Removal of 5-hydroxytryptamine by rat lungs.

Isolated rat lungs perfused with Krebs solution removed free radioactive 5-Hydroxytryptamine (5 HT or serotonin) from the fluid perfusing them. However, when platelets labelled with 111In-oxine to tag them individually, and with 14C-labelled 5 HT were also perfused via the lungs, there was no significant removal of the labelled 5 HT from the platelets. Paper chromatography showed that 46.7% of the platelet bound 5 HT was metabolished to an unidentified material. Rat lungs remove free 5 HT from plasma but not when it is platelet bound.