The renotrophic factor, a persistent stimulus that crosses the placenta in mice.

1. Twenty 7-week female mice underwent right nephrectomy and twenty others were sham operated. A week later all animals were made pregnant. Pregnancy was repeated five more times consecutively and various renal parameters were assessed in the pups. 2. Fractional fresh kidney weight (relative to body weight) was significantly increased in the pups of nephrectomized mothers while percentage renal water and protein content expressed as mg/g kidney weight were not statistically different in the two groups of pups. Thus dry kidney weight and amount of protein per kidney were increased in the experimental group. This was true for the newborns of all six pregnancies. 3. Renal morphometric studies performed in newborns of first pregnancies showed that the mean number of glomeruli per microscopic field, mean fractional cumulative glomerular area (relative to microscopic field area) and the mean number of cells per glomerulus were significantly greater in the experimental group. Mean glomerular radius was not statistically different in the two groups. 4. The results indicate that: (1) the renotrophic factor(s) crosses the placenta in mice; (2) its activity in maternal circulation following uninephrectomy is sustained for a relatively long period; and (3) fetal response to enhanced maternal renotrophin stimulation consists of increased renal dry weight and renal protein, formation of super-physiological numbers of glomeruli and cellular hyperplasia of the glomeruli.