Inhibitory effects of dithiothreitol and sodium bisulfite on isolated rat ileum and atrium

The utility of sodium bisulfite and dithiothreitol as reducing agents in $\text{in}$$\text{vitro}$ preparations such as isolated rat atrium and ileum has been investigated. The right atria and 3 cm long ileal segments from male Sprague Dawley rats (250–350 g, sacrificed by cervical dislocation) were suspended in a 10 ml Magnus bath containing Tyrode's solution maintained at 37°C. Sodium bisulfite (0.955 - 9.55 mM) and dithiothreitol (5–50 μM) significantly depressed (P < .05) the duration of spontaneous atrial beating and the magnitude of methacholine-induced ileal contractions. The ileal inhibitory effects of these antioxidants became more pronounced with successive concentration-responses in the presence of methacholine but not with duration of exposure in the absence of methacholine, suggesting depletion of cellular energy stores by the antioxidants with successive ileal contractions. Depression of heart and intestinal tissues by bisulfite and dithiothreitol severelylimits their use as antioxidants to protect readily air oxidizable drugs during pharmacological testing with these standard tissue preparations.