Effect of small doses of 5-hydroxytryptamine (serotonin) on pulmonary circulation in the closed-chest dog

¹ Sections of Physiology and Surgical Research, Mayo Clinic and Mayo Foundation, Rochester, Minnesota

5-Hydroxytryptamine (serotonin) was infused into anesthetized dogs at a rate of 20 µg/kg/min. In nine sets of observations on three dogs the increase in the difference of pressure between the pulmonary artery and the left atrium, which averaged 55%, consistently exceeded the increase in pulmonary blood flow, which averaged 16%. 5-HT therefore is a potent constrictor of pulmonary vessels, even in small concentrations. No changes in the pulmonary-artery wedge and pulmonary-vein pressures were detected during the infusions of 5-HT, nor was there any change in the volume of blood between the pulmonary artery and the root of the aorta. With this dose of 5-HT the principal site of the increased resistance to flow through the lungs appeared to be in the precapillary vessels. In the isolated perfused lung, moderate constriction of pulmonary veins also was produced by large doses of 5-HT.