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KMID : 0376219920290020263
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Chonnam Medical Journal
1992 Volume.29 No. 2 p.263 ~ p.272
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Inhibitory effect of atropine analogues on α-adrenoceptors in isolated thoracic aorta of rabbit
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Abstract
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To investigate the relationship of atropine analogues and α-adrenoceptors, effects of atropine analogues on contractile responses to α-adrenoceptor agonists were observed in isolated thoracic aortae of rabbits. Pheylephrine (PE) 10E-5 M,
clonidine
(CN) 10E-5 M, norepinephrine (NE) 10E-6 M, histamine (HA) 10E-5 M and KCI 35 mMproduced constant contraction in intact endothelial rings and the contractions of 4 agents except KCI were significantly potentiated by the removal of the endothelium.
PE-induced contractions in both rings with and without the endothelium were inhibited by cumulative addition of atropine in a dose-dependent fashion and the IC50s were 1.2×10E-5M and 1.5×10E-5M, respectively. There was no difference between
both
values. Atropine (AT) inhibited all contractions induced by CN, NE and HA as well as PE in a dose-dependent manner and the IC50s were 2.6×10E-5M, 1.4×10E-5 and 6.1×10E-6 M, respectively. However, Kci-induced contraction was not affected by AT.
Homatropine (HAT) 10E-4 M inhibited significantly contractions of 4 vasoconstrctors except KCI, but the inhibition was much less than that of AT. Scopolamine (SP) 10E-4 M did not affect CN-induced contraction but significantly inhibited
contractions of
other 3 agents. Methylatropine (MA) did not inhibit all contractions of 4 vasoconstrictors at all. Summerized above data the inhibitory potency order of four atropine analogues to contractions induced by four vasoconstrictors was AT
〉〉HAT〉SP〉〉MA
and the sensitivity order of four vasoconstrictors to three atropine analogues except MA was HA〉PE=NE〉CN.
Above results suggest that atropine analogues directly block α-adrenoceptors in rabbit thoracic aorta and the antagonizing effect is more selective to α1-subtype than to α2-subtype.
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