SYNERGISTIC BOMBESIN AND INSULIN STIMULATION OF DNA-SYNTHESIS IN HUMAN FETAL KIDNEY IN SERUM-FREE CULTURE

The respective influences of growth factors during kidney development can be directly evaluated using the chemically-defined serum-free cult ure system perfected in our laboratory. Since, in this culture model, conditions are minimal for growth and differentiation, DNA synthesis s harply decreases during the first 48 h. The addition of epidermal grow th factor (EGF, 100 ng/ml), insulin (5 mug/ml) and transferrin (5 mug/ ml) significantly restores this important cellular function. The objec tive of the present study was to determine the influence of bombesin, a potent mitogen, supplemented alone or in combination with insulin, t ransferrin and/or EGF. Cortical explants of human fetal kidneys (17-20 weeks) were maintained during 5 days in culture. When compared with 5 day controls (L-15 medium only), bombesin generated a maximal though weak effect on DNA synthesis at a concentration of 0.3 nM, correspondi ng to a stimulation index (SI) of 22%. When combined with either trans ferrin or EGF, or with transferrin plus EGF, bombesin did not alter th e SI of individual factors. Insulin, in turn, greatly increased DNA sy nthesis (SI = 169%), while bombesin strongly potentiated this effect ( SI = 275%). Transferrin also enhanced insulin SI from 169 to 240%. Whe n added as a third factor, bombesin further potentiated the effectiven ess (SI = 338%) of the combination insulin plus transferrin. These res ults indicate that bombesin controls cell proliferation in synergism w ith other regulators and hence may act as a competence growth factor d uring nephrogenesis.