Figure 4.

Contractile response of lateral saphenous veins (expressed as percentage of the maximal response induced by 1 × 10⁻⁴ M norepinephrine) to increasing concentrations of nitrobiphenyline oxalate (NBP), an α_2C-adrenergic receptor agonist in: (a) Experiment 1 on Days 0, 7, 14, and 28 (−logEC₅₀ = 4.91, 5.23, 5.19, and 4.99, respectively) after steers were removed from a tall fescue pasture and placed on a non-toxic diet (day × NBP concentration interaction was not significant (p = 0.41)); and (b) Experiment 2 on Days 0, 21, 42, and 63 (−logEC₅₀ = 4.87, 5.05, 4.95, and 5.17, respectively) after steers were removed from a tall fescue pasture and placed on a non-toxic diet (day × NBP concentration interaction was significant (p = 0.017)). Comparison of contractile responses of lateral saphenous veins biopsied from steers that had grazed toxic tall fescue (red lines) and non-toxic bermudagrass (black lines) pastures at (c) 0 and (d) 63 days after removal from pasture in Experiment 2.