Modulation of Smooth Muscle Relaxation by Short and Long Carbon Based Chemicals

Abstract

Introduction: Short and long-chained based carbon chemicals derived from plants are found in many household products and are widely used in complementary medicine. It has been suggested anecdotally that some of these chemicals have the ability to relax smooth muscle tissues, and to test this concept, this study examines the effects of 1,8-cineole, 1-heptanol, α-pinene, cis-3-hexen-1-ol and trans-2-hexenal on neurotransmission and contraction of mouse and rat vas deferens. Methods: Focal extracellular recordings from the surface of mouse vas deferens of electricallyevoked nerve terminal impulses (NTIs) and electrically-evoked excitatory junctional currents (EJCs) were examined in both the presence and the absence of each chemical. Likewise, noradrenaline-evoked contractile forces of rat vas deferens were examined in both the presence and the absence of each chemical. Results: Relative to the respective controls, 1,8-cineole, 1-heptanol and trans-2-hexenal each statistically significantly decreased both smooth muscle contractile forces and EJC amplitudes, with 1-heptanol and trans-2-hexenal also statistically significantly decreasing NTI amplitudes. On NTI and EJC amplitudes the effects of 1,8-cineole and 1-heptanol were reversible whereas the effects of trans-2-hexenal were irreversible. Conclusion: Our results demonstrate that 1,8-cineole and trans-2-hexenal decrease smooth muscle neurotransmission and contraction and thereby cause smooth muscle relaxation, thus suggesting that these chemicals may have clinical applications and health benefits.Key words: 1,8-cineole, cis-3-hexen-1-ol, 1-heptanol, α-pinene, smooth muscle, relaxation, trans-2-hexenal. SUMMARY• 1,8-Cineole, 1-heptanol and trans-2-hexenal decrease nerve terminal impulse (NTI) amplitudes and smooth muscle contractile forces.• 1,8-Cineole, 1-heptanol and trans-2-hexenal also decrease excitatory junction current (EJC) amplitudes.• Reductions in NTIs and EJCs by 1-heptanol and 1,8-cineole were reversible, but reductions caused by trans-2-hexenal were irreversible.• Minor structural differences between the chemicals can lead to significant changes in their effects on smooth muscle neurotransmission and contraction. PICTORIAL ABSTRACTAbbreviations used: ATP: Adenosine 5'-triphosphate, EJC: Excitatory junction current, NTI: Nerve terminal impulse. Correspondence:Matthew James Cheesman, School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, 4072, Australia.Email: m.cheesman@uq.edu.au DOI : 10.5530/pc.2015.4.6 INTRODUCTIONPlant-derived chemicals are found in many household products and are widely used in complementary medicines for their fragrance and perceived soothing or calming effects. 1-3 Beyond these sensory and psychological benefits, the topical use of some plant-derived chemicals has been shown to cause smooth muscle relaxation. [4][5][6][7] The long-chained plantderived carbon based chemicals 1,8-cineole ( Figure 1a) and α-pinene ( Figure 1b) and the short-chained plant-derived carbon based chemicals cis-3-hexen-...