Effects of 5-hydroxytryptamine and related agents on endothelial cell oxidative metabolism in vitro

A recently described microrespirometric method was used to determine the influence of 5-hydroxytryptamine (5-HT), nialamide, imipramine and ouabain alone and in combinations on oxidative metabolism in monolayer cultures of endothelial cells from the rat pulmonary artery. It was found that exposure to 5-HT increased oxygen uptake in the cultures, while imipramine or ouabain decreased respiration; nialamide had no obvious effect. When used in combinations, the effect of ouabain or imipramine dominated over the 5-HT effect. The explanation for this 5-HT stimulating effect on endothelial cell oxidative metabolism, previously undescribed, is suggested to be that 5-HT exposure stimulated individual cells to contract. This active contraction resulted in an increased energy demand reflected in elevated oxygen consumption, an effect inhibited by ouabain or imipramine.