Observations on Reactive Hyperaemia as Related to Histamine, on Drugs Antagonizing Vasodilatation Induced by Histamine and on Vasodilator Properties of Adenosinetri phosphate

Abstract

A method is described for quantitative studies of reactive hyperaemia in the hind limbs of cats and dogs. In cats the sensitivity of the small vessels to histamine varies within a very wide range, the magnitude of reactive hyperaemia, however, was found to be independent of the sensitivity of the vessels to histamine. The magnitude of reactive hyperaemia is not reduced by rendering the small blood vessels completely insensitive to histamine in physiological concentrations. Benadryl and related compounds completely annul the vasodilator effect of the minimal doses of histamine which produce maximal vasodilatation. The effect of larger doses of histamine, 5 times greater than the minimum dose and upwards, depending on the basic sensitivity to histamine, is not annulled or even diminished by any amount of antagonistic drug. It is suggested that there are two types of receptors sensitive to histamine only one of which can be blocked by benadryl and related compounds. It is demonstrated that adenosinetriphosphate is a very potent vasodilator, 0.1 ±0.2 y causing profound vasodilatation in the hind limbs when injected in the artery.