Increase in placental lactogen and somatomedins after nephrectomy.

To investigate the relationship between renal agenesis and fetal growth retardation, 6 fetal sheep underwent bilateral nephrectomy and carotid artery catheterization between 105 and 125 days of gestation. Five fetal sheep were catheterized at a similar age as controls and all but one were delivered between 134 days and 147 days gestation. The weights of the fetuses did not differ significantly but the nephrectomized fetuses were shorter than their controls (P less than 0.01). Hydranencephaly was observed in two nephrectomized animals and the mean brain weight was reduced in this group (P less than 0.01). Fetal lung weights were likewise reduced (P less than 0.01). The mean plasma concentrations of maternal and fetal immunoreactive insulin and prolactin did not differ significantly in the two groups, nor did fetal ovine growth hormone and maternal ovine placental lactogen, also measured by radioimmunoassay. However, there were greater concentrations of ovine placental lactogen in the plasma of the nephrectomized lambs than in the controls (P less than 0.005). Somatomedin-like receptor activity was measured by receptor assay using [125I] multiplication-stimulating activity. The mean activity in unextracted serum from nephrectomized lambs was greater than that of the controls (p less than 0.05). When the fetal serum was chromatographed on Sephadex G-150 and the eluted fractions assayed for somatomedin-like activity three peaks of activity were observed. Two, with indicated molecular sizes of approximately 100,000 and 10,000 were greater in serum from nephrectomized animals than from the controls (P less than 0.01). The increased concentrations of placental lactogen and somatomedins after nephrectomy suggest that the kidney has a role in clearance of these hormones in the fetus. The growth retardation after fetal nephrectomy may be due to increased binding of somatomedin peptides by serum proteins or to an inhibition of somatomedin action by an unidentified serum component.