Effect of oxytocin and its analogues on the chemotaxis of Tetrahymena: Evolutionary conclusions

Oxytocin and its five analogues (arginin vasopressin included) were studied in chemotaxis assays using Tetrahymena as unicellular model cells. Exclusi vely the two real hormones (oxytocin and vasopressin) were consequently rep ellent, other analogues (with exchanged or missed amino acids) were neutral , attractant or unbalanced. Tetrahymena was not able to differentiate quali tatively between oxytocin and vasopressin, however it sharply discriminated the real hormones from the analogues. Considering that in earlier experime nts oxytocin and vasopressin also equally influenced the function of the co ntractile vacuole, it is supposed that the uniformity of the effect of thes e hormones is not a chance event and they had to be diverged (in function) later, during the evolution.