Mechanisms of neonatal increase in glomerular filtration rate

vestigate the mechanisms responsible for the neonatal increase in glomerular filtration rate (GFR), renal function studies (whole kidney and micropuncture) were carried out in anesthesized fetal sheep (133–140 days gestation; term 150 days) and lambs (12–18 days). Fetuses were delivered and placed in a water bath (39.5°C), keeping the umbilical cord moist and intact. Lambs were studied on a ther-mostatically controlled heating pad. Animals were prepared for either blood flow studies or micropuncture measurements. Expected differ-ences in blood composition and cardiovascular and renal function were observed between fetuses and lambs, and values obtained for most variables were similar to those measured in chronically catheterized unanesthetized animals. Fetal GFR was much lower than that of lambs (0.20 vs. 0.62 ml min1 g kidney1, P 0.001). Free-flow, stop-flow, and net filtration pressures (NFP) were lower in the fetuses than the lambs (NFP 20.8 vs. 23.8 mmHg, P 0.001), as was the calculated ultrafil