The effect of directly and indirectly acting sympathomimetic amines on bronchospasm in the guinea-pig during CO2 inhalation

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Abstract
The bronchodilator effects of nine sympathomimetic amines were tested by reduction of histamine-induced bronchospasm in guinea-pigs. Their order of potency was: isoprenaline > adrenaline > noradrenaline > orciprenaline > ethylnoradrenaline > phenylephrine > amphetamine = tyramine > ephedrine. In guinea-pigs ventilated with 10% CO2 in air, there was a marked decrease in the bronchoconstrictor activity of histamine. Under these conditions, isoprenaline, adrenaline, noradrenaline and orciprenaline were as effective as bronchodilators as they had been in guinea-pigs ventilated with air, ethylnoradrenaline was less effective, phenylephrine, amphetamine and tyramine were completely inactive, and ephedrine potentiated the bronchoconstrictor action of histamine. After returning the guinea-pigs to ventilation with air, the bronchoconstrictor activity of histamine and the bronchodilator effects of the sympathomimetic amines were restored. The cardiovascular effects of histamine and of all the sympathomimetic amines used were diminished during ventilation with 10% CO2 in air and were restored after ventilation with air was resumed.

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