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The effects of 8 imidazoline derivatives on pre- and postsynaptic alpha-adrenoceptors and [3H]norepinephrine release were investigated in the rat vas deferens and were compared with those of reference drugs, yohimbine, phentolamine, tolazoline, and prazosin. K-6341 and K-6343 activated postsynaptic alpha 1-adrenoceptor and were antagonized by prazosin. The order of potency series as alpha 1-antagonist, prazosin greater than phentolamine greater than yohimbine greater than K-4011 greater than K-3827 greater than K-4300, tolazoline was found in antagonism against phenylephrine. Many derivatives exhibited an antagonistic action against clonidine, and the potency series as alpha 2-antagonist was revealed as follows: phentolamine greater than yohimbine greater than K-3827 greater than K-4011 greater than K-6341 greater than K-6343 greater than K-4300, tolazoline greater than prazosin greater than K-4299. The antagonistic effect was more selective on presynaptic (alpha 2) than postsynaptic (alpha 1) adrenoceptor and the rank order of selectivity (KB-post/KB-pre) was K-3827 greater than yohimbine greater than K-4011 greater than tolazoline, K-4300 greater than phentolamine greater than prazosin. Imidazoline derivative increased [3H]norepinephrine release, the actions of K-3827, K-6341 and K-4300 being particularly potent. From these results, the structure-activity relationship was summarized. First, when 2',3'-methylenedioxyphenyl group is connected with the imidazoline ring via an amino or methylene residue, these compounds become alpha 1-agonist. Secondly, when the methylenedioxyphenyl group and the imidazoline ring are connected via an amino residue, these compounds show a weak agonistic and potent antagonistic characteristics at the presynaptic alpha 2-adrenoceptor. Thirdly, an addition of a methylenedioxy radical to the phenyl ring increased the affinity of the compounds to presynaptic alpha 2-receptor.
K Takeuchi, and
K Akatsuka, and
K Goto, and
Y Kasuya
December 1979,
Archives internationales de pharmacodynamie et de therapie,
K Takeuchi, and
K Akatsuka, and
K Goto, and
Y Kasuya
October 1984,
British journal of pharmacology,
K Takeuchi, and
K Akatsuka, and
K Goto, and
Y Kasuya
January 1983,
Journal de pharmacologie,
K Takeuchi, and
K Akatsuka, and
K Goto, and
Y Kasuya
June 1987,
Pharmacological research communications,
K Takeuchi, and
K Akatsuka, and
K Goto, and
Y Kasuya
November 1983,
European journal of pharmacology,
K Takeuchi, and
K Akatsuka, and
K Goto, and
Y Kasuya
December 1981,
British journal of pharmacology,
K Takeuchi, and
K Akatsuka, and
K Goto, and
Y Kasuya
March 1986,
European journal of pharmacology,
K Takeuchi, and
K Akatsuka, and
K Goto, and
Y Kasuya
July 1985,
Archives internationales de pharmacodynamie et de therapie,
K Takeuchi, and
K Akatsuka, and
K Goto, and
Y Kasuya
April 1982,
Planta medica,
K Takeuchi, and
K Akatsuka, and
K Goto, and
Y Kasuya
February 1983,
Japanese journal of pharmacology,
