The effects of the essential oil of the plant Croton zehntneri (EOCz) in the concentration range 1–200 μg/mL were studied on the mechanical activity of various in vitro smooth muscle preparations of the guinea-pig. In isolated ileum EOCz induced a variable response such that in 57% of tissues basal tone was reduced (EC50 5 μg/mL) whereas the rest remained unaffected by the oil. In concentrations above 10 μg/mL EOCz induced spontaneous oscillatory contractions in all preparations. In contrast the basal tone of the aorta, portal vein and bladder remained unaltered by the oil. In the portal vein EOCz concentration-dependently inhibited the amplitude of spontaneous contractions (IC50 109 μg/mL) without reducing frequency, whereas in the bladder such activity was increased by the oil (EC50 44 μg/mL). In ileum precontracted with 60 mM KCl, EOCz induced a complete and concentration-dependent relaxation with an IC50 value of approximately 26 μg/mL. In contrast EOCz did not relax KCl-induced tone in the aorta or bladder, whilst eliciting less than 20% relaxation of the precontracted portal vein. Thus our data show that EOCz exerts differential modulatory effects on the contractility of various smooth muscles of the guinea-pig. That EOCz appears to selectively relax intestinal smooth muscle may support its use in folk medicine as a gastrointestinal antispasmodic.
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Coelho‐de‐Souza et al. (1998) studied this question.