5‐HYDROXYTRYPTAMINE. PHARMACOLOGICAL ACTION AND DESTRUCTION IN PERFUSED LUNGS

Abstract

1. 5‐Hydroxytryptamine (HT) caused vasoconstriction and bronchoconstriction in cats' lungs perfused with blood. These actions were antagonized by dihydroergotamine or lysergic acid diethylamide. 2. The HT‐equivalent of the plasma was estimated by extraction with acetone and assay on rat's uterus in comparison with synthetic HT. This was low immediately after bleeding, but rose rapidly to about 1 mg. per litre. 3. The HT‐equivalent of the plasma fell exponentially during perfusion with a halving time of 4‐20 min. 4. When the rate of circulation was increased the rate of disappearance of HT rose.