Effects of prenatal and postnatal exposure to gentamicin on renal differentiation in the rat.

Pregnant rats were injected daily, from the 10th day of gestation to term, with 75 mg/kg of gentamicin. They gave birth about 15 h later than control pregnant rats injected with saline to pups with various degrees of growth retardation. In pups born of gentamicin-treated mothers, the number of nephrons present at birth, as well as the final number of nephrons, were reduced by at least 20%. Observation of the kidneys by light microscopy showed focal tubular lesions on the mature nephrons. The intrarenal concentration of gentamicin was higher in the severely growth retarded pups than in the others. In another series of experiments, rats were given 75 mg/kg of gentamicin daily from days 1 to 13 after birth. Although under these conditions the concentration of gentamicin reached in the postnatal kidney was higher than that reached after exposure in utero, no reduction of the final number of nephrons was observed. It is concluded that administration of gentamicin to pregnant rats caused focal tubular lesions in the developing kidney and a reduced rate of early nephrogenesis. The latter was probably due to growth retardation, though a more direct effect of gentamicin on early nephrogenesis may also have been involved.