AN ANALYSIS OF THE DEPRESSOR RESPONSES TO HISTAMINE IN THE CAT AND DOG: INVOLVEMENT OF BOTH H1- AND H2-RECEPTORS

Abstract

The depressor responses to histamine, in anaesthetized cats and dogs, have been shown to involve both histamine H 1 ‐ and H 2 ‐ receptors. In both species, histamine caused dose‐dependent falls in blood pressure. The dose‐response curve could be displaced to the right by administration of mepyramine 2.5 × 10 −6 mol/kg i.v. The displacement was maximal with a dose‐ratio of less than ten. Metiamide alone, up to 2 × 10 −6 mol kg −1 min −1, had no significant effect on the histamine dose‐response curve. When administered in the presence of mepyramine, metiamide, 4 × 10 −7 and 2 × 10 −6 mol kg −1 min −1, caused dose‐dependent displacements to the right, of the histamine dose‐response curve greater than could be achieved with mepyramine alone. The results indicate the presence of both histamine H 1 ‐ and H 2 ‐receptors in the cardiovascular system of the cat and dog. Both receptors produce a common response, i.e. a fall in blood pressure.