Figure 1.

Influence of the level of precontraction on the vascular response to l-NA. (A) Increase in tone induced by the application of 100 μM l-NA to vessels precontracted under isometric conditions with 0.1–1 μM PGF_2α to between 10% and 60% of the maximal 10 μM phenylephrine-induced tone. Data are presented as the mean ± SEM of nine separate experiments. ∗, P < 0.05; ∗∗, P < 0.01; both indicate a significant l-NA-induced increase in vascular tone. (B) Effect of l-NA (100 μmol/liter, hatched columns) on the tone of endothelium-intact rabbit aortic rings precontracted to ≈35% of the maximum phenylephrine-induced contraction (10 μM) (open bars) with either phenylephrine (PE, 30–100 nM), PGF_2α (0.1–1 μM), or indolactam (Indo, 0.1–1 μM). Data are presented as the mean ± SEM of 5–12 separate experiments. ∗, P < 0.05; ∗∗∗, P < 0.001 vs. in the absence of l-NA.