MEASUREMENT OF NET SODIUM INTAKE BY THE OVINE FETUS WITH OESOPHAGEAL LIGATION

1. If the fetal sheep is in sodium balance, then the net intake of sodium is equal to the sum of the losses of sodium in fetal urine and lung liquid plus the rate of deposition of sodium with growth. 2. In seven fetal sheep with oesophageal ligation net sodium intake was 23.1 ± 2.8 (s.e.m.) μmol/min per kg; 11.8 ± 1,4 μmol/min per kg was excreted by the lungs and 8.7 ± 2.3 μmol/min per kg was excreted by the kidneys. The excretion of sodium by the lungs accounted for 52.8 ± 4.8% of the total amount of sodium; the excretion of sodium by the kidneys accounted for 34.9 ± 5.4% and the calculated variable, that is, sodium deposited due to growth was 12.3 ± 1.4%. 3. All but one fetus excreted more sodium from the lungs than from the kidneys. There was no relationship between the clearance of sodium by the lungs and net sodium intake but there was a direct relationship between renal sodium clearance and net sodium intake (r=0.92, P < 0.005). This suggests that fetal urinary sodium excretion is dependent upon net sodium intake by the fetus. This animal model shows that normally there must be sodium fluxes from allantoic and/or amniotic cavities to either the fetus or the ewe.