Relaxin influences the growth of MCF‐7 breast cancer cells. Mitogenic and antimitogenic action depends on peptide concentration

Background. The effects of relaxin (RLX) on the human breast adenocarcinoma cell line MCF‐7 have been evaluated. Methods. The cells were maintained in culture with Dulbecco's modified Eagle's medium with 1% and 10% fetal calf serum. Highly purified porcine RLX was added at concentrations ranging between 10−11 and 10−6 M, and, after 96‐hour incubation in the presence of the peptide, cell proliferation, intracellular cyclic adenosine monophosphate (CAMP) content, percent cycling cells, and structural and ultrastructural pattern were studied. Results. The results indicate that RLX is a direct modulator of MCF‐7 cell proliferation, stimulating growth at low concentrations and inhibiting growth at high concentrations. Determinations of percent cycling cells and intracellular CAMP accumulation agree with the results of the growth studies. Addition of different concentrations of 8‐Br‐CAMP to the culture medium results in a dose‐related stimulation of MCF‐7 cell proliferation. Morphologic examination shows that, in the current experiments, RLX does not induce any clear‐cut signs of differentiation of MCF‐7 cells in terms of activation of secretion or intracellular lipid deposition. Conclusion. These findings indicate that RLX should be regarded as a novel agent involved in the control of growth of human breast cancer cells. Cancer 1992; 70:639–643.