Effect of different concentrations of serotonin, histamine and insulin on the hormone (serotonin and ACTH) production of Tetrahymena in nutrient-free physiological milieu

► Tetrahymena was treated with hormones in 10-6-10-21 M concentrations. ► Serotonin and ACTH content was measured inside the cells. ► In nutrient-free conditions hormonal effects differ from the nutrient-rich condition. ► Hormonal effects have an optimal zone which is dependent on the hormone given. ► The hormone receptors of Tetrahymena are very sensitive.