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  • Title: Histamine H2-receptor antagonism of T-593: studies on positive chronotropic responses in guinea pig atria.
    Author: Arai H, Nakagawa M, Tanada K, Yamaguchi H, Hirai S.
    Journal: Jpn J Pharmacol; 1994 Apr; 64(4):251-6. PubMed ID: 7914553.
    Abstract:
    Histamine H2-antagonistic properties of the novel H2-antagonist T-593, (+-)-N-[2-hydroxy-2-(4-hydroxyphenyl)ethyl]-N'-[2- [[[5-(methylamino)methyl-2-furyl]methyl]thio]ethyl]-N"- (methylsulfonyl) guanidine were investigated on the histamine-induced positive chronotropic responses in isolated guinea pig right atria. T-593 at 3 x 10(-7)-3 x 10(-6) M suppressed the maximal responses of the histamine concentration-response curves in a concentration-dependent fashion, indicating that T-593 is an unsurmountable antagonist. The pD'2 values were 5.50 for T-593 and 5.61 for famotidine; and the IC50 values at 1 x 10(-5) M histamine were 1.05 x 10(-6) M for T-593, 1.59 x 10(-6) M for ranitidine and 1.67 x 10(-7) M for famotidine. T-593 is a racemic compound composed of two enantiomers, (-)-T-593 and (+)-T-593. The histamine H2-antagonistic activity of (-)-T-593 was 1.5-fold more potent than that of racemic T-593, but (+)-T-593 scarcely inhibited the histamine-induced positive chronotropic response. Histamine H2-antagonism by racemic T-593 was mainly attributed to (-)-T-593. Isoproterenol-induced positive chronotropic responses were not affected by T-593 even at 3 x 10(-5) M. Pretreatment of ranitidine for 10 min prior to application of T-593 protected H2-receptors from unsurmountable antagonism by T-593. Reversibility of H2-antagonism was determined every 1 hr after a 30-min treatment of H2-antagonists. T-593 inhibited the positive chronotropic responses for over 6 hr in contrast to fast recovery from inhibition by ranitidine or famotidine. This result showed that T-593 is a slowly dissociable, long-acting histamine H2-antagonist.
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