Observations on Reactive Hyperaemia as Related to Histamine, on Drugs Antagonizing Vasodilatation Induced by Histamine and on Vasodilator Properties of Adenosinetri phosphate
- 1A method is described for quantitative studies of reactive hyperaemia in the hind limbs of cats and dogs.
- 2In 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.
- 3The magnitude of reactive hyperaemia is not reduced by rendering the small blood vessels completely insensitive to histamine in physiological concentrations.
- 4Benadryl 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.
- 5It is suggested that there are two types of receptors sensitive to histamine only one of which can be blocked by benadryl and related compounds.
- 6It 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.