Effects of hormones on chemotaxis in Tetrahymena: investigations on receptor memory

The peptide type hormones such as insulin and adenocorticotropic hormone (ACTH) have a positive chemoattractant effect on Tetrahymena. Non-hormone protein-sulphate provoked negative chemoattraction. Of the amino acid type hormones, serotonin produced negative, and the histamine and di-iodotyrosine induced positive chemotactic effects. The first encounter with these molecules may modify the chemotactic behaviour of the progeny cells. In a significant number of cases there was a different response after repeated encounters of cells and hormones.