The cells of the NIH 3T3 fibroblast line responded to primary interaction with insulin by a positive imprinting, i.e. by an increased binding capacity for the hormone on re-exposure. Positive imprinting, although to a lesser degree, was also induced by thyrotropin. However, oncogenic transformation by polyoma virus oncogens resulted in decreased imprinting in both the middle-T-antigen (MT3) and small-T-antigen-expressing (N4) cells.

Studies based on treatment with antibodies to thyrotropic hormone, luteotropic hormone, growth hormone or adrenocorticotropic hormone have shown that although the unicellular Tetrahymena does not possess sui generis receptors to all polypeptide hormones, such binding structures may arise, or become established in the membrane of the unicellular Tetrahymena in the presence of exogenous hormone. The Tetrahymena subjected to hormonal imprinting still contained an increased amount of hormone after six generation changes, which suggested that either hormone production had been induced by treatment, or the internalized hormone had not been degraded intracellularly. Thus the role of hormonal imprinting in receptor formation has also been substantiated by the immunocytochemical approach used in the present study.

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.