On the bronchoconstrictor effect of serotonin. Bronchographic studies on rabbits and guinea‐pigs

Abstract

Serotonin is known to be an effective bronchoconstrictor in animals (Herxheimer, 1953;Konzett, 1956; Balzer, Greef & Westermann, 1956). In man a clinical sign of this action is the fact that patients suffering from metastasizing carcinoid tumour often have asthmatic attacks; and Herxheimer (1955) found that although inhalation of serotonin aerosol in four normal cases had no effect, in three out of six asthmatics it elicited severe asthmatic attacks which were abolished by iso-propyladrenaline.The observations made on the bronchoconstrictor action of serotonin have been based on indirect measurements. But it is a straightforward procedure to render the bronchial tree oftest animals visible by the methods of clinical bronchography with radio-opaque substances; this technique has therefore been used to demonstrate the effects of serotonin on the bronchi. METHODSTwenty rabbits and fifteen guinea-pigs were used. Sixteen rabbits were anaesthetized with urethane intravenously, four with ether; all the guinea-pigs were anaesthetized with ether.Most of the animals examined received reserpine (7 mglkg) 24 hr before the experiment in order to abolish the effects of the natural stores of serotonin.The trachea of the anaesthetized animal was exposed, and a polythene catheter introduced into it. The contrast agent used was Dionosil Aqueous (Glaxo Laboratories, Ltd.). In some experiments (see Table 1) serotonin was administered through the catheter before the injection of the contrast agent; in other experiments serotonin was administered intravenously. After the lungs had been filled with the contrast agent by letting it flow freely into the lungs while the animal was turned about, the trachea was tied and the lungs were removed.The lungs were radiographed with a Siemens' fine-structure tube equipped with a copper anode at 30 kVp, with Crystallex (Kodak) fine-grain X-ray film developed in D 76 fine-grain developer. This technique allowed a magnifcation by about ten diameters.Physiol. 159 25