In vitro growth-stimulatory property of pigeon milk

Five cell lines were employed to test the growth-stimulating property of pigeon milk in vitro. All the cell lines except A431 showed good growth response to crude homogenates of pigeon milk. Enhancement of DNA synthesis in quiescent Chinese hamster ovary (CHO) cells by pigeon milk was dose dependent up to a concentration of 1%. In vitro growth stimulation by 1% pigeon milk was approximately equal to that by 2% foetal bovine serum (FBS) when CHO cells were used, growth stimulation of Vero cells by 1% pigeon milk was roughly three times of that by 2% FBS. In contrast, 1% pigeon milk was only half as active as 2% FBS on NIH/3T3 cells and five times less active than 2% FBS on human foetal lung fibroblast cells. After dialysis using a relative mass (M(r)) cutoff of 3500, the pigeon milk mitogenic activity was retained in the dialyzed solution, although it decreased by 40-60% when dialyzed with M(r) cutoffs of 8000 and 12,000-14,000. The growth-stimulating activity of pigeon milk was resistant to heat, acid, alkali, and the action of urea, guanidine hydrochloride, dithiothreitol, and trypsin. We suggest that pigeon milk is a new source of growth factor(s) capable of stimulating in vitro the growth of many mammalian cell types.