Histamine increased specifically the phagocytic activity of the unicellular Tetrahymena, whereas insulin had no influence on it. Insulin antagonized the phagocytosis stimulating action of histamine after simultaneous exposure and after preexposure two days earlier as well, although in the latter case to a lesser degree. Double exposure to a combination of histamine + insulin didn't influence the phagocytic activity at all, demonstrating the histamine antagonizing effect of insulin in this model.

Of the L and D configurations of four amino acids (phenylalanine, valine, tryptophan, tyrosine) tested for influence on the growth rate of Tetrahymena, only L-tyrosine was able to induce imprinting in Tetrahymena pyriformis Zeuthen. D-valine stimulated the division of T.pyriformis NT-1, but failed to induce imprinting. The experiments have substantiated the selectivity of the amino acid receptors of Y.pyriformis, and the extraordinary imprinting potential of tyrosine as well, as judged by its influence on the growth rate.

Certain non-hormone oligopeptides have a greater imprinting effect on Tetrahymena than others. The imprinting potential is unrelated to the length of the peptide chain, but seems greatly dependent on the amino acid sequence. The direct growth-stimulant action developed by the peptides at the first interaction is unrelated to their imprinting effect.