Effect of Growth Conditions on Serotonin Content of Tetrahymena pyriformis*

SYNOPSIS The serotonin content of Tetrahymena was measured under several growth conditions and after exposure to drugs. Serotonin was maximal during stationary phase, then declined to a level typical of logarithmically growing cells. Addition of 5-hydroxytryptophan to the culture increased cellular serotonin content, but neither L-tryptophan, reserpine, p-chlorophenylalanine, nor desmethylimipramine altered the serotonin content.