THE INFLUENCE OF LUNG DISTENSION UPON THE RESPONSE OF THE BRONCHIOLES TO EPINEPHRINE AND TO HISTAMINE

¹ Department of Pharmacology, McGill University, Montreal, Canada

Dogs deeply anesthetized with pentothal sodium and vagotomized, were used. The changes in the bronchioles (Jackson Method) and the blood pressure were recorded simultaneously.

It is shown that after histamine bronchoconstriction and fall in blood pressure, repeated injections of epinephrine induced only submaximal bronchodilatation, and often complete refractoriness of the bronchioles to epinephrine was observed, despite the fact that the blood pressure was still responsive. At this time, a brief period (5 to 10 seconds) of lung distension with positive pressure (40 mm. of mercury) induced marked and sustained maximal bronchodilatation.

The bronchoconstrictor action of histamine under these conditions may also be partially or completely antagonized by lung distension with positive pressure.

It is suggested that these effects of lung distension are due primarily to mechanical stretching of the elastic tissue of the lungs.

It is also shown that epinephrine is a more effective bronchodilator agent when sprayed directly into the lungs, than when injected; and conversely, histamine is a less effective bronchoconstrictor agent when sprayed than when injected.