Renal response of fetal lamb to complete occlusion of umbilical cord

The renal response of the fetal lamb to repeated complete occlusion of the umbilical cord was studied in nine chronically instrumented animals. Five episodes of occlusion of the umbilical cord, each lasting for two minutes, produced a twofold rise in fetal urine osmolality and sodium, chloride, and potassium concentrations. Output of urine and glomerular filtration rate remained essentially unchanged while free water clearance decreased from a control of +0.10 to -0.02 ml. per kilogram per minute at the end of the fifth episode. Electrolyte concentrations in urine remained elevated for at least two hours following the occlusions. In addition to changes in urine composition, there was a 50- to 200-fold increase in the fetal plasma concentration of vasopressin. These studies indicate that complete interruption of the umbilical circulation, even though of short duration, produces disturbances in fetal renal function that can lead to loss of electrolytes in the urine. They provide an explanation for the low sodium levels reported in asphyxiated newborn infants in renal failure.