Pharmacological significance of biogenic amines in the lungs: Noradrenaline and dopamine

1. The noradrenaline concentration in the lung was less than 0.5 mug/g in eight animal species.2. In the cat, dog, rabbit and goat, tyramine produced a fall in pulmonary resistance, which was reduced by the administration of either reserpine or cocaine. Although an infusion of noradrenaline increased the content of this amine in the lung of the cat, previously depleted by reserpine, the bronchodilator property of tyramine was not restored. The infusion of isoprenaline did not restore the response to tyramine. The role of either catecholamine in mediating the bronchomotor response to tyramine could not be ascertained.3. The concentration of dopamine was as high as 6.4 mug/g in the goat lung and less than 0.5 mug/g in the lungs of the cat, rabbit, dog, rat, mouse, guinea-pig and man. Dopamine, injected intravenously into the cat, dog, rabbit and goat, produced a slight rise in pulmonary resistance. This increase was blocked by tolazoline, indicating that the response was mediated by alpha-adrenoceptors in the bronchial passages. No procedure has been observed to influence the dopamine content of the lung. The release of dopamine cannot, however, be excluded until the blood in the bronchial veins has been analysed.