Renal response of the lamb fetus to partial occlusion of the umbilical cord.

The role of the fetal kidney during impairment of placental exchange was studied in eight fetal lambs, intact in utero; a standard asphyxial insult for a period of 1 hour was produced by occluding the umbilical cord sufficiently to lower the fetal heart rate by 35 +/- 5 beats/min and the pH by 0.15 units. This asphyxial stress caused a fall in urine output from a control of 0.17 to 0.03 ml/kg/min and of glomerular filtration rate from 1.2 to 0.3 ml/min; release of the occlusion was followed by mild diuresis. The fall in urine output was accompanied by a rise in total primary solutes including concentrations of electrolytes; this rise continued for 1 to 2 hours following the release of the occlusion. Because of the low urinary output during the period of occlusion, there was a fall in excretion of electrolyte; an increase in net acid excretion occurred only after the release of the cord. These experiments show that, although the fetal kidney is capable of contributing to elimination of acid following compression of the cord, there may be an associated net loss of water and electrolytes.