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

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 X 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 X 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.