Studies on the action of cell growth inhibiting factor partially purified from bovine colostrum.

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It has been reported that bovine colostrum contains high levels of growth promoting factors that stimulate DNA synthesis and cell division. Human milk sampled at 1-day postpartum has also been reported to contain the highest level of immunoreactive IGF-I,levels falling rapidly thereafter, by 80% within 48-h after delivery. In this study, we found a cell-growth inhibiting factor in partially purified fraction from bovine colostrum with ion-exchange chromatography. The activity was measured in three cell lines, mouse LM fibroblast, rat L6 myoblast, and Balb/c 3T3 cells. The cell-growth inhibiting activity was observed only in LM cells, whereas the fraction stimulated cell proliferation in L6 and Balb/c 3T3 cells in low FCS condition. IGF-I concentration of the fraction was determined by RIA,and it contained about 50ng/ml of IGF-I.Then, effects of IGF-I on cell growth of these three cell lines were studied. To our surprise, IGF-I inhibited proliferation of LM cells, while it stimulated cell growth of L6 and Balb/c 3T3 cells in low FCS condition. These data suggest that the inhibitory action of the fraction to LM cells is mainly due to IGF-I.