Minimal growth factor requirements of human fetal kidney in serum- and glucose-free culture.

The addition of insulin plus transferrin to Leibovitz's L-15 medium was previously shown to restore important cellular functions in a serum-free system developed in our laboratory for human fetal kidney explants. The objective of the present study was to compare the effectiveness of this insulin plus transferrin combination with one used in other in vitro systems whereby serum is substituted by a mixture of five hormones (insulin, transferrin, hydrocortisone, triiodothyronine and prostaglandin E1). In fetal kidney it was found that the combination of insulin plus transferrin was as effective as the five-hormone mixture on DNA synthesis after 5 days of culture and was even more effective in younger fetuses (10-13 weeks) compared with older fetuses (16-19 weeks). However, protein synthesis was more sensitive to the five-hormone combination. Selective deletion of individual hormones showed that insulin is the essential factor for the growth of cultured kidney explants. Differentiation of brush border membranes in nephrons, as evaluated by alkaline phosphatase and gamma-glutamyl-transferase activities, was not significantly modified by either of the two combinations. The present results indicate that insulin plus transferrin represents the optimizing condition for our culture model. The response to supplements varies according to fetal age and possibly to tissue proliferation states and/or cell type.