THE EFFECTS OF HISTAMINE AND SOME HISTAMINE‐LIKE AGONISTS ON BLOOD PRESSURE IN THE CAT

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Abstract
1 The effects of histamine on blood pressure have been compared with the effects caused by four histamine-like agonists in anaesthetized cats. 2 It has been confirmed that the depressor responses to histamine involve both H1- and H2-receptors: depressor responses also follow the administration of selective H1- and H2 -receptor agonists. 3 2-Methylhistamine, in doses up to 1 × 10−7 mol/kg, lowers blood pressure by interaction with H1-receptors. Larger doses of 2-methylhistamine also lower blood pressure but this may involve H2-receptors. 4 4-Methylhistamine, in doses up to 1 × 10−7 mol/kg, lowers blood pressure by interaction with H2-receptors. Larger doses of 4-methylhistamine also lower blood pressure but this may involve H1-receptors. 5 2-(2-Aminoethyl)pyridine and 2-(2-aminoethyl)thiazole both lower blood pressure by interaction with H1-receptors only. 6 The potential value and limitations of these compounds as tools to investigate the cardiovascular effects of histamine are discussed.