxia, and “hypoxia” was averaged 30–40 minutes post injection. A: Changes in heart rates, normalized to the time of injection. The addition of ephedrine at 20 mg/kg IP significantly increased heart rates, alone and combined with ambrisentan. Heart rates remained significantly elevated under hypoxia in ephedrine treated groups (one-way ANOVA/Bonferroni, p<0.01, N = 7–13). B: Changes in blood perfusion velocity in hind leg muscle after treatment, measured directly on the muscle, using a laser Doppler probe. Both ephedrine and the combination significantly enhanced muscle blood flow under hypoxia (N = 6–9). The onset of hypoxia triggered a distinct increase in muscle flow in all groups containing ephedrine, and to a lesser degree in control treated animals (example laser Doppler tracings from rat leg muscle; EA = ephedrine and ambrisentan; C = combination; first arrow: injection, second: hypoxia). C: Repeated injection of combined ephedrine (20 mg/kg) and ambrisentan (0.1 mg/kg) significantly enhances heart rates, and concomitantly, pulmonary blood flow, measured by pulmonary window blood flow measurements, and pulse oximetry (paired T-test, corrected for multiple comparison, p<0.05, N = 5). D: injection of ephedrine, alone or in combination with ambrisentan, caused a significant increase of breathing rates (one-sided ANOVA with Bonferroni correction, p<0.001, N = 5–13/group). Hypoxia further increased breathing rates in all groups (repeated measures ANOVA/Bonferroni, p<0.001). E: Changes in blood oxygenation after treatment: HbO2 decreased significantly in all treatment groups after onset of inspired hypoxia (repeated measure ANOVA/Bonferroni, p<0.001), but there was no difference in this parameter between treatment groups (one-way ANOVA/Bonferroni, N = 5–9).
Figure 3.
Blood pressure effects of ephedrine treatment.
“Pre-injection” were averaged data −5 to 0 minutes pre injection, “post injection” was averaged −5 to 0 minutes before onset of hypoxia, and “hypoxia” was averaged 30–40 minutes post injection. A, B: Treatment with high dose ephedrine (20 mg/kg), alone and combination with ambrisentan, significantly increased MAP and PAP, under normoxia and hypoxia, compared to baseline (repeated measures ANOVA with Bonferroni correction, p<0.05), and compared to the other treatment groups (one-way ANOVA/Bonferroni, p<0.001). Onset of hypoxia significantly decreased MAP in these groups (repeated measures ANOVA with Bonferroni correction, p<0.05). In the control group, PAP increased significantly after onset of hypoxia (N = 7–14). C: Experimental schedule to measure the influence of treatment on oxygen concentration in the hind muscle. Tissue hypoxia was measured by pO2 needle electrode tracings during inspired normoxia (1) and hypoxia at baseline (2), before (3) and after injection under normoxia (4), and during post-injection hypoxia (5). D: under post-treatment normoxia (panel D time point #4), ephedrine alone and in combination with ambrisentan significantly increased muscle oxygenation, compared to pre-treatment pO2 (one-way ANOVA with Bonferroni correction, N = 4–8, p<0.05). E: Under post-treatment hypoxia (panel D #5), only the combination of high ephedrine and ambrisentan significantly increased muscle oxygen tension. Re-oxygenation after combo treatment was significantly higher than in all other treatment groups (one-way ANOVA/Bonferroni, N = 4–8, p<0.05 * or 0.01**). F: Low dose ephedrine (2 mg/kg) significantly increases blood flow in the hind leg muscle when combined with ambrisentan, but not alone.
Table 1.
Averaged tissue pO2 values in mmHg (means ± SD), acquired with Oxylite probes.