RELEASE OF A MITOGENIC FACTOR BY ADULT-RAT LUNG SLICES IN CULTURE

In an effort to develop a suitable bioassay for testing lung growth fa ctors that might be operative during compensatory lung growth followin g partial pneumonectomy, a simple and inexpensive lung organ culture s ystem was characterized. The culture employs lung tissue slices obtain ed by means of a device allowing thicknesses of 500 mu m to be cut rep roducibly. To avoid the collapse of the organ, the alveolar spaces wer e filled prior to culture with Noble agar containing Eagle's-Dulbecco' s modified medium. Lung tissue sections could be maintained ultrastruc turally intact for at least one week. The results showed that upon cul ture, a part of the type II pneumocytes undergo differentiation into t ype I pneumocytes, thus demonstrating that the culture system may be s uited for differentiation studies. One surprising feature of this cult ure system was the mitogenic impulse associated with culture. Radioact ively labeled thymidine incorporation was strongly stimulated in the c ulture, mainly affecting the epithelial cells, as could be established by ''back-to-back'' autoradiography. With a reconstruction experiment , it was possible to demonstrate the local release of a mitogenic fact or following slicing, mincing; or dissection of the lung tissue, which could be assayed by its ability to induce serum-starved Balb/c 3T3 ce lls to synthesize DNA in culture.