Effect of N-butylscopolammonium bromide on equine ileal smooth muscle activity in an ex vivo model.

Abstract: N-butylscopolammonium bromide (NBB) is an anticholinergic agent used to treat spasmodic colic in horses. Intestinal smooth muscle spasm also occurs in horses with intraluminal intestinal obstructions, such as ileal impactions. The antispasmodic effects of NBB may be useful in managing ileal impactions, but the effects of NBB on equine ileal smooth muscle are unknown. Objective: To investigate the effects of NBB on spontaneous and induced contraction of the equine ileum in an ex vivo model. Methods: Ex vivo biomechanical study assessing contractile properties in isolate equine ileal smooth muscle with and without exposure to NBB. Methods: Ileal tissue was collected from 6 healthy horses after euthanasia, and isolated circular and longitudinal smooth muscle strips were connected to isometric force transducers in organ baths. After equilibration, the effect of NBB (1 nmol/l to 100 μmol/l) on spontaneous and carbachol-induced contraction was determined and compared with responses in control tissue. Results: At ≥30 μmol/l, NBB inhibited spontaneous contractions in all muscle strips that exhibited spontaneous activity. N-butylscopolammonium bromide pre-treatment inhibited carbachol-induced contraction in circular (NBB-treated half maximal effective concentration [EC₅₀] 0.530 × 10(-8) mol/l vs. control EC₅₀ 41.57 × 10(-8) mol/l) and longitudinal muscle strips (NBB-treated EC50 0.243 × 10(-8) mol/l vs. control EC₅₀ 90.84 × 10(-8) mol/l). Abolition of carbachol-induced contraction with NBB was observed at lower concentrations in circular than longitudinal muscle strips. Pretreatment with NBB significantly inhibited carbachol-induced contractions; NBB-treated tissue required greater carbachol concentrations to produce sustained contractions than control muscle strips. Histamine-evoked contraction was not affected by NBB. Conclusions: N-butylscopolammonium bromide inhibits spontaneous and cholinergically mediated contraction in equine ileal smooth muscle strips ex vivo. Thus, NBB might reduce intestinal spasm in equine ileal impactions and could be useful for medical management of these cases, although further study is needed to confirm these effects in vivo.