Figure 3.

Plasma norepinephrine concentrations (pg/ml) at baseline, 60 minutes after study drug administration, and at the end of the study session after sildenafil (open circles) and placebo (filled squares) administration. After sildenafil administration, plasma norepinephrine significantly increased compared with baseline and placebo and was significantly different from placebo at 60 minutes (P = 0.03) and at the end of the study session (P = 0.001) (P = 0.02 group × time interaction). Plasma norepinephrine did not significantly increase from baseline following placebo (P = 0.12). Abbreviation: ANOVA, analysis of variance.