Role of endothelium and adventitia on eugenol-induced relaxation of rabbit ear artery precontracted by histamine.
Eugenol (> or = 0.1 mM) inhibited the contractions induced by various stimulants, such as 90 mM extracellular K+ solution ([K+]0), histamine and noradrenaline in the rabbit ear artery. Inhibitory actions of eugenol occurred in a concentration-dependent manner, however, eugenol more dominantly inhibited the histamine-induced contraction than those induced by either 90 mM [K+]0 solution or noradrenaline. Removal of both endothelium and adventitia did not change the inhibitory actions of eugenol on the 90 mM [K+]0- and noradrenaline-induced contractions, however, attenuated those on the histamine-induced contraction. Chlorphenylamine abolished the histamine-induced contraction, but neither cimetidine, ranitidine nor thioperamide modified the eugenol actions on the contractions induced by histamine. Pretreatment with nitric oxide syntheses inhibitor NG-nitro-L-arginine (LNNA; 100 microM), but not soluble guanylate cyclase inhibitor methylene blue (MB; 10 microM), prevented endothelium/adventitia-dependent augmentation of the eugenol-induced relaxation on the histamine-induced contraction. When an intact tissue, but not an endothelium/adventitia-denuded tissue, was placed at the up-stream close to the other denuded preparation (test preparation), histamine-induced contraction observed in the test preparation tended to be augmented. Similarly, eugenol-induced relaxation was also augmented by the same treatment. Eugenol (0.3 mM) inhibited the excitatory junction potentials (EJPs) without hyperpolarization of the membrane. However, a high concentration of eugenol (1 mM) slightly hyperpolarized the membrane (ca. 5 mV). No transient enhancement of amplitude of EJP was recorded. These results suggest that eugenol may inhibit the histamine-induced muscle contraction directly, and the inhibition is augmented by the adventitia and endothelium partly by vasoactive substances, which were released from the adventitia/endothelium-derived substances in rabbit ear artery.
Nishijima
H
H
Department of Health and Sports Science, Kawasaki University of Medical Welfare, Okayama, Japan.
Uchida
R
R
Kawakami
N
N
Shimamura
K
K
Kitamura
K
K
D000818:Animals; D004423:Ear / Q000098:blood supply*; D004730:Endothelium, Vascular / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005054:Eugenol / Q000737:chemistry / Q000494:pharmacology*; D006632:Histamine / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D008751:Methylene Blue / Q000494:pharmacology; D015394:Molecular Structure; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D019335:Nitroarginine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D019800:Phenol; D011817:Rabbits; D014664:Vasodilation