The action of dopamine on the arterial blood pressure of the guinea-pig.

The depressor action of dopamine (beta-3:4-dihydroxyphenylethylamine) upon the arterial blood pressure of the guinea-pig has been studied. This effect begins without a latent period. It is often enhanced after the intravenous injection of iproniazid (Marsilid). The depressor response is sufficiently sensitive to serve as a method of bioassay of dopamine in microgram quantities. Observations on the depressor action of L-dopa have also been made. This effect is also enhanced by iproniazid; it begins after a latent period. Epinine (beta-3:4-dihydroxyphenylethylmethylamine) caused a pressor response, followed by a fall of arterial blood pressure. No evidence was obtained in support of the suggestion that the two amines, which are oxidized at similar rates by amine oxidase, cause a fall of blood pressure after their conversion to an aldehyde by the action of amine oxidase.