Eucalyptol, an essential oil, reduces contractile activity in rat cardiac muscle.
Eucalyptol is an essential oil that relaxes bronchial and vascular smooth muscle although its direct actions on isolated myocardium have not been reported. We investigated a putative negative inotropic effect of the oil on left ventricular papillary muscles from male Wistar rats weighing 250 to 300 g, as well as its effects on isometric force, rate of force development, time parameters, post-rest potentiation, positive inotropic interventions produced by Ca2+ and isoproterenol, and on tetanic tension. The effects of 0.3 mM eucalyptol on myosin ATPase activity were also investigated. Eucalyptol (0.003 to 0.3 mM) reduced isometric tension, the rate of force development and time parameters. The oil reduced the force developed by steady-state contractions (50% at 0.3 mM) but did not alter sarcoplasmic reticulum function or post-rest contractions and produced a progressive increase in relative potentiation. Increased extracellular Ca2+ concentration (0.62 to 5 mM) and isoproterenol (20 nM) administration counteracted the negative inotropic effects of the oil. The activity of the contractile machinery evaluated by tetanic force development was reduced by 30 to 50% but myosin ATPase activity was not affected by eucalyptol (0.3 mM), supporting the idea of a reduction of sarcolemmal Ca2+ influx. The present results suggest that eucalyptol depresses force development, probably acting as a calcium channel blocker.
Soares
M C M S
MC
Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, ES, Brasil.
Damiani
C E N
CE
Moreira
C M
CM
Stefanon
I
I
Vassallo
D V
DV
D000818:Animals; D003511:Cyclohexanols / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D000077591:Eucalyptol; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D039821:Monoterpenes / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects*; D009822:Oils, Volatile / Q000494:pharmacology*; D010210:Papillary Muscles / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000187:drug effects*; D024744:Skeletal Muscle Myosins / Q000187:drug effects
D003511:Cyclohexanols; D039821:Monoterpenes; D009822:Oils, Volatile; D024744:Skeletal Muscle Myosins; D000077591:Eucalyptol