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  • Title: alpha-Adrenoceptor blocking properties of a new antihypertensive agent, 2-[4-(n-butyryl)-homopiperazine-1-yl]-4-amino-6,7-dimethoxyquinazoline (E-643).
    Author: Shoji T, Daiku Y, Igarashi T.
    Journal: Jpn J Pharmacol; 1980 Dec; 30(6):763-72. PubMed ID: 6113297.
    Abstract:
    Postsynaptic alpha-receptor blocking properties of E-643 were studied in vivo and in vitro and compared with these same properties of phentolamine and phenoxybenzamine. In anesthetized rats, E-643 (i.v.) attenuated pressor response to adrenaline dose-dependently and an adrenaline-reversal was seen with large doses. The in vivo alpha-adrenoreceptor blocking effect of E-643 was 3.4 times more potent than that of phentolamine. On the other hand, hypotensive action of E-643 was 9.4 times more potent than that of phentolamine. In the isolated rabbit aorta, E-643 blocked noradrenaline-induced contraction of the aorta with a parallel shift of the dose-response curve to the right. The pA2 values for E-643 and phentolamine were 8.60 and 7.65, respectively. The alpha-blocking effect of E-643 was reversible. E-643 protected alpha-receptors against irreversible inhibition by phenoxybenzamine. E-643 neither exhibited significant blocking effects on K+-, Ba2+- and angiotensin-induced contractions of the aorta nor caused relaxation of the aorta contracted by Ca2+. These data suggest that E-643 is a specific and competitive inhibitor of noradrenaline at the alpha-adrenoceptors.
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