Osteoinductive activity of the transitional epithelium in the urinary bladder increased by more than 3 times in aging guinea pigs. The count of inducible osteogenic precursors and their sensitivity to urinary bladder osteoinductive factor decreased by several times with age. Our experiments show that proliferation of some stromal precursors in the spleen requires not only platelet-derived factors, but also growth factors produced by urinary bladder transitional epithelium.

Efficiency of colony formation of stromal precursor cells in cultured bone marrow transplants from old (24 month) CBA mice implanted to young (2-month-old) mice almost 3-fold surpassed that in cultured transplants implanted to old recipients. The content of nucleated cells in bone marrow transplants from senescence accelerated mice SAMP increased more than 2-fold, if SAMR mice with normal aging rate were used as the recipients instead of SAMP mice. Bone marrow taken from old and young CBA mice endured the same number of transplantations if the recipient mice were of the same age (5 month). It was concluded that stromal tissue considerably changes with age and is under strict control of the body.

Elimination of platelets from guinea pig splenocyte suspension (lacking megakaryocytes) with EDTA considerable reduces the efficiency cloning of splenic stromal precursor cells. It means that platelet-derived growth factors are necessary for stromal precursor cells from different organs (bone marrow, thymus, and spleen). The dependence on the platelet growth factors can vary within a wide range in descendants from cultured bone marrow precursor cells (passaged bone marrow fibroblasts at different stages of differentiation.